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1.
文章使用开放流动反应装置研究了中低温热液矿床中常见脉石矿物碳酸盐(白云石、菱锰矿)在25℃～250℃水中化学动力学溶解反应速率。在25℃条件下,碳酸盐矿物的溶解速率r(Ca)>r(Mn)>r(Mg)。碳酸盐矿物在水中200℃时具有最大溶解速率。随着温度的继续升高,Mg、Mn碳酸盐的溶解反应速率会下降,容易形成白云石和锰碳酸盐。实验研究结果有助于理解中低温环境下,金属矿石的主要伴生碳酸盐矿物与水反应的化学动力学限制,试图说明中低温矿石伴随白云石和锰碳酸盐的沉淀机理。 相似文献
2.
中地壳温度压力条件下的水-岩作用化学动力学实验 总被引：2，自引：1，他引：2
为模拟中地壳条件下水.岩相互作用,本文作者重点做了大于300℃,在水的近临界区至超临界区条件下的硅酸盐矿物与水反应的化学动力学实验。矿物(钠长石(Ab)、透辉石(Di)、阳起石(Act))的溶解反应动力学实验是使用流体通过叠层反应器的开放体系在25℃～400℃和22MPa下完成的。实验发现矿物在300至400℃范围内,在跨越水临界点时出现反应速率的涨落。多金属氧化物硅酸盐与水反应时的各个元素溶解到溶液里的释放速率一般不一样。硅酸盐矿物的最大溶解反应速率多是在300℃,如,硅的最大释放速率是在300℃。其余元素如Na、K、Mg、Ca、Fe、Al等释放速率在<300℃、22MPa时都高于硅的释放速率,在>300℃时硅的释放速率要高于其它元素的释放速率。我们还完成了玄武岩与水在25℃～400℃条件下的反应动力学实验。实验发现,硅的最大释放反应速率也多是在300℃。中地壳的流体处于由亚临界态进入超临界流体的演化过程,这时流体的性质会有剧烈变化。这一变化会引起水/岩相互作用的反应动力学涨落。流体性质的突变和水岩相互作用涨落会导致中地壳岩层的许多性质变化,硅酸盐矿物格架的解体,岩石被淋失,岩层的崩塌。 相似文献
3.
极端条件下水热化学反应是一个新的科学问题。借助于高温超高压原位直接测量方法、各种谱学方法和同步辐射光源技术研究地球内部流体物质相互作用,可以获得反应过程的产物的分子-原子尺度信息,这些信息可以提供认识极端条件下水和矿物(岩石)反应动力学的新实验途径。地球内部的流体性质随所处高温高压条件发生变化。水的密度、介电常数等物理参数随温度压力变化而改变,在临界态会出现突变。水的性质的剧变会影响水与岩石(矿物)相互作用。文中报道了在极端条件下(20～435℃和23～35MPa)实验测量矿物(钠长石、辉石、石英和阳起石等)和岩石(玄武岩、正长岩)在水溶液里的溶解反应速率的研究结果,发现矿物里各种不同类型金属离子与水反应的速率不同,随温度变化而改变。在升温过程中,进入临界态时,矿物(岩石)与水反应出现一次反应速率的涨落。在恒压升温过程中(临界压力,或略高于临界压力),硅酸盐矿物溶解速率会逐步升高,如硅近临界区(300℃)抵达最大值,然后随升温溶解反应速率减低。地球内部的流体由深处上升到浅处,会从超临界区域进入近临界的气与液的两相不混溶区域。含金属流体里的金属会在气相与液相分离时出现再分配。实验表明:金属Au、Cu、Sn、W、Zn会进入气相,气体可以迁移金属。事实说明:地球内部流体结构和性质从深到浅在不断变化,在跨越临界区时的水的性质异常变化会导致水与矿物(岩石)反应动力学涨落,并且促使金属在临界区出现沉淀和在气液相分离过程中进行再分配及迁移。 相似文献
4.
