砷氢化物是砷的重要迁移形式

通过对砷氢化物的理化特性、形成条件,砷氢化物与纳米砷、硫、硫氢化物的亲合性、相关性,氢在太阳系尤其是对地球形成、演化的重大贡献,与内生砷矿物共伴生矿物的流体包裹体气相成分,内生砷矿物、含砷矿物的化学成分的探讨,认识到砷及砷合金氢化物是砷的重要迁移形式,它们随岩浆、热液、热气迁移至地壳浅部,被氧化成砷矿物,或与硫、硫氢化物作用生成硫砷化物矿物。     

江西高砷铜矿石的含砷特征

砷是铜精矿冶炼中的主要有害杂质之一。高砷铜矿石经过选矿,铜精矿中砷含量仍较高,给工业利用带来困难。在地质勘探阶段,应加强砷的性状、分布规律的研究,查明不同的矿石类型、块段、矿体中砷的含量和分布,以便在采选冶过程中采取措施,降低铜精矿中的砷含量。     

中国砷矿资源概述

砷在自然界中无处不有,雄黄矿是中国著名的砷矿产。砷与人类文明生活息息相关。中国砷矿主要分高中温岩浆热液硫砷化物矿床和低温非岩浆热液单硫化物雄黄雌黄矿床,系中国东部中新生代地质多旋回构造 岩浆作用下活化的产物     

砷矿资源开发与环境治理

砷矿床,从其地球化学特点看,绝大部分均以共、伴生形式复合于有色金属硫化物矿床中,单一的砷矿床较为少见。由于砷的毒性,在开采利用有色金属矿时,砷除少量回收外,绝大部分均以“三废”形式排放,形成环境污染。我国探明砷储量为世界砷总储量的70％,当前生产利用中普遍存在浪费资源、污染环境的问题,应引起环保部门重视,为保护资源,化害为利,提出了综合治理的建议。     

湄公河下游地下水域中的砷

通过对亚洲东南部多数冲积含水层的水进行调查，更进一步加强了人们对砷的认识，其调查结果使人们增加了对湄公河流域下游地下水水域中砷的关注。本文作者对此进行了新的研究并且回顾了许多以前小规模研究，提供了柬埔寨和越南Cuu Long三角洲含水层中砷的综合概况。天然砷一般起源于湄公河流域的下游，而不是起源于某一有地质特征的地区，而且发现浓度介于8ppm和16ppm（干重）之间的砷广泛分布于土壤中。与天然冲积层的砷相比，工业和农业用的砷是有限的。含水层地下水的砷浓度不低于10μgL^-1，但是，在离散的反常区域，砷的浓度在10-30μgL^-1也是常见的，有时也可能有暂时的砷异常，砷浓度可达到600μgL^-1，。最严重的是，洪积平原中的铁和富含有机质的沉积物容易受到洪水水位大的波动的影响，在氧化条件下．产生不稳定的毒砂。而一般情况下，地下水中高浓度的砷，由于受到吸附和解吸的袭夺作用，在还原和带轻微碱性的条件下，砷适宜释放。在水位埋深浅的含水层和100—200米较深的含水层中，地下水的砷浓度高。砷蔓延的过程没有明显的迹象，但是砷对健康有严重的局部危害，而且通过间接方式（诸如通过污染的稻米和水产品）摄取低浓度砷也存在着一定的风险。土壤中含砷几乎是普遍存在的，加之将来地下水抽取量的快速增加的可能性，这就要求在整个区域开发水资源时要持续保持警惕性。     

威远气田水中砷的存在形式及脱砷

根据威远气田水中含H2S和Fe2+的特性,认为地下气田水处于还原环境中,应用Ca﹣As(Ⅲ)﹣H2O系的[Me]T-pH图,指出气田水中砷以AsO2-存在,并结合气田水的一般综合利用工艺流程,阐明了砷的流程分布和走向。检测结果表明,产品食用盐砷含量达到国家标准。     

