Recovery of High Purity Calcium Sulfate from Phosphogypsum I: Thermodynamic Study of SO42- Purification
April 29-May 4, 2018
Chemical agents SO42- and Ca2+ in phosphogypsum could be recycled to make high-purity calcium sulfate whisker. A key step in this process is to decompose phosphogypsum using NaOH solution to obtain Na2SO4 solution and Ca(OH)2 residue. In this decomposition process, thermodynamic analysis indicates that the majority of impurities reports to the residue phase Ca(OH)2，with minor amounts of Si and Al impurities end up in Na2SO4 solution in forms of Na2SiO3 and KAlO2. Based on phase diagram at 25oC for the Na2SO4-SiO32--AlO2- system, Si and Al impurities may be removed via precipitation by adjusting pH value of the Na2SO4 solution. In verification tests on a sodium phosphate solution of pH 13.2 with 17.7mg/L of Al and 3.41mg/L of Si, when pH was adjusted to 12 no Al was detected in the solution with 8.48% Si removal. After solution pH was further lowered to 7, Al was still negligible in the liquid phase, but Si removal was increased to 75.89%..
Zeqiang Zhang, Chaode Huang, Hong Yun, and Patrick Zhang, "Recovery of High Purity Calcium Sulfate from Phosphogypsum I: Thermodynamic Study of SO42- Purification" in "Beneficiation of Phosphates VIII", Dr. Patrick Zhang, Florida Industrial and Phosphate Research Institute, USA Professor Jan Miller, University of Utah, USA Professor Laurindo Leal Filho, Vale Institute of Technology (ITV), Brazil Marius Porteus, Foskor-Mining Division, South Africa Professor Neil Snyders, Stellenbosch University, South Africa Mr. Ewan Wingate, WorleyParsons Services Pty Ltd., Australia Prof. Guven Akdogan, Stellenbosch University, South Africa Eds, ECI Symposium Series, (2018). http://dc.engconfintl.org/phosphates_viii/42