4.4 Thermochemische Reststoffbehandlung und Wertstoffrückgewinnung
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The use of highly water-soluble phosphorus (P) fertilizers can lead to P fixation in the soil, reducing fertilization efficiency. Waste-derived, low water-solubility sources can potentially increase sugarcane’s P uptake compared to triple superphosphate by reducing adsorption to the soil.
Aims:We aimed to test struvite, hazenite, and AshDec® for their agronomic potential as recycled fertilizers for sugarcane production in a typical tropical soil.We hypothesize that these sources can reduce P fixation in the soil, increasing its availability and sugarcane’s absorption.
Methods: In a greenhouse pot experiment, two consecutive sugarcane cycles, 90 days each, were conducted in a Ferralsol. The recovered sources struvite, hazenite, AshDec®, and the conventional triple superphosphate were mixed in the soil in three P doses (30, 60, and 90 mg kg–1), aside a control (nil-P). At both harvests, sugarcane number of sprouts, plant height, stem diameter, dry mass yield, shoot phosphorus, and soil P fractionation were investigated.
Results: At 90 days, struvite and hazenite performed better for dry mass yield (70.7 and 68.3 g pot–1, respectively) than AshDec® and triple superphosphate (59.8 and 57.4 g pot–1, respectively) and for shoot P, with 98.1, 91.6, 75.6, and 66.3 mg pot–1, respectively. At 180 days, struvite outperformed all treatments for dry mass yield (95.3 g pot–1) and AshDec® (75.5 mg pot–1) for shoot P. Struvite was 38% and hazenite 21% more efficient than triple superphosphate in P uptake, while AshDec® was 6% less efficient. Soil had higher labile P under struvite, hazenite, and AshDec® than triple superphosphate by the end of the first cycle, while only the later increased nonlabile P by the end of the experiment (180 days).
Conclusions:Waste-derived P sources were more efficient in supplying P for sugarcane and delivering labile P in 180 days than triple superphosphate.
Thermochemische Behandlung von Klärschlammaschen - Phosphorrückgewinnung mit dem AshDec Prozess
(2021)
Klärschlammaschen können eine hohe Phosphatkonzentration aufweisen und stellen damit einen geeigneten Sekundärrohstoff für die Produktion von Phosphatdüngemitteln dar. Bisher wird dieses Potential der Klärschlammaschen für die Phosphor-Rückgewinnung jedoch kaum genutzt, da die in den Aschen enthaltenen Phosphate für Pflanzen kaum verfügbar und die Aschen teilweise mit toxischen Schwermetallen belastet sind.
Im AshDec®-Verfahren wird die Klärschlammaschen im Drehrohrofen im Temperaturbereich 800-1000°C unter Zugabe von Alkali-Additiven (bsp. Na2CO3) thermochemisch behandelt, um ein wirksames und schadstoffarmes Phosphatdüngemittel herzustellen. Aktuell bereitet die Firma Emter GmbH den Bau der ersten großtechnischen AshDec®-Anlage mit einer Kapazität von 30.000 Jahrestonnen Klärschlammasche am Standort ihrer Klärschlammverbrennungsanlage (Altenstadt / Oberbayern) vor. Die erste Ausbaustufe dieser Anlage wird durch das BMBF-Projekt R-Rhenania im Rahmen der Förderinitiative RePhoR begleitet.
Future nutrient recovery from sewage sludge regarding three different scenarios - German case study
(2022)
Agricultural sewage sludge utilization becomes less important in Germany. In 2017, new fertilizer and waste laws caused the agricultural sewage sludge utilization to collapse by more than a quarter. From 2029, German wastewater treatment plants (WWTPs) must recover phosphorus (P) from sewage sludge if it contains more than 2 wt % P. Agricultural utilization will be prohibited for large WWTPs >100,000 population equivalents (pe) from 2029 and >50,000 pe from 2032. In Germany, each federal state must annually report amounts and quality of agriculturally utilized sewage sludge which was 16% of the total disposal in 2019. The reports of 10 states were evaluated for 2016 and 2017 representing approx. 60% of the total agriculturally used sludge volume. In 2016, 60% of the WWTPs’ sludges exceeded the recovery limit of 2 wt % P which is 70% of the amount of sludge and 85% of the phosphorus load. Other nutrients are not affected by the recovery obligation. However, many P recovery processes recover other nutrients, too. Considering three different scenarios for future German sewage sludge disposal shows that 70–77% of the P load in sewage sludge will probably be recovered in the future. At the same time, this applies for about 0–16% nitrogen, 36–52% of calcium, 31–53% of potassium, and 40–52% of magnesium. However, these recovered nutrients loads can substitute only 1% or less of the commercial fertilizer demand except from phosphorus which is up to 43% of the demand.
Agricultural sewage sludge utilization becomes less important in Germany. In 2017, new fertilizer and waste laws caused the agricultural sewage sludge utilization to collapse by more than a quarter. From 2029, in German wastewater treatment plants (WWTPs) phosphorus (P) must be recovered from sewage sludge ifit contains more than 2 wt % P. Agricultural utilization will be prohibited for large WWTPs > 100,000 population equivalents (pe) from 2029 and > 50,000 pe from 2032. In Germany, each federal state must annually report amounts and quality of agriculturally utilized sewage sludge which was 17 % of the total disposal in 2019. The reports of 10 States were evaluated for 2016 and 2017 representing approx. 60 % ofthe total agriculturally used sludge volume. Whereas phosphorus recovery is mandatory this does not apply to other nutrients. However, many P recovery processes recover other nutrients, too.
Considering three differentscenariosfor future German sewage sludge disposal Shows that 70 - 77 % ofthe P load in sewage sludge will probably be recovered in the future.
At the same time, this applies for about 0 - 16 % of nitrogen, 36 - 52 % of calcium, 31-53 % of potassium, and 40 - 52 % of magnesium. However, these recovered nutrient loads can substitute only 1 % or less ofthe commercial fertilizer demand except from phosphorus which is about 45 % ofthe demand.
Gleichwertigkeit der nach AbfKlärV zulässigen Verfahren zur Phosphorbestimmung in Klärschlamm
(2021)
In dem Meeting wurde den Notifizierern und Ausrichtern des jährlichen länderübergreifenden Ringversuchs Klärschlamm die Ergebnisse zu Untersuchungen hinsichtlich der Gleichwertigkeit verschiedener nach AbfKlärV zulässiger Verfahren zur Phosphorbestimmung in Klärschlamm vorgestellt. Die Untersuchungen an 15 Klärschlammproben ergaben die höchsten Ergebnisse für das Messverfahren ICP-OES und das Aufschlussverfahren in der Mikrowelle. Diese Ergebnisse wurden im Ringversuch bestätigt.
Die Ergebnisse des extraWERT-Vorhabens wurden Vertreter*innen des Umweltministeriums von Bund und Ländern vorgestellt und im Zusammenhang mit dem Vollzug der AbfKlärV diskutiert. Es ging um die Phosphorschwankungen in kommunalem Klärschlamm und eine Empfehlung der Untersuchungshäufigkeit, um den Phosphorgehalt rechtssicher festzustellen. Des weiteren wurde die Performance verschiedener nach Verordnung gleichwertiger Analyseverfahren für Phosphor in Klärschlamm diskutiert anhand von Ringversuchsergebnissen und Eigenuntersuchungen an 15 Klärschlammproben.
Agricultural sewage sludge utilization becomes less important in Germany. In 2017, new fertilizer and waste laws caused the agricultural sewage sludge utilization to collapse by more than a quarter. From 2029, in German wastewater treatment plants (WWTPs) phosphorus (P) must be recovered from sewage sludge ifit contains more than 2 wt % P. Agricultural utilization will be prohibited for large WWTPs > 100,000 population equivalents (pe) from 2029 and > 50,000 pe from 2032. In Germany, each federal state must annually report amounts and quality of agriculturally utilized sewage sludge which was 17 % of the total disposal in 2019. The reports of 10 States were evaluated for 2016 and 2017 representing approx. 60 % ofthe total agriculturallyused sludge volume. Whereas phosphorus recovery is mandatory this does not apply to other nutrients. However, many P recovery processes recover other nutrients, too. Considering three differentscenariosfor future German sewage sludge disposal shows that 70 - 77 % ofthe P load in sewage sludge will probably be recovered in the future. At the same time, this applies for about 0 - 16 % of nitrogen, 36 - 52 % of calcium, 31-53 % of potassium, and 40 - 52 % of magnesium. However, these recovered nut rient loads can substitute only 1 % or less ofthe commercial fertilizer demand except from phosphorus which is about 45 % ofthe demand.
