Abstract

Heavy metals toxicity has led to the continuous study of new and efficient methods for their removal from the environment. Solvent extraction method was used to study the potentials of the auxiliary complexing agents Ethylenediaminetetraacetic acid (EDTA), Oxalate (C2O42-), Thiocyanate (SCN-) and Tartrate (C4H4O62-) ions in the simultaneous extraction of Cadmium, Iron, Nickel and Lead from aqueous solutions buffered to either pH 4.75 or 7.5 using the organic extractant 4,4´-(1E,1E´)-1,1´-(ethane-1,2-diylbis(azan-1-yl-1ylidene))bis(5-methyl-2-phenyl-2,3-dihydro-1H-pyrazol-3-ol) (H2BuEtP) alone or in the presence 4-butanoyl-2-4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-one (HBuP). 0.001 to 0.1 M of the auxiliary complexing agents and equilibration time of 60 min was used. Distribution ratios and percentage extraction was calculated using raffinates and metal standard absorbances. EDTA, Oxalate and Thiocyanate ions and pH 4.75 was found not suitable for the multi-metal extraction of the four metals attributed to the formation of very stable complexes with these auxiliary complexing agents’ ions masking the extraction of the metals, although statistically, there were no significant differences in most cases between the extractions of the metals in the two buffers. Using the ligand H2BuEtP alone with a buffer of pH 7.5 and 0.001 M Tartrate, 7 batches of extraction are theoretically required to achieve 99.9% simultaneous extraction of the four metals as the best result while with the mixed ligands H2BuEtP/HBuP organic extractant system, 7 batches are required for 0.001 to 0.005 M Tartrate, 5 batches for 0.05 M Tartrate and 4 batches for 0.01 M Tartrate as the best results. Statistically, there was no significant difference between the two organic phases with the exception being Thiocyanate for Nickel with buffer of pH 7.5 that showed slight synergic effect of HBuP.

Key words: Auxiliary complexing agents, ligands, multi-metal, buffers, extraction.