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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.
Incineration of sewage sludge is expected to increase in the future due to growing concerns about the direct use of sludge in agriculture. Sewage sludge is the pollutant sink of wastewater treatment and thus loaded with contaminants that might pose environmental hazards. Incineration degrades organic pollutants efficiently, but since the ash is currently mostly disposed of, all valuable component like phosphorus (P) and technologically relevant metals present in the sewage sludge ash (SSA) are removed from the economic cycle entirely. We conducted a complete survey of SSA from German mono-incineration facilities and determined the theoretical recovery potential of 57 elements. German SSA contains up to 19,000 t/a P which equals approximately 13% of phosphorus applied in the German agriculture in form of phosphate rock based mineral fertilizers. Thus, SSA is an important secondary resource of P. However, its P-solubility in ammonium citrate solution, an indicator for the bioavailability, is only about 26%. Treatment of SSA is recommended to enhance P bioavailability and remove heavy metals before it is applied as fertilizer. The recovery potential for technologically relevant metals is generally low, but some of these elements might be recovered efficiently in the course of P recovery exploiting synergies.
Recovery of rare earth elements - optimized elemental analysis of fluorescent lamp shredder waste
(2016)
Rare earth elements (REE) are a crucial component of fluorescence lamps. Several procedures have been developed to recovery these technological important elements. Nevertheless, actual REE recycling from fluorescence lamps is scarce so far (recovery rate of less than 1 %), with current recycling approaches concentrating on glass recovery. Since most recycling processes include several, also wet-chemical steps, a complete knowledge of the actual elemental composition of the respective mass flows is necessary for an efficient REE recovery. We tested seven different reagent mixtures for microwave-assisted digestion of fluorescent lamp shredder, including HF, HClO4, and H2O2. We determined the concentrations of 25 of the most relevant rare earth and other trace elements in the respective dilutions. Two independent digestions, one a mixture of perchlorid/nitric/hydrofluoric acid and the other aqua regia, showed the highest concentrations of 23 of these elements, excluding only Sn and Tb. The REE concentrations in the tested lamp shredder sample (stated in g/kg) were 10.2 (Y), 12.1 (La), 7.77 (Ce), 6.91 (Eu), 1.90 (Gd), and 4.11 (Tb).
Phosphorus is essential for all animate beings and not replaceable in its functions. Recovered phosphorus from secondary sources is expected gain importance in the future due to supply risks and environmental concerns regarding fossil phosphate rock, the single source of phosphorus so far. Existing regulations, standards, and analytical methods are basically configured for well-established organic and mineral fertilizer but not for the emerging recycling products. Consequently, the respective procedures have to be adapted, especially in terms of matrix effects and so far not regulated pollutants like uranium and emerging pollutants of concern.
Recovery potential of Scandium and other critical raw materials from European industrial by-products
(2017)
Technological evolution and modern advances in the field of renewable energies are connected to an increasing demand on critical raw materials and especially technological metals.
Recently, interest in the element scandium (Sc) has started to grow due to its positive influence on material properties e.g. in high performance-alloys, solid-oxide-fuel cells and solid-state lasers. Therefore, a rise in value and demand is expected in the near future.
This study focuses on the reliable and sufficient methodology of measuring Sc and other critical raw materials in secondary waste products from the Al2O3- and Ti2O producing industry. It also targets the examination of Sc-bearing phases and their potential influence in the recovery of Sc from above mentioned materials. Essentially, chemical and structural analyses and characterization of European red muds and its Sc-bearing mineral phases are carried out.
Furthermore, analogue investigations are performed for filter cakes and acid slurries that incur during TiO2 production.
Red muds and TiO2 filter cakes from several European countries have been analyzed by X-ray diffraction, X-ray-fluorescence, ICP-MS and -OES. Analytical procedures performed are based on previous studies and different methods are tested and compared to ensure reliable data from ICP-MS and -OES measurements.
Red mud samples were found to contain ~60-100 mg/kg Sc. Main mineral phases are Hematite, Gibbsite, Boehmite, Cancrinite, Diaspore, Perovskite, Rutile, Katoite and Quartz in variable amounts. Samples from TiO2-production contain up to 400 mg/kg of Sc and significant amounts of niobium and cerium. The main mineral phases are Rutile, Calcite, Quartz, Graphite and Iron-Oxide-Chloride. Generally, it is assumed that Sc is associated with iron and titanium-bearing phases such as Ilmenite and Rutile as it was found in REE deposits in China. Hence, These phases are studied in more detail with advanced structural analyses such as X-ray Absorption near edge structure (XANES) and point-based mineral chemistry analyses by electron microprobe. The study is incorporated in the SCALE project (GA No. 730105) funded by European Union's Horizon 2020 research and innovation program and aims to secure a European supply chain for Sc from metallurgical by-products.
Recovery of rare earth elements - optimized elemental analysis of fluorescent lamp shredder waste
(2016)
Rare earth elements (REE) are a crucial component of fluorescence lamps. Several procedures have been developed to recovery these technological important elements. Nevertheless, actual REE recycling from fluorescence lamps is scarce so far (recovery rate of less than 1 %), with current recycling approaches concentrating on glass recovery. Since most recycling processes include several, also wet-chemical steps, a complete knowledge of the actual elemental composition of the respective mass flows is necessary for an efficient REE recovery. We tested seven different reagent mixtures for microwave-assisted digestion of fluorescent lamp shredder, including HF, HClO4, and H2O2. We determined the concentrations of 25 of the most relevant rare earth and other trace elements in the respective dilutions. Two independent digestions, one a mixture of perchlorid/nitric/hydrofluoric acid and the other aqua regia, showed the highest concentrations of 23 of these elements, excluding only Sn and Tb. The REE concentrations in the tested lamp shredder sample (stated in g/kg) were 10.2 (Y), 12.1 (La), 7.77 (Ce), 6.91 (Eu), 1.90 (Gd), and 4.11 (Tb).