Thiocyanate-induced labilization of schwertmannite: Impacts and mechanisms

Schwertmannite is an amorphous iron(III)-oxyhydroxysulfate that forms in acid mine drainage(AMD) environments. The characteristic of high heavy metal adsorption capability makes schwertmannite a potentially useful, environmentally friendly material in wastewater treatment. Unstable schwertmannite is prone to recrystallization.Understanding the mechanisms that induce schwertmannite labilization and affect its capacity to remove heavy metals are of great environmental and geochemical significance.Thiocyanate(SCNˉ) is a hazardous pseudohalide that is also normally found in AMD.However, little is known about the impact of Fe(III)-binding ligand SCNˉ on schwertmannite stability and its subsequent capacity to bind trace elements. Here, we investigated the adsorption of SCNˉ on schwertmannite and subsequent mineral transformation to characterize this little-known process. The appearance of Fe2+indicated that the interactions between schwertmannite and SCNˉ may involve complexation and reduction reactions. Results showed that the majority of the adsorbed-SCNˉ was immobilized on schwertmannite during the 60-days transformation. The transformation rates of schwertmannite increased with increasing concentrations of SCNˉ. Goethite was detected as the dominant transformation product with or without SCNˉ. The mechanisms of SCNˉ-promoted dissolution of schwertmannite can be described as follows:(1) formation of Fe(III)–NCS complexes on the schwertmannite surface and in solution, a process which increases the reactivity of solid phase Fe(III);(2) the extraction of Fe(III) from schwertmannite by SCNˉ and subsequent schwertmannite dissolution; and(3) the formation of secondary minerals from extracted Fe(III). These findings may improve AMD treatment strategies and provide insight into the use and potential reuse of schwertmannite as a trace element sorbent.     

2014年北京地区云内云下的降水化学分析

为了解现阶段北京地区降水的化学特征和云下/云内的清除作用,于2014年采用分段采样的方式针对25场降水进行收集,分析了降水中各离子组分浓度.结果发现,2014年北京地区降水中NH₄⁺、SO₄^2-、NO₃^-和Ca²⁺浓度最高,雨量加权平均离子浓度分别为240、162、91和65 μeq·L^-1,与早期研究相比均有所下降.SO₄^2-/NO₃^-比值为1.8,NO₃^-和NH₄⁺的比重显著增加.综合利用相关性分析、主因子分析及后向轨迹等方法,探讨了北京地区降水中各离子组分的来源.结果表明,东南气团中主要离子NO₃^-、SO₄^2-及NH₄⁺的浓度较高,主要受人为活动排放的影响.总体上各离子的云下冲刷作用略大于云内清除,其中,Na⁺、Ca²⁺及NO₃^-云下冲刷的贡献大于SO₄^2-和NH₄⁺.与其他城市相比,北京地区云内清除的贡献略大,表明长距离输送的影响不可忽视.     

Case study of dust event sources from the Gobi and Taklamakan deserts: An investigation of the horizontal evolution and topographical effect using numerical modeling and remote sensing

A severe dust event occurred from April 23 to April 27, 2014, in East Asia. A state-of-the-art online atmospheric chemistry model, WRF/Chem, was combined with a dust model, GOCART, to better understand the entire process of this event. The natural color images and aerosol optical depth (AOD) over the dust source region are derived from datasets of moderate resolution imaging spectroradiometer (MODIS) loaded on a NASA Aqua satellite to trace the dust variation and to verify the model results. Several meteorological conditions, such as pressure, temperature, wind vectors and relative humidity, are used to analyze meteorological dynamic. The results suggest that the dust emission occurred only on April 23 and 24, although this event lasted for 5 days. The Gobi Desert was the main source for this event, and the Taklamakan Desert played no important role. This study also suggested that the landform of the source region could remarkably interfere with a dust event. The Tarim Basin has a topographical effect as a “dust reservoir” and can store unsettled dust, which can be released again as a second source, making a dust event longer and heavier.     

Aeration optimization through operation at low dissolved oxygen concentrations: Evaluation of oxygen mass transfer dynamics in different activated sludge systems

In wastewater treatment plants(WWTPs)using the activated sludge process,two methods are widely used to improve aeration efficiency — use of high-efficiency aeration devices and optimizing the aeration control strategy. Aeration efficiency is closely linked to sludge characteristics(such as concentrations of mixed liquor suspended solids(MLSS)and microbial communities)and operating conditions(such as air flow rate and operational dissolved oxygen(DO)concentrations). Moreover,operational DO is closely linked to effluent quality. This study,which is in reference to WWTP discharge class A Chinese standard effluent criteria,determined the growth kinetics parameters of nitrifiers at different DO levels in small-scale tests. Results showed that the activated sludge system could meet effluent criteria when DO was as low as 0.3 mg/L,and that nitrifier communities cultivated under low DO conditions had higher oxygen affinity than those cultivated under high DO conditions,as indicated by the oxygen half-saturation constant and nitrification ability. Based on nitrifier growth kinetics and on the oxygen mass transfer dynamic model(determined using different air flow rate(Q′_(air))and mixed liquor volatile suspended solids(MLVSS)values),theoretical analysis indicated limited potential for energy saving by improving aeration diffuser performance when the activated sludge system had low oxygen consumption; however,operating at low DO and low MLVSS could significantly reduce energy consumption. Finally,a control strategy coupling sludge retention time and MLVSS to minimize the DO level was discussed,which is critical to appropriate setting of the oxygen point and to the operation of low DO treatment technology.     

