Removal Of Heavy Metals From Wastewater By Adsorption

Chemical precipitation is usually a cost-effective process for heavy metals removal from wastewater, of which slime precipitation is often more inexpensive. Unfortunately, concentrations of heavy metals in the effluent flows from precipitation usually could not meet the increasingly strict limitations for discharge of heavy metals. Therefore, investigations on advanced treatment of effluent flows from precipitation by slime with high concentration of calcium ions are urgently needed. Removal of heavy metals by adsorption has been considered to be one of cost-effective methods, and selecting and developing of suitable adsorbents for treatment of heavy metal wastewater is of great importance. Waste activated sludge discharged from wastewater treatment plants shows the potential for adsorbing heavy metal ions due to the its easy availability, low cost, recycling of resource, and proper characteristics for absorbents.In this paper, waste actived sludge was chosen for preparation of two types of adsorbents, the dried activated sludge particles and the activated sludge carbon. Performances of adsorption for cadmium ions by the dried activated sludge particles were investigated individually under high concentrations of calcium ions, and adsorption properties of the activated sludge carbon for cadmium removal form wastewater. Moreover, the kinetics, thermodynamics and mechanisms of the adsorption were also examined.Results of adsorption of cadmium by dried activated sludge particles show that the highest removal rate for cadmium ion was24.8%the dried activated sludge particles when concentration of calcium ion was lg/L,pH was6.0, adsorption time was150min,and a dosage of activated sludge of1.0g/L. When the pH was6.0, adsorption time was150min,and a dosage of activated sludge of1.0g/L,cadmium removal efficiency by the activated sludge particles was58.7%without the presence of calcium ions. It can be found that there is a calcium ion under the conditions of activated sludge on the cadmium removal rate decreases. Cadmium adsorption equilibrium thermodynamics in line with the Langmuir adsorption isotherm; and the adsorption kinetics are in line with the pseudo-second kinetic equation.These experiments can show that surplus activated sludge has certain application value while used to remove cadmium ions in the waste water which contain high concentrations of calcium.Preparation of modified sludge activated carbon adsorption of Cd2+experiment suggests that waste activated sludge carbon has a good adsorption capacity and removal efficiency of cadmium.when pH was5.0, an initial concentration of Cd2+was100mg/L, and a dosage of activated carbon was2.0g/L, the adsorption of cadmium adsorption capacity was8.45mg/g; acid modified sludge activated carbon of Cd2+adsorption capacity than the unmodified sludge activated carbon, and of Cd2+adsorption capacity of the23.35mg/g. Cd2+has a better adsorption capacity, nitric acid modified, the modified and unmodified sludge activated carbon significantly improves the performance of sludge activated carbon adsorption of Cd2+. Modified sludge activated carbon adsorption of Cd2+to the Langmuir adsorption isotherm at room temperature.At the same time,it can show that activated carbon sludge has the very good prospects of application in heavy metal wastewater treatment.