Staged purification of phosphogypsum using pH-dependent separation process

• Published in: Environmental science and pollution research international 2024-02, Vol.31 (7), p.9920-9934
• Main Authors: Chanouri, Hamza, Agayr, Khalid, Mounir, El Mahdi, Benhida, Rachid, Khaless, Khaoula
• Format: Article
• Language: English
• Subjects: Acetic acid; Aluminum oxide; Aquatic Pollution; Atmospheric Protection/Air Quality Control/Air Pollution; Calcium sulfate; Calcium sulfate dihydrate; Cations; Cement hydration; Chelation; Chemical Sciences; Earth and Environmental Science; Ecotoxicology; Edetic acid; Environment; Environmental Chemistry; Environmental Health; Environmental perception; Ethylenediaminetetraacetic acids; Ferric oxide; Filtrate; Fluorides; Impurities; Ion currents; LCT Applied to Solid Waste Management Systems with Appropriate Technologies; pH effects; Phosphogypsum; Phosphorus; Phosphorus pentoxide; Purification; Quartz; Solubilization; Sulfuric acid; Waste Water Technology; Water Management; Water Pollution Control
• ISSN: 1614-7499; 0944-1344; 1614-7499
• DOI: 10.1007/s11356-023-26199-8

Phosphogypsum (PG) is an industrial by-product of the transformation of phosphate rocks. For decades, PG has been a source of environmental concern due to the massive amount produced thus far, i.e., 7 billion tons, with a current production rate of 200–280 million tons per year. Phosphate minerals contain various impurities that precipitate and concentrate within PG. These impurities hinder PG usability in various sectors. This paper aims to purify PG using an innovative process based on staged valorization of PG. Initially, PG dissociation by ethylenediaminetetraacetic acid (EDTA) was optimized. After screening of different parameters and monitoring the ionic conductivity of solutions, it was disclosed that a pH-dependent solubilization process in the presence of EDTA resulted in high solubility of PG, up to 11.82 g/100 mL at pH > 11. Subsequently, a recovery of the purified PG by selective precipitation of calcium sulfate dihydrate (CSD) from obtained filtrate through pH adjustment to 3.5 were investigated. An abatement of 99.34% Cr, 97.15% Cd, 95.73% P 2 O 5 , 92.75% Cu, 92.38% Al 2 O 3 , 91.16% Ni, 74.58% Zn, 72.75% F, 61.43% MgO, 58.8% Fe 2 O 3 , 56.97% K 2 O, and 55.41% Ba was achieved. The process relied on the variation of EDTA chelation properties towards monovalent, divalent, and trivalent cations at different pHs. According to the findings of this study, a staged purification process in the presence of EDTA is an effective method for removing impurities from the industrial PG.