Use of phytic acid for selective precipitation of undesirable metals (Al, Fe, Pb) contained in the leachates from hydrometallurgical processes

Abstract

In hydrometallurgical processes, chemical precipitation is used either to recover dissolved valuable metals or to remove undesirable elements before electrolysis. Beside conventional reagents (Ca(OH)2, NaOH, Na2CO3…) many authors tried to replace them by bio-sourced compounds, but unfortunately, without necessarily leading to an industrial use. This paper describes a study on the possibility to use phytic acid to remove Al3+, Fe3+ and Pb2+ from acidic leachates. This reagent, present in cereals and considered as an antinutrient, can be recovered from soaking waters of corn. In this work, five metal phytates were synthesized and characterized by TGA and ICP-OES leading to the following formulae: Al3C6H9P6O24,7H2O, Cu6C6H6P6O24,8H2O, Fe3.5C6H7.5P6O24,15H2O, Pb6C6H6P6O24,10H2O and Zn6C6H6P6O24,6H2O. Solubility of each metal phytate was measured in pure water at 20 °C in order to determine their solubility product Ks not available in literature. The conditional solubility as a function of the pH was then established to predict the possibility to perform selective precipitation. The results showed that phytic acid could be an interesting alternative precipitation reagent, able, from a thermodynamical point of view, to remove Al3+, Fe3+ and Pb2+ from copper or zinc leachates.