Novel approach evaluating powdered raw and hydrothermally treated syenite as stonemeal for tropical environments: Potential effects on groundwater quality and agricultural suitability.

Soluble fertilizers, particularly potash, are often prohibitively expensive or unavailable in Africa. Consequently, alternatives such as powdered silicate rocks, both raw and hydrothermally treated, are being explored as potential solutions, especially for acidic tropical soils. This study investigates the possible impacts of these rocks (syenite) on groundwater quality, which is a critical factor for agricultural activities. The powdered raw material underwent chemical and mineralogical characterization, including X-ray fluorescence and X-ray diffraction, followed by quantitative evaluation of materials by scanning electron microscopy. Both raw and 46 hydrothermally treated materials were subjected to sequential leaching cycles (1, 24, and 192 h) using deionized water, and the resulting leachates were analyzed by inductively coupled plasma atomic emission spectroscopy. Parameters such as electrical conductivity, total dissolved solids, soluble sodium percentage, sodium adsorption ratio, magnesium hazard, Kelly's ratio, and permeability index were also evaluated. Results from the 47 leachates indicated that 64 % of the samples exhibited excellent to acceptable water quality for irrigation purposes across all parameters. Conversely, 6 % to 13 % fell into the doubtful category, and 2 % to 24 % were classified as unsuitable. Consistency index and ratios of approximately 0.07 and 0.042, respectively, were determined using multi-criteria decision analysis (analytic hierarchy process: AHP), confirming the coherence of the decision and pairwise comparison matrix. The weighted coefficients for each criterion ranged from 0.06 to 0.2. Consequently, the optimal sample (Treatment 23) was identified, showing a hydrothermal temperature of 176 °C, a time of 3.9 h, a normality of 4.62, and a liquid-solid ratio of 0.24. This treatment met all high-water quality standards, including low salinity and sodium hazard, as corroborated by the US salinity laboratory and Wilcox diagrams. Furthermore, due to their nutrient release, low concentration of toxic elements, and effective buffering capacity (pH âˆ¼ 10.6), these powdered syenites are suitable for application in acidic soils.

Environmental assessment of phosphogypsum: A comprehensive geochemical modeling and leaching behavior study.

Understanding the variations in the geochemical composition of phosphogypsum (PG) destined for storage or valorization is crucial for assessing the safety and operational efficacy of waste management. The present study aimed to investigate the environmental behavior of PG using different leaching tests and to evaluate its geochemical behavior using geochemical modeling. Regarding the chemical characterization, the PG samples were predominantly composed of Ca (23.03-23.35 wt%), S (17.65-17.71 wt%), and Si (0.75-0.82 wt%). Mineralogically, the PG samples were primarily composed of gypsum (94.2-95.9 wt%) and quartz (1.67-1.76 wt%). Moreover, the automated mineralogy revealed the presence of apatite, fluorine and malladrite phases. The overall findings of the leaching tests showed that PG could be considered as non-hazardous material according to US Environmental Protection Agency limitations. However, a high leachability of elements at a L/S of 2 under acidic conditions ([Ca] = 166.52-199.87 mg/L, [S] = 207.9-233.59 mg/L, [F] = 248.62-286.65 mg/L) is observed. The weathering cell test revealed a considerable cumulative concentration over 90 days indicating potential adverse effects on the nearby environment (S: 8000 mg/kg, F: 3000 mg/kg, P: 700 mg/kg). Based on these results, it could be estimated that the surface storage of PG could have a serious impact on the environment. In this context, a simulation model was developed based on weathering cell results showed encouraging results for treating PG leachate using CaO before its disposal. Additionally, PHREEQC was used to analyze the speciation of major elements and calculate mineral phase saturation indices in PG leaching solutions. The findings revealed pH-dependent speciation for Ca, S, P, and F. The study identified gypsum, anhydrite, and bassanite as the key phases governing the dissolution of these elements.

Sustainable phosphate mining: Enhancing efficiency in mining and pre-beneficiation processes.