孟加拉国砷污染回顾

目前，孟加拉国居民的健康正面临着严重威胁，8，500，000人的饮用水和粮食作物受到了砷污染。孟加拉国的地下水砷污染问题在世界上是最严重的。由于孟加拉国对地表水管理不当，97％居民的饮用水和家庭用水来源于地下水。在孟加拉国，地下水严重受到砷污染引起大量砷中毒事件。砷污染回顾着重于综述近年来砷污染的调查结果和统计数据，尤其是土壤、水和食物的砷污染。世界卫生组织（WHO）规定的饮用水中砷的额定浓度为10μg/L。现有勘查着重于孟加拉国64个地区深水井的地下水中砷的浓度。调查结果显示：59个深水井的地下水中砷的浓度大于10μg／L；43个深水井的地下水中砷的浓度大于50μg／L。受砷污染的地下水常被用于浇灌水稻（居民主要的粮食作物）。这种农业习惯（把受污染的地下水用于灌溉）引起土壤中砷的浓度增加。现有研究显示，稻米和蔬菜中85％-95％的砷是无机砷。在孟加拉国，土壤、地下水和植物中砷的浓度（基于孟加拉国4％的地区）超过报导的最大允许浓度或者正常范围，这（砷浓度大于最大允许浓度）对孟加拉国居民和家畜的健康造成了严重威胁，强调了开展科学研究的必要性，例如，较好地描述自然环境中砷的存在形态以及确定所有潜在的砷污染途径的科学研究。     

武山铜矿北矿带ICu矿体砷的分布规律

武山铜矿化矿带ＩＣｕ矿体是高砷矿体,分析了砷在各金属矿物中含量及分配情况和含砷量的分布规律,确定了高砷采场或矿段,指出了进行矿石质量控制,配矿管理的降砷途径。     

氢化物原子荧光法测定煤中微量砷

煤中砷的测定已有成熟方法,一般采用半熔分解样品,砷钼蓝比色测定。这种方法操作周期长,手续繁琐试剂耗费量大。近年来,有关氢化物原子荧光测定砷已有较多报道,但有关煤中砷的测定未见报道,笔者采用原子荧光技术测定煤中的砷,方法简便快速,获得满意的结果。 一、仪器和试剂 仪器:WYD-2型双道氢化物无色散原子荧光分析仪(江苏宝应无线电厂生产)。 激发光源:砷无极灯(北京电光源研究所产)。     

中国煤中的砷

砷是煤中最有害的微量元素之一,本文对全国已发表的1915个煤样数据资料统计,我国多数煤中砷含量处于0.4～10mg/kg,平均值为4～5mg/kg。贵州一些地区二叠纪煤的含砷量最高可达3570mg/kg,可谓世界之最。砷的赋存方式主要为:类质同象赋存于黄铁矿中;以粘土矿物和稀有的含砷矿物为载体;缔合于有机质中。燃用富砷煤是引发环境污染的原因,而多数煤中砷含量并不高。加强煤中砷含量的调查,控制和预防砷的危害还是可以做到的。     

Removing arsenic and hydrogen sulfide production using arsenic-tolerant sulfate-reducing bacteria

Environmental remediation technologies that involve the use of sulfate-reducing bacteria constitute a feasible alternative to the remediation of sites polluted with heavy metals and metalloids. The present study evaluates hydrogen sulfide production and arsenic removal by two microbial consortia (C1 and C2) in batch systems exposed to different arsenic concentrations and oxidation states. We identify the following three consecutive stages of arsenate removal: (1) hydrogen sulfide production/accumulation, (2) arsenate reduction to arsenite associated with the incomplete oxidation of hydrogen sulfide to elemental sulfur and (3) arsenic polysulfide precipitation as the main arsenic removal mechanism from aqueous solution. Kinetic parameters are determined in regard to the arsenic oxidation state through the fit of hydrogen sulfide production. The r _max reached by C1 and C2 is increased seven- or eightfold when 250 mM As[+5] was used instead 250 mM As[+3]. Arsenic removal by extracellular precipitation of arsenic polysulfides associated with elemental sulfur precipitation detected through scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy (SEM–EDS) can explain the exceptional value of r _max observed at 250 mM during As[+5] exposition.     

