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

Fatima Akfas; Abdellatif Elghali; Youssef Toubri; Kamal Samrane; Manuel Munoz; Jean-Louis Bodinier; Mostafa Benzaazoua

doi:10.1016/j.jenvman.2024.120929

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

J Environ Manage. 2024 Apr 25:359:120929. doi: 10.1016/j.jenvman.2024.120929. Online ahead of print.

Authors

Fatima Akfas¹, Abdellatif Elghali², Youssef Toubri¹, Kamal Samrane³, Manuel Munoz⁴, Jean-Louis Bodinier⁵, Mostafa Benzaazoua¹

Affiliations

¹ Geology & Sustainable Mining Institute, Mohammed VI Polytechnic University, Lot-660, Benguerir 43150, Morocco.
² Geology & Sustainable Mining Institute, Mohammed VI Polytechnic University, Lot-660, Benguerir 43150, Morocco. Electronic address: abdellatif.elghali@um6p.ma.
³ Sustainability & Green Industrial Development, OCP Group S.A, Morocco.
⁴ Geoscience Montpellier, University of Montpellier, Montpellier- Cedex 5- 34095, France.
⁵ Geology & Sustainable Mining Institute, Mohammed VI Polytechnic University, Lot-660, Benguerir 43150, Morocco; Geoscience Montpellier, University of Montpellier, Montpellier- Cedex 5- 34095, France.

PMID: 38669878
DOI: 10.1016/j.jenvman.2024.120929

Abstract

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.

Keywords: Element speciation; Environmental behavior; Geochemical modeling; Leaching assessment; Phosphogypsum.