Unveiling the organic nature of phosphogypsum foam: Insights into formation dynamics, pollution load, and contribution to marine pollution in the Southern Mediterranean Sea

The foamability of dissolved phosphogypsum from the phosphate fertilizer factories of Gabes (SE Tunisia) is a spectacular phenomenon that has not yet been thoroughly studied. The main objective of this research was to investigate the organic properties of phosphogypsum foam (PGF) to understand its formation process, determine the origin of its enhanced radiochemical contaminants load, and identify its role in pollutants dispersion in marine environment of the Southern Mediterranean Sea. This study identified PGF as an unnatural, surfactant-stabilized, and ephemeral aqueous foam. PGF-forming process comprises three main steps: (i) formation (through phosphogypsum dissolution), (ii) stabilization (facilitated by organic surfactants and gypsum crystals), and (iii) destabilization (geochemical (involving the dissolution of the PGF skeleton gypsum) and/or mechanical (influenced by wind and wave action)). The amphiphilic nature of PGF organic matter and the presence of specific organic groups are responsible for its high toxic contaminants load. PGF contributes, through its elevated pollutants content and its ability to migrate far from its source, to the marine dispersion of industrial toxic radiochemical contaminants. It is therefore recommended to mitigate the environmental and health risks associated with PGF, including banning the discharge of untreated phosphogypsum and other industrial wastes into the coastal environment of Gabes.