氯化铁对老化黏土矿物中Pb(Ⅱ)解吸效果的研究

Desorption of Pb(Ⅱ)from Aged Clay Minerals by Ferric Chloride

为提高淋洗技术在高黏性土壤中的适用性,选取代表黏性土壤细粒径组分的4种黏土矿物,通过180 d的铅(Pb)污染老化,采用振荡淋洗试验研究了氯化铁对4种老化污染后黏土矿物中Pb(Ⅱ)的解吸效果,探讨了氯化铁浓度、液固比和淋洗时间等因素对老化黏土矿物中Pb(Ⅱ)解吸效果的影响,并结合动力学拟合对Pb(Ⅱ)解吸过程进行了分析,利用三步提取法识别了氯化铁解吸前后老化黏土矿物中Pb(Ⅱ)的赋存形态变化。结果表明:随着氯化铁浓度的升高和液固比的增大,4种老化黏土矿物中Pb(Ⅱ)的解吸率会逐渐增加并趋于稳定;当氯化铁浓度为20 mmol/L、液固比为50 mL/g时,蒙脱石、伊利石、绿泥石和蛭石中Pb(Ⅱ)的解吸率分别为66.9%、79.7%、73.7%和63.5%;准一级动力学方程对蒙脱石的解吸过程拟合度较高,Elovich模型方程能更好地描述伊利石和蛭石的解吸过程;而绿泥石的pH值缓冲能力强,使得其解吸的Pb(Ⅱ)会因pH值的上升而发生重吸附和共沉淀现象;形态分析显示,4种老化黏土矿物中层间吸附态Pb(Ⅱ)的占比最高,而氯化铁能够有效地解吸层间吸附态Pb(Ⅱ),在氯化铁浓度为20 mmol/L、液固比为50 mL/g的条件下,蒙脱石、伊利石、绿泥石和蛭石中层间吸附态Pb(Ⅱ)的解吸率分别为60.1%、91.2%、87.1%、56.48%。该研究结果可为南方地区高黏性土壤中重金属污染的修复提供技术参考。

To improve the applicability of leaching technology in highly cohesive soil,this paper selects four kinds of clay minerals representing fine particle size components of cohesive soil for 180 days of lead Pb(Ⅱ)pollution aging and applies the oscillatory leaching test to studying the Pb(Ⅱ)desorption in the clay minerals by ferric chloride.The paper analyzes the effects of the concentration of ferric chloride,the liquid-solid ratio,and the leaching time on the Pb(Ⅱ)desorption,and the desorption process by the kinetic fitting.After that,the paper applies a three-step extraction method to identifying the speciation changes of lead in clay minerals before and after Pb(Ⅱ)desorption.The results show that the desorption rate of Pb(Ⅱ)all clay minerals will gradually increase and then tend to become stable with the increase of ferric chloride concentration and liquid-solid ratio.The desorption rates of Pb(Ⅱ)in montmorillonite,illite,chlorite,and vermiculite are 66.9%,79.7%,73.7%,and 63.5%in a ferric chloride concentration of 20 mmol/L and a liquid-solid ratio of 50 mL/g.The Pb(Ⅱ)desorption from montmorillonite is fitted by quasi-first-order kinetic equation well,while the Elovich model equation can better describe the Pb(Ⅱ)desorption from illite and vermiculite.Chlorite,however,with strong pH buffering capacity,leads to the re-sorption and coprecipitation of desorbed Pb(Ⅱ)due to the pH increase.The results of species analysis show that ferric chloride effectively removes the adsorption states of Pb(Ⅱ)in the interlayer,which accounts for the largest proportion of Pb(Ⅱ)in all clay minerals.A desorption rate of Pb(Ⅱ)in interlayer adsorption states can reach up to 60.1%,91.2%,87.1%,and 56.48%from montmorillonite,illite,chlorite,and vermiculite,respectively,when the ferric chloride concentration is 20 mmol/L and the liquid-solid ratio is 50 mL/g.The study results can provide technical reference for the remediation of heavy metal pollution in highly cohesive soils in south China.