粉煤灰基土壤调理剂中重金属赋存形态和溶出规律

Occurrence and Dissolution of Heavy Metals in Fly Ash-based Soil Conditioner

明确粉煤灰中重金属的赋存形态和溶出规律,是实现粉煤灰在农业上大宗利用的先决条件。作者以内蒙古锡林郭勒盟未进行重金属预脱除粉煤灰改性制备的土壤调理剂作为研究对象,首先采用BCR连续浸提法初步探究其重金属赋存形态,然后在模拟土壤酸碱条件下研究其溶出规律,即采用水平振荡方法,在水溶液中25℃、液固体积质量比恒定为20∶1、pH 4~10、作用时间0~120h下研究典型五大重金属Hg、Pb、Cd、As、Cr的溶出规律,并与地表水、地下水毒理学指标进行对比,最后结合重金属溶出规律和BCR法形态分析结果,明晰调理剂中重金属的具体赋存形式。结果表明:在粉煤灰未进行重金属预脱除处理的情况下,调理剂中五大重金属的弱酸可溶态含量均小于10%,除As主要以可还原态形式存在外,其他重金属主要以残渣态形式存在。调理剂在不同pH值、不同时间下其中的重金属虽有少量溶出,但五大重金属在整个溶出过程中的溶出量均低于地下水Ⅳ类标准限值、地表水Ⅴ类标准限值,符合农业用水标准,环境风险较小。综合BCR法分析结果和重金属在不同条件下溶出规律,可知Cr、As、Cd、Hg、Pb主要存在形式分别为晶格Cr、As^(5+)、Cd(OH)_(2)、HgS和PbS,各占总量的61%、91%、54%、70%和95%。

The prerequisite to make the maximum utilization of fly ash in agriculture is to specify the occurrence and dissolution laws of heavy metals in fly ash.Taking the soil conditioner made from fly ash without the preremoval of heavy metals in Xilinggol League,Inner Mongolia as the research object,BCR continuous extraction method is first used to explore the speciation of heavy metals of Hg,Pb,Cd,As,Cr,then the method of horizontal oscillation is taken to study their dissolution under simulating acidic and alkaline soil conditions.The detailed leaching conditions are as following:to dissolve in water solution of 25℃,constant volume and mass ratio of liquid to solid at 20∶1,pH of the solution of 4~10,and duration of 0~120 h.The dissolving concentrations of heavy metals are consequently compared with the toxicology indexes of surface water and ground water.Finally,the specific occurrence forms of heavy metals in the soil conditioner are defined by combining with the analysis of heavy metal dissolution and BCR method.The result shows that in the case of fly ash without the preremoval of heavy metals,the soluble content of the five heavy metals in the conditioner is less than 10%.Except arsenic mainly exists in the reducible form,other heavy metals mainly exist in the form of residue.There are a small amount of dissolution of heavy metals in the conditioner when dissolving at different p H and time,but the dissolutions of the heavy metals are less than nationalⅣclass standard limit value of groundwater andⅤclass standard limit of surface water,according with the standard of agricultural water.So,their environmental risk is small.From the analysis results of BCR method and the dissolution of heavy metals under different conditions,it can also be seen that the main forms of Cr,As,Cd,Hg and Pb are lattice Cr,As^(5+),Cd(OH)_(2),HgS and PbS,accounting for 61%,91%,54%,70%and 95%of the total,respectively.