Circular economy strategies in sedimentary phosphate mine reclamation: Development of technosol from phosphate waste rock

Abstract

Proper management of mine waste plays a crucial role in minimizing environmental impacts. One potential solution to tackle this problem involves transforming mine waste rock into soil to facilitate the process of mine restoration. The aim of this study was to assess the mineralogical, chemical, and physical characteristics of technosol derived from phosphate mine waste dumps. Following this evaluation, a novel rehabilitation strategy was proposed. For this purpose, a total of 32 samples were systematically collected across a 4 ha area of technosols, which had been established in accordance with the waste rock soil rehabilitation strategy involving geomorphic reshaping. According to the findings, phosphate mining left the soil with a sandy texture, resulting in a degraded soil structure with severely unfavorable crop growth conditions, notably poor stability, and low water retention. The chemistry of the studied soils was characterized by the dominance of CaO (29.02 wt%± 1.01) > SiO2 (27.61 wt% ± 0.61) > P2O5 (11.34 wt% ± 0.23) > MgO (5.97 wt%±0.16). Mineralogically, the samples were mainly formed by quartz, dolomite, calcite, apatite, and clay minerals. The prevalence of dolomite played a significant role in enhancing the accessibility of Mg as an essential nutrient and the occurrence of apatite in the soil resulted in the presence of P2O5. However, the abundance of Ca was linked to three major minerals: calcite, apatite, and dolomite. X-ray fluorescence analyses demonstrated that the concentrations of Fe2O3, K2O, and SO3 did not exceed 2 wt%.Organic matter, represented by SOC <0.2% and N < 0.02%, demonstrated an extraordinary deficiency in the study area. The analysis of element bioavailability confirmed that the soil was rich in Ca (10383,26 mg/kg), Mg (278,47 mg/kg), Zn (12,82 mg/kg), and Cu (3,7 mg/kg) but deficient in other essential nutrients such as P, K, S, Mn, and Fe. Our research results provide a set of recommendations aimed at enhancing existing mine rehabilitation practices applicable to both pre- and post-rehabilitation phases, leveraging automated mineralogy and circular economy principles. Notably, we propose a rehabilitation strategy to be implemented prior to the geomorphic reshaping phase, which is intended to reduce costs and efforts associated with soil reconstitution.