Phosphorus (P) resource availability and quality is declining and recycling P-fertilizers from waste materials are becoming increasingly important. One important secondary P resource is sewage sludge (SSL) where P is often bound as aluminum phosphate (Al-P), iron phosphate (Fe-P) and polyphosphate (poly-P), respectively. Thermal treatment in different ways is a promising way in P recycling to produce highly plant-available P-fertilizers. To investigate mechanisms behind transformation of hardly available P-species toward plant-available P forms we treated a model SSL containing different kinds of defined P sources by low-temperature conversion (LTC) at 500 °C and subsequent thermochemical treatment of the LTC product with Na additives (TCT) at 950 °C, respectively. Pot experiments with ryegrass were carried out to determine the plant availability of P of the different treatments. The poly-P (here pyrophosphates) based fertilizers had a very high plant availability after both thermal treatments. During LTC treatment the plant availability of the Fe-P and Al-P variants increased because of the Formation of Fe(II) phosphates and/or pyro-/polyphosphates. Especially the formation of Al-polyphosphate shows a high plant availability. The subsequent TCT further increased strongly the plant availability of the Fe-P variants because of the formation of highly plant-available CaNaPO4. Thus, a direct TCT without prior LTC probably also produce CaNaPO4 and is recommended for Fe-P based SSL. However, a molar Ca/P ratio of 1 in the fertilizer is favorable for CaNaPO4 formation. Thus, the knowledge on the source of primary P in SSL is essential for choosing the accurate thermal treatment method to produce highly plant-available P-fertilizers from SSL.
Phosphorus (P) fertilizers from secondary resources became increasingly important in the last years. However, these novel P-fertilizers can also contain toxic pollutants. Chromium in its hexavalent state (Cr(VI)) is regulated with low limit values for agricultural products due to its high toxicity, but the determination of Cr(VI) in these novel fertilizer matrices can be hampered by redox processes that lead to false results. Thus, we applied the passive sampler technique Diffusive Gradients in Thin-films (DGT) for the determination of Cr(VI) in fertilizers and compared the results with the standard wet chemical extraction method (German norm DIN EN 15192) and Cr K-edge X-ray absorption near-edge structure (XANES) spectroscopy. We determined an overall good correlation between the wet chemical extraction and the DGT method. DGT was very sensitive and in most cases selective for the analysis of Cr(VI) in P-fertilizers. However, hardly soluble Cr(VI) compounds cannot be detected with the DGT method since only mobile Cr(VI) is analyzed. Furthermore, Cr K-edge XANES spectroscopy showed that the DGT binding layer also adsorbs small amounts of mobile Cr(III) compounds which leads to overestimated Cr(VI) values. The results of certain types of P-fertilizers containing mobile Cr(III) or partly immobile Cr(VI), showed that optimization of the DGT method is required to avoid over- or underestimation of Cr(VI).
The aim of this study was to investigate the passive sampler method Diffusive Gradients in Thin-films (DGT) for ammonium and nitrate in amended soils. Therefore, we used soils from a pot experiment with maize where nitrogen (N) was supplied as ammonium sulfate nitrate (ASN), without and with a nitrification inhibitor (NI). The additional use of a NI can delay the nitrification in the soil and making the ammonium available for a longer period in the soil solution after its application. Homogenized soil samples were collected directly from each pot after one week of incubation before sowing and after harvesting the maize. Nitrate and ammonium in these soil samples were extracted using DGT devices equipped with a Putolite A520E (for nitrate) and Microlite PrCH (for ammonium) binding layer. Ammonium DGT which determined the mobile and labile ammonium forms based on diffusion and the resupplies from the solid soil phase, only showed a significantly higher amount of extractable ammonium with NI compared to that without NI for some samples. However, significantly lower values were found for nitrate of treatments with NI compared to without NI after harvest. Thus, the lower nitrate amounts for treatments with NI compared to the treatments without NI after harvest indicated the delay of the nitrification process by the NI. Furthermore, we compared also the ammonium and nitrate
DGT results to chemical extraction with KCl solutions. The results demonstrated that the trends of DGT results and chemical extraction were complimentary through all the treatments.
Gypsum is widely used in the construction sector, and its worldwide consumption has been increasing now for several decades. Currently, the gypsum demand is met up to 60% by FGD gypsum (a by-product from coal-fired power plants) in Germany. The natural gypsum deposits cover the remaining gypsum demand. Due to national climate protection goals and the related shutdown of coal-fired power plants, the FGD gypsum supply will decrease significantly in the coming years and, therefore, other gypsum sources must be found.
Depending on the lifetime of the used gypsum products in the construction sector, an increase of gypsum in construction and demolition waste is to be expected. With regard to an upcoming shortage of gypsum, several approaches are being tested to recover gypsum from construction and demolition waste. Gypsum plasterboard recycling is already implemented on an industrial scale. Furthermore, new processes to recycle different types of gypsum products from construction and demolition waste are being examined. Of particular interest are different types of gypsum boards because they are well suited for selective dismantling. Therefore, they can be recovered comparatively free of impurities which is most important for the gypsum recycling.
In the research project “GipsRec 2.0”, funded by the Federal Ministry of Education and Research, recycling methods for gypsum fiberboards are being investigated. Additionally, the suitability of different types of synthetic gypsum as substitutes for FGD gypsum is being considered. Currently, the quantities of recycled gypsum are not sufficient with regard to the reduction of FGD gypsum. An increase of gypsum recycling should be achieved to narrow the future gypsum gap that will occur in the near future.
Phosphorus rich sewage sludge ash is a promising source to produce phosphorus recycling fertilizer. However, the low plant availability of phosphorus in these ashes makes a treatment necessary. A thermochemical treatment (800–1000 °C) with alkali additives transforms poorly plant available phosphorus phases to highly plant available calcium alkali Phosphates (Ca,Mg)(Na,K)PO4. In this study, we investigate the use of K2SO4 as additive to produce a phosphorus potassium fertilizer in laboratory-scale experiments (crucible). Pure K2SO4 is not suitable as high reaction temperatures are required due to the high melting point of K2SO4.
To overcome this barrier, we carried out series of experiments with mixtures of K2SO4 and Na2SO4 resulting in a lower economically feasible reaction temperature (900–1000 °C). In this way, the produced phosphorus potassium fertilizers (8.4 wt.% K, 7.6 wt.% P) was highly plant available for phosphorus indicated by complete extractable phosphorus in neutral ammonium citrate solution. The added potassium is, in contrast to sodium, preferably incorporated into silicates instead of phosphorus phases. Thus, the highly extractable phase (Ca,Mg)(Na,K)PO4 in the thermochemical products contain less potassium than expected. This preferred incorporation is confirmed by a pilot-scale trial (rotary kiln) and thermodynamic calculation.
Conventional phosphate fertilizers are usually highly water-soluble and rapidly solubilize when moistened by the soil solution. However, if this solubilization is not in alignment with plants demand, P can react with the soil colloidal phase, becoming less available over time. This is more pronounced in acidic, oxidic tropical soils, with
high P adsorption capacity, reducing the efficiency of P fertilization. Furthermore, these fertilizers are derived from phosphate rock, a non-renewable resource, generating an environmental impact. To assess these concerns, waste-recycled P sources (struvite, hazenite and AshDec®) were studied for their potential of reducing P Fixation by the soil and improving the agronomic efficiency of the P fertilization. In our work, we compared the solubilization dynamics of struvite, hazenite, AshDec® to triple superphosphate (TSP) in a sandy clay loam Ferralsol, as well as their effect on solution pH and on soil P pools (labile, moderately-labile and non-labile) via an incubation experiment. Leaching columns containing 50 g of soil with surface application of 100 mg per column (mg col 1) of P from each selected fertilizer and one control (nil-P) were evaluated for 60 days. Daily leachate samples from the column were analyzed for P content and pH. Soil was stratified in the end and submitted to P
fractionation. All results were analyzed considering p < 0.05. Our findings showed that TSP and struvite promoted an acid P release reaction (reaching pHs of 4.3 and 5.5 respectively), while AshDec® and hazenite reaction was alkaline (reaching pHs of 8.4 and 8.5 respectively). Furthermore, TSP promoted the highest P release among all sources in 60 days (52.8 mg col 1) and showed rapid release dynamic in the beginning, while struvite and hazenite showed late release dynamics and lower total leached P (29.7 and 15.5 mg col 1 P respectively). In contrast, no P-release was detected in the leachate of the AshDec® over the whole trial period. Struvite promoted
the highest soil labile P concentration (7938 mg kg 1), followed by hazenite (5877 mg kg 1) and AshDec® (4468 mg kg 1), all higher than TSP (3821 mg kg 1), while AshDec® showed high moderately-labile P (9214 mg kg 1), reaffirming its delayed release potential.
