Equilibrium, kinetic and thermodynamic studies, modeling and optimization of the experimental data for the removal of chromium (vi) from waste water using low cost adsorbents

Abstract

Chromium has been widely used in various industries like textile, leather, chemical manufacture, metal finishing, paint etc. The effluents from these industries contain chromium in the form of trivalent chromium (Cr+3) and hexavalent chromium (Cr+6). The hexavalent chromium is a priority toxic, mutagenic and carcinogenic chemical, hence it is very much required to remove chromium (VI) from the industrial effluents before allowing it to enter any water system or on to the land. The conventional treatment methods like filtration, chemical precipitation, membrane process, solvent extraction, ion exchange, electrochemical treatment etc are used when chromium is present in large quantities and when recovery of chromium is economically feasible. The adsorption technique for the removal of chromium metal is preferred because it is a potential alternative treatment method and an economically viable method, especially when chromium is present in minor quantities. In the present study, the removal of hexavalent chromium from synthetic waste water by adsorption on cheap and naturally available agriculture waste materials prepared as adsorbents such as Ragi husk powder, Custard apple peel powder and Elephant apple hull powder are investigated in the batch experiments. The Ragi (Eleusine Coracana) husk (agriculture waste obtained from the village Tamarakhandi, Vizianagaram, A.P, India), Custard apple (Annona reticulate) peel (solid waste from the local market) and hull of Elephant apple (Limonia acidissima) (solid waste from local market) were washed, dried, and crushed in primary crusher and air dried in sun for several days until its weight remains constant. After drying, it is crushed in roll crusher and hammer mills. The material obtained through crushing and grinding is screened through BSS meshes. The effect of the agitation time, the adsorbent size, adsorbent dosage, initial chromium concentration, temperature and solution pH on the metal uptake and percentage removal of chromium are studied by conducting batch