Heterogeneous Sorption of Heavy Metal Cadmium by a Waste Material from Aquaculture Ponds: A Duality Approach

Abstract

Attention of the researchers, at present, is deserved by the heavy metal burden on the mankind and the environment. The issue is specially triggered with continuous anthropogenic inputs of chemical substances supposed to be rich in heavy metals. In particular, heavy metals such as cadmium (Cd) and arsenic (As) are considered as one of the causes of the Chronic Kidney Diseases of uncertain etiology (CKDu) in Sri Lanka. Consequently, management of such heavy metal inputs to the environment and also amputation of them are accounting priority area of research. Naturally forming aquaculture pond waste material (aqua waste) has demonstrated promising adsorption characteristics adding a value to the waste and reducing the burden of Cd in aqueous phase at ambient conditions simultaneously. This duality approach showed that under the optimized conditions of as little contact time and settling time as 30 minutes, unmodified aqua waste showed 98% removal of Cd from 10 mg dm-3 aqueous solution at 1:20 adsorbent/solution ratio. Amongst different adsorption isotherm models, the Freundlich model in its linear form depicted validity of the adsorbent- adsorbate (Cd) adsorption system at equilibrium with a high regression coefficient of 0.933. Such an adsorption is characterized by non-ideal sorption on heterogeneous surfaces, which explains multilayer sorption. Thus, the aqua waste exhibits its potential towards real time applications as an adsorbent for heavy metal Cd from aqueous solutions without prior modification of the material