CF Pyro: Stofflich-energetische Verwertung von carbonfaserhaltigen Abfällen in der Pyrometallurgie
(2021)
Despite its contribution to tackling climate change by lightweight design, growing CFRP production also results in a global waste generation of 62 kt/a. Accordingly, the energy-intensive production process of carbon fibers (CF) necessitates sustainable recycling solutions.
Herein we will give an overview of current recycling processes, discuss their limitations and present a novel approach for safe treatment of CF unsuitable for material recovery . Our project CF Pyro examines feedstock recycling in pyrometallurgical processes, focusing on reactivity of CF, process stability and prevention of hazardous WHO fiber release. Besides fundamental experimental breakthroughs, their broader impact on circular economy will be presented.
Basic oxygen furnace slag (BOFS) is a by-product of the steelmaking process, of which about 10.4 Mt are produced annually in the European Union. Besides its predominant use in road construction, earthwork, and hydraulic engineering, it is also possible to use BOFS as a source material for Portland cement clinker.
The main difference in the chemical composition of BOFS from the chemical composition of Portland cement clinker is its high content of iron oxides (7-50 wt.%). In recent decades, many researchers have investigated the production of both Portland cement clinker and crude iron from BOFS via thermochemical reductive treatment. Carbothermal treatment of liquid BOFS causes reduction of iron oxides to metallic iron, which separates from the mineral phase due to its higher density.
In this study, German BOFS was reduced in a small-scale electric arc furnace using petrol coke as reducing agent. The produced low-iron mineral product was chemically similar to Portland cement clinker and contained the most important Portland cement mineral alite (Ca3SiO5) as main component. Besides alite, the mineral product contained other Portland cement clinker constituents such as belite (β-Ca2SiO4) and tricalcium aluminate (Ca3Al2O6).
The production of Portland cement clinker and crude iron from BOFS has economic and ecological benefits for both the cement and steel industry. Cement clinker from reduced BOFS may be used as a substitute for cement clinker from conventional cement production, thereby CO2 emissions will be reduced. The steel industry benefits from a high-value application for its by-products that avoids cost expensive landfilling and may even bring economic advantages. However, reductive treatment requires high temperatures and, for economic reasons, has to be carried out immediately after casting of the liquid BOFS, which is a logistical challenge for most steel plants. A cost-benefit analysis is therefore essential.
Basic oxygen furnace slags (BOFS) are a by-product of steel production. In 2016, 10.4 Mt of BOFS were produced in the European Union (EU). The main part of BOFS is used in road construction, earthwork and hydraulic engineering. A smaller part is returned to the metallurgical circle, used as fertilizer or landfilled. However, it is also possible to produce higher value products from BOFS. For example, many researchers have investigated the possibility of producing Portland cement clinker and crude iron from BOFS by a carbothermal post-treatment.
In this study, German BOFS was reduced in a small-scale electric arc furnace using petrol coke as reducing agent. The carbothermal treatment reduces the iron oxides in the BOFS to metallic iron, which accumulates at the bottom of the furnace by density separation. In addition to metallic iron, the process generates a mineral product rich in the tricalcium silicate solid solution alite. As the main constituent of Portland cement clinker, the hydraulic reactive mineral alite is of high economic importance.
In previous studies, the hydraulic reactivity of the mineral product was investigated by testing the compressive strength of blends with 70 wt.% ordinary Portland cement (OPC). Recent investigations focused on the hydraulic properties of the pure mineral product from the reduced BOFS. The heat of hydration of the mineral product was measured by isothermal calorimetry and compared with the heat of hydration of a synthetic low-iron slag and OPC. In addition, the formation of hydration products was investigated with differential scanning calorimetry (DSC) and x-ray diffraction analysis (XRD) on freeze-dried samples after defined curing times. The results of the calorimetric measurements indicate that the mineral product produced less heat of hydration and its reaction was delayed compared to the synthetic low-iron slag and OPC. Hydration products such as portlandite and calcium silicate hydrates (C-S-H) formed later and in lower amounts.
The production of a hydraulic material from BOFS by reductive treatment is of great interest to both the cement and steel industries. The substitution of cement clinker in OPC with a hydraulic material such as reduced BOFS leads to a reduction in greenhouse gas emissions from cement production. The steel industry benefits from an application for its by-products that avoids cost expensive landfilling and may even bring economic advantages. Furthermore, it may be possible to return the recovered crude iron to production.
During iron and steel production, several by-products such as slags, dusts and sludges are generated in addition to pig iron and steel as primary products. While established recycling routes exist for slags, there are still considerable recycling problems for other residual materials, especially for filter dusts and sludges containing zinc and lead from waste gas purification. However, the high heavy metal contents make landfilling these dusts and sludges cost-intensive and ecologically problematic. In addition, the relatively high zinc and iron loads represent a valuable material potential, which can make reprocessing of the material with recovery of the zinc and iron loads as secondary raw materials ecologically as well as economically attractive. Against this background, a process is being developed in a cooperative project between Ferro Duo GmbH and the Federal Institute for Materials Research and Testing (BAM), in which the heavy metals (zinc, lead, cadmium, etc.) contained in the filter dusts and sludges are selectively converted into chlorides in a thermochemical process after the addition of a chlorine donor and evaporated at temperatures between 650 and 1100 °C. This process can be used to recover zinc and iron as secondary raw materials.
Experiments to date in a batch reactor show that >99% of the zinc and lead can be removed from the treated material. However, a continuous process is necessary for an economical process, which is why this process is transferred to a rotary kiln and relevant process parameters are identified and optimized. The results of these investigations will be presented here.
The steel industry is an important engine for sustainable growth, added value, and high-quality employment within the European Union. It is committed to reducing its CO2 emissions due to production by up to 50% by 2030 compared to 1990′s level by developing and upscaling the technologies required to contribute to European initiatives, such as the Circular Economy Action Plan (CEAP) and the European Green Deal (EGD). The Clean Steel Partnership (CSP, a public–private partnership), which is led by the European Steel Association (EUROFER) and the European Steel Technology Platform (ESTEP), defined technological CO2 mitigation pathways comprising carbon direct avoidance (CDA), smart carbon usage SCU), and a circular economy (CE). CE ap-proaches ensure competitiveness through increased resource efficiency and sustainability and consist of different issues, such as the valorization of steelmaking residues (dusts, slags, sludge) for internal recycling in the steelmaking process, enhanced steel recycling (scrap use), the use of secondary carbon carriers from non-steel sectors as a reducing agent and energy source in the steelmaking process chain, and CE business models (supply chain analyses). The current paper gives an overview of different technological CE approaches as obtained in a dedicated workshop called “Resi4Future—Residue valorization in iron and steel industry: sustainable solutions for a cleaner and more competitive future Europe” that was organized by ESTEP to focus on future challenges toward the final goal of industrial deployment.
Basic oxygen furnace slags (BOFS) are by-products of the steelmaking process. Several researchers have studied the production of Portland cement clinker and metallic iron from BOFS via a reductive treatment.
In this study, we applied a carbothermal reduction of BOFS in a technical-scale electric arc furnace and characterised the clinker-like products. Those clinker-like non-metallic products (NMPs) had a chemical and mineralogical composition comparable to clinker for ordinary Portland cement (OPC) and contained large elongated alite crystals as major component. The pure NMPs reacted more slowly and achieved a lower degree of hydration compared with commercial OPC.
If the reactivity of the products can be further increased by employing specific adaptations, it can be used as a full clinker substitute for OPC. Nevertheless, it is also an option to use the material without further modifications as a cement component or concrete addition, which contributes to the strength development in both cases.