中地壳的水-岩作用对相关的地球物理性质影响 总被引：1，自引：0，他引：1
对于地壳的地球物理详细探测发现中地壳普遍存在着高导层和低速层.高温高压下的矿物(岩石)-流体反应的化学动力学实验和水的性质研究可以提供我们认识地壳的地球物理探测结果的新信息.通常,中地壳大致位于15至25km的深度范围.高导层和低速层普遍存在于中地壳.各地的地壳厚度不同,但是中地壳和高导-低速层的深度范围十分相似.中地壳的顶界温度处于300℃,底界为450℃～500℃范围.为了认识中地壳的高导低速层的起因,作者重点做了模拟中地壳条件下水-岩相互作用实验,同时,分析了水在近临界区至超临界区的突变性质.矿物(钠长石、透辉石、阳起石)与水,玄武岩与水反应的化学动力学实验是使用流体通过叠层反应器的开放体系在25℃～400℃和22MPa下完成的.与水反应的矿物或岩石里的各个元素溶解到溶液里的释放速率一般不一样.硅酸盐矿物的硅的最大释放速率是在300℃.其它元素,如Na、K、Mg、Ca、Fe、Al等释放速率在＜300℃时都高于硅的释放速率,在＞300℃时硅的释放速率要高于其它元素的释放速率.在水中的硅的大释放速率会导致硅酸盐矿物格架解体.作者假定地壳里普遍存在水占1%(体积).这时,地壳里会发生水-岩相互作用.中地壳的流体处于300℃～500℃.在由亚临界态进入超临界区的演化过程中,在跨越临界温度时水的性质发生剧烈变化.如密度、介电常数等热力学参数.这一变化会引起水/岩相互作用的反应动力学涨落,会导致中地壳岩层的硅的淋失,硅酸盐矿物解体,岩石崩塌.同时,在临界区水的性质强烈变化还有水的电导率、迁移性质、等,这会影响中地壳一些物理性质,如中地壳高导层和低速层的出现. 相似文献
5.
化学动力学在地球化学中的某些应用 总被引：2，自引：0，他引：2
Shi Pingfang Yu Chongwen 《地球科学》1986,(4)
化学动力学在地球化学（特别是成矿作用地球化学）研究中有极其重要的作用,其主要应用包括七个方面。本文重点介绍了地球化学中化学动力学的实验研究方法以及碳酸盐、硅酸盐、氧化物和硫化物等矿物的反应动力学实验成果;介绍了Helgeson的质量迁移理论及其研究热液在围岩中的运移方面的应用,并在热力学性质和动力学行为两方面研究了围岩的离解作用、蚀变作用与矿化作用及其相互关系。 相似文献
6.
鄂尔多斯白垩系盆地地下水水-岩反应的锶同位素证据 总被引：3，自引：0，他引：3
利用鄂尔多斯白垩系盆地地下水锶同位素和水化学资料,对该区水-岩作用机制进行了分析,并采用反向水文地球化学模拟的方法对锶同位素示踪水-岩反应的分析结论进行了验证。结果表明:研究区主要发生了石膏、少量碳酸盐矿物及铝硅酸盐矿物的溶解反应,且北区地下水对石膏等硫酸盐矿物的溶滤作用强于南区,而南区地下水对铝硅酸盐矿物的溶滤作用强于北区;同时,南区碳酸盐矿物发生了溶解/沉淀的不一致性,即白云石发生溶解反应而方解石发生沉淀反应。采用锶同位素方法得出的水-岩作用结论与反向水文地球化学模拟结果相一致。 相似文献
7.
地质流体 岩石反应的地球化学动力学方法 总被引：3，自引：1，他引：2
摘 要 提出了一个以矿物生成和溶解的速率确定体系矿物沉淀的量来模拟水 岩反应的新方
法。新固相在体系中沉淀的量只依赖于沉淀速率而不是依赖于水 岩之间的平衡。考察了一
个矿物溶解生成次生矿物最终趋于平衡的溶解沉淀反应演化结果表明在水 岩体系中对于次
生矿物的部分平衡假定在许多情况下都不能成立。在这样的反应演化过程中亚稳矿物与溶液
之间总保持过饱和态矿物的沉淀速率随反应的进展而变化。同时当主要溶解矿物达到平
衡而溶解作用停止时次生矿物沉淀尚未停止直到体系饱和指数全部趋于0时才达到总
体平衡。用动力学方法处理地球化学过程中的水 岩反应比准稳平衡的简单假设更合理因为
动力学方法更符合自然情况同时产生了关于时间过程的时间尺度信息。 相似文献
8.