基于水足迹强度的江苏省水资源利用效率分析

水足迹强度是可以量化水资源利用效率的指标,文章在计算江苏省水足迹的基础上,选取6项水足迹强度指标,分部门比较各地市水资源利用效率的差异,并基于ESDA研究水足迹强度的空间自相关性,构建空间集聚图。研究表明:2002~2014年江苏省各市水足迹总体呈现上升趋势,水资源压力增大;总体上苏南和苏北地区的农业水足迹强度都偏高,农业水资源利用效率低;苏南地区工业产值高但耗水量大,因此工业水足迹强度也偏高;苏北地区的灰水足迹强度偏高,水资源压力较大;江苏省水足迹强度具有不断增强的全局自相关性,地市出现集聚现象,不同地市的集聚分布也日益明显;大部分苏北地区属于高高集聚并且向外扩张,低低集聚主要分布在苏南地区。研究结果为政府部门分析地市间水资源利用效率差异,制定高效的水资源利用政策等提供依据。     

页岩气开采对水环境的影响及其治理技术研究

页岩气是一种清洁、低碳、高储量的非常规天然气能源,已成为全国油气资源勘探开发的新亮点,其快速发展影响着世界能源格局.然而,页岩气开采带来了巨大的环境风险,如水污染、大气污染、固体废弃物污染和土壤污染等.文章主要分析了页岩气钻井过程、压裂过程及采气过程可能出现的水环境问题,如水资源消耗、地表水污染及地下水污染等;总结了针对不同类型废水的处置措施及处理技术,以期为处理页岩气开采过程中产生的不同类型的废水提供理论依据.     

宜昌城区冬季大气污染的气象成因对比分析研究

2016年冬季,宜昌城区空气质量比上年冬季明显改善,通过采用对比分析、相关分析及后向轨迹分析等方法,诊断可能的原因.结果表明,宜昌城区冬季空气污染主要是由于细颗粒物导致,2016年冬季PM2.5、PM10、SO2浓度较2015年冬季明显降低,主要原因包括含硫燃料燃烧明显减少、外源性污染物的输入明显减少、降水清除以及减排措施有力等.后向轨迹分析结果显示,两年冬季污染最严重时段的污染物路径来源不同,2015年冬季最严重的污染过程主要是由于上游北方远距离的外源性污染的快速输入、在本地下沉导致,2016年冬季最严重的污染过程则是由于来自偏南路径近距离的气团叠加本地污染源,在垂直方向累积造成.     

汽车4S店表面涂装有机废气监测的研究

汽车4S店表面涂装有机废气排放现已成为城市重要的污染排放源之一,中国目前暂未针对该行业废气排放制定相关标准.对汽车4S店有机废气的监测情况及国外、国内地方相关标准做了简单的介绍,对表面涂装工艺和污染治理提出一些对策.对多家汽车4S店的监测情况进行了概述,建议加强汽车4S店表面涂装大气污染物排放控制和管理,改善区域大气环境质量,促进表面涂装工艺和污染治理技术的进步,尽快规范相应管理措施,才能有效控制汽车表面涂装大气污染物的排放.     

废旧锂电池中有价金属的回收技术研究

锂电池以其优异的性能得到了广泛的应用,其废弃量也在逐步增加.如果不对其进行有效的处理回收,不仅给环境保护带来巨大的压力,而且也会造成钴、锂、镍和锰等有价金属的极大浪费.综述了国内外对废旧锂电池回收技术的研究现状,比较了不同回收途径的优缺点,讨论了回收技术的发展方向,着重介绍了共沉淀法在废旧锂电池有价金属回收中的应用.此外,随着锂离子电池生产技术的发展,新的电极材料将会出现并取代过渡金属氧化物,同时也需要相应的电解液与之匹配,这将向废旧锂电池回收技术提出了新的要求.     

广东省春节期间空气质量特征及预报方法研究

2017年春节期间广东省环境空气质量自动监测站的数据分析结果表明:春节假期广东省空气质量等级变化较大.除夕全省空气质量为良;初一,全省以良和轻度污染为主,粤东出现重度污染,粤西和粤北出现中度污染,可能与除夕夜烟花爆竹燃放有关;初二起,全省空气质量逐渐转为优良.首要污染物以PM2.5和O3为主.现有的NAQPMS和CMAQ空气质量预报模型在污染相对严重的初一表现较差,主要是因为数值模型未能考虑到烟花爆竹燃放等排放源的输入.