Studies on heavy metal removal from aqueous solutions and effluent

Abstract

The objective of this study was to convert the precursors Hevea brasiliensis saw dust, Agave sisalana fiber and Moringa oliefera wood to activated carbons using phosphoric acid to remove Ni, Cu and Zn from synthetic solutions and effluents. The proximate analysis of the adsorbents was studied by thermo gravimetric analysis. Batch experiments were conducted to remove Ni, Cu and Zn from synthetic solutions using the activated carbon samples. Effects of various operating variables namely solution pH, contact time, AC loading, metal ion concentration and temperature on the adsorption capacity of the adsorbents have been studied. The isotherm models such as Langmuir, Freundlich, Temkin and Dubinin-Radushkevich models were used to analyze the equilibrium data at different temperatures. Kinetic studies showed that the adsorption followed a pseudo second-order model. The intraparticle diffusion rate constants and effective diffusion coefficient for different temperatures were evaluated and discussed. The continous column experiments were carried out for the adsorption of Ni, Cu and Zn from aqueous solution using the above mentioned AC samples to assess the effect of various process variables such as the effect of bed height, flow rate, initial feed concentration and temperature on breakthrough time and adsorption capacity. An attempt was also made to model the data generated from column studies using the empirical relationship based on Adam-Boharts model and Thomas model. The model constants were also evaluated. The SEM images of ACHB, ACAS and ACMO after adsorption were analyzed. It was observed that the surface morphology of the AC samples have undergone changes during the adsorption process.