SORPTION OF HEAVY-METALS BY MINERAL-HUMIC ACID SUBSTRATES

The effect of humic acid on the sorption of metals by minerals was stu died in relation to the separate interactions of the humic acid with t he minerals, the humic acid with the metals, and the metals with the m inerals. Sorption of the metals in combined mineral-humic acid systems can be explained in terms of generalised sorption reactions. Sorption of the metals in mineral-humic acid systems is dependent on sorption of humic acid by the mineral and on the solubility of the metal-humic acid complex. Sorption is enhanced in the combined systems for the min erals goethite and silica due to secondary reactions in which metal-hu mic acid complexes are adsorbed by the minerals. Sorption of the metal -humic acid complex in the combined systems for ct-alumina and kaolini te is not enhanced, possibly due to competing reactions associated wit h the sorption of the humic acid by these minerals.