Despite its contribution to tackling climate change by lightweight design, growing CFRP production also results in a global waste generation of 62 kt/a. Accordingly, the energy-intensive production process of carbon fibers (CF) necessitates sustainable recycling solutions.
Herein we will give an overview of current recycling processes, discuss their limitations and present a novel approach for safe treatment of CF unsuitable for material recovery . Our project CF Pyro examines feedstock recycling in pyrometallurgical processes, focusing on reactivity of CF, process stability and prevention of hazardous WHO fiber release. Besides fundamental experimental breakthroughs, their broader impact on circular economy will be presented.
Ab 2029 gilt für alle Kläranlagen in Deutschland eine Pflicht zur Rückgewinnung von Phosphor (P) aus Klärschlamm. Ausgenommen sind nur Anlagen mit Schlämmen mit weniger als 20 g P/kg bezogen auf die Trockenmasse (TM). Für eine Überprüfung der Phosphorschwankungen im Klärschlamm wurden neun verschiedene Kläranlagen ausgewählt mit Phosphorgehalten nahe der "Rückgewinnungsgrenze" von 20 g/kg TM. Der entwässerte Klärschlamm dieser Anlagen wurde monatlich beprobt und auf seinen Phosphorgehalt geprüft. Die Phosphorschwankungen betrugen je nach Anlage zwischen 4 % und 13 % (relative Standardabweichung), im Mittel rund 7 %.
Phase formation and evolution was investigated in the CaO–SiO2 system in the range of 70–80 mol% CaO. The samples were container-less processed in an aerodynamic levitation system and crystallization was followed in situ by synchrotron x-ray diffraction at the beamline P21.1 at the German electron synchrotron (DESY). Modification changes of di- and tricalcium silicate were observed and occurred at lower temperatures than under equilibrium conditions. Despite deep sample undercooling, no metastable phase formation was observed within the measurement timescale of 1 s. For the given cooling rates ranging from 300 K s−1 to about 1 K s−1, no decomposition of tricalcium silicate was observed. No differences in phase evolution were observed between reducing and oxidizing conditions imposed by the levitation gas (Ar and Ar + O2). We demonstrate that this setup has great potential to follow crystallization in refractory oxide liquids in situ. For sub-second primary phase formation faster detection and for polymorph detection adjustments in resolution have to be implemented.
There is an ongoing debate on European scale concerning the criticality of phosphorus. In Switzerland and Germany, phosphorus recovery from phosphorus-rich waste streams will become obligatory. Sewage sludge ash is rich in phosphorus and may become an important secondary feedstock. Thermochemical treatment of sewage sludge ash with sodium sulphate under reducing conditions was shown to remove heavy metals from the solid product and produce the fully plant available crystalline phase CaNaPO4. Pilot-scale experiments in a rotary kiln were carried out at temperatures between 750 and 1000 °C and were compared to laboratory-scale experiments with crucibles. Process upscaling was successfully demonstrated but a series of differences were noticed: In comparison to laboratory-scale, solubility of phosphorus in samples from pilot-scale experiments was lower at all chosen treatment temperatures because of shorter retention time and incomplete decomposition of sodium sulphate. X-ray diffraction analysis revealed remaining phase fractions of whitlockite (Ca3-x(Mg,Fe)x(PO4)2) and sodium sulphate from the starting materials in products and thus indicated incomplete reaction. In contrast to the results of laboratory-scale experiments, the crystalline phase CaNaPO4 was clearly absent in the products from the rotary kiln but instead a Mg-bearing phase (Ca,Mg)NaPO4 was formed. Laboratory-scale experiments confirmed (Ca,Mg)NaPO4 is an intermediate phase between whitlockite and CaNaPO4. However, both crystalline phases are characterized by high plant availability. It was shown that heavy metal removal increased at higher temperatures whereas solubility and thus plant availability of phosphorus already reached its maxima at temperatures of 950 °C in pilot-scale and 875 °C in laboratory-scale experiments.
Recycled fertilizers produced using processes for the recovery of phosphate from residual materials such as wastewater, sewage sludge and sewage sludge ashes show very good bioavailability, but it is still a product largely unknown to the market. The aim of CLOOP is therefore to document the properties and effects of such fertilizers through chemical, mineralogical and ecological analyses as well as analytical method development and pot and field plant growth trials.
Outotec focused on 3 points in CLOOP: Experimental campaigns, process simulations as well as economic analyses with focus on the AshDec process, respectively the design of a large-scale AshDec plant for phosphorus recovery. The laboratory scale trials as well as the semi-industrial scale campaign provided valuable insights into the operating parameters of the process and the plant. As a result, for example, the temperature range could be significantly lowered, and the additive addition reduced by approx. 20 %. They have further shown that the AshDec process is not susceptible to operating fluctuations and that the product can be consistently produced at high quality. With the selection of suitable operating parameters, heavy metals (As, Pb, Cd, (Zn)) can be removed. Within the campaign, about 1.5 t of fertilizer for the plant trials in CLOOP could be produced. An AshDec plant process was digitally created in simulation software, allowing valuable process parameters to be simulated at various operating parameters. On this basis, a full-scale plant was designed. The data obtained in the project were used for a detailed economic analysis including a sensitivity analysis. It was possible to show under which conditions this plant can be operated economically.
At BAM, the AshDec fertilizer was synthesized with different additives and then applied to plant experiments at Uni Bonn. The goal hereby was to check differences in plant uptake. Because of the promising results of AshDec synthesized with sodium-carbonate and because this AshDec version does not require special off gas treatment for sulfur recovery (compared to AshDec synthesized with sodium-sulfate), all project partners agreed on continuing working with this AshDec variation. It was then used as a raw P-source for formulating it into NPK-fertilizers, by granulation with ammonium-sulfate and straw ash as potassium source. These recycling fertilizers were applied to plant- and field experiments by project partners in Brazil (University of Sao Paulo) and Australia (University of Queensland). Furthermore, in leaching experiments, the solubility of phosphorus in AshDec was compared to triple super phosphate. The experiments were carried out on soils with a varying phosphorus buffering index. Results show, that the phosphorus form in AshDec is way less soluble in water. This indicates that AshDec has the potential for a so-called next generation fertilizer – a fertilizer which’s nutrients remain in the soil and supply the plant according to its needs. At the moment, this behavior gets examined more in depth in lysimeter experiments in cooperation with University of Technology Berlin.
The focus of KWB is the Life Cycle Assessment (LCA) of different NextGen fertilizers to evaluate the entire process chain from recovery to fertilizer application. The NextGen fertilizer is credited by the amount of plant available nutrients in the product, which replace nutrients from conventional fertilizer. The LCA covers N-struvite precipitation from municipal wastewater, K-struvite precipitation from industrial wastewater and the AshDec-product from sewage sludge. The LCA task is almost complete. It could be shown that struvite precipitation has comprehensive environmental benefits, mainly since positive side effects occur in sewage sludge treatment (e.g. reduced sludge volume). In principle, the energetic and ecological profile of the AshDec process compared to direct use of sewage sludge ash cannot be assessed as being generally beneficial or negative. Regarding the global warming potential, the Ashdec process shows that the expenses (e.g. energy, chemicals) cannot be covered by the P fertilizer credit. In contrast, the impact categories “terrestrial acidification potential”, and “freshwater eutrophication potential” show positive results as the credits for conventional fertilizer are higher than the burdens for the process.
At University Bonn, the standardized pot experiments were conducted with several AshDec variations, using ryegrass, soybean, and spinach on a slightly acidic sandy soil and an organic-free standard substrate. P-uptake and biomass production of different AshDec variations were generally like those of triple super phosphate and struvite, and clearly outperformed untreated sewage sludge ash and rock phosphate. Field trials in Australia and Brazil with sugarcane on acidic soils are still ongoing and results are expected by the end of 2021.
