Removal of Hexavalent Chromium from Aqueous Solution Using Unmodified Saw Dust: Batch and Column Studies

Abstract

The effects of contact time at three initial concentrations and temperature in batch process and the effects of three initial concentrations and three bed heights in column process were used to evaluate the potentials of unmodified saw dust, a low cost adsorbent in removing Cr(VI) with highly mutagenic and carcinogenic properties from aqueous solution. The material characterized using point of zero charge, FTIR and Scanning Electron Microscopy (SEM) showed that it has good adsorbent properties. Nearly 99% of Cr(VI) was removed in two minutes attaining equilibrium in five minutes for all the initial concentrations tested in batch operation. Langmuir and Dubinin-Radushkevich (D-R) isotherms best fitted the adsorption with maximum adsorption capacities of over 196 mg/g. Adsorption on unmodified saw dust can be physical, ion exchange and chemical depending on the initial concentration and the process is spontaneous and endothermic. The removal efficiency increases with increasing bed height but decreases with increase initial concentration, however, adsorption capacity increases with increase in initial concentration but decreases with increase bed height for column operation. Thomas kinetic model best described the column adsorption over other tested model. Unmodified saw dust can effectively remove Cr(VI) from wastewater in batch and column operations.