Rice husk, an agricultural waste, was studied as a potential scavenger of lead from various aqueous solutions. Physicochemical parameters such as selection of appropriate electrolyte, shaking time, and the concentrations of adsorbent and adsorbate were studied to optimize the conditions to be utilized on a commercial scale for the decontamination of effluents using a batch technique. Maximum adsorption was observed with 0.01 moldm" 3 acid solutions (HNO 3 , HC1, H 2 SO 4 and HC1O 4 ) using 1000 mg of adsorbent for a 4.82 X 10" 5 moldm" 3 lead concentration in less than 10 minutes equilibration time. Studies show that the adsorption decreases with an increase in the concentrations of all the acids. The adsorption data follows the Freundlich isotherm over the 9.65 X 10~5to4.83 X 10~3 moldm" 3 range of lead concentration. The characteristic Freundlich constants, i.e., \ln = 0.93 ± 0.04 and A = 19.86 ± 0.82 mmolg" 1 , have been computed for the sorption system. Thermodynamic parameters, i.e., A C , AS", and A//°, have also been calculated for the system.
The adsorption of cadmium ions from aqueous solutions on rice husk has been exploited. Physicochemical parameters such as selection of appropriate electrolyte, shaking time, concentration of adsorbent and adsorbate were studied to optimize the conditions in which this material can be utilized as adsorbent. The radiotracer technique was used to determine the distribution of cadmium. Maximum adsorption was observed at 0.01 mol dm"' acid solutions (HN0 3 , HCl, H 2 S0 4 and HC10 4 ) using 1.0 g of adsorbent for 1.03 Χ 10" 3 mol dm" 3 cadmium concentration in ten 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 1.03 X 10 3 to 2.07 X10" 2 mol · dm -3 cadmium concentration. The characteristic Freundlich constants i.e. 1 In = 0.81 ±0.05 and A = 2.84±0.07 m · mol · g" 1 have been computed for the sorption system. Thermodynamic parameters i.e. Δ G'\ JS° and AH 0 have also been calculated for the system. The sorption process was found to be endothermic.
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