Purification of wet process phosphoric acid by desulfurization and ammonization
Abstract
We studied the processes of desulfurization of phosphoric acid obtained by wet process from washed and roasted concentrate and subsequent purification of acid from bivalent and trivalent metals and fluorine via partial ammonization (at pH of 2 to 4). Purified ammoniated slurry containing 16.96% P2O5, 8.06% N, 0.09% CaO, 0.58% MgO, 0.004% Fe2O3, 0.031% A12O3, 0.78% SO3 and 0.52% F was fabricated by the removal of precipitates at the stages of desulfurization and partial ammonization. The rheological properties of ammoniated slurry with 40% moisture were studied. When the temperature is increased from 40 to 800C, both the density and viscosity decrease from 1.395 to 1.365 g cm–3 and from 80.8 to 48.7 cP, respectively. Ammoniated suspension with pH of 5.5 and 8.5 was applied to prepare mono- and diammonium phosphates with the ratio P2O5:N of 52:14 and 48:18, respectively. The sludge obtained after desulfurization and ammonization processes can be used as a slow-release fertilizer.