Study On The Cr(Ⅵ) Adsorption From Groundwater By Composite Adsorbent

Chromium is a heavy metal used widely in industry.Chromium compounds,which are important chemical raw materials, used extensively in some industries suchas leather tanning, printing and dyeing, paint, electroplating, wood preservation, finechemicals, organic synthesis and so on. In particularly, Cr (Ⅵ) has carcinogenic,teratogenic, mutagenic effects on human body, which is listed as one of the mostharmful chemicals to human health, also is one of the three internationally recognizedcancer-causing metals. The direct discharge of chromium-containing wastewater inchrome ore processing and chemical production will cause serious pollution togroundwater, also with the long-term piled up of chromium residue withoutdealing.Groundwater is an important water supply source of human, once sufferedfrom pollution will be difficult to reverse. It is urgent to settle the problems ofgroundwater pollution.This study can improve the defects of the Cr (Ⅵ) adsorption using a singlematerial, and the excellent characteristics of the composite adsorbent will beexpressed. The applicability of new composite adsorbents: kaoline-chitosan andnatural zeolite modified by hydrotalcite for the removal of Cr (Ⅵ) from groundwaterwas investigated. When the optimum reaction conditions are as follows：The massratio of kaoline and chitosan is0.06, the pH value is4, adsorbing time60min andadsorbent dosage2.0g/L, respectively, the removal efficiency is up to94.67%.Especially, The Cr (Ⅵ) concentration of the disposed groundwater is from0.5down to0.026mg/L, which can meet the Ⅲ grade groundwater quality standard(≤0.05mg/L). Factors such as pH, adsorbent dosage, adsorption time and initialconcentration of the Cr (Ⅵ) adsorption by the natural zeolite modified by hydrotalcitewere investigated. At the optimum reaction conditions of pH value4-6, dose1.5g/Lfor30min, the removal efficiency was up to95%, which can meet the standard.The adsorption data of the two composite adsorbents could be well interpreted bythe Freundlich, Langmuir and D-R adsorption isotherms. And the mechanisms areboth primarily based on physical adsorption. The SEM results showed that the microsurface porosity of kaolin loaded chitosan increases obviously; the obvious porestructure of the zeolite modified by hydrotalcite can be seen, meanwhile, the specificsurface area and the surface energy have been increased significantly.The inital concentration of Cr(Ⅵ) from0.5-30mg/L and30-50mg/L, respectively, are favorableto the composite adsorbents to play the adsorption performance efficiently.The results of experiments show that the two economic and efficient compositeadsorbents can provide theoretical and technical reference for the Cr (Ⅵ) removal.