基于集合方法铅镉在磁性蒙脱石上竞争吸附点位的计算

On calculation of competitive adsorption sites of lead and cadmium in collection approach at magnetic montmorillonite

采用水热合成法制备磁性蒙脱石,并分别在单独及竞争体系下,通过批试验研究其对铅镉的吸附特性,并采用集合的方法定量计算铅镉在磁性蒙脱石上的公共吸附点位和独立吸附点位。结果表明,磁性蒙脱石对Pb(Ⅱ)和Cd(Ⅱ)的吸附过程为混乱度增加、可自发进行的吸热反应。与单独体系相比,在竞争体系下,Pb(Ⅱ)和Cd(Ⅱ)在磁性蒙脱石上的吸附量下降,吸附速率减慢,表明Pb(Ⅱ)和Cd(Ⅱ)对磁性蒙脱石表面的吸附点位存在明显的竞争。与Cd(Ⅱ)相比,竞争作用对Pb(Ⅱ)的影响较大。由铅镉所占据的磁性蒙脱石公共吸附点位的比值Qj(Pb)/Qj(Cd)>1,表明铅对磁性蒙脱土表面吸附点位的竞争力要大于镉。另外,升高温度,Qj(Pb)/Qj(Cd)有下降的趋势,表明提高温度有利于提高Cd的竞争力。Pb(Ⅱ)和Cd(Ⅱ)在公共吸附点位和独立吸附点位之间的分布会影响它们对公共吸附点位的竞争。

In given paper,we have managed to prepare the magnetic montmorillonite with the hydrothermal synthesis method in a form of batch experiments.As a result,we have made clear the adsorption characteristic features of Pb(Ⅱ)and Cd(Ⅱ)on the magnetic montmorillonite under the condition of single-metal and binary-metal case samples.What is more,we have also quantitatively calculated the common adsorption sites and specific adsorption sites of Pb(Ⅱ)and Cd(Ⅱ)on the magnetic montmorillonite through the collection approach.The results of the above study show that the adsorption process of Pb(Ⅱ)and Cd(Ⅱ)on the magnetic montmorillonite can be realized in a spontaneous,endothermic and randomly increasing process.When compared with the single-metal system,the adsorption quantity of Pb(Ⅱ)and Cd(Ⅱ)on the magnetic montmorillonite under the binary-metal system,has been found decreasing,in which the adsorption rate has been slowing down,with the competitive adsorption rate between Pb(Ⅱ)and Cd(Ⅱ)being noticeably observed or noticed.The effect of the competition on Pb(Ⅱ)has been stronger than that of Cd(Ⅱ).The distribution status of Pb(Ⅱ)and Cd(Ⅱ)between the specific sites and the common sites can be expressed in the ratios of Q(Cd)/Qj(Cd)and Q(Pb)/Qj(Pb).And,the ratios between Q(Cd)/Qj(Cd)and Q(Pb)/Qj(Pb)have been found greater than 1,which suggests that the adsorption strength of Pb(Ⅱ)and Cd(Ⅱ)on the specific sites of montmorillonite should be smaller or easier than that on the common adsorption sites.And,when the initial solution concentrations stand at 10 mg/L,the Q(Cd)/Qj(Cd)ratios would become 7.4(25℃),14.4(35℃)and 15.8(45℃)times stronger than the ratios of Q(Pb)/Qj(Pb)respectively.This indicates that the adsorption of Cd on the specific sites of montmorillonite turns out to be easier than that of Pb at the lower metal concentrations.And,if the Qj(Pb)/Qj(Cd)ratios were greater than 1,it would imply that the competitiveness of Pb(Ⅱ)to the adsorption sites on the surface of magnetic montmorillonite should be greater than that of Cd(Ⅱ).In addition,with the increase of temperature,Qj(Pb)/Qj(Cd)should have a declining trend,indicating that the increase of the temperature is conducive to the improvement of the competitiveness of Cd(Ⅱ).Besides,the distribution status of Pb(Ⅱ)and Cd(Ⅱ)between the specific sites and the common sites can also affect their adsorption point for competition.