含砷难浸金矿的研究及应用

文中介绍了焙烧预氧化、加压预氧化和细菌预氧化含砷金矿预处理技术的基本原理、特点及工业应用实践。总结了含砷难浸金矿的化学预处理技术、电化学预处理技术和微波预处理技术的研究现状，指出了这些技术的应用前景和发展趋势。     

Geochemical modeling of arsenic sulfide oxidation kinetics in a mining environment

Arsenic sulfide (AsS (am), As₂S₃ (am), orpiment, and realgar) oxidation rates increase with increasing pH values. The rates of arsenic sulfide oxidation at higher pH values relative to those at pH∼2 are in the range of 26-4478, 3-17, 8-182, and 4-10 times for As₂S₃ (am), orpiment, AsS (am), and realgar, respectively.Numerical simulations of orpiment and realgar oxidation kinetics were conducted using the geochemical reaction path code EQ3/6 to evaluate the effects of variable DO concentrations and mineral reactivity factors on water chemistry evolution during orpiment and realgar oxidation. The results show that total As concentrations increase by ∼1.14 to 13 times and that pH values decrease by ∼0.6 to 4.2 U over a range of mineral reactivity factors from 1% to 50% after 2000 days (5.5 yr). The As release from orpiment and realgar oxidation exceeds the current U.S. National Drinking Water Standard (0.05 ppm) approximately in 200-300 days at the lowest initial dissolved oxygen concentration (3 ppm) and a reactivity factor of 1%. The results of simulations of orpiment oxidation in the presence of albite and calcite show that calcite can act as an effective buffer to the acid water produced from orpiment oxidation within relatively short periods (days/months), but the release of As continues to increase.Pyrite oxidation rates are faster than orpiment and realgar from pH 2.3 to 8; however, pyrite oxidation rates are slower than As₂S₃ (am) and AsS (am) at pH 8. The activation energies of arsenic sulfide oxidation range from 16 to 124 kJ/mol at pH∼8 and temperature 25 to 40°C, and pyrite activation energies are ∼52 to 88 kJ/mol, depending on pH and temperature range. The magnitude of activation energies for both pyrite and arsenic sulfide solids indicates that the oxidation of these minerals is dominated by surface reactions, except for As₂S₃ (am). Low activation energies of As₂S₃ (am) indicate that diffusion may be rate controlling.Limestone is commonly mixed with sulfide minerals in a mining environment to prevent acid water formation. However, the oxidation rates of arsenic sulfides increase as solution pH rises and result in a greater release of As. Furthermore, the lifetimes of carbonate minerals (i.e., calcite, aragonite, and dolomite) are much shorter than those of arsenic sulfide and silicate minerals. Thus, within a geologic frame time, carbonate minerals may not be present to act as a pH buffer for acid mine waters. Additionally, the presence of silicate minerals such as pyroxenes (wollastonite, jadeite, and spodumene) and Ca-feldspars (labradorite, anorthite, and nepheline) may not be important for buffering acid solutions because these minerals dissolve faster than and have shorter lifetimes than sulfide minerals. However, other silicate minerals such as Na and K-feldspars (albite, sanidine, and microcline), quartz, pyroxenes (augite, enstatite, diopsite, and MnSiO₃) that have much longer lifetimes than arsenic sulfide minerals may be present in a system. The results of our modeling of arsenic sulfide mineral oxidation show that these minerals potentially can release significant concentrations of dissolved As to natural waters, and the factors and mechanisms involved in arsenic sulfide oxidation warrant further study.     

微生物氧化脱砷浸取金的方法

选用了耐砷能力强、具有分解硫化矿能力的氧化亚铁硫杆菌1s、1号和马兰3种菌株作为实验用菌,对DBF矿样做氧化浸出实验,就其氧化过程中砷含量、pH变化和金的最佳浸出条件均做了详细的研究。给出细菌氧化金矿过程随时间变化的规律及金的最佳浸出条件。     

Aerobic oxidation of mackinawite (FeS) and its environmental implication for arsenic mobilization