为了模拟庐枞火山盆地基底的水热反应和正长辉长岩-二长岩-正长岩与水相互作用,深入剖析深部流体携带金属来源的可能性,本文利用开放流动体系的叠层流动反应器实验研究25~435℃、23~35MPa条件下二长岩-正长岩与水相互作用的化学动力学过程。研究表明,造岩元素、成矿元素和痕迹元素,在低温至水临界态的升温过程中溶解产物在水中的浓度(或溶解速率)不断变化,它们的最大溶解速率出现在不同温度。主要元素Si、Al等最大溶解速率出现在300~400℃范围,即,在跨越水的临界温度时出现溶解速率的涨落。或者说,正长岩-H2O体系中元素的溶解速率主要是温度的函数,此外,压力也对大部分元素的溶解速率产生影响,但是,对于各元素溶解速率随温度而变化的基本规律影响不大。实验重要的发现:相当于中地壳的温度即300~400℃时反应很特殊。硅酸盐矿物的硅被强烈溶失和矿物岩石会垮塌。实验表明:相当于中地壳温度(300~400℃)发生的二长正长岩与水相互作用对庐枞火山盆地深部矿床形成产生重要影响。长期的含金属流体活动造成了金属矿石的形成。水/岩反应动力学过程的温度因素:不同金属元素的最容易溶解和沉淀温度的区别导致了金属-蚀变分带性。实验还揭示,纯水与二长正长岩的反应可以淋滤出大量有色金属元素,在溶液的浓度可以到几百×10~(-9),如Ni、Mn、Cu、Zn,它们从二长正长岩里被溶解释放速率也很高。以往,研究表明火山盆地铁矿的物质来源于围岩。这次实验研究显示:水与二长正长岩的反应同样影响着盆地金属矿的形成和盆地深部、上中地壳的流体性质。实验对于理解上中地壳发生的水岩相互作用也有普适性意义。 相似文献
9.
热液金属矿床成因研究过程中,观测与实验始终是密切结合的。上世纪70年代,平衡热力学的实验数据的快速积累,使人们用热力学理论计算可以预测和反演矿石和岩石的成因。但是,没有矿物-水溶液的反应速率数据,又没有与流体力学的结合,搞清楚矿石成因是困难的。七、八十年代,开始研究矿物与水溶液的反应动力学实验。科学家们开始瞄准了从平衡-封闭-静态转向非平衡-开放-动力学研究的这个大方向。1992年我们建立地球化学动力学开放研究实验室。研究高温高压矿物与水反应速率,发现固液的开放体系的自组织现象。实验发现温度影响矿物的各个元素反应速率改变,发现在跨越水临界态时矿物与水反应速率涨落、在近临界的气-液两相不混溶区一些金属进入气相、超临界流体的氧化作用及特别的溶剂性能影响矿物溶解性质。实验证实:临界态区流体与矿石成因有关。水岩相互作用的反应动力学实验温度从低温到550度,揭示矿石的金属来源、迁移、金属与蚀变分带机制。一大批大于300度的矿物与水反应动力学实验在国际界是少有报道的。九十年代,超高压的科学发展,与同步辐射光源的技术进步的结合,使固体地球科学又迈向了地球深内部。我们发展了高温高压流体性质的原位直测(测量850℃水溶液)红外谱,发现深部流体的新性质:气液两相流体的新结构,在临界温度区(300~400℃),水分子氢键网络的破坏受压力影响不大(23MPa~3GPa),同时,出现水的高电导率。研发新仪器为开放-流动-非平衡的反应动力学实验与极端条件下物质性质的直接观测结合,在科学前沿领域开辟了创新道路。 相似文献
10.
长江中下游火山岩盆地中金属矿床和蚀变分带的的地球化学研究表明,它们具有内带深色蚀变带和外带浅色蚀变带,形成于600℃到100℃范围。两类蚀变带分界温度大致是300℃。大金属矿床蚀变分带剖面显示出热液系统存在有明显的温度梯度。通过与背景岩石(玄武岩石)对比研究表明,自下而上的不同蚀变岩石中主要元素含量显著变化,交代作用中的代出和代入元素在空间上是演化的。25~400℃和23MPa下矿物(钠长石、阳起石、透辉石、钙铁辉石)-H2O、岩石(玄武岩)-H2O反应的化学动力学实验表明,金属元素释放速率是温度的函数。在恒压升温过程中,从20℃到400℃,硅酸盐矿物、玄武岩中Si溶解速率不断上升;在300~350℃时,Si、Al溶解速率到最大数值。随后,温度再上升导致溶解速率下降。在300℃时,大部分矿物中Ca、Mg、Fe、Na溶解速率较高,溶液里的Ca/Si、Mg/Si、Fe/Si、Na/Si等都高于矿物中对应元素的计量比。矿物反应后的表面存在富集硅的淋失层,或有富硅铝矿物(粘土矿物)出现。在300℃时,Si溶解快于其他金属元素,溶液中金属元素与硅摩尔浓度比(Ca/Si、Mg/Si、Fe/Si、Na/Si)等都低于矿物中的计量比。矿物反应后的表面缺少硅的淋失层,或者有贫硅矿物和铁氧化物出现。作者还进行23~35MPa、20~550℃玄武岩与水反应实验。上述高温高压下矿物在水溶液中的溶解反应动力学实验和流体-玄武岩相互作用实验,对于理解金属矿床及蚀变分带形成机制提供新的依据。 相似文献
11.
