Isotherm Studies for Heavy Metal Adsorption on Rice Husk

A number of methods for heavy metal removal from waste water have been used, but most have several disadvantages, such as continuous input of chemicals, high cost, toxic sludge generation or incomplete metal removal. The use of rice husk not only provides a less costly sorbent to activated carbon or synthetic ion-exchanger as it is cheap, but also available in abundant quantity. Various modifications on rice husk have been reported in order to enhance sorption capacities for metal ions and other pollutants. The study reported in this paper deals with the adsorption of heavy metals such as lead (Pb), copper (Cu), zinc (Zn) and manganese (Mn) on the low cost adsorbents such as Rice Husk (RH) and Phosphate treated Rice Husk (PRH) from the synthetic solutions. Batch studies were conducted to find out the optimum dose of adsorbent, optimal pH and contact time for individual metal solution, both with RH and PRH. It was found that the equilibrium was attained after 30 min for Pb, 40 min for Cu and 50 min both for Zn and Mn and the maximum removal efficiency was attained at a pH of 6 for Pb, pH of 7 for Zn, Cu and Mn for the single metal solutions. The adsorption data could be fitted with Freundlich, Langmuir isotherm equation to find the characteristic parameters. It was found that linear form of Freundlich isotherm seems to produce a better model than linear form of Langmuir equation.