Adsorption of rhodamine B by metals chloride -activated castor bean residue carbon

Abstract

Zinc chloride (ZnCl2) is a well-known pollutant which is toxic to the aquatic organisms. A study of adsorption of rhodamine B was conducted to investigate the performance of metals chloride activated carbon prepared from castor bean residue. Rhodamine B was selected as the model dye due to its high stability with change in pH and hazardous properties. Castor bean residue is suitable to be used as precursor to replace conventional activated carbon due to its low cost and high carbon content. The preparation of activated carbons was conducted through impregnation with ZnCl2, potassium chloride, magnesium chloride, ferric chloride and metals chloride composite at various impregnation ratios from 0.5 to 2.5. Activated carbons were characterized based on proximate analysis, elemental analysis, textural characteristics and chemical properties. The adsorption data were analysed using isotherm models, kinetics models and thermodynamics properties. The regeneration of activated carbon was carried out by hot water and irradiated water at three regeneration cycles. The specific surface area of activated carbons of ratio 1.0 are in descending order of potassium chloride (KCBR-1.0), ferric-zinc chloride (FZCBR), magnesium-zinc chloride (MZCBR), zinc chloride (ZCBR-1.0), ferric chloride (FCBR-1.0), potassium-zinc chloride (KZCBR), magnesium chloride (MCBR-1.0). ZCBR-1.0 demonstrated a greater rhodamine B adsorption of 175 mg/g compared to the other activated carbons counterparts. Nevertheless, the composite activated carbons, MZCBR and FZCBR displayed adsorptive capacity of 114 and 115 mg/g, respectively, which indicates the mixtures of less hazardous metal chloride salts as the promising activating agents. The adsorption capacity of rhodamine B by activated carbons of ratio 1.0 are in descending order of ZCBR-1.0, FZCBR, MZCBR, FCBR-1.0, MCBR-1.0, KCBR-1.0, KZCBR. Adsorption mechanism of ZCBR-1.0 obeyed Langmuir isotherm and pseudo-second-order kinetics model. The rate-limiting step in the adsorption of rhodamine B is film diffusion. The positive values of enthalpy change and entropy change indicate of that the adsorption process is endothermic and spontaneous at high temperature. Hot water regeneration onto rhodamine B loaded activated carbon showed a better performance with 37.7 % regeneration efficiency and 34.4% recovery.