Gypsum is widely used in the construction sector and its worldwide consumption has been increasing for several decades. Depending on the life-time of the used gypsum products, an increase of gypsum in construction and demolition waste follows. Especially against the background of a circular economy, the recycling of waste gypsum is of growing importance. However, the use of recycled gypsum makes only sense if it is environmentally friendly. Therefore, an evaluation of the environmental impacts of an industrial-scale processing for the recycling of post-consumer gypsum waste was conducted. The evaluation was performed with an established life cycle assessment software. Original data provided by industry and complementary data from a database for life cycle assessments were used for the calculations. Two scenarios for recycled gypsum with different transportation distances were calculated. These results are compared with results of the environmental evaluation of gypsum derived from coal-fired power plants (FGD gypsum) and natural gypsum. The results show that utilization of recycled gypsum can be environmentally advantageous compared to the use of natural gypsum or FGD gypsum, especially in the impact categories land transformation and resource consumption (abiotic depletion potential). For most environmental impact categories the specific transportation distances have a strong influence.
This paper focuses on the scandium speciation in bauxite residues of different origin. Insights into mineralchemical similarities and differences of these materials will be presented and links to their natural geological background discussed. The presented research should provide fundamental knowledge for the future development of efficient and viable technologies for Sc-recovery from bauxite residues derived from different bauxites and accumulating at different localities. In total, five bauxite residues were investigated which originated from Greece, Germany, Hungary and Russia (North Ural & North Timan) using a combination of different analytical tools. Those included: laser ablation inductively coupled plasma mass spectrometry, X-ray absorption near Edge structure (XANES) spectroscopy, μ-Raman spectroscopy as well as scanning electron microscopy and electron microprobe analyses. X-ray fluorescence and inductively coupled plasma mass spectrometry were used to determine the overall chemical composition. The investigated samples were found to exhibit a relatively homogenous distribution of Sc between the larger mineral particles and the fine-grained matrix except for Al-phases like diaspore, boehmite and gibbsite. These phases were found to be particularly low in Sc. The only sample where Sc mass fractions in Al-phases exceeded 50 mg/kg was the Russian sample from North Ural. Fe-phases such as goethite, hematite and chamosite (for Russian samples) were more enriched in Sc than the Al-phases.
In fact, in Greek samples goethite showed a higher capacity to incorporate or adsorb Sc than hematite. Accessory minerals like zircon, rutile/anatase and ilmenite were found to incorporate higher mass fractions of Sc (>150 mg/kg), however, those minerals are only present in small amounts and do not represent major host phases for Sc. In Russian samples from North Ural an additional Ca–Mg rich phase was found to contain significant mass fractions of Sc (>500 mg/kg). μ-XANES spectroscopy was able to show that Sc in bauxite residue occurs adsorbed onto mineral surfaces as well as incorporated into the crystal lattice of certain Fe-phases. According to our observations the bauxite type, i.e. karstic or lateritic, the atmospheric conditions during bauxitization, i.e. oxidizing or reducing, and consequently the dominant Sc-bearing species in the primary Bauxite influence the occurrence of Sc in bauxite residues. In karstic bauxites, underlying carbonate rocks can work as a pH-barrier and stabilize Sc. This prevents the Sc from being mobilized and removed during bauxitization. Hence, karstic bauxites are more prone to show a Sc enrichment than lateritic bauxites. Reducing conditions during bauxitization support the incorporation of Sc into clay minerals such as chamosite, which can dissolve and reprecipitate during Bayer processing causing Sc to be redistributed and primarily adsorb onto mineral surfaces in the bauxite residue. Oxidizing conditions support the incorporation of Sc into the crystal lattice of Fe-oxides and hydroxides, which are not affected in the Bayer process. The genetic history of the bauxite is therefore the major influential factor for the Sc occurrence in bauxite residues.
New developments in legislation and technology development for P-recovery were presented with focus on the situation in Germany.
As one of the most energy and carbon consuming industries, steelmakers have an intrinsic interest in the development of technologies, reducing their carbon footprint as well as their carbon input. Besides generating new feedstocks from biomass or waste polymers, the valorization of carbon fiber reinforced polymer (CFRP) waste streams seems to be extremely promising based on the high carbon content of carbon fibers (CF), chars from CFRP and even unprocessed CFRP waste of >92%, 98% and 79%, respectively. Although, reduction of environmental impact from those high-performance materials was achieved by the development of smart recycling solutions, the continuous truncation by mechanical treatment of CF over multiple cycles, analogous to paper fibers, and the large global CFRP waste stream of 62 kt/a demand for a sustainable management of end-of-life (EOL) CFRP. Recently it was demonstrated that CF can be used safely as reductant in pyrometallurgical processes in a downhole electric furnace without significant WHO fiber emission. Therefore we anticipate a huge potential of CF based materials as sustainable reductant for steelmaking in an electric arc furnace (EAF). To facilitate the applicability of EOL CFRP in steelmaking, we investigated the interaction between CF based materials and liquid metal phases, appearing during the process, on different scales. Particularly, we examined the reactivity, wettability and dissolution behavior of CF and CFRP concerning liquid slag and steel. The presented results indicate that understanding the impact of the microstructure of CF on their behavior is crucial for their application in EAF steelmaking without risking potential hazards by WHO fiber emission. Besides the detailed elucidation of structure reactivity relationships of CF, the broader impact on circular economy will be presented.
In Bayern wird Klärschlamm aus der kommunalen Abwasserreinigung weitgehend verbrannt. Monoverbrennungsanlagen - ausschließlich für kommunalen Klärschlamm - gibt es in Altenstadt, München, Gendorf, Straubing, Neu-Ulm und zukünftig auch in Augsburg. Die Anlage in Altenstadt verbrennt jährlich ca. 55.000 t Klärschlamm-Trockensubstanz und produziert dabei rund 15.000 t phosphatreiche Aschen.
Die Asche aus Altenstadt wird zurzeit überwiegend direkt landwirtschaftlich genutzt. Aufgrund der niedrigen Schadstoffgehalte ist diese Nutzung nach den düngemittelrechtlichen Regelungen gesetzlich zulässig. Um der Intention der neuen Düngeverordnung (26. Mai 2017) nach hocheffizienten, d.h. gut pflanzenverfügbaren Düngemitteln zu entsprechen, ist eine Aufbereitung der Klärschlammasche geplant. Im Rahmen des R-Rhenania Projektes errichten der Betreiber der Klärschlammverbrennungsanlage Altenstadt in Bayern Emter GmbH - und der Düngemittelhersteller sePura GmbH gemeinsam eine AshDec®-Demonstrationsanlage, die im Jahr 2023 den Betrieb aufnehmen soll. Das angewandte AshDec®-Verfahren schließt die Phosphate in der Klärschlammasche thermisch im Drehrohrofen auf und macht diese für Pflanzen vollständig verfügbar. Gleichzeitig werden Schadstoffe wie Arsen, Blei und Cadmium entfernt. Den thermischen Aufschluss kennt man bereits vom erfolgreichen, aber nicht mehr produzierten Düngemittel „Rhenania-Phosphat“, das auf der Basis von Rohphosphaten hergestellt wurde.
Die geplante Anlage wird neben den Aschen aus Altenstadt zusätzlich die Aschen aus weiteren bayerischen Verbrennungsanlagen verwerten und für eine Kapazität von 30.000 Jahrestonnen Asche ausgelegt sein. Der Projektpartner sePura plant den produzierten Dünger vollständig in Bayern zu verwerten. Dies verringert die Umweltbelastung durch lange Transportwege und fördert die Regionalität des Vorhabens.
Bei der Stahlproduktion fallen verfahrensbedingt große Mengen an Nebenprodukten und Abfällen wie Stahlwerksschlacken, Filterstäube und Gichtgasschlämme an. Hohe Anteile dieser Stoffströme werden aufgrund ihrer Zusammensetzung immer noch deponiert, obwohl sie ein hohes Wertstoffpotential aufweisen. An der Bundesanstalt für Materialforschung und -prüfung (BAM) werden Verfahren untersucht und entwickelt, welche eine Verwertung und Kreislaufführung dieser Materialströme ermöglichen. Aus sogenannten Linz-Donawitz-(LD)-Schlacken können durch carbothermische Nachbehandlung Roheisen und ein dem Portlandzementklinker (PZK) ähnliches Bindemittel erzeugt werden. Aus Elektroofenstäuben und Gichtgasschlämmen kann Zink gewonnen und die Anteile an Eisen und Kohlenstoff in den Stahlproduktionsprozess zurückgeführt werden. Durch diese technischen Maßnahmen kann es gelingen die Deponierung von Abfällen der Stahlproduktion zukünftig deutlich zu reduzieren.
