Removal of iron from silica sand by leaching with oxalic acid

The removal of iron from silica sand with oxalic acid has been studied under various experimental conditions in order to optimise the process parameters and reach a high degree of iron removal at minimum operating cost. The parameters studied were: temperature, pH of the solution, oxalate concentration, Ar purging, and ferrous ions addition to the solution. For the specific silica sand sample used, at temperatures varying between 90–100°C the maximum iron extraction that can be achieved is approximately 40%. At temperatures lower than 80°C this extraction is decreased to 30%. At these temperatures purging of the oxalate solution with Ar and ferrous ions addition has no effect on the iron extraction, while at temperatures lower than 25°C iron dissolution is accelerated with the addition of ferrous ions. Iron dissolution is significantly affected by the pH, while it is practically independent of the oxalate concentration and the pulp density. Without the addition of bivalent iron, iron extraction is optimised in high acid solutions; when ferrous ions are added in the oxalate solution, best results are achieved at pH 3.