环境条件变化对土壤中稀土元素溶解释放的影响

以模拟污染红壤为实验材料，在pH值为3.5、5.5和7.5条件下，通过向土壤悬浊液中通入O2或N2改变氧化还原电位Eh为－100，0和400mV，研究了氧化还原电位和pH值对红壤中稀土元素La和Ce溶解释放的影响．结果表明，随着pH值或Eh的减小，La和Ce释放量逐渐增大，Ce受电位的影响较La更为明显．同时还观察到La和Ce的释放量与Fe、Mn的释放量呈显著正相关，表明La和Ce可能主要吸附在Fe－Mn氧化物表面或滞留在Fe－Mn氧化物中．实验还发现，pH值和氧化还原电位的改变会影响红壤中La和Ce形态的变化，分离后沉淀物中的交换态和Fe－Mn氧化物结合态稀土随pH值或氧化还原电位的减小而减小．多元相关逐步回归分析表明．红壤中La和Ce两种元素的释放主要来自交换态和Pe－Mn氧化物结合态．

The effects of change of environmental conditions on the release and species transformation of rare earth elements (REEs) in soil

The influence of redox potential and PH value on the release of rare earth elements (La and Ce) in simulated-contamination soil was investigated under PH values of 3.5, 5.5 and 7.5 and change of redox potential to Eh-100,0 and 400mV. Results indicated that REEs release increased gradually with the decrease of PH value or Eh, and the influence of redox potential on Ce was more remarkable than on La. At the same time, it was Observed that REEs release was positively correlated with the release of Fe and Mn elements, indicating that REEs might mostly be adsorped on the surface of Fe-Mn oxide or occluded into the oxide. Moreover, it was found that alteration of PH value and redox potential might affect the change of REEs species in soil. The concentration of La and Ce in exchangeable fraction and Fe-Mn oxide fraction decreased with the decrease of PH value and redox potential. Multiple stepwise regression analysis showed that exchangeable fraction and Fe-Mn oxide fraction predominately contributed to the La and Ce release. In short, low PH value and redox potential were favorable to REEs release following the change of REEs species, and the REEs concentrations in exchangeable fraction and Fe-Mn oxide fraction are the main contributors tO their release.