Hydroxide precipitation of complexed metals

Abstract

Abstract In this study, theoretical analysis of the complexed metal treatment by conventional hydroxide precipitation is made. The analysis is aimed to evaluate the mechanism of ligand-sharing effect of metals which are added to wastewater to ensure effective removal of complexed heavy metals. Theoretical expression of the analysis is made using phase diagrams. Cadmium, copper and nickel are selected as heavy metals. EDTA, NTA and succinic acid are selected as organic complex formers of different strengths. Calcium is used as the ligand binding agent. Theoretical solutions are made for, single metal-single ligand system and several metal and ligand combinations in the closed system and single metal-single ligand in the open system. Theoretical solutions are interpreted considering the solubility, stability and ionization constants and their relative magnitudes. Experimental studies are conducted to check the theoretical predictions. Result indicate that high pH precipitation is applicable to the cases where organic ligand can be effectively bound by calcium or any other coagulant or pH adjustment agent thus freeing the heavy metal to form hydroxide or carbonate solids. Theoretical diagrams can be used to predict the favorable conditions for precipitation and as a guide to determine the operating conditions.