Remediation and restoration of metal-contaminated sites： Concepts and appfications to mining areas

Metals, including heavy metals and metalloids, are a common group of environmental contaminants. Their sources in the environment are geogenic or anthropogenic. The growing trend in global industrialization ensures that more metals could be dispersed even in pristine ecosystems. To fuel industrialization, more metal ore mines have to be discovered and explored. These explorations often result in landscape disturbance, soil degradation and environmental contamination by unwanted mining constituents. Mine tailings brought up to the ground surface often serve as the main source of contaminants when these pyrite-rich materials oxidize. The oxidation of mine tailings results in proton generation, coupled with the dissolution of metals and other cations Unwanted anionic constituents are also produced. The so-called ＂acid mine drainage＂ may affect the productivity of farmlands and stability of receiving streams and other bodies of water-acidifying the waters and enriching the ecosystem with metals, i.e., high total dissolved solids. The acidified overburden materials become inhospitable to plant and microbial life as they are typically low in organic matter content and infertile. This exposes the landscape to runoff and erosion.     

增强型AlGaN/GaN高电子迁移率晶体管高温退火研究

深入研究了两种增强型AlGaN/GaN高电子迁移率晶体管(HEMT)高温退火前后的直流特性变化.槽栅增强型AlGaN/GaN HEMT在500 ℃ N₂中退火5 min后,阈值电压由0.12 V正向移动到0.57 V,器件Schottky反向栅漏电流减小一个数量级.F注入增强型AlGaN/GaN HEMT在 400 ℃ N₂中退火2 min后,器件阈值电压由0.23 V负向移动到-0.69 V,栅泄漏电流明显增大.槽栅增强型器件退火过程中Schottky有效势垒     

Rare-earth element mobility during ore-forming hydrothermal alteration: A case study of Dongping gold deposit Hebei Province,China

REE mobility during hydrothermal ore-forming processes has been extensively investigated in recent years and the potential of REE to provide information about ore forming processes has commonly been recognized.The Dongping gold deposit,which is located in northwestern Hebei Province,China,occurring in the inner contact zone of the Shuiquangou syenite complex,is spatially,and probably genetically,related to the syenite,the deposit was formed under the moderate to high temperature(220℃ to 320℃),weakly acidic to weakly alkaline,rather high fo2(lgfo2=-30～-34)environment.The REE study of the host rocks,altered wall rocks,ores and gangue minerals from the deposit suggests that the REEs have been mobilized and differentiated during K-feldspathization and silicification.The extremely altered syenite enveloping auriferous quartz vein shows positive Ce anomaly and larger LREE/HREE ratio than that of the unaltered syenite.The REE concentrations and patterns of the ores are determined by the ore types and mineral assemblages,LREE/HREE ratios in the gangue quartz and hydrothermal Kfeldspars are relatively low.The most significant observation is that the gangue quartz shows significant positive Eu anomaly,whereas the hydrothermal K-feldspars show less significant or no positive Eu anomaly at all relative to the primary feldspar in the unaltered syenite. It is evident that the REEs are mobile during K-feldspathization and silicification in the ore forming process.Weak to moderate K-feldspathization caused REE mobility without apparent differentiation with the exception of extreme K-feldspathization and silicification which resulted in significant depletion of HREE and Eu and relative enrichment of Ce.The REE,Y,U,Th and Au contents of the syenite decrease as the degrees of K-feldspathization and silicification of the rocks increase towards the auriferous quartz veins.As the ores were deposited under a rather oxidized environment,Ce^4 predominated over Ce^3 .The precipitation of the former in the form of CeO2 or absorpted onto the secondary mineral assemblage resulted in the inconsistent removal of the REE and the relative Ce enrichment in the strongly altered rocks.in contrast,Eu was present mainly in a low valence state (Eu^2 ).The geochemical differences from the other REE^3 and much less sites in the secondary minerals to accommodate the Eu released form the original minerals resulted in the enrichment of Eu in the fluids.The mobility and differentiation of REE and the coherent mobilities of Y,U,Th and Au also support the argument that the syenite is one of the source rocks for gold mineralization.The REE contents and patterns of the altered rocks enveloping the auriferous quartz vein could be used as a guide for locating ore veins in mineral exploration.     

