Optimization and kinetics of oxalic acid treatment of feldspar for removing the iron oxide impurities

The presence of iron impurity in feldspar lowers its commercial value due to imparting unwanted colors to the final products. This study concerns the dissolution of iron from an Iranian feldspar using oxalic acid as the leaching agent. In this regard, initial tests were conducted to fix primary parameters at the best values: pH, 2; agitation rate, 1000 rpm; particle size, -150 mu m, and to find the suitable range of acid concentration. Then, using a central composite experimental design, the optimum condition (85% iron removal) was obtained at 70 degrees C, 5% pulp density, 20 g/l oxalic acid, and time of 90 min. The iron dissolution kinetics was investigated within 40-80 degrees C and showed a reasonable match with the shrinking core model with a mixed control mechanism. The activation energy was calculated as 28.61 kJ/mol at 80 degrees C. Two- and three-stage leaching experiments were also performed using a baffled reactor at different pulp densities of 5-25%. Iron removal at the highest pulp density was improved from 36% at the first to about 72% at the third stage that indicates oxalic acid leaching can be industrially implemented as an efficient method for removing iron from feldspars.