Temperature Effect on Heavy Metal Adsorption by α-Aluminium Hydroxide

Adsorption of Cu²⁺, Zn²⁺, Co²⁺, and Ni²⁺ from aqueous solution on α-aluminium hydroxide is studied as a function of temperature, using the method of potentiometric titrations. Adsorption is found to be endothermic in nature and follows the order Cu²⁺ > Zn²⁺ > Co²⁺ > Ni²⁺ in the temperature rangc 20-50 °C. The adsorption stoichiometry and apparent stability constants of the surface complex of the type [(AIO)_n M^2-n]are also evaluated. In case of Cu²⁺ and Ni²⁺ the process is favoured by positive values of the ΔS⁰, while in case of Cu²⁺ and Zn²⁺ the process is favoured both by the negative values of ΔG⁰ and positive values of ΔS⁰.