富镉铅锌矿床表生地球化学研究及其环境意义－以贵州都匀牛角塘矿床为例

丰富的铅锌矿资源为我国经济社会的发展作出了重要贡献，但也不可避免带来严重的环境污染，特别是酸性矿山废水及重金属污染已成为当今世界面临的两大环境难题。最让人们不安的是，即使在矿山关闭数十年、数百年，甚至更长时间，矿山尾矿等浸出液对矿区生态环境的影响依然存在。闪锌矿是铅锌矿中主要矿物之一，也是镉的主要载体矿物，而镉是有毒重金属元素，其毒性仅次于汞。大量含硫化物废石、尾矿暴露于地表环境，发生水－岩－气之间的反应(即氧化淋滤作用)产生酸性矿山废水和释放大量Zn、Cd等重金属元素，进入矿区水体、土壤，影响甚至破坏矿区生态环境，危害人类健康。通过表生环境条件下矿石风化淋滤实验和闪锌矿氧化动力学实验研究，认识铅锌矿石及闪锌矿氧化淋滤过程、速率及其影响因素，揭示Zn、Cd等重金属元素的释放、迁移及富集规律，并建立定量模型，为正确预测、评价和控制铅锌矿山的环境污染提供科学依据。 本文以牛角塘富镉锌矿床为研究对象，主要通过闪锌矿氧化动力学实验、矿石风化淋滤实验及矿区环境调查将闪锌矿氧化－矿石风化淋滤－环境污染有机地联系在一起，主要取得以下几点认识： 1、矿石风化淋滤实验表明，牛角塘铅锌矿石淋滤后淋滤液主要呈碱性，淋滤释放出大量Zn2+、Cd2+、Ca2+、Mg2+等阳离子及SO42-、CO32-等阴离子，淋滤过程中形成大量以石膏为主要成分的沉淀物，淋滤液中Zn、Cd主要以沉淀形式存在(可能被沉淀吸附或包裹)，而水溶态Zn、Cd浓度极低。 2、牛角塘矿床中黄铁矿锌矿石中Zn和Cd淋滤率较半氧化锌矿石低得多，表明半氧化或氧化锌矿石的风化淋滤作用更强烈。 3、在Fe2(SO4)3为氧化剂时，闪锌矿氧化速率随着Fe3+浓度的增加、温度升高、pH值降低而增加，且闪锌矿氧化过程中Zn、Cd的释放速率大致相同；在有限实验时间内(本文中小于60h)黄铁矿的混入对闪锌矿氧化速率起抑制作用，可能是黄铁矿与闪锌矿与Fe3+反应过程中存在竞争关系；反应的活化能分别为Ea(Zn)41.75 kJ.mol-1、Ea(Cd)42.51 kJ.mol-1，说明闪锌矿氧化速率受矿物表面反应控制。氧气氧化闪锌矿时，随着pH值的变化闪锌矿的氧化机理发生变化，在2＜pH≤6范围内，闪锌矿氧化速率随着pH值的增加而降低，而在6＜pH≤7.8范围内，随着pH值增加，闪锌矿氧化速率反而增加。Fe3+和氧气均对闪锌矿的氧化起重要作用，但以Fe3+氧化为主。 4、大多数闪锌矿氧化实验中Zn、Cd的溶解曲线非常相似、活化能相近，表明Zn和Cd存在相似的地球化学行为。但在闪锌矿溶解过程中Zn、Cd的释放速率存在差异，在酸性介质条件下Cd的释放速率比Zn略快，而中碱性介质条件，Cd的释放速率比Zn慢。这与Zn、Cd同处元素周期表第ⅡB族，它们之间既存在许多相似的地球化学性质，也存在不少差异有关。 5、利用双对数图法处理实验数据，得出表生环境条件下闪锌矿氧化速率公式为： 或 该公式可用于估算一定时间内闪锌矿氧化所释放的Zn、Cd等重金属元素的总量，为正确预测、评价和控制铅锌矿山的环境影响提供科学依据。 6、牛角塘矿区环境调查结果表明，牛角塘矿山水体主要呈中碱性，水体污染较轻，大多水体中Zn、Cd含量未超过农业灌溉标准及饮用水国家标准，这主要受矿区碳酸盐岩地层的影响。但矿区土壤、河流沉积物及植物中Zn、Cd均超过相关国家标准，遭到不同程度污染。 7、本文研究表明，闪锌矿氧化及铅锌矿风化淋滤过程中，将产生矿山酸性废水和释放Zn、Cd等重金属元素，污染矿区及其下游生态环境，危害人类健康。我们可以采取以下措施进行防范和控制环境污染：第一，提高矿区水体pH值，降低闪锌矿等硫化物矿物氧化速率；第二，尽量减少废石、尾矿直接暴露于空气、Fe3+等氧化剂环境中，如可在废石（渣）、尾矿表面盖上覆土等，也可降低闪锌矿等硫化物矿物的氧化速率。

Estimation of soil organic partition coefficients: from retention factors measured by soil column chromatography with water as eluent

The retention factors (k) of 104 hydrophobic organic chemicals (HOCs) were measured in soil column chromatography (SCC) over columns filled with three naturally occurring reference soils and eluted with Milli-Q water. A novel method for the estimation of soil organic partition coefficient (K-oc) was developed based on correlations with k in soil/water systems. Strong log K-oc versus log k correlations (r>0.96) were found. The estimated K-oc values were in accordance with the literature values with a maximum deviation of less than 0.4 log units. All estimated K-oc values from three soils were consistent with each other. The SCC approach is promising for fast screening of a large number of chemicals in their environmental applications. (C) 2002 Elsevier Science B.V. All rights reserved.

Construction of habitat suitability models (HSMs) for benthic macroinvertebrate and their applications to instream environmental flows: A case study in Xiangxi River of Three Gorges Reservior region, China

Based on a long-term ecological monitoring, the present study chose the most dominant benthic macroinvertebrate (Baetis spp.) as target organisms in Xiangxi River, built the habitat suitability models (HSMs) for water depth, current velocity and substrate, respectively, which is the first aquatic organisms model for habitat suitability in the Chinese Mainland with a long-term consecutive in situ measurement. In order to protect the biointegrity and function of the river ecosystem, the theory system of instream environmental flow should be categorized into three hierarchies, namely minimum required instream flow (hydrological level), minimum instream environmental flow (biospecies level), and optimum instream environmental flow (ecosystem level). These three hierarchies of instream environmental flow models were then constructed with the hydrological and weighted usable area (WUA) method. The results show that the minimum required instream flow of Xiangxi River calculated by the Tennant method (10% of the mean annual flow) was 0.615 m(3) s(-1); the minimum instream environmental flow accounted for 19.22% of the mean annual flow (namely 1.182 m(3) s(-1)), which was the damaged river channel. ow in the dry season; and 42.91% of the mean annual flow (namely 2.639 m(3) s(-1)) should be viewed as the optimum instream environmental flow in order to protect the health of the river ecosystem, maintain the instream biodiversity, and reduce the impact of small hydropower stations nearby the Xiangxi River. We recommend that the hydrological and biological methods can help establish better instream environmental. ow models and design best management practices for use in the small hydropower station project. (C) 2008 National Natural Science Foundation of China and Chinese Academy of Sciences. Published by Elsevier Limited and Science in China Press. All rights reserved.