Oxidation of mackinawite (FeS) and concurrent mobilization of arsenic were investigated as a function of pH under oxidizing conditions. At acidic pH, FeS oxidation is mainly initiated by the proton-promoted dissolution, which results in the release of Fe(II) and sulfide in the solution. While most of dissolved sulfide is volatilized before being oxidized, dissolved Fe(II) is oxidized into green rust-like precipitates and goethite (α-FeOOH). At basic pH, the development of Fe(III) (oxyhydr)oxide coating on the FeS surface inhibits the solution-phase oxidation following FeS dissolution. Instead, FeS is mostly oxidized into lepidocrocite (γ-FeOOH) via the surface-mediated oxidation without dissolution. At neutral pH, FeS is oxidized via both the solution-phase oxidation following FeS dissolution and the surface-mediated oxidation mechanisms. The mobilization of arsenic during FeS oxidation is strongly affected by FeS oxidation mechanisms. At acidic pH (and to some extent at neutral pH), the rapid FeS dissolution and the slow precipitation of Fe (oxyhydr)oxides results in arsenic accumulation in water. In contrast, the surface-mediated oxidation of FeS at basic pH leads to the direct formation of Fe (oxyhydr)oxides, which provides effective adsorbents for As under oxic conditions. At acidic and neutral pH, the solution-phase oxidation of dissolved Fe(II) accelerates the oxidation of the less adsorbing As(III) to the more adsorbing As(V). This study reveals that the oxidative mobilization of As may be a significant pathway for arsenic enrichment of porewaters in sulfidic sediments.     

Speciation and natural attenuation of arsenic and iron in a tidally influenced shallow aquifer

The mobility of subsurface arsenic is controlled by sorption, precipitation, and dissolution processes that are tied directly to coupled redox reactions with more abundant, but spatially and temporally variable, iron and sulfur species. Adjacent to the site of a former pesticide manufacturing facility near San Francisco Bay (California, USA), soil and groundwater arsenic concentrations are elevated in sediments near the prior source, but decrease to background levels downgradient where shallow groundwater mixes with infiltrating tidal waters at the plume periphery, which has not migrated appreciably in over two decades of monitoring. We used synchrotron X-ray absorption spectroscopy, together with supporting characterizations and sequential chemical extractions, to directly determine the oxidation state of arsenic and iron as a function of depth in sediments from cores recovered from the unsaturated and saturated zones of a shallow aquifer (to 3.5 m below the surface). Arsenic oxidation state and local bonding in sediments, as As-sulfide, As(III)-oxide, or As(V)-oxide, were related to lithologic redox horizons and depth to groundwater. Based on arsenic and iron speciation, three subsurface zones were identified: (i) a shallow reduced zone in which sulfide phases were found in either the arsenic spectra (realgar-like or orpiment-like local structure), the iron spectra (presence of pyrite), or both, with and without As(III) or As(V) coordinated by oxygen; (ii) a middle transitional zone with mixed arsenic oxidation states (As(III)–O and As(V)–O) but no evidence for sulfide phases in either the arsenic or iron spectra; and (iii) a lower oxidized zone in the saturated freshwater aquifer in which sediments contained only oxidized As(V) and Fe(III) in labile (non-detrital) phases. The zone of transition between the presence and absence of sulfide phases corresponded to the approximate seasonal fluctuation in water level associated with shallow groundwater in the sand-dominated, lower oxic zone. Total sediment arsenic concentrations showed a minimum in the transition zone and an increase in the oxic zone, particularly in core samples nearest the former source. Equilibrium and reaction progress modeling of aqueous-sediment reactions in response to decreasing oxidation potential were used to illustrate the dynamics of arsenic uptake and release in the shallow subsurface. Arsenic attenuation was controlled by two mechanisms, precipitation as sulfide phases under sulfate-reducing conditions in the unsaturated zone, and adsorption of oxidized arsenic to iron hydroxide phases under oxidizing conditions in saturated groundwaters. This study demonstrates that both realgar-type and orpiment-type phases can form in sulfate-reducing sediments at ambient temperatures, with realgar predicted as the thermodynamically stable phase in the presence of pyrite and As(III) under more reduced conditions than orpiment. Field and modeling results indicate that the potential for release of arsenite to solution is maximized in the transition between sulfate-reduced and iron-oxidized conditions when concentrations of labile iron are low relative to arsenic, pH-controlled arsenic sorption is the primary attenuation mechanism, and mixed Fe(II,III)-oxide phases do not form and generate new sorption sites.     

