Characterization and treatment of the phosphoric gypsum transport water

This paper presents a new treatment procedure applied on phosphogypsum transport water. Untreated transport water is highly acidic (pH 1.79), having fluoride content of 1540 mg/L and elevated values of phosphates (215 mg/L) and heavy metals (Fe = 25.8 mg/L; Zn = 5.7 mg/L; Mn = 2.7 mg/L, V = 1.7 mg/L). Neutralization/purification of the transport water was carried out with wood fly ash, otherwise a rich source of calcium, composed of calcite, dipotassium calcium carbonate and hydroxylapatite. Maximum removal efficiency of fluoride was observed at pH 7 (99.99%) and phosphate at pH 9 (96.29%). The removal of fluorides was a consequence of the formation of fluorite and fluorapatite mineral phases derived from the reaction of calcium (released from the fly ash minerals) and fluorides (from the transport water). The removal of phosphates resulted from the formation of fluorapathite and hydroxilapatite. At the optimum conditions removal efficiencies for the elements Pb, V, Cr(VI), Mn, Fe, Ni, Cu, and Zn were 95%, 98.14%, 91.11%, 100%, 99.71%, 96.33%, 97.24%, and 99.65%, respectively. Optimal heavy metal removal occurred in major cases at pH 7.