煅烧磁改性牡蛎壳对水/土壤溶液中镉的吸附性能与机制研究

Study on the adsorption performance and mechanism of calcined magnetically modified oyster shells on cadmium in water/soil solution

为获得易于回收且对重金属吸附性能强的磁性材料,实验以牡蛎壳为原材料,磷酸铁和碳酸亚铁为铁源,通过共沉淀法制备磁性材料,并对其煅烧改性得到煅烧磷酸铁牡蛎壳(CPO)和煅烧碳酸亚铁牡蛎壳(CCO)磁性材料。通过不同初始pH值、吸附等温线及动力学等探究材料对Cd(Ⅱ)的吸附特性,采用SEM-EDS、XRD、FTIR和XPS等表征手段对材料吸附Cd(Ⅱ)的机理进行分析,同时在实际Cd污染土壤中进行实验研究,探究材料对土壤溶液中总Cd与各形态Cd的去除效果。结果表明:两种材料对Cd(Ⅱ)的最佳吸附pH值在4~6之间;在35℃时,CPO和CCO在水体中对Cd(Ⅱ)的最大理论吸附量可达214.20、116.04 mg·g^(-1),吸附过程均符合Langmuir模型,表明为单层吸附;CPO和CCO在100 min时达到吸附平衡,吸附过程均符合拟二级动力学,表明为化学吸附。表征结果表明,CPO和CCO对Cd(Ⅱ)的吸附机制以化学吸附为主,包括静电作用,材料表面的羧基、羟基与Cd(Ⅱ)的络合作用,以及磷酸根、碳酸根等与Cd(Ⅱ)的沉淀作用。在土壤实验中,CPO和CCO处理的土壤总Cd去除率为28.67%和22.05%,回收率为92.39%和89.72%,去除的Cd主要为酸提取态和可还原态,可氧化态和残渣态无显著变化。综上所述,本研究制备的煅烧磷酸铁牡蛎壳和煅烧碳酸亚铁牡蛎壳对Cd(Ⅱ)吸附量较大,且回收率高,具有较好的应用潜力。

The aim of this study was to obtain magnetic materials that are easy to recycle and have strong adsorption properties for heavy metals.Oyster shells were used as raw materials and iron phosphate and ferrous carbonate were used as iron sources.Magnetic materials were prepared using the co-precipitation method,and calcined and modified to obtain calcined iron phosphate oyster shells(CPO)and calcined ferrous carbonate oyster shells(CCO).The adsorption characteristics of Cd(Ⅱ)were explored using different initial pH values,adsorption isotherms,and kinetics,and the mechanism of adsorption of Cd(Ⅱ)were analyzed using by SEM-EDS,XRD,FTIR,and XPS.The experimental studies were carried out in Cd-contaminated soil to explore the removal effect of materials on total Cd and various forms of Cd in soil solution.The results showed that the optimal pH value of Cd(Ⅱ)adsorption between the two materials was between 4–6.The maximum theoretical adsorption capacity of Cd(Ⅱ)by CPO and CCO in water reached 214.20 mg·g^(-1) and 116.04 mg·g^(-1) at 35℃.The adsorption process conformed to the Langmuir model,indicating that it is a single-layer adsorption.The adsorption equilibrium of CPO and CCO was reached at 100 min,and the adsorption process was in line with the quasi-second-order kinetics,indicating chemical adsorption.The characterization results showed that the adsorption mechanism of Cd(Ⅱ)by CPO and CCO was mainly chemisorption,including electrostatic interaction,the complexation of carboxyl and hydroxyl groups and Cd(Ⅱ)on the surface of the material,and the precipitation of phosphate,carbonate,and Cd(Ⅱ).The removal rates of total Cd were 28.67% and 22.05%,and the recovery rates were 92.39% and 89.72%in the soil experiments.In conclusion,the calcined iron phosphate and calcined ferrous carbonate oyster shells prepared in this study had a large adsorption capacity of Cd(Ⅱ)and a high recovery rate,which had good application potential.