Effects of iron on arsenic speciation and redox chemistry in acid mine water

Concern about arsenic is increasing throughout the world, including areas of the United States. Elevated levels of arsenic above current drinking-water regulations in ground and surface water can be the result of purely natural phenomena, but often are due to anthropogenic activities, such as mining and agriculture. The current study correlates arsenic speciation in acid mine drainage and mining-influenced water with the important water-chemistry properties Eh, pH, and iron(III) concentration. The results show that arsenic speciation is generally in equilibrium with iron chemistry in low pH AMD, which is often not the case in other natural-water matrices. High pH mine waters and groundwater do not always hold to the redox predictions as well as low pH AMD samples. The oxidation and precipitation of oxyhydroxides deplete iron from some systems, and also affect arsenite and arsenate concentrations through sorption processes.     

Sulfide-driven arsenic mobilization from arsenopyrite and black shale pyrite

We examined the hypothesis that sulfide drives arsenic mobilization from pyritic black shale by a sulfide-arsenide exchange and oxidation reaction in which sulfide replaces arsenic in arsenopyrite forming pyrite, and arsenide (As−1) is concurrently oxidized to soluble arsenite (As+3). This hypothesis was tested in a series of sulfide-arsenide exchange experiments with arsenopyrite (FeAsS), homogenized black shale from the Newark Basin (Lockatong formation), and pyrite isolated from Newark Basin black shale incubated under oxic (21% O₂), hypoxic (2% O₂, 98% N₂), and anoxic (5% H₂, 95% N₂) conditions. The oxidation state of arsenic in Newark Basin black shale pyrite was determined using X-ray absorption-near edge structure spectroscopy (XANES). Incubation results show that sulfide (1 mM initial concentration) increases arsenic mobilization to the dissolved phase from all three solids under oxic and hypoxic, but not anoxic conditions. Indeed under oxic and hypoxic conditions, the presence of sulfide resulted in the mobilization in 48 h of 13-16 times more arsenic from arsenopyrite and 6-11 times more arsenic from isolated black shale pyrite than in sulfide-free controls. XANES results show that arsenic in Newark Basin black shale pyrite has the same oxidation state as that in FeAsS (−1) and thus extend the sulfide-arsenide exchange mechanism of arsenic mobilization to sedimentary rock, black shale pyrite. Biologically active incubations of whole black shale and its resident microorganisms under sulfate reducing conditions resulted in sevenfold higher mobilization of soluble arsenic than sterile controls. Taken together, our results indicate that sulfide-driven arsenic mobilization would be most important under conditions of redox disequilibrium, such as when sulfate-reducing bacteria release sulfide into oxic groundwater, and that microbial sulfide production is expected to enhance arsenic mobilization in sedimentary rock aquifers with major pyrite-bearing, black shale formations.     

电解锌渣场环境工程技术问题与实例分析

铅锌矿冶电解锌浸出渣含有害成份,也含可再生利用成份。堆存处置方法与一般尾矿不相同。本文结合兰坪铅锌矿工程实例,探讨了电解锌浸出渣堆存技术问题。     

The role of arsenic-bearing rocks in groundwater pollution at Zimapán Valley, México

 Interaction of groundwater with As-bearing rocks has been proposed as one of three main sources of arsenic at Zimapán valley, México. The complexity of the geology and hydrogeology of the valley make it difficult to identify the natural causes of arsenic poisoning. Samples from the different rock outcrops and water from wells tapping various rock formations were analyzed. The rocks from mineralized areas contained higher concentrations of arsenic with respect to the same formations in non-mineralized areas. The arsenic minerals arsenopyrite, scorodite, and tennantite were identified in some rock samples. Higher temperature and lower Eh values were found for those wells containing more arsenic. The physicochemical characteristics of these naturally polluted well waters could be produced by arsenopyrite oxidation. The geochemical model PHREEQCI was used to perform the inverse modeling of two wells located along the same fault. Arsenopyrite oxidation and scorodite dissolution appear to be the geochemical processes producing the natural pollution according to the model. The release and transport of arsenic mainly occur through fractures within the cretaceous limestones where the most productive wells are drilled. The presence of arsenic should be expected also in other formations near mineralized zones in the Zimapán Valley. Field determinations of Eh and T could be used to detect potentially polluted wells. Received: 29 April 1999 / Accepted: 18 July 2000