黑腐酸对Cd2+的吸附响应面优化及机理研究

Adsorption of Cd 2+by humin:response surface methodology and mechanism study

以山西褐煤为原材料制备黑腐酸,选择吸附温度、时间、pH值、黑腐酸用量和Cd2+初始浓度5个影响因素,采用Box-Behnken响应面法对吸附条件进行优化,分别建立黑腐酸对Cd2+的吸附容量和吸附率的二次多项式模型,确定最优吸附条件.将吸附过程拟合等温吸附方程,进行热力学分析,并对材料进行表征.结果表明,pH值、黑腐酸用量和底物浓度为黑腐酸吸附Cd的显著影响因素,优化后的条件为温度308K、时间107.82min、p H=5.55、黑腐酸用量0.05g,底物浓度95.56mg/L,表明黑腐酸是一种良好的吸附材料,吸附效果随温度的升高而增大,能够处理高浓度重金属污染.吸附过程符合Langmuir模型,308K下最大吸附量为54.20mg/g;热力学分析得ΔG0<0、ΔH0>0、ΔS0>0,即反应是自发的吸热熵增反应;黑腐酸表面粗糙多孔,具备良好的比表面积与孔隙结构,具有多种官能团,吸附反应有羟基、羧基等参与形成氢键,并与无机矿物发生离子交换.本研究可为揭示黑腐酸对重金属的吸附机理提供理论依据.

In order to explore the the adsorption mechanism of humin(HM)for heavy metal,lignite was selected as the material for preparing HM and optimized the adsorption conditions.The conditions were optimized by response surface method with Box-Behnken design,whereas quadratic polynomial models of adsorption capacity and adsorption rate of Cd2+on HM could be established.The results showed that the pH,dosage of HM and initial concentration of Cd2+presented the higher effect on Cd2+adsorption of HM.It indicated that the optimum adsorption conditions were obtained at the temperature of 308K,107.82 min,pH 5.55,dosage of HM 0.05g and Cd2+initial concentration of 95.56mg/L.In addition,the adsorption isotherm could be better fitted by Langmuir models than that by Freundlich.The maximum adsorption capacity(54.20mg/g)of Cd2+on HM was obtained at the temperature of 308K,and the thermo dynamic parameters(ΔG0<0,ΔH0>0,ΔS0>0)indicated that this adsorption was an endothermic and spontaneous process when the entropy of the system increased.Besides,according to SEM-EDS and FTIR,the HM surface exhibited higher specific surface area and porous volume.Moreover,it hosted lots of functional groups,such as carboxyl,hydroxyl.This suggested that the Cd2+adsorption on HM was attributed to the hydrogen bond generated by the oxygen groups and the ion exchange between Cd2+inorganic mineral substance on HM surface.This study could provide theoretical foundation for revealing the adsorption mechanism of HM on heavy metals.