我国典型农田土壤中Cr(Ⅵ)的老化过程及主控因子

Aging kinetics and main controlling factors of Cr(Ⅵ)in typical farmland soils in China

土壤性质对外源Cr(Ⅵ)的老化具有重要影响。我国土壤类型多样,对Cr(Ⅵ)在不同农田土壤中的老化过程及主控因子的研究尚不完善。本研究采集了我国12种性质不同的农田土壤,采用0.05 mol·L^-1 EDTA作为有效态提取剂,耦合HPLC-ICP-MS联用技术、动力学模型拟合和多元线性回归等手段,探讨了外源Cr(Ⅵ)在老化过程中有效态Cr(Ⅵ)和Cr(Ⅲ)动态变化过程及主控因子。结果表明,外源Cr(Ⅵ)添加到土壤后起初60 d,土壤中有效态Cr(Ⅵ)从6.71%~68.71%迅速下降到4.53%~45.17%,之后趋势变缓并逐渐平稳(3.25%~34.35%)。二级动力学模型可以较好地描述所有土壤中有效Cr(Ⅵ)的老化过程(R^2>0.99);土壤性质与二级动力学模型中老化速率的逐步回归分析结果表明,土壤pH是控制Cr(Ⅵ)老化速率的主控因子。基于二级动力学模型,推导得出Cr(Ⅵ)进入土壤后的近似老化平衡时间为6~158 d,其主控因子为pH和有机质。此外,Cr(Ⅵ)老化过程中,还原产生的有效态Cr(Ⅲ)在2 d到30 d呈现快速上升,到达最高值(0.27%~3.27%)后迅速下降,最后趋于稳定(0.01%~2.19%),其老化过程可能与Cr(Ⅵ)的还原与老化及Cr(Ⅲ)自身老化有关。

Soil properties play an important role in aging of Cr(Ⅵ).Owing to the diversity of soil types in China,the aging process and main controlling factors of Cr(Ⅵ)in different farmland soils still need to be investigated.In the present study,12 farmland soils with different properties,in China,were collected and spiked with Cr(Ⅵ).A solution of 0.05 mol·L-1 EDTA was used to extract available Cr(Ⅵ)and Cr(Ⅲ).Their dynamic process and main controlling factors were investigated using a combination of HPLC-ICP-MS,dynamic model fitting,and multiple linear regression.Results showed that the available Cr(Ⅵ)decreased rapidly from 6.71%~68.71% to 4.53%~45.17% at the initial time(t<60 d),and then decreased slowly and equilibrated gradually(3.25%~34.35%).Pseudo-second-order model described well the aging process of Cr(Ⅵ)in all soils during the entire aging time(R^2>0.99).Results of multiple stepwise regression analysis showed that soil pH was the main factor controlling the aging rate of Cr(Ⅵ).Based on the pseudo-second-order model,the approximate aging equilibrium time of spiked Cr(Ⅵ)was derived to be from 6 to 158 days;soil pH and organic matter content were the main controlling factors.In addition,the available Cr(Ⅲ)generated from the reduction of Cr(Ⅵ)increased rapidly and peaked(0.27%~3.27%)at 2 to 30 days,then decreased rapidly,and finally attained equilibrium(0.01%~2.19%).The aging process of Cr(Ⅲ)may be related to Cr(Ⅵ)reduction and aging and Cr(Ⅲ)self-aging.