Adsorpotion Of Cd²⁺ And Zn²⁺ From Aqueous Solutions By Raw Bean Dregs

Water pollution by heavy metals remains an important environmental issue associated negatively with the health and economy. The removal of heavy metal contaminants from aqueous solutions is one of the most important environmental concerns because metals are biorefractory, and are toxic to many life forms. The common methods for removing metal ions from wastewater include ion-exchange chormatography, reverse-osmosis, chemical precipitation, oxidation-reduction, membrane filtration and adsorption. Among these, adsorption as an effective and economical wastewater treatment process has aroused considerable interest during recent years. The use of commercially available activated carbon as an adsorbent is limited, especially in developing countries, because of its relatively high cost and the difficulties associated with its regeneration. As a result, several non-conventional adsorbents have been used by a number of investigators. The removal of heavy metals by plant tissues or by biomass by-product from agricultural, industrial or pharmaceutical industry has been proved with high efficiency and very low-cost. Cone biomass of Thuja orientalis, Cone biomass of Pinus sylvestris, rice husks, wheat shell, sawdust, sunflower leaves, and etc., which are tested good as substitutes for the expensive drugs and live biomass.RBD is a by-product of bean curd process, which is in a large quantity and high nutrition. But as the deficiency of corruptibility and unconveniency in conservation and transportation, most of bean dregs are wasted and cause many pollution problems to the environment. Up to now, very few researches have been made on RBD's removal efficiency and characteristics of heavy metals. So the utilization of RBD as a low-cost and environmental effective biosorbent to remove heavy metals has a considerable of attraction of research.The by-product of bean curd process, raw bean dregs (RBD), was used to removal Cd²⁺ and Zn²⁺ from aqueous solutions in this study. The contact time, optimum pH range, concentration of selected heavy metals and biosorbent dosage were investigated to optimize the sorption condition. Most sorption of Cd²⁺ and Zn²⁺ occurred at pH around 7 and 6, respectively. Kinetics of adsorption obeyed pseudo-second-order equation well indicating that chemisorption may be the rate-limiting mechanism through sharing or exchange of electron between sorbent and sorbate. It was proved that Langmuir isotherms fitted the experimental data better compared to Freundlich isotherms. The maximum uptake of Cd²⁺ and Zn²⁺ was 19.61 mg/g and 11.11 mg/g, respectively, when simulated with Langmuir model, which showed the potential biosorption capacity of this biomaterial. Comparing to the sorption capacity of some agricultural by-products and activated carbon on Cd²⁺ and Zn²⁺, it can be included that the raw bean dregs has characteristics of easy acquiring, low cost, environmental effective, rapid uptake, high sorption capacity and etc. there is a wide research value and practical foreground.