Investigations On The Removal Of Cr(â…¥) Ions By Modified Oyster Shells

Cr (Ⅵ) ions as a widespread source of pollution, is highly toxic and greatlydangerous to the society. The treatment of chromium-containing wastewater hasalways been the focus of scientific research. As Ningde is a coastal city, Largequantities of oyster shells are abandoned, which cause severe environmentalpollution and wasting of resources. To make good use of rich ca resource of thewaste oyster shells for raw material, the calcium carbonate in oyster shells wasmodified into hydrated calcium silicate by the silica powders for the removal of Cr(VI) ions from chromium containing simulated wastewater. Based on using waste totreat waste, the adsorption of Cr (VI) ions by using unmodified oyster shells andmodified oyster shells with silica powders was studied in this paper, which offertheoretical evidence for the comprehensive utilization of oyster shell via preventingthe chromium pollution.In this paper, firstly, technological condition of preparing modified oyster shellswere introduced and the influence factors, such as adsorption time, temperature,concentration and pH value of the initial solution, for the removal of Cr (VI) ions byusing unmodified oyster shells and modified oyster shells with silica powders wereinvestigated. Secondly, the dynamic adsorption of Cr (VI) ions based on a fixed bedof modified oyster shells was studied.At the same time, adsorption materials werecharacterized by means of environmental scanning electron microscope, energyspectrum analysis, XRD.Main conclusions of this work are drawn as follows:Taking unmodified oyster shells as an adsorbent, five factors influencingadsorption effects of Cr (VI) ion from the simulated wastewater were discussed,including unmodified oyster shells fineness, the initial wastewater concentration ofchromium, ambient temperature, adsorption time and the pH value of the solutions.The experimental results demonstrate that unmodified oyster shells cannot besuitable for treating wastewater containing Cr (VI) ions.The influences of the adsorption capacity for Cr (VI) ions by modified oystershells were presented in the preparation process and the results indicated that theoptimum condition is as followed: the sintering temperature is650℃, the hydration temperature is120℃and the hydration time is12h.This work show that the absorption capacity for Cr (VI) ions by modified oystershells was affected by the initial simulated wastewater concentration of Cr (VI) ions,ambient temperature, adsorption time and the pH value of the solutions. Theexperimental results demonstrate that the modified modified oyster shells havegreater removal capacity for Cr (VI) ions as compared with unmodified oyster shells,so they have a good application perspective in treating wastewater containing Cr (VI)ions.The experimental study indicate that the adsorbing capacity of oyster shells,modified with silicon powder as a new sportive material, is0.12mg/g.As theadsorption capacity for Cr (VI) ions by modified is lower, it is necessary to makefurther researches into the adsorbent to improve removal capacity, considering thenew method of using waste to treat waste and the low-cost of modified oyster shells.