雷州半岛玄武岩母质砖红壤铬（Cr）富集机制及其环境行为特征

Although far from the industrial pollution sources, the Oxisol developed from basalt rock contains high amounts of Cr relative to those derived from granite or sandstone. which has been attributed to the characters of parent materials and soil-forming factors. However, the mechanisms by which Cr was enriched in the soil and its environmental behaviors were still not well understood. In the present project, the evolutive sequence of Cr host phases would be revealed by differentitating the minerals crystallization in weathering profile together with correlation analysis between Cr content and soil physic-chemical propertites. In addition, to assess the leaching and mobility of Cr in soil profiles, chemical fraction of Cr in soils was differentited by use of the sequential extraction methods. Moreover, batch experiments a were conducted to elucidate the influence of pH and Eh on Cr release, especially the relationship between mineral dissolution and Cr release. Finally, the column experiments were also performed with aim to reveal the effect of acid depositions on the release of Cr as well as the transformation of chemical valences and fraction. The project would improve our understanding on the geochemical behavior of elements during the process of soil formation, and was meaningful for assessment and regulation of harmful elements in soils.

受母岩特性和成土因素影响，玄武岩母质砖红壤内源性Cr含量异常偏高，但其富集机制还不明确。这部分Cr在一定条件下可释放到土壤溶液，被植物吸收或迁移到地下水，从而带来严重环境污染风险。当前土壤Cr污染研究主要关注外源性Cr，很少关注土壤发育过程中所富集的内源性Cr。本项目将围绕砖红壤内源性Cr富集机制及其环境行为等科学问题，采用X-射线衍射等技术，研究土壤不同发生层矿物晶型特征及其理化性状，探明土壤内源性Cr富集矿物及其风化演替规律；采用选择性顺序提取法，研究土壤不同发生层Cr的赋存形态，阐明土壤内源性Cr富集特征及其与成土过程的关系；通过室内模拟田间不同氧化-还原状况，研究pH和Eh等因素对内源性Cr释放的影响；通过酸雨淋溶模拟，研究酸雨影响下土壤内源性Cr释放、迁移特征，揭示Cr离子形态和价态的转化规律。本项目将推动成土过程元素地球化学行为研究，为土壤Cr污染控制及其风险防范提供理论支撑。

本项目主要研究了雷州半岛玄武岩母质砖红壤中Cr的富集、形态转化、淋溶-迁移等环境行为特征及其影响因素，所取得的主要成果有：（1）揭示了氧化铁是玄武岩母质砖红壤中Cr富集的主要矿物载体。一方面，不同剖面层次Cr含量与相应层次氧化铁含量之间存在显著相关性；另一方面，细小颗粒针铁矿因其比表面积大、表面晶格缺陷多，对Cr有更强的吸附作用。（2）锰氧化物的晶型和含量是控制三价铬在砖红壤中向六价铬转化的主要因素，针铁矿、高岭石等共存矿物对上述氧化过程没有影响，但可以通过吸附氧化产物—六价铬而降低后者的环境风险。（3）玄武岩母质砖红壤中六价铬在有机物存在条件下，可被还原为三价铬，溶液中铁、锰离子可显著提高该反应速率，且反应主要在溶液中进行而非土壤固相表面。（4）室内土柱模拟实验发现，玄武岩母质砖红壤对六价铬的吸附容量较大，使得后者的淋溶-迁移量较低；添加有机肥可使六价铬向三价铬转化，从而进一步降低其淋溶-迁移量；磷酸根和酸雨沉降将促进六价铬的淋溶过程。（5）初步揭示了玄武岩母质砖红壤成土过程中，铁、锰氧化物富集程度差异的部分原因，并指出玄武岩母质砖红壤中铬的环境行为主要受氧化铁所控制。本项目不仅为系统地阐明铬在雷州半岛玄武岩母质砖红壤的环境行为提供了理论知识，而且为调控其环境风险提供了技术依据。