Biosorption of Cr(III) Ions by Wheat Straw and Grass: a Systematic Characterization of New Biosorbents

Recently, increased interest in the application of various biosorbents in metal ions removal has been observed. The paper presents a systematic characterization of new and commonly abundant low-cost biosorbents: above-ground plant parts of wheat straw and grass. Cr(III) was chosen as a model sorbate. The effect of the most significant process parameters (temperature, pH, initial concentration of Cr(III) ions on kinetics, as well as temperature and pH) on biosorption equilibrium was studied. Biosorption was found to be a quick process. The equilibrium was reached within 10-20 minutes. Biosorption capacity of the studied sorbents was intermediate when compared with other sorbents of plant origin ca. 20 mg/g, but since these materials are commonly abundant and of minimal cost, it is possible to improve wastewater treatment efficiency by increasing the concentration of the sorbent. The kinetics of the process in the case of both biomaterials was described with pseudo-second order equation and the equilibrium of biosorption by wheat straw was described with the Freundlich equation and by grass with the Langmuir model. The above equations were chosen to achieve the best consistency of experimental data with the model results. Also, the mechanism of biosorption was investigated, and was determined to be physical adsorption. The paper also discusses the possible methods of utilization of metal-laden biomass, including non-destructive elution with the regeneration of the biosorbent and ashing as the method of destruction and further concentration of metal.