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With regard to the depletion of global phosphorus reserves and with the aim of ensuring sustainable soil fertility on agricultural soils, a fundamental understanding of mechanisms of fixation and mobilization of inorganic phosphorus in soils is required. Amongst others, phosphorus availability is affected by ad- and desorption reactions on pedogenic Fe- and Al-hydroxide surfaces. The characterization of phosphate binding on those contrasting mineral surfaces can help to find solutions for enhancing the mobilization of fertilized but not available soil inorganic phosphate. Fourier-transform infrared spectroscopic experiments were carried out during phosphorus adsorption on crystalline gibbsite, poorly crystalline 2-line-ferrihydrite and amorphous Fe:Al-hydroxide mixtures. Desorption experiments with CaCl₂, CaSO₄, citric acid (C₆H₈O₇), and humic acid (C₉H₉NO₆) were conducted to determine the capacity of phosphate fixation and mobilization in short- and long-term. Additionally, phosphorus release from the Fe- and Ca-phosphates vivianite and hydroxyapatite were analyzed.
For gibbsite, the formation of AlHPO₄ and Al₂HPO₄ can be assumed, while for ferrihydrite, a FeHPO₄ or Fe₂PO₄ complex and the precipitation of FePO₄ with longer equilibration time were observed. Fe₂HPO₄ or a Fe₂PO₄ surface complex was deduced for amorphous Fe-hydroxides, an AlH₂PO₄ surface complex was identified for Al-hydroxides. The weakly associated amorphous FeO(OH) molecules enhance the precipitation of FePO₄. With high Al content, a weaker phosphate binding of both inner- and outer-sphere complexes and either no or minor quantities of precipitate were formed. Ferrihydrite showed a more rigid structure and a lower extent of precipitation compared to amorphous Fe-hydroxide. The cumulative phosphorus desorption followed the order CaCl₂ < CaSO₄ < humic acid < citric acid for crystalline and amorphous Fe- and Al-hydroxides as well for vivianite and hydroxyapatite. While inorganic anion exchange took part at easily available binding sites and fast exchangeable phosphorus, organic acids additionally affect the more heavily available binding sites and slow exchangeable phosphorus. For humic acid, the accumulation of metal-organic complexes in the desorption solution was suggested, whereas for citric acid the dissolution of the minerals was maintained. The cumulative release rates of the Flow-Through-Reactor setup were higher compared to batch due to a short residence time and a continuous concentration gradient. This could lead either to an over- or underestimation of the available phosphorus pools and influenced the comparability of both methods.
Designing and implementing comprehensive reclamation programme during mine operations can minimize environmental damage and decrease potential legal liability. Although Regulation (23) of the Ghana Environmental Assessment Regulation (1999) requires mine proponents to have plans for reclamation, it has been revealed most degraded mine-sites have not been reclaimed. Even in cases where some mining companies made reclamation attempts, such efforts could not produce any favourable outcome due to the failure in adopting such best reclamation management practices as slope stabilization and substrate amendment to promote vegetation establishment. Subsequently, this study was undertaken to (a) investigate the role of biological geotextiles in erosion control and (b) examine effects of organic amendments with stockpiled subsoil on tree growth and on ground vegetation cover. A waste-rock dump was graded to 33% slope and covered with a 70 cm layer of subsoil at the Amoma Pit of Newmont Ghana Gold Limited Ahafo-South project. To achieve the first objective, two kinds of biological geotextiles; Elephant-grass mat and “York” mat, were used with bare ground as control, in a randomized block design with two replications each. Mat performance against erosion was expressed as a percentage from the total sediment yield. Results showed both the Elephant-grass mat and the York mat significantly (p < 0.05) reduced soil loss by 56.6% and 97.3%, respectively, compared to the control. The mats acted as cover and protected the graded mine-slope against erosion and allowed vegetation to establish and grow through them.
Two experimental plots (24 × 15 m) were established on a different portion of the waste-rock dump for the second objective. The treatments, manure (23 t ha-1) and control (no manure), were applied, followed by seeding of Cowpea (Vigna unguiculata) and planting of potted-seedlings of five forest-tree species. The Laser-point-quadrat method was used to estimate ground vegetation cover, whereas erosion was visually observed. Diameter and height data of the planted trees were collected. The results indicated the manure had significant positive influence on tree growth and on ground vegetation cover which facilitated superior soil stabilization, compared to the control. Manure supplied sufficient N to overcome N deficiency of the subsoil and additionally increased soil organic matter that boosted microbial activity and mineralization. The findings of the study highlight the urgent need of implementing best reclamation management practices in protecting the environment and securing successful reclamation during mine operations in Ghana. The achievement of this will promote responsible mining and further contribute to Ghanaians’ acceptability of mining as a sustainable developmental land use activity, rather than as a curse.