Zhang Hua, Selim H M
Department of Agronomy and Environmental Management, Sturgis Hall, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
Environ Sci Technol. 2005 Aug 15;39(16):6101-8. doi: 10.1021/es050334u.
Adsorption-desorption of arsenic is the primary factor that impacts the bioavailability and mobility of arsenic in soils. To examine the characteristics of arsenate [As(V)] adsorption-desorption, kinetic batch experiments were carried out on three soils having different properties, followed by arsenic release using successive dilutions. Adsorption of As(V) was highly nonlinear, with a Freundlich reaction order N much less than 1 for Olivier loam, Sharkey clay, and Windsor sand. Adsorption of arsenate by all soils was strongly kinetic, where the rate of As(V) retention was rapid initially and was followed by gradual or somewhat slow retention behavior with increasing reaction time. Freundlich distribution coefficients and Langmuir adsorption maxima exhibited continued increase with reaction time for all soils. Desorption of As(V) was hysteretic in nature and is an indication of lack of equilibrium retention and/or irreversible or slowly reversible processes. A sequential extraction procedure provided evidence that a significant amount of As(V) was irreversibly adsorbed on all soils. A multireaction model (MRM) with nonlinear equilibrium and kinetic sorption successfully described the adsorption kinetics of As(V) for Olivier loam and Windsor sand. The model was also capable of predicting As(V) desorption kinetics for both soils. However, for Sharkey clay, which exhibited strongest affinity for arsenic, an additional irreversible reaction phase was required to predict As(V) desorption or release with time.
砷的吸附-解吸是影响土壤中砷生物有效性和迁移性的主要因素。为了研究砷酸盐[As(V)]的吸附-解吸特性，对三种性质不同的土壤进行了动力学批量实验，随后通过连续稀释进行砷释放实验。As(V)的吸附具有高度非线性，对于奥利维尔壤土、沙基黏土和温莎砂，弗伦德利希反应级数N远小于1。所有土壤对砷酸盐的吸附都具有强烈的动力学特性，As(V)的保留速率最初很快，随后随着反应时间的增加逐渐或有点缓慢地保留。所有土壤的弗伦德利希分配系数和朗缪尔吸附最大值都随着反应时间持续增加。As(V)的解吸本质上具有滞后性，这表明缺乏平衡保留和/或存在不可逆或缓慢可逆过程。连续提取程序提供的证据表明，大量的As(V)不可逆地吸附在所有土壤上。一个具有非线性平衡和动力学吸附的多反应模型(MRM)成功地描述了奥利维尔壤土和温莎砂中As(V)的吸附动力学。该模型还能够预测这两种土壤中As(V)的解吸动力学。然而，对于对砷表现出最强亲和力的沙基黏土，需要一个额外的不可逆反应阶段来预测As(V)随时间的解吸或释放。