Bei der Stahlproduktion fallen verfahrensbedingt große Mengen an Nebenprodukten und Abfällen wie Stahlwerksschlacken, Filterstäube und Gichtgasschlämme an. Hohe Anteile dieser Stoffströme werden aufgrund ihrer Zusammensetzung immer noch deponiert, obwohl sie ein hohes Wertstoffpotential aufweisen. An der Bundesanstalt für Materialforschung und -prüfung (BAM) werden Verfahren untersucht
und entwickelt, welche eine Verwertung und Kreislaufführung dieser Materialströme ermöglichen. Aus sogenannten Linz-Donawitz-(LD)-Schlacken können durch carbothermische Nachbehandlung Roheisen und ein dem Portlandzementklinker (PZK) ähnliches Bindemittel erzeugt werden. Aus Elektroofenstäuben und Gichtgasschlämmen kann Zink gewonnen und die Anteile an Eisen und Kohlenstoff in den Stahlproduktionsprozess zurückgeführt werden. Durch diese technischen Maßnahmen kann es gelingen die Deponierung von Abfällen der Stahlproduktion zukünftig deutlich zu reduzieren.
In recent times, as the need for new high-tech materials is growing steadily to fulfil future sustainability goals, more and more looks turn towards industrial waste streams as potential sources of valuable metals. Bauxite residue (BR), accumulating during alumina production, is one of the major waste streams in the metal industry. Suitable re-use possibilities for BR are intensively investigated including approaches for the recovery of scandium (Sc). This transition metal, even though rarely recognized by the broader audience yet, has recently gained the interest of e.g. aerospace industries and SOFC-producers since its use is strongly improving the performance and durability of the respective materials.
Even though many sources classify Sc as one of the REE, there are many aspects, such as its ionic radius, which significantly differentiate Sc from the REE and cause its behaviour to be distinct as well. The large ionic potential (radius/charge) causes Sc to be incompatible in most rock forming minerals, which results in generally low concentrations in the earth’s crust and rare occurrences of natural Sc-deposits.
The general occurrence of enriched concentrations of Sc in some BRs compared to the earth’s crust is known for some time now and has especially been investigated for Greek materials. However, the (geo)chemical and mineralogical behaviour, the Sc speciation, the association and the variation of Sc occurrences in BRs of different origin is still not fully understood. This study aims to gain better knowledge on the different kinds of Sc-occurrences and their possible impact on future recovery schemes. We therefore apply a diverse set of analytical methods including novel measurement techniques such as X-ray absorption near edge structure (XANES) spectroscopy as well as standard techniques such as electron microprobe analyses, and Raman spectroscopy on BRs from Germany, Hungary and Greece. Information on the local distribution of Sc is determined by high-resolution laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) mappings.
Sc in Greek BR seems to have an affinity towards Fe-Phases such as Goethite and Hematite. However, whereas some of these phases show distinct enrichment of Sc, others are particularly barren, which might be a result of the different input materials. By means of XANES measurements it was possible to show that Sc in the Greek samples occurs adsorbed on the surface of those Fe-Phases, likely in the form of amorphous Sc-hydroxide or -oxyhydroxide or can be incorporated into the crystal lattice as well. The general affinity of Sc to those kinds of phases has been reported for natural rocks such as laterites before, where similar investigations were made using the XANES method [8]. Likewise, the Fe-association has been observed for Greek BR by Vind et al. [7]. Hungarian BRs show similar results as the Greek samples and LA-ICP-MS mappings show distinct Sc enrichment rims surrounding mineral particles. In German BR, Fe as well as Ti-phases occur to be partially enriched in Sc. Depending on the original primary bauxite, the source rock of the bauxite and the bauxite processing route, it is likely that many different parameters influence the occurrence and species of Sc in the BR. Theoretically, it either can therefore remain within its original carrier or can be partially or fully redistributed within the BR. Since the processing of the bauxite involves elevated temperatures, pressure and dissolving reagents, it is however very likely that some of the Sc will be redistributed and adsorb on mineral surfaces of smaller and larger particles, making beneficiation steps rather ineffective.
The study shows that there is no general rule defining how Sc is associated mineralogically or chemically within BRs. Therefore, the effective development of a recovery method needs a case specific background knowledge on the Sc-species present in the BR of interest. This research has received funding from the European Community’s Horizon 2020 Programme SCALE (H2020/2014-2020) under grant agreement n° 730105.
Phosphorus (P) recovery from sewage sludge ash (SSA) is one of the most promising approaches of phosphate rock substitution in mineral fertilizers and might be a sustainable way to secure supply of this raw material in the future. In the current investigation, the process of thermochemical treatment of SSA was applied to SSA coming from selected mono-incineration plants of municipal sewage sludge in Poland (Cracow, Gdansk, Gdynia, Lodz, Kielce and Szczecin).
The Polish SSA was thermochemically converted in the presence of sodium (Na) additives and a reducing agent (dried sewage sludge) to obtain secondary raw materials for the production of marketable P fertilizers. The process had a positive impact on the bioavailability of phosphorus and reduced the content of heavy metals in the obtained products. The P solubility in neutral Ammonium citrate, an indicator of its bioavailability, was significantly raised from 19.7–45.7% in the raw ashes and 76.5–100% in the thermochemically treated SSA. The content of nutrients in the recyclates was in the range of 15.7–19.2% P2O5, 10.8–14.2% CaO, 3.5–5.4% Na2O, 2.6–3.6% MgO and 0.9–1.3% K2O. The produced fertilizer raw materials meet the Polish norms for trace elements covered by the legislation: the content of lead was in the range 10.2–73.1 mg/kg, arsenic 4.8–22.7 mg/kg, Cadmium 0.9–2.8 mg/kg and mercury <0.05 mg/kg. Thus, these products could be potentially directly used for fertilizer production. This work also includes an analysis of the possibilities of using ashes for fertilizer purposes in Poland, based on the assumptions indicated in the adopted strategic and planning documents regarding waste management and fertilizer production.
Gypsum (calcium sulfate dihydrate) has excellent building material properties and has been widely used in constructions in the last decades in many countries. Accordingly, an increase of waste gypsum in C&D waste is expected in the upcoming years. On one hand, sulfates are unwanted in other secondary building materials (particularly in recycled concrete aggregates) and should be minimized for quality reasons. On the other hand, used gypsum from CDW can also be used in gypsum production if the high quality requirements for the recycled gypsum – especially regarding the sorting accuracy - are met.
A large percentage of the gypsum from buildings was installed as gypsum plasterboards in interior fittings so far. Gypsum plasterboards are comparatively simple to remove and to separate during selective dismantling. Therefore, a high sorting purity can be achieved. In addition, techniques for the recycling of gypsum plasterboards already exist and high quality standards can be achieved. Also, the reuse in gypsum production has been improved in the last decade. Furthermore, an environmental evaluation of the whole process of gypsum plasterboard recycling and reuse showed that this approach can be environmentally advantageous. Therefore, a closed-loop recycling of gypsum plasterboards is feasible.
This poster will show the development of gypsum consumption in different countries as well as a prognosis for the upcoming of gypsum in CDW in the future decades in Germany. Furthermore, a simplified scheme of the recycling process and selected results from an environmental evaluation will be presented.
Popioły pochodzące z instalacji do spalania komunalnych osadów ściekowych, znajdującej się na terytorium Polski, poddano procesom termochemicznego przekształcania, dzięki czemu otrzymano produkty nawozowe spełniające kryteria dopuszczające je do obrotu jako nawozy mineralne. Ponadto dokonano analizy możliwości wykorzystania popiołów na cele nawozowe zgodnie z obecnie przyjętymi dokumentami strategicznymi i planistycznymi dotyczącymi gospodarki odpadami na poziomie krajowym i europejskim.