Phosphate holds a critical role as a vital, limited, strategic, and irreplaceable resource. Throughout its production chain, residual phosphate can be found in waste streams. This study aims to enhance production efficiency by exploring methods to limit residual phosphate presence in waste stocks. It investigates the presence of residual phosphate in a phosphate mining site. The presence of residual phosphate throughout the production chain is investigated. Through meticulous analyses of extraction, destoning, and screening processes, the study identifies three primary stages where residual phosphate exists, the study simulates different scenarios of residual phosphate recovery and prevention. The principal data sources are data from mining site, recent literature, and information from a lithological log, the study meticulously analyzes the extraction, crushing, and sieving processes to assess the persistence of residual phosphate. The production chain diagnostic revealed that 76% of resource present is recovered (either integrated into the value chain or stored in the mine for future use), from which 8% goes to the destoning waste rocks (75% of which is residual phosphate) and the screening waste rocks (72% of which is residual phosphate), with an average grade that reaches 25% P2O5. Approximately, 24% of the initial phosphate rock (with an average grade of 22% P2O5) remains as residual phosphate which is retained in the spoil piles. To recover and prevent the presence of residual phosphate, the study proposes four new scenarios for improvement, including an integrated scenario where all the solutions are combined for a comprehensive approach. Both quantity and grade of recovered residual phosphate are assessed in each scenario. To evaluate these enhancements, the study utilizes the AnyLogic software to simulate existing process configuration and the maximal recovery of each scenario. The current flowsheet indicates that extracted phosphate can be directed either to pre-beneficiation and expedition or stored for future use. By prioritizing the extraction of phosphate over the final product, the simulation results suggest that implementing these novel scenarios could potentially save 25% of the total phosphate resource and increase storage by twofold, preserving phosphate that would otherwise be unused. This recovered phosphate can then be destined to various uses, meeting the company's present or future needs. Considering this, the study opts to keep stocks separated based on their grades and avoid mixing new phosphate streams with the final product. The implications of this research extend to sustainable mining practices, with direct ramifications for environmental impact mitigation and the conservation of valuable resources.

A review of organic and inorganic amendments to treat saline-sodic soils: Emphasis on waste valorization for a circular economy approach.

Soil salinization poses a significant challenge to the sustainable advancement of agriculture on a global scale. This environmental issue not only hampers plant growth and soil fertility but also hinders the advancement of the national economy due to restrictions on plant development. The utilization of organic and/or inorganic amendments has demonstrated the ability to mitigate the detrimental impacts of salt stress on plant life. At the outset, this review, in addition to summarizing current knowledge about soil amendments for saline-sodic soils, also aims to identify knowledge gaps requiring further research. The organic or inorganic amendments modify soil conditions and impact plant development. For instance, organic amendments have the potential to improve the structure of the soil, augment its capacity to retain water, and stimulate microbial activity. As this occurs, salts gradually leach through the porous structure of the soil. Conversely, inorganic amendments, such as gypsum and phosphogypsum, displace sodium from soil-negative sorption sites reducing the salinity, they also increase base saturation, altogether positively impacting plant growth conditions. This review emphasizes that, under adequate rates, the combination of organic and inorganic amendment has a high potential to enhance the poor physicochemical properties of saline-sodic soils, thereby reducing their salinity. Consequently, an in-depth examination of the mineral composition, texture, and chemical composition of the soil is required to choose the most effective amendment to implement. Future research necessitates a thorough investigation of techno-economic and life cycle assessment, with active involvement from stakeholders, to enhance the decision-making process of the amendments in specific localities.

Geochemical and mineralogical characterization of phosphogypsum and leaching tests for the prediction of the mobility of trace elements.

