Adsorption of cadmium and copper by manganese oxide

Abstract

Cadmium and copper adsorption by δ-MnO2was investigated by potentiometric titration over a range of pH. Adsorption increased with increasing pH because of hydrolysis of metal cations and/or variable charge sites on δ-MnO2δ-MnO2. The surface acidity constant for δ-MnO2was determined using the Triple Layer Model to be pKint,a2= 5.34. The data from titrations with pH as master variable were analyzed to determine the Triple Layer Model intrinsic stability constants, (Equation presented), (Equation presented), p*Kint,cd2+= 1.66, and (Equation presented) for cadmium and copper adsorption onto δ-MnO2. Titrations with metal ion as the master variable were performed at constant pH to estimate the adsorption capacities. The data conformed to a Langmuir isotherm and could be modeled with the Triple Layer Model constants. For cadmium, at pH 5.5, 7.0, and 8.0, the adsorption capacity is 0.434, 1.08, and 1.92 mmol/g, respectively. The affinity of δ-MnO2for Cu, 1.54 mmol/g at pH 5.5, is greater than that for cadmium. The results show δ-MnO2has high adsorption capacities and high adsorption affinities for cadmium and copper even in acidic conditions. © 1991 Williams & Wilkins.