Adsorption of cadmium on husk of Lathyrus sativus: physico-chemical study

Adsorption of cadmium (II) from aqueous solution by low-cost biosorbents was investigated. Husk of Lathyrus sativus (HLS) was found to be the most efficient in this respect and removed approximately 95% of the metal. The influence of pH, temperature, contact time and metal ion concentration on the adsorption process by HLS was studied. Hydrogen ion concentration of the solution greatly influenced the process with an optimum at pH 5.0-6.0, whereas temperature had no significant effect. The process was very fast and more than 90% of the total adsorption took place within the first 5 min and was found to follow pseudo-second order rate kinetics. The adsorption data can better be explained by Langmuir isotherm model and the calculated maximum adsorption capacity was 35 mg/g of HLS at pH 5.0 and 30 degrees C. Scanning electron micrographs showed that cadmium was present as micro precipitate on the surface of the adsorbent. Cadmium replaced calcium of the biomass as revealed from the EDX analysis indicating that the adsorption proceeds through ion exchange mechanism. Cadmium could be desorbed from the loaded biomass by lowering pH approximately 1.0 with mineral acid.