典型土壤和沉积物中多金属形态分布特征

土壤和沉积物作为地表矿物岩石风化过程的重要产物,对金属元素的地球化学循环起着至关重要的作用。由于土壤和沉积物记录了矿物溶解、吸附、沉淀及生物吸收等综合地质过程的叠加作用,如何准确判定某个单一过程对金属地球化学的影响和贡献仍是当前研究难题。土壤和沉积物中金属的形态分布特征研究可帮助判定元素在地表风化过程中经历的特定过程。本文选择我国广泛分布的五种典型土壤类型(砖红壤、黄棕壤、棕壤、红壤、水稻土)、一种水系沉积物和一个玄武岩自然风化剖面土壤样品,运用改进的BCR形态提取法开展典型金属形态分布特征研究,明确了具有潜在生理毒性的Cr和Pb、代表性过渡金属Ni、Cu、Zn、V、Co以及相关研究较少的碱金属Cs、碱土金属Sr和难溶元素Zr在不同土壤、沉积物中的分布特征,刻画了这些金属在典型砖红壤风化剖面上的连续变化规律,初步判定了不同地质环境金属形态分布不同的控制因素。V、Zr和Sr受自身性质控制,在不同的地质样品中都表现出相似的形态分布,均以残渣态为主,而其他金属则表现出不同的形态分布趋势,其中,Ni、Zn、Cs、Pb和Cu的形态分布受它们的理化特性和外部环境共同影响,Co形态则可能受到锰矿物、TOC含量的影响。研究结果为进一步认识流域金属地球化学行为及其环境效应提供了基础数据。

Characterization of Metal Speciation Distributions in Typical Soils and Sediment by Sequential Extraction Procedure

Surface soil and sediment, as the important products of continental weathering, play important roles in the global biogeochemical cycle of elements. As the total contents of metals in soil and sediment were derived from multiple geological processes such as mineral dissolution, adsorption, precipitation, biological uptake and even anthropogenic impact, it is hard to determine the impact and contribution of a specific process or source using only bulk metal content. The research on the speciation distribution characteristics of metals in soil and sediment would help the understanding of the behavior of metals in the process of surface weathering, migration and transformation. In this study, five typical soils that widely distributed in China (latosol, yellow brown, brown, red and paddy soils), a sediment from the mining area, and a series of natural samples from a typical basalt weathering profile were selected for investigating the distribution of various metals species, and a systematic comparison of these samples was carried out to better constrain metal behaviors under different surface weathering regimes. The modified BCR speciation extraction method was used and the potential toxic metals Cr, Pb, the transition metals V, Co, Ni, Cu, Zn and metals Zr, Sr and Cs that are rarely studied were investigated. The results showed that, the geochemistry of V, Zr and Sr is mainly controlled by their properties, with principal presence in the residual fraction, showing similar speciation distributions no matter the kind of soil and sediment, while other metals display variable trends. For example, Cr in the latosol profile is similar to that of brown soil, and Co is mainly affected by principally manganese minerals, while the speciation distribution of Ni, Zn, Cs, Pb and Cu unevenly distribute in different fractions, which would be controlled by both their physicochemical characteristics and external environmental factors. For the latosol profile, though all metals undergone the same weathering processes, they show clearly different distribution trends. Our results provide useful information on the geochemistry and environmental effect of these metals in fluvial catchment and relative environments.