Physicochemical Conditions for Adsorption of Lead from Water by Rice Husk Ash

The effects of physico-chemical parameters such as pH, temperature, and lead concentration on the efficiency of lead adsorption by rice husk ash were determined. Rice husk was incinerated at 800 degrees C for 6 h and then activated with 0.5 M HCI. Rice husk and rice husk ash (RHA) were characterized using scanning electron microscopy and X-ray fluorescence. Batch adsorption tests were conducted at different pH, temperature, and initial lead concentration. Kinetic studies were conducted at optimum pH of 3.0. The optimum lead removal of 80% was recorded at pH 3.0. Efficiency of lead removal by RHA decreased to 45% as pH increased to 9.0. Freundlich, Langmuir, Temkin, and Dubinin Radushkevich (D-R) isotherms performed acceptably well, with R-2 values of 0.954< R-2< 0.991, 0.965< R-2< 0.996, 0.949< R-2< 0.979, and 0.970< R-2< 0.997, respectively. Lead removal efficiency decreased from 75% to 50% as temperature increased from 30 degrees C to 40 degrees C. The adsorption of lead by RHA was by ion exchange in the acidic pH range and by physisorption in the alkaline pH range. Thermodynamic studies revealed that the process was exothermic and spontaneous and further confirmed the feasibility of the process with -22.34< AG 0<-24.94. The intraparticle diffusion model and the pseudo first order kinetic model fit the experimental data very well, with average R-2 values of 0.985 and 0.987, respectively.