title: Reducement of cadmium adsorption on clay minerals by the presence of dissolved organic matter from animal manure.
abstract: Clay minerals are the most popular adsorbents/amendments for immobilizing heavy metals in contaminated soils, but the dissolved organic matter (DOM) in soil environment would potentially affect the adsorption/immobilization capacity of clay minerals for heavy metals. In this study, the effects of DOM derived from chicken manure (CM) on the adsorption of cadmium (Cd2+) on two clay minerals, bentonite and zeolite, were investigated. The equilibrium data for Cd2+sorption in the absence or presence of CM-DOM could be well-fitted to the Langmuir equation (R2> 0.97). The presence of CM-DOM in the aqueous solution was found to greatly reduce the adsorption capacity of both minerals for Cd2+, in particular zeolite, and the percentage decreases for Cd2+sorption increased with increasing concentrations of Cd2+as well as CM-DOM in aqueous solutions. The adsorption of CM-DOM on zeolite was greater than that on bentonite in the absence of Cd2+, however, a sharp increase was observed for CM-DOM sorption on bentonite with increasing Cd2+concentrations but little change for that on zeolite, which can be attributed to the different ternary structures on mineral surface. The CM-DOM modified clay minerals were utilized to investigate the effect of mineral-adsorbed CM-DOM on Cd2+sorption. The adsorbed form was found to inhibit Cd2+sorption, and further calculation suggested it primarily responsible for the overall decrease in Cd2+sorption on clay minerals in the presence of CM-DOM in aqueous solutions. An investigation for the mineral surface morphology suggested that the mineral-adsorbed CM-DOM decreased Cd2+sorption on bentonite mainly through barrier effect, while in the case of zeolite, it was the combination of active sites occupation and barrier effect. These results can serve as a guide for evaluating the performance of clay minerals in immobilizing heavy metals when animal manure is present in contaminated soils.
authors.affiliation: Department of Environmental Science, Zhejiang University, Hangzhou, Zhejiang 310058, China(1); Geological Research Center for Agricultural Applications, China Geological Survey, Hangzhou, Zhejiang 311203, China(1). Electronic address: wenjunzhou@zju.edu.cn.
authors.forename: Wenjun
authors.initials: W
authors.lastname: Zhou
authors.affiliation: Department of Environmental Science, Zhejiang University, Hangzhou, Zhejiang 310058, China(1).
authors.forename: Lingwei
authors.initials: L
authors.lastname: Ren
authors.affiliation: Department of Environmental Science, Zhejiang University, Hangzhou, Zhejiang 310058, China(1); Geological Research Center for Agricultural Applications, China Geological Survey, Hangzhou, Zhejiang 311203, China(1).
authors.forename: Lizhong
authors.initials: L
authors.lastname: Zhu
mesh_terms: D000327:Adsorption; D000538:Aluminum Silicates / Q000737:chemistry*; D000818:Animals; D001546:Bentonite / Q000737:chemistry; D002104:Cadmium / Q000737:chemistry*; D002681:China; D000077215:Clay; D004787:Environmental Pollution; D008372:Manure; D008903:Minerals / Q000737:chemistry; D011200:Poultry; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000737:chemistry*
chemical_list: D000538:Aluminum Silicates; D008372:Manure; D008903:Minerals; D012987:Soil; D012989:Soil Pollutants; D002104:Cadmium; D001546:Bentonite; D000077215:Clay
keywords: Adsorption; Cadmium; Clay mineral; Dissolved organic matter; Farmland soil