The kinetics of Cd, Pb and Cr extraction from artificially polluted soils

The kinetics of Cd, Pb and Cr extraction with HCl from polluted chernozem and humous alluvial soils was investigated. The efficiency of the extraction was more than 90% for Cd and more than 80% for Pb. In both cases, the extraction reached the equilibrium state. For Cd and Pb, the metal-ion removal processes in the first 4 h of extraction can be modelled by two simultaneous, pseudo-first-order, irreversible reactions. One of the reactions is fast and can be attributed to H⁺–Mⁿ⁺ exchange reaction occurring on the surface of inorganic minerals as well as in the metal–humic acid complexes and to the dissolution of the water-insoluble precipitates.The minor portion of the metal ions took part in a rather slow reaction, where H⁺ ions exchange with metal ions bound in the internal lattice sites. The slow dissolution of the metal compounds should also be considered. The slow extraction partly can be attributed to slow irreversible processes (e.g., diffusion from the internal lattice sites).In the case of Cr(III), the extraction was found to be a very slow process; the efficiency of removal was less than 25%. The system did not attain the equilibrium state. Presumably, the rates of extraction processes are intermediate between those of the slow and fast reactions.     

两种典型耕作土壤粘粒矿物XRD光谱特性分析

以东北粮食主产区典型耕作黑土和黑钙土为研究对象,在测定同一气候和地理位置下两种耕作土壤颗粒组成特征情况的基础上,采用X射线衍射(XRD)分析方法,对两种耕作土壤的粘粒矿物组成及相关差异进行分析,深入探讨其内在变化机理,是土壤矿物研究的新视角。结果表明：两种供试土壤颗粒组成均以砂粒为主,粘粒、粉粒次之;当颗粒累积率达到50%时,中央粒径分布在15～130 μm区间,除胜利乡黑土剖面外,各采样地两类土壤的剖面中粘粒含量的分布顺序呈现出与中央粒径大小相反的趋势。土壤粘粒在两种土壤剖面中呈现不同的分布规律,黑土剖面中粘粒在表层富集(18.82%),而黑钙土剖面中在钙积层富集(17.41%)。除泉眼岭黑土剖面外,其余采样地的土壤剖面中粘粒含量均在母质层中最少。XRD图谱分析显示,不同土壤中粘粒矿物图谱的差异不仅表现在衍射峰的强度及部分衍射峰位的变化上,还表现在矿物组成上。黑土、黑钙土均以2∶1型粘粒矿物为主,黑土组成为蒙伊混层-伊利石-蛭石型,黑钙土为蒙伊混层-伊利石-蒙脱石型,且均含有少量的高岭石、绿泥石、石英等原生矿物。