Characterisation of Zinc-bearing sulphate phases formed during the synthesis of phosphoric acid and Zinc removal by the ligands of Opuntia ficus-indica

Phosphogypsum (PG) is a solid waste generated from phosphate fertilisers industries. It represents a serious threat to the aquatic and terrestrial environment because of its acidity and its high content in heavy metals and radionuclides. The aim of this work is to describe the formation of PG during the synthesis of the phosphoric acid, the entrapment of Zinc (Zn) in PG and its lixiviation in presence of a natural organic matter extracted as powder from the cladodes of Opuntia ficus-indica (OFI) using physical and chemical characterisation techniques such as FTIR, XRD, SEM-EDX, laser diffraction, and AAS. The formation of PG mainly occurs in the pH range between 4.6 and 3 and it accompanies the transformation of H-2(PO4)(-) into phosphoric acid H3PO4. The maximal Zn incorporation within the PG was reached at pH 6 and decreased progressively with pH. Zinc was found to have a great tendency to migrate from PG particles to OFI's suspensions since a maximum Zn removal percentage of 93% was achieved.