APPLICATION OF THE CENTRAL COMPOSITE DESIGN AND RESPONSE SURFACE METHODOLOGY TO REMOVE ARSENIC FROM INDUSTRIAL PHOSPHORUS BY OXIDATION

Oxidation is applied to remove arsenic from industrial phosphorus, and nitric acid is chosen as the main oxidant and molysite (Fe3+) as the oxidation intensifier to oxidise arsenic selectively prior to oxidise phosphorus. The central composite design (CCD) and response surface methodology (RSM) are applied to this purification process. The factors considered for experimental design are the concentration of nitric acid, stirring rate, the mass ratio of iron to arsenic, and the volume ratio of nitric acid to phosphorus. The significant factors are optimised using a 2(4) full factorial CCD of orthogonal type. The quadratic models between the responses and the independent parameters are built. The response surface models are tested with analysis of variance (ANOVA) and the optimal conditions are found: 12.5% for the concentration of nitric acid, 80 for the mass ratio of iron to arsenic, 319 rpm for stirring rate, and 3.14 for the volume ratio of nitric acid to phosphorus with the prediction of 99.9996% of the arsenic removal ratio (ARR) and 74.64% of phosphorus yield (PY). The experimental results indicate that oxidation could remove almost all arsenic from industrial phosphorus, which could prepare low arsenic phosphoric products.