The formation of Sr-humate precipitate was studied colourimetrically and radiometrically at different pH's. It was found that,
increasing of the Sr2+ concentration or the pH value of the solution increases the precipitated complex. The competition effect of Mg2+, Ca2+, Ni2+, and Ba2+ on the complexation of Sr2+ by humic acid indicated that both Mg2+ and Ni2+ substitute Sr2+ in humate complex, while Ba2+ has a very little effect. In case of Ca2+, increasing of its concentration enhances the precipitation of Sr2+ with humic acid.