模拟降雨淋洗对土壤重金属释放规律的研究

Study on the release of heavy metals from soil by simulated rainfall leaching

为探究酸沉降地区降雨淋洗条件下土壤中重金属的释放规律,选择桂林市郊典型菜地土进行模拟降雨淋洗土柱实验,探索不同pH(4、5、6、7、8)的模拟降雨对重金属迁移的影响。结果表明:随着模拟降雨pH降低,供试土壤淋出液溶解性总固体(TDS)呈递增变化;随着淋溶时间的增加,TDS先快速下降而后缓慢下降,而淋出液pH则为先迅速上升而后缓慢上升。淋出液pH与TDS呈负相关关系,与重金属累积淋出量呈正相关关系。模拟降雨作用于供试土壤时,土壤中不同重金属元素呈现不同的释放规律。Zn、Cd总体上分为快速释放和相对缓慢释放两个阶段,Pb则分为快速释放阶段和稳定释放阶段,而Cu、Hg、As、Sb总体上则呈一段式匀速增长。利用一级动力学方程、Elovich方程、双常数方程及抛物线扩散方程进行拟合,建立了降雨淋溶条件下土壤中重金属的释放动力学模型。通过拟合发现,重金属的释放过程不适合使用一级动力学方程拟合,且不同重金属最适合的拟合方程也有所不同。

To investigate the release pattern of heavy metals from soils under rainfall drenching conditions in acid deposition areas,a typical suburban Guilin vegetable soil was selected for a simulated rainfall drenching soil column experiment to explore the effects of simulated rainfall with different pH(4,5,6,7 and 8)on heavy metal migration.The experimental results showed that the total dissolved solids(TDS)of the test soils showed increasing changes as the pH of simulated rainfall decreased.TDS decreased rapidly and then slowly with the increase of drenching time,while the pH of drenching solution increased rapidly and then slowly.The pH of the leachate was negatively correlated with TDS and positively correlated with the cumulative leaching of heavy metals.It was also found that different heavy metals showed different leaching patterns when the simulated rainfall was applied to the test soils.Zn and Cd leaching was divided into two stages of rapid release and relatively slow release,Pb was divided into rapid release and stable release stages,and Cu,Hg,As and Sb leaching was generally in a period of uniform growth.The kinetic model of heavy metal release from soil under rainfall leaching conditions was developed by fitting the first-order kinetic equation,Elovich equation,double constant equation and parabolic diffusion equation.The fitting revealed that the release process of heavy metals was not suitable for the use of the first-order kinetic equation and the most suitable equations varied for different heavy metals.