| At present, improvement technologies for municipal sewage treatment is still an urgent problem to be solved in China. In many cites and towns municipal sewage is often mixed partially in the sewage transporting system with different types of wastewaters form industry of which some conatins high amount of heavy metals. It is therefore necessary to develop effective techniques for removal of heavy metal contaminants in the process of municipal sewage treatment.Adsorption technology is an effective method in reducing heavy metals concentration in wastewaters. Application of constructed wetland technology for sewage treatment has become a hotspot in both research and practice. Therefore it is important to choose a adsorbent with high adsorption-desorption capacities, high removal rate and could be recycled for constructed wetland technology to reduce the concentration of heavy metals from wastewater.In present study, the examined adsorbent is vermiculite with high adsorption and better desorption capacities. In connection with the current serious polluted waste water containing zinc and cadmium, the study was conducted to analyze theoretically and study experimentally the problem of adsorption-desorption of zinc, cadmium with vermiculite.The results are summarized as follows:(1) Vermiculite had a high effect on the adsorption of Zn2+.The adsorption rate was very high in the first 120 min. After that period, it gradually decreased and finally approached to zero at approximately 8 h.(2) The adsorption density qe of Zn2+ in vermiculite increased with the increase of original concentration C0 of heavy metals, decreased with the increase of adsorbent concentration W0.(3) The adsorption of Zn2+ in vermiculite was an endothermic reaction. Between 15℃and 45℃, the adsorption density qe of Zn2+ increased slightly with temperature. Desorption of Zn2+and Cd2+ in vermiculite was an exothermic reaction.Between 15℃and 45℃,the desorption density decreased slightly with temperature. Although increasing temperature benefited to adsorption and didn't benefit to desorption, the impact was not obvious.(4) pH value was an important factor affecting the adsorption. Zn2+ adsorption density qe increased with pH value.(5) In the tested vermiculite-water solution adsorption system, after ions were adsorbed onto solid surface, the rate of ion desorption in aqueous solution was found to be very slow, showing that ion adsorption is rather irreversible under natural condition.(6) Addition of electrolyte enhanced the desorption rate of the target ionic species due to occurrence of ion exchange. When electrolyte concentration increased, the desorption amount of vermiculite increased too.(7) Vermiculite had a better effect on desorption of Zn2+and Cd2+.The desorption rate was slower than the adsorption. It needed approximately 12h to approach to balance.(8) The desorption of Vermiculite-aqueous adsorption system is ion-exchange desorption. The desorbed target ionic species can be desorbed from the adsorbent, but the desorbed amount of Zn2+ and Cd2+ was found to be always lower than the adsorbed amount of the exchanged ionic species.The results of this study would be of high value in improving conditions of adsorption and desorption and promoting the application of adsorption and desorption technology in waste water treatment.
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