Phosphoric acid manufacturing generates large amounts of phosphogypsum (PG); a by-product generally disposed in the surface or evacuated in the seawater without any pretreatment. Phosphogypsum may host non-negligible amounts of valuable elements such as rare earth elements (REEs), which are critical elements on the global market. Surface disposal of PG may be a sustainable option to allow further processing in order to recover valuable elements. However, surface disposal exposes PG to atmospheric conditions (e.g., water, oxygen) which may increase their reactivity and accelerate the release rate of chemical species. This study aims to evaluate the trace element release rate from PG at atmospheric conditions. The studied PG samples were collected from a Moroccan phosphate treatment plant. The samples were characterized for their (i) chemical composition using inductively coupled plasma optical emission spectrometry (ICP-OES) for major elements and inductively coupled plasma mass spectrometry (ICP-MS) for trace elements; (ii) mineralogical composition by X-ray diffraction (XRD), scanning electron microscope equipped with energy-dispersive spectrometer (SEM-EDS), laser-induced breakdown spectroscopy (LIBS), and the mineral chemical composition was analyzed by electron probe microanalyzer (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS); and (iii) chemical species release rate using leaching tests over 24 h at 25 and 60 °C. Chemically, the PG samples were mainly composed of Ca (23.03-23.35 wt.%), S (17.65-17.71 wt.%), and Si (0.75-0.82 wt.%), and non-negligible amounts of trace elements: REE (344-349 ppm), Cd (3.5-7.4 ppm), U (9.3-27.4 ppm). Mineralogically, the PGs are mainly formed by gypsum (94.2-95.9 wt.%) and quartz (1.67-1.76 wt.%). In terms of chemical species release, the PGs showed a higher reactivity at 60 °C compared to room temperature with a higher release rate at the beginning of the leaching tests. Quantitatively, the PG samples released 3.57-4.11 µg/L/day of REE, 3.18-17.29 µg/L/day of U, and 1.67-5.49 µg/L/day of Cd. Based on the leaching results, we concluded that the trace elements (e.g., U, Cd, REE) are incorporated in PG crystal lattice, which may explain their low concentrations in the leachates. Consequently, total digestion of PG matrix is required to solubilize REE.

Role of secondary minerals in the acid generating potential of weathered mine tailings: Crystal-chemistry characterization and closed mine site management involvement.

Mine tailings exposed to water and oxygen generate acid mine drainage (AMD) when the neutralizing minerals are insufficient to buffer the acid produced by sulfide oxidation. Mineral reactivity, such as sulfide oxidation and carbonate dissolution, leads to several changes within mine tailings in terms of their physical, mineralogical, and geochemical properties, which may lead to the release of metal(oid)s (e.g., As, Cu, Zn, Fe, S) into the environment. Fresh and oxidized tailings were sampled at two vertical profiles in a tailings storage facility (TSF). The TSF contains tailings from gold ore processing at a mine that has been closed for more than 25 years. Oxidized tailings have formed by in-situ oxidation of fresh tailings over more than 20 years. The collected samples were analyzed for: i) chemical composition by inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray fluorescence (XRF), and total S/C; and ii) mineralogical composition by X-ray diffraction (XRD), Mineral Liberation Analyzer (MLA), Mossbauer spectroscopy, and Fe L-edge X-ray absorption near-edge spectroscopy (XANES). Mineralogically, the fresh tailings included more than 22 wt% carbonates and more than 10 wt% sulfides. In contrast, the oxidized tailings were composed mainly of secondary minerals such as iron oxy-hydroxides and gypsum. Geochemically, the fresh tailings exhibited a circumneutral behavior during weathering cell experiments and contaminants such as As were negligibly released (<0.3 mg/L). The latter is explained by formation of secondary iron oxy-hydroxides, which are known for the capacity to uptake several contaminants from the leachate. Long term oxidation of fresh tailings will lead to highly oxidized tailings similar to those collected in situ. The oxidized tailings exhibited an acidic behavior despite sulfide depletion due to latent acidity. The geochemical behavior was strongly controlled by the reactivity of secondary minerals (e.g., dissolution of gypsum and iron oxy-hydroxides). Quantitatively, the oxidized tailings released 163 mg/kg Fe, around 12,000 mg/kg S, and around 6 mg/kg Zn.