Removal and recovery of malachite green from wastewater using an agricultural waste material, de-oiled soya

Abstract

De-oiled soya is a waste product obtained during the processing of soyabean in soya oil extraction mills. Attempts have been made to exploit this wonder crop for different purposes to mitigate many of our problems. This laboratory utilized de-oiled soya as waste material and low cost adsorbent for the removal of toxic textile dye ‘malachite green’. The characterization of the adsorbent was done through IR and DTA curves and preliminary investigations were carried out by batch adsorption technique, which includes effect of pH, adsorbate concentration, sieve size, adsorbent dosage, contact time, temperature, etc. Tenable mechanism of the ongoing adsorption process and thermodynamic parameters were also obtained from Langmuir and Freundlich adsorption isotherm models. The kinetic measurements helped in determining the specific rate constant confirming the applicability of the first-order rate expression. To identify whether the on-going process is particle diffusion or film diffusion, the treatment given by Boyd and Reichenberg was employed. To assess the practical utility of the adsorbent a fixed bed column was designed and necessary parameters were calculated by applying mass transfer kinetic approach. Experiments were also performed for recovery of loaded dye through chemical regeneration of spent column and an estimate of the operational cost was also calculated.