Microspectroscopy reveals dust-derived apatite grains in acidic, highly-weathered Hawaiian soils
(2021)
Dust deposition is an important source of phosphorus (P) to many ecosystems. However, there is little evidence of dust-derived P-containing minerals in soils. Here we studied P forms along a well-described climatic Gradient on Hawaii, which is also a dust deposition gradient. Soil mineralogy and soil P forms from six sites along the climatic gradient were analyzed with bulk (X-ray diffraction and P K-edge X-ray absorption near edge structure) and microscale (X-ray fluorescence, P K-edge X-ray absorption near edge structure, and Raman) analysis methods. In the wettest soils, apatite grains ranging from 5 to 30 μm in size were co-located at the micro-scale with quartz, a known continental dust indicator suggesting recent atmospheric deposition. In addition to co-location with quartz, further evidence of dust-derived P included backward trajectory modeling indicating that dust particles could be brought to Hawaii from the major global dust-loading areas in central Asia and northern Africa. Although it is not certain whether the individual observed apatite grains were derived from long-distance transport of dust, or from local dust sources such as volcanic ash or windblown fertilizer, these observations offer direct evidence that P-containing minerals have reached surface layers of highly-weathered grassland soils through atmospheric deposition.
One of the typical wastes produced in blast-furnace (BF) ironmaking is BF sludge, which mostly consists of carbon and iron oxides, but also contains toxic trace metals such as Zn, Pb, Cd, As, and Hg that render the material hazardous. Due to the lack of an established recycling process, BF sludges are landfilled, which is ecologically questionable and costly. Here, we investigate selective removal of Zn, Pb, and Cd from BF sludge by chlorination–evaporation reactions using thermodynamic modelling and laboratory-scale experiments. Specifically, BF sludge was thermochemically treated at 650–1000 °C with a spent iron(II) chloride solution from steel pickling and the effects of process temperature and retention time on removal of Zn, Pb, and Cd were investigated. Zinc and Pb were quantitatively removed from BF sludge thermochemically treated at 900–1000 °C, whereas Fe and C as well as other major elements were mostly retained. The Zn, Pb, and Cd contents in the thermochemically treated BF sludge could be lowered from ∼56 g/kg, ∼4 g/kg, and ∼0.02 g/kg to ≤0.7 g/kg, ≤0.02 g/kg, and ≤0.008 g/kg, respectively, thus rendering the processed mineral residue a non-hazardous raw material that may be re-utilized in the blast furnace or on the sinter band.
This paper presents an inventory of sewage sludge ashes (SSA) generated in the mono-incineration plants for municipal sewage sludge in Poland. This research focused on the detailed study of mass flows, chemical composition, and phosphorus recovery potential. There are currently 11 sludge mono-incineration plants operated with a total capacity of 160,300 Mg dry weight (d.w.) of sludge annually. Recently, a significant increase in the amount of SSA generated in these plants has been observed, reaching 26,756 Mg in 2018. Chemical composition of SSA showed significant amounts of the main nutrients: calcium (~14%), phosphorus (~13%), magnesium (~3%), and potassium (~1%). Additional main elements were iron (~14.5%), silicon (~13%), and aluminium (~6%). The main trace elements in the SSA were zinc (~3750 mg/kg) and copper (~899 mg/kg). Pollutants, according to fertilizer regulations of different countries, present in Polish SSA were chromium(~703 mg/kg), nickel (~260 mg/kg), lead (~94 mg/kg), and Cadmium (~9 mg/kg). The radionuclides, uranium, and thorium often present in higher amounts in commercial phosphate rock-based fertilizers, were only detected in SSA t low levels of 4–9 mg/kg and 2–3 mg/kg, respectively. Theoretical phosphorus recovery potential from the SSA (from plants in Cracow, Lodz, Gdansk, Gdynia, Szczecin, and Kielce) was estimated at 1613.8 Mg, of which 33.9% is bioavailable. Currently, in Poland, the recommended approach is the production of fertilizers as a result of the extraction of phosphorus from the SSA with its use in the production of secondary mineral fertilizers.
Further research in this area is required considering Polish conditions and legislation.
Gegenstand dieser Arbeit ist die Untersuchung eines bestehenden pyrometallurgischen Prozesses zur Rückgewinnung von Tantal und Niob aus metallurgischen Reststoffen mit vorwiegend niedriger Wertstoffkonzentration.
Zur näheren Erforschung der im vorliegenden Stoffsystem ablaufenden Reduktionsprozesse wurden in einem Elektrolichtbogenofen Schmelzversuche im Pilotmaßstab durchgeführt. Als Reduktionsmittel diente Koks, welcher mithilfe einer Argon-gespülten Eisenlanze in die flüssige mineralische Schmelze eingebracht wurde. Während der Reduktionsbehandlung werden Refraktärmetalle wie Tantal und Niob in ihre Carbide überführt und anschließend in der erschmolzenen eisenbasierten Metallphase am Boden des Reaktors angereichert. Neben Tantal und Niob gelangt auch ein Teil des im Einsatzmaterial enthaltenen Titans als unerwünschtes Begleitelement in die Metallphase.
Sein Großteil verbleibt jedoch als Oxid in der Schlacke und wird dort hauptsächlich im Mineral Perowskit (CaTiO3) gebunden. Die erstarrten Schlackeproben wurden mit verschiedenen Methoden wie Röntgenfluoreszensanalyse, Röntgenbeugung und Rasterelektronenmikroskopie mit gekoppelter energiedispersiver Röntgenanalyse untersucht, um die Bildung tantalhaltiger Mineralphasen zu verschiedenen Stadien des Reduktionsprozesses zu verfolgen.
Die hier gewonnenen Erkenntnisse zeigen, dass weniger die durch das Einblasen von Koks verursachte Reduktionsreaktion, sondern das Absinken der tantalreichen Eisentröpfchen in der flüssigen mineralischen Schmelze, gefolgt von ihrer Anreicherung in die Metallphase, für die Kinetik ausschlaggebend ist.
Weltweit werden etwa 80–85 % aller abgebauten Rohphosphate für die Produktion von Düngemitteln verwendet. Bei noch steigendem Bedarf an Phosphor (P) geht man derzeit davon aus, dass die weltweiten P-Reserven noch über 200 Jahre ausreichen. Um den P-Vorrat langfristig abzusichern, sollte der in Reststoffen enthaltene Phosphor möglichst umfänglich genutzt werden. Dieser Forderung trägt das von der Bundesregierung 2012 erstmals beschlossene Deutsche Ressourceneffizienzprogramm ProgRess Rechnung. Rohphosphat wird auch seitens der Europäischen Kommission aufgrundseiner ökonomischen Bedeutung und des unsicheren Angebots als „kritischer Rohstoff“ eingestuft. Vor diesem Hintergrund hat die Bundesregierung in der Verordnung zur Neuordnung der Klärschlammverwertung vom 27. September 2017 in Deutschland eine verpflichtende technische Rückgewinnung von Phosphor für Abwasserbehandlungsanlagen ab einer Ausbaugröße von 100.000 Einwohnerwerten (12 Jahre nach Inkrafttreten der Verordnung) bzw. ab einer Ausbaugröße von über 50.000 Einwohnerwerten (15 Jahre nach Inkrafttreten der Verordnung) vorgeschrieben. Die Verordnung enthält keine Vorgaben hinsichtlich der anzuwendenden Technologie bei der Phosphorrückgewinnung. Ausgenommen von der Rückgewinnungspflicht sind Klärschlämme mit niedrigen Phosphorgehalten (weniger als 20 Gramm Phosphor je Kilogramm Klärschlamm-Trockenmasse). Auch die im Jahre 2017 verabschiedeten neuen Rechtsvorschriften für die Düngung verlangen zukünftig einen nachhaltigen und ressourceneffizienten Umgang mit Nährstoffen bei der landwirtschaftlichen Erzeugung und schränken die P-Zufuhr insbesondere auf hoch versorgten Böden ein (Düngeverordnung vom 26. Mai 2017). Dies wird zu einem mehr am Pflanzenbedarf orientierten und ggf. vermehrt überbetrieblichen Einsatz von wirtschaftseigenen Düngern führen. Um den politischen und gesetzlichen Anforderungen gerecht zu werden, müssen einerseits wirksame und kosteneffiziente technische Verfahren zum P-Recycling (weiter)entwickelt werden. Andererseits müssen die Recyclingprodukte die Anforderungen für eine direkte Verwendung in der Landwirtschaft oder als Rohstoff für die Herstellung von Düngemitteln erfüllen. In dem vorliegenden Standpunkt wird zunächst der potenzielle Beitrag von Reststoffen zur Deckung des P-Bedarfs in der deutschen Pflanzenproduktion geschätzt. Für die wichtigsten Reststoffe werden technische Verfahren zur P-Rückgewinnung bzw. Aufarbeitung skizziert. Auf Basis der Anforderungen der Landwirtschaft bzw. der Düngemittelindustrie
an die P-Recyclingprodukte werden deren Herstellungsverfahren bewertet. Schließlich wird der Regelungs- und Forschungsbedarf formuliert.
