No abstract

The adsorption potential of rice husk was investigated for arsenic ions from aqueous solution as a function of the appropriate electrolyte, contact time, concentrations of the adsorbent and adsorbate, effect of diverse ions and temperature. A radiotracer technique has been used to determine the distribution of arsenic employing a batch method. Maximum adsorption was observed at 0.01 mol/l acid solution (HNO3, HCl, H2SO4 and HClO4) using 1.0 g of adsorbent for 5.97 × 10−3 mol/l arsenic concentration and an equilibration time of 5 min. Studies showed that adsorption decreased with an increase in the concentration of all the acids studied. The adsorption data conformed to the Freundlich isotherm over the concentration range from 8.69 × 10−5 to 1.73 × 10−3 mol/l arsenic. Characteristic Freundlich constants, i.e. 1/n = 0.83 ± 0.06 and K = 4.43 ± 0.16 mmol/g were computed for the sorption system. The uptake of arsenic increased with increasing temperature. Thermodynamic quantities, i.e. ΔG0. ΔS0 and ΔH0, were also calculated for the system. The sorption process was found to be endothermic.

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 (HNO 3, HCI, H2SO 4 and HCIO4) using 3.0g of adsorbent for 2.73 -I 0 -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 tool dm -~ chromium concentration. The characteristic Freundlich constants, i.e., 1/n = 0.86+0.06 and A = 2.35_+0.06 mmol .g-~ have been computed for the sorption system. Thermodynamic parameters, i.e., AG ~ AS ~ and AH ~ 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.