Investigating the removal of heavy metal ions from wastes using triple super phosphate (TSP)

Heavy metal pollution is one of the global problem due to the increase of industrial and mining activities (power plants, mineral processing, metallurgical extraction, petrochemical, etc.). To solve this heavy metal pollution problem, triple superphosphate (TSP) was investigated thoroughly in this thesis for the removal of heavy metal ions from wastes. TSP was selected amongst various phosphate-based materials and fertilizers to act as the source of orthophosphate (PO43-) which is a powerful tool for metal fixation in soil and water. The objective of this study was to investigate the stability conditions of metal ions in an aqueous system and the treatment of contaminated wastes with triple superphosphate, an alternative to lime. TSP or monocalcium phosphate monohydrate with a chemical formula of [Ca(H2PO4)2H2O] is widely used as fertilizer in the agriculture area. In this investigation, firstly, stability diagrams (Eh-pH diagrams) were constructed with HSC chemistry software to establish the predominance areas of the different species and solid/solution equilibrium in the TSP solution. Later, precipitation tests were carried out with pure metals and real wastes in TSP solutions to verify the obtained metal phosphate at the conditions determined from the stability area diagrams and confirm them through the XRD analyses of precipitated samples. The experimental results demonstrated that TSP effectively removes heavy metals of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr and Zn from aqueous solution and real wastes. The performance of the TSP process is influenced by reaction times, metal ions and TSP concentrations. The results of XRD analysis also revealed the formation of insoluble metal phosphates [Cd3(PO4)2, Co3(PO4)2, Cu2(PO4)OH, Fe3(PO4)2, FePO4.2H2O, Mn3(PO4)2, Pb3(PO4)2, ZnHPO4 and Zn3(PO4)2] in the precipitated and describe the mechanism of TSP on heavy metal removal which includes the dissolution of TSP and precipitation of metal ions.