Mineralogical and Geochemical Constraints on Arsenic Mobility in a Philippine Geothermal Field

Arsenic is usually associated with sulphide minerals formed in the geothermal environment. However, sulphide minerals are prone to dissolution after contact with meteoric water under surface oxidizing conditions. Secondary precipitates that form from the dissolution of the primary sulfides exert a greater influence on arsenic mobility in the geothermal environment. Fe-hydroxides have very good affinity with dissolved arsenate and are stable under most surface oxidizing conditions. Both amorphous silica directly precipitated from geothermal fluids and possibly a kaolinite alteration can host a small significant amount of arsenic. These silicates are also more stable under a wide range of pH and redox conditions.     

向海湿地沉积剖面化学元素相对迁移特征分析

旨于探索沉积剖面元素迁移强度的描述方法,讨论向海沼泽湿地沉积物化学元素的迁移积聚等基本地球化学特征,以深化对沼泽湿地沉积化学行为的某些认识。冬季在向海两处沼泽采集了代表一定范围汇水区与人类活动影响的沉积芯。利用Tessier等(1979)提出的连续提取法对沉积物中多种常量与微量元素地球化学相进行分离。可迁移系数、潜在迁移系数、非迁移系数的计算结果表明,在向海沼泽沉积剖面中,化学元素相对迁移强度为:Ca、Sr、Mn、Pb潜在活性最大,Ti、Al、K、Rb潜在活性最小,以此为依据,Ti、Al、K、Rb等元素适宜作为示踪元素。为消除沉积物构成组织的影响,以Al为参考元素对重金属元素形态两种分量进行归一化后,重金属环境非迁移分量与相对迁移分量均表现出在表层的富集,尤其表现在上游霍林河煤矿开发后20余年这一时期,人类活动的介入加速了重金属元素通过河流搬运向下游湿地的输入。     

Arsenic mobility from arsenopyrite-rich gold mine waste in Snow Lake, Manitoba, Canada

Local water contamination by arsenic can be caused by gold mining activities as in Snow Lake, Manitoba. This project was to f＇md the source （s） and pathways of the arsenic contamination and describe arsenic attenuation in ground and surface water. The project was initiated because arsenic concentrations average 16.0 mg/L in one groundwater monitoring well （MW17）. One potential source of arsenic is the 50 year-old Arsenopyrite Residue Stockpile （ARS）, 100 m upgrade of MW17. Between 1948 and 1959, 250000 tons of cyanide treated, arsenopyrite concentrate were stored in a waste rock impoundment, which was left open until 2000 when it was capped with layers of waste rock, clay and silt to minimize water infiltration and the oxidative release of arsenic.     

石油类污染物在包气带土层中的水化学迁移率测定

水化学迁移率是反映污染质在水-土孔隙介质中迁移锋面速度的参数,参数值的大小与土壤介质性质、水流状态、污染物质的物理化学性质有关。利用淋滤土柱的动态平衡试验法,模拟自然降雨入渗条件下,石油类污染物在吉林油田区包气带土层中的迁移转化过程。试验结果表明,其水化学迁移过程可分为淋溶阶段、吸附阶段和平衡阶段;微生物分解作用比较弱;不同厚度土层的淋滤液浓度衰减曲线趋势极为相似。考虑室内实验与野外自然环境之间存在的尺度效应,合理确定了阻滞因子、水化学迁移率。     

北京地区垃圾填埋对地下水的污染及垃圾填埋场选址分区

本文介绍了北京市生活垃圾处理现状及由于垃圾填埋而引起的地下水污染问题。以北京西郊南部北天堂垃圾填埋场的污染状况为例进行研究,通过建立数学模型来模拟污染物在地下水中的运移及补救效果,对污染控制进行了模拟,分析及提出相关建议;并对北京市生活垃级填埋场遗址进行了分区。     

垃圾渗滤液有机污染组分在包气带中衰减规律的模拟研究

用若干土柱模拟试验研究了垃圾渗滤液有机污染组分在不同岩性、不同厚度包气带介质中的运移规律,并计算了有机污染组分在包气带中运移的有关水化学迁移参数(阻滞因子R和水化学迁移率E).结果表明,有机污染组分在不同岩性介质中的R值顺序为:粘土＞亚粘土＞砂土,在相同岩性中随着厚度的增加R呈正相关增大.从而为评价和预测垃圾场对地质环境影响提供技术参数,并为垃圾场的选址提供理论依据.