Increasing the filtration rate of phospho-gypsum using surfactant

Phospho-gypsum is a by-product of processing phosphate rock for phosphoric acid production by acidulation with sulfuric acid. The size distribution of phosphor-gypsum is a major factor for the economics of the process as it greatly affects the filterability of the acid. Surface active agents proved to be very effective additive for growth of gypsum crystals. Two phosphate concentrates, one from Egypt (New Valley) and the other from USA (South Florida) were tested for phosphoric acid production with modification of gypsum crystals using non-ionic surfactant (CMR-100) containing a mixture Of C-6-C-22 sorbitan esters. The studies were carried out using a semi-continuous laboratory-scale unit simulating the dihydrate process conditions. The mean diameter of the phospho-gypsum crystals increases in the presence of surfactant for both phosphate concentrates. The surfactant leads to decreasing the viscosity and modification of gypsum crystals through decreasing the fine size fractions and attainment of large and uniform crystal shape. The mean diameter of New Valley phosphor-gypsum increases from about 30.0 mu m to 36.6 mu m while the mean diameter of South Florida phospho-gypsum increases from about 30.3 mu m to about 38.4 mu m. On the other hand, the average surface area of both New Valley and South Florida phosphor-gypsum were decreased from 4461 and 8069 cm(2)/g without surfactant to 3284 and 3995 cm(2)/g with surfactant, respectively. In addition, the surfactant leads to an increase in P2O5 recovery of 1-2%, which consequently improves plant productivity. (C) 2006 Elsevier B.V. All rights reserved.