Rice husk, an agricultural waste product, was studied as a potential decontaminant for chromium in the effluents of leather
tanning industries. Physico-chemical parameters such as selection of appropriate electrolyte, shaking time, concentration
of adsorbent and adsorbate were studied to optimize the best conditions in which this material can be utilized on commercial
scale for the decontamination of effluents. The radiotracer technique was used to determine the distribution of chromium.
In certain cases atomic absorption spectrophotometry was also employed. Maximum adsorption was observed at 0.01 mol·dm−3 acid solutions (HNO3, HCl, H2SO4 and HClO4) using 3.0 g of adsorbent for 2.73·10−3 mol·dm−3 chromium concentration in five minutes equilibration time. Studies show that the adsorption decreases with the increase in
the concentrations of all the acids. The adsorption data follows the Freundlich isotherm over the range of 2.73·10−3 to 2.73·10−2 mol·dm−3 chromium concentration. The characteristic Freundlich constants, i.e., 1/n=0.86±0.06 andA=2.35±0.06 mmol·g−1 have been computed for the sorption system. Thermodynamic parameters, i.e., ΔG0, ΔS0 and ΔH0 have also been calculated for the system. Application of the method to a test case of a medium size industry showed that
21 kg of rice husk was sufficient to maintain the NEQS limits of chromium for industrial effluents.