Heavy metals’ mobility from phosphate washing effluents discharged in the Gafsa area (southwestern Tunisia)

Wet processing of natural phosphate to increase the P2O5 content and eliminate non-desired fraction (both coarse and fine fractions) took place in various laundries of the Gafsa-phosphatic area. Effluents of those laundries often contain various contaminants that are directly discharged to the receiving waterbody, representing a serious threat to the environment. Physico-chemical characterization of those effluents showed elevated levels of sulfates, fluorine, and metals. The bordering land showed gypseous soils. Those soils are covered by the discharged phosphate-washing sludge. The effect of which on the structure and the permeability of the soils seemed to be significantly harmful. Batch tests were conducted to evaluate the mobility of various metals on the surrounding area of phosphate laundries. Leaching results revealed low cadmium and uranium mobilities. However, Cd concentrations in the studied samples leached from soils exceeded the standards. This suggested the contamination by cadmium.