The effect of humic acid on the sorption of metals by minerals was studied inrelation to the separate interactions of the humic acid with the minerals, thehumic acid with the metals, and the metals with the minerals. Sorption of themetals in combined mineral–humic acid systems can be explained in termsof generalised sorption reactions.Sorption of the metals in mineral–humic acid systems is dependent onsorption of humic acid by the mineral and on the solubility of themetal–humic acid complex. Sorption is enhanced in the combined systemsfor the minerals goethite and silica due to secondary reactions in whichmetal–humic acid complexes are adsorbed by the minerals. Sorption of themetal–humic acid complex in the combined systems for α-alumina and kaolinite is not enhanced, possibly due to competing reactions associated withthe sorption of the humic acid by these minerals.