A New Method for the Determination of Phosphorus and Iodine in Phosphate Rock by Ion Chromatography After Continuous Acid Digestion and Distillation

A new method was developed for the determination of phosphorus (P) and iodine (I) in phosphate rock. First, the phosphate rock was digested with HCl solution to generate H 3 PO 4 , then the remaining HCl was evaporated by distillation, the generated H 3 PO 4 reacted with NaAc to generate HAc, and HAc was evaporated by distillation finally. The processes were conducted continuously in the same apparatus; the escaping gases including HI, I 2 , HCl and HAc were absorbed by a diluted solution of NaOH and Na 2 SO 3 . Cl − , Ac − and I − in the absorption solution were determined by ion chromatography (IC) and the content of P in phosphate rock was confirmed according to the Ac − determination. The results showed that the optimal operating parameters were, respectively, 4.0 mol L −1 HCl, 50 ℃ and 35 min for the acid digestion of phosphate rock, 160 ℃ and 40 min for HCl evaporation, and 140 ℃ and 40 min for H 3 PO 4 reaction and HAc evaporation (HRHE). The correlation coefficients of P and I in this method were good ( R 2 > 0.999), the relative standard deviations (RSDs) of the measured values and the recoveries of P and I ranged from 1.28 to 7.21% and from 91.90 to 98.62%, respectively; the measured values of P and I were in good agreement with the certified reference values (CRVs) of the certified reference materials (CRMs). This method exhibits suitable accuracy and precision, with simple and mild operating conditions and is good for determining P and I in phosphate rock.