Effect of surfactants on phosphogypsum crystallization and filtration during wet-process phosphoric acid production

A nonionic surfactant (CMR-100) containing a mixture of C-6-C-22 sorbitan esters was tested to improve the filtration rate of phosphogypsum produced from a South Florida phosphate concentrate at different sulfate levels. Tests were carried out on a lab-scale under operating conditions that simulate, to a large extent, the industrial parameters. It was found that the mean diameter of the formed crystals was increased by addition of the surfactant. Equally important, a narrower size distribution was obtained as compared to that in the absence of the surfactant. A significant increase (23 to 31%) in filtration rate, expressed as tons P2O5/m(2).day, was achieved due to the surfactant's addition. A correlation between crystal size distribution of phosphogypsum and filtration rate is presented in this paper.