Distribution of some trace metals in Syrian phosphogypsum

Distribution of Cu, Cd, Zn and U in a Syrian phosphoric acid plant byproduct, phosphogypsum, has been determined. Uranium, Cd, Zn and Cu were found to be more enhanced in small phosphogypsum particles (45-75 mum) where the highest concentration was found for Cu (51.7 ppm). In addition, the element transfer factors (Trace element concentration in phosphogypsum (mg/kg)/Trace element concentration in phosphate rock (mg/kg) x 100) from Syrian phosphate rock to phosphogypsum were calculated and found to be 30, 8 and 17% for Zn, Cd and U, respectively. Moreover, laboratory leaching experiments of phosphogypsum by distilled water, dilute H2SO4 Solutions and selective extractants have been performed. Leaching results have shown that around 20% of the U and 100% of the Zn are transferred to the aqueous phase. Batch-wise leaching with dilute H2SO4 solutions shows increased solubility of U, Zn, Cu and Cd from phosphogypsum, while leaching with selective extractants has been performed to determine the amount of exchangeable trace metals which are adsorbed, on gypsum particle surfaces, the amount of trace metals present inside the gypsum lattice, the amount of trace metals associated with organic materials and the amount of trace metals soluble in acids. The results obtained in this study can be utilized to verify the environmentally safe use of phosphogypsum as an amendment to agricultural soils. (C) 2003 Elsevier Ltd. All rights reserved.