The Brazilian sugarcane industry produced around 173 million tons (Mt) of bagasse in 2018. Bagasse is a by-product of juice extraction for ethanol and sugar production and is combusted in order to generate power, producing up to 10 Mt of ash per year. This ash contains various concentrations of plant nutrients, which allow the ash to be used as a crop fertilizer. However, the concentration and extractability of phosphorus (P), an essential plant nutrient, are low in bagasse ash. To increase the P content, we co-gasified and co-combusted bagasse with P-rich chicken manure. The resulting ash was thermochemically post-treated with alkali additives (Na2SO4 and K2SO4) to increase the availability of P to plants. We aimed to: (i) investigate the effect of thermochemical post-treatment of co-gasification residue and co-combustion ash on P availability to soybeans, (ii) explore the potential of chemical extraction methods (citric acid, neutral ammonium citrate, formic acid, and Mehlich-I) and diffusive gradients in thin films (DGT) to predict the availability of P to soybeans, and (iii) identify the responsible P-phases using X-ray diffraction . We evaluated P availability to soybeans growing in Brazilian Oxisol soil in two independent greenhouse pot experiments. The positive effect of thermochemical treatment on P availability from gasification residue was confirmed through the observation of increased P uptake and biomass in soybean plants. These findings were confirmed by chemical extraction methods and DGT. The gasification residue contained whitlockite as its main P-bearing phase. Thermochemical post-treatment converted whitlockite into highly soluble CaNaPO4. In contrast, co-combustion ash already contained highly soluble Ca(Na,K)PO4 as its main P-bearing phase, making thermochemical post-treatment unnecessary for increasing P availability. In conclusion, increased extractability and availability of P for soybeans were closely connected to the formation of calcium alkali phosphate. Our findings indicate that this combined methodology allows for the prediction of P-fertilization effects of ash.
Phosphorus (P) fertilizers from secondary resources became increasingly important in the last years. However, these novel P-fertilizers can also contain toxic pollutants such as chromium in its hexavalent state (Cr(VI)). This hazardous form of chromium is therefore regulated with low limit values for agricultural products even though the correct determination of Cr(VI) in these fertilizers may be hampered by redox processes, leading to false results. Thus, we applied the novel diffusive gradients in thin-films (DGT) technique for Cr(VI) in fertilizers and compared the results with the standard wet chemical extraction method (German norm DIN EN 15192) and Cr K-edge X-ray Absorption near-edge structure (XANES) spectroscopy. We determined an overall good correlation between the wet chemical extraction and the DGT method. DGT was very sensitive and for most tested materials selective for the analysis of Cr(VI) in P-fertilizers. However, hardly soluble Cr(VI) compounds cannot be detected with the DGT method since only mobile Cr(VI) is analyzed. Furthermore, Cr K-edge XANES spectroscopy showed that the DGT binding layer also adsorbs small amounts of mobile Cr(III) so that Cr(VI) values are overestimated. Since certain types of the P fertilizers contain mobile Cr(III) or partly immobile Cr(VI), it is necessary to optimize the DGT binding layers to avoid aforementioned over- or underestimation. Furthermore, our investigations showed that the Cr K-edge XANES spectroscopy technique is unsuitable to determine small amounts of Cr(VI) in fertilizers (below approx. 1% of Cr(VI) in relation to total Cr).
Das Element Phosphor ist für alle Lebewesen essenziell und wird beispielsweise von Pflanzen in Form von Phosphaten aufgenommen.
In der landwirtschaftlichen Produktion werden dem Boden die Phosphate durch Wachstum und Ernte der Pflanzen entzogen und müssen ihm in Form von Phosphatdüngemitteln wieder zugeführt werden, um die Nahrungsmittelproduktion zu sichern. Rohphosphat stellt die Grundlage unserer derzeitigen Phosphatdüngemittel dar, ist aber gleichzeitig ein endlicher Rohstoff.
Des Weiteren sind insbesondere sedimentäre Rohphosphate oftmals mit erheblichen Konzentrationen toxischer Schadstoffe wie Cadmium, Uran und Thorium belastet. Eine Kreislaufführung des Phosphats sollte erfolgen, um natürliche Rohstoffvorkommen zu schonen und den Eintrag von Schadstoffen auf unsere Böden zu unterbinden.
Based on recently published research on leaching control mechanisms in electric arc furnace (EAF) slags, it is assumed that a FeO/SiO2 ratio of around one leads to low leached V and Cr concentrations. This ratio influences the mineral phase composition of the slag toward higher amounts of spinel and a lower solubility of calcium silicate phases by suppressing the formation of magnesiowuestite and highly soluble calcium silicate phases. To evaluate this hypothesis, laboratory and scaled up tests in an EAF pilot plant were performed on slag samples characterized by elevated V and Cr leaching and a high FeO/SiO2 ratio. Prior to the melting experiments, the optimum FeO/SiO2 ratio was calculated via FactSageTM. In the melting experiments, the ratio was adjusted by adding quartz sand, which also decreased the basicity (CaO/SiO2) of the slag. As a reference, remelting experiments without quartz sand addition were conducted and additionally, the influence of the cooling rate of the slag was examined. The remelted (without quartz sand) and the remelted modified slags (with quartz sand) were analyzed chemically and mineralogically and the leaching behavior was investigated. The modification of the slags yielded a minimized release of V and Cr, supporting the hypothesis that the FeO/SiO2 ratio influences the mineralogy and the leaching behavior.
Calcium alkali phosphates Ca(Na,K)PO4 are main constituents of bioceramics and thermochemically produced phosphorus fertilizers because of their bioavailability. Sparse thermodynamic data are available for the endmembers CaNaPO4 and CaKPO4. In this work, the missing data were determined for the low-temperature phase modifications of the endmembers CaNaPO4 and CaKPO4 and three intermediate Ca(Na,K)PO4 compositions. Standard enthalpy of formation ranges from - 2018.3 ± 2.2 kJ mol-1 to - 2030.5 ± 2.1 kJ mol-1 and standard entropy from 137.2 ± 1.0 J mol-1 K-1 to 148.6 ± 1.0 J mol-1 K-1 from sodium endmember b-CaNaPO4 to potassium endmember b0-CaKPO4.
Thermodynamic functions are calculated up to 1400 K for endmembers and the sodium-rich intermediate phase b-Ca(Na0.93K0.07)PO4. Functions above 640 K are extrapolated because of the phase transition from low- to high-temperature phase. Impurities in the synthesized intermediate phases c-Ca(Na0.4K0.6)PO4 and c-Ca Na0.35K0.65)PO4 and one additional phase transition around 500 K impeded the determination of high-temperature thermodynamic functions. In general, data for phase transition temperatures agree with the previously reported phase diagrams.
Da das Recycling von tantalhaltigen Post-Consumer-Abfällen praktisch nicht existiert, stellen metallurgische Reststoffe eine äußerst wichtige Rohstoffquelle für das Tantalrecycling dar. Die meisten Zinnerze enthalten von Natur aus erhebliche Mengen an Refraktärmetallen. Diese Elemente werden in den Schlacken der pyrometallurgischen Primärzinngewinnung angereichert. Aufgrund ihrer vergleichsweise hohen Wertstoffkonzentration und ihrer Funktion als zusätzlicher Schlackenbildner stellen diese Schlacken einen wertvollen Rohstoff für die Verhüttung tantalhaltiger Reststoffe dar. In der vorliegenden Arbeit wird ein existierendes Verfahren zur Tantalrückgewinnung diskutiert, dem hauptsächlich pyrometallurgische Rückstände geringer Wertstoffkonzentration als Einsatzstoff dienen. Mit Hilfe des Verfahrens sollte dasoxidisch vorliegende Tantal vollständig reduziert und in der Metallphase angereichert werden. Weiterhin sollte vermieden werden, dass unerwünschte Elemente wie Titan in die Metallphase überführt werden. Ziel der Untersuchung war es, die ablaufenden Reduktionsprozesse besser zu verstehen, um so Ansätze für die Prozessoptimierung identifizieren zu können.