Release and recovery of fluorine and iodine in the production and concentration of wet-process phosphoric acid from phosphate rock

Abstract

The recovery of fluorine and iodine in the production and concentration of wet-process phosphoric acid (WPA) can not only reduce environmental pollution, but also increase the added value of production. In this work, the phosphate rock was digested with H2SO4, and the remaining H2SO4 in the WPA was removed with Ca(H2PO4)2, then the WPA was concentrated under vacuum and different temperatures. Fluorine and iodine in the absorption solution were recovered in the forms of CaF2 and I2, respectively. The results showed, under the optimal digestion condition of phosphate rock, the release rate of phosphorus was 97.21 %, with 25.14 % of P2O5 in WPA; in gas and liquid phase, the mass percentages were 1.35 % and 94.87 % for fluorine, and 65.21 % and 29.89 % for iodine, respectively. In the concentration of WPA under 15–17 kPa, the release rates were 89.79 % for fluorine at 80–130 °C and 62.44 % for iodine at 80 °C, with 52.34 % of P2O5 in WPA at 130 °C. Recovery rates and purity were 93.26 % and 97.24 % for fluorine, 85.63 % and 99.47 % for iodine, respectively. Therefore, this method was simple, low consumption, high recovery and purity for fluorine and iodine.