《Applied Geochemistry》2004,19(2):169-180
Arsenic is present in aqueous environments in +III and +V oxidation states. In oxidizing environments, the principle attenuation mechanism of As migration is its adsorption on Fe(III) oxide and hydroxides. The adsorption affinity is higher for As(V) under lower pH conditions and for As(III) under higher pH conditions. Ferric oxide and hydroxides can dissolve under low Eh and pH conditions releasing adsorbed As. Oxidation-reduction processes often involve high organic matter content in sediments and also contamination by organics such as BTEX. Arsenic may desorb under high pH conditions. Changes of pH can be related to some redox reactions, cation exchange reactions driving dissolution of carbonates, and dissolution of silicates. In very reducing environments, where SO4 reduction takes place, secondary sulfide minerals like As-bearing pyrite and orpiment, As2S3, can incorporate As. Geochemical modeling can be divided into two principal categories: (a) forward modeling and (b) inverse modeling. Forward modeling is used to predict water chemistry after completion of predetermined reactions. Inverse modeling is used to suggest which processes take place along a flowpath. Complex coupled transport and geochemistry programs, which allow for simulation of As adsorption, are becoming available. A common modeling approach is based on forward modeling with surface complexation modeling (SCM) of As adsorption, which can incorporate the effect of different adsorbent/As ratios, adsorption sites density, area available for adsorption, pH changes and competition of As for adsorption sites with other dissolved species such as phosphate. The adsorption modeling can be performed in both batch and transport modes in codes such as PHREEQC. Inverse modeling is generally used to verify hypotheses on the origin of As. Basic prerequisites of inverse modeling are the knowledge of flow pattern (sampling points used in model have to be hydraulically connected) and information about mineralogy including As mineral phases. Case studies of geochemical modeling including modeling of As adsorption are presented. 相似文献
12.
地球化学反应平衡模型的建模方法 总被引：1，自引：1，他引：1
简要介绍了各种地球化学反应模型及建模思想 ,重点介绍了最基本的地球化学反应平衡模型建立过程中的一些基本概念和建模的一般方法 ,并就模型实际应用中 ,在概念模型的确立、热力学数据资料的使用范围、模型计算中离子强度、温度、压力、p H值等方面存在的问题和影响因素 ,作了较为全面的说明。 相似文献
13.
环境地球化学模拟是环境科学、地球化学等学科交叉的一个重要领域。这里在总结形态与饱和度模型、表面吸附模型、反应途径模型、逆向模型、复合反应溶质运移模型以及动力学模型原理的基础上,对包含上述模型的各种地球化学模拟软件进行了优缺点比对。总结了各模型在当前环境地化研究领域的重要应用课题,这将为从事相关领域的研究提供一些相对较新、较综合的信息,最后还针对环境地球化学模型的不足进行了相关探讨,对地球化学模型的发展趋势进行了预测。 相似文献
14.
Aurélie Verney-Carron Stéphane Gin Guy Libourel 《Geochimica et cosmochimica acta》2010,74(8):2291-18706
To improve confidence in glass alteration models, as used in nuclear and natural applications, their long-term predictive capacity has to be validated. For this purpose, we develop a new model that couples geochemical reactions with transport and use a fractured archaeological glass block that has been altered for 1800 years under well-constrained conditions in order to test the capacity of the model.The chemical model considers three steps in the alteration process: (1) formation of a hydrated glass by interdiffusion, whose kinetics are controlled by a pH and temperature dependent diffusion coefficient; (2) the dissolution of the hydrated glass, whose kinetics are based on an affinity law; (3) the precipitation of secondary phases if thermodynamic saturation is reached. All kinetic parameters were determined from experiments. The model was initially tested on alteration experiments in different solutions (pure water, Tris, seawater). It was then coupled with diffusive transport in solution to simulate alteration in cracks within the glass. Results of the simulations run over 1800 years are in good agreement with archaeological glass block observations concerning the nature of alteration products (hydrated glass, smectites, and carbonates) and crack alteration thicknesses. External cracks in direct contact with renewed seawater were altered at the forward dissolution rate and are filled with smectites (400−500 μm). Internal cracks are less altered (by 1 or 2 orders of magnitude) because of the strong coupling between alteration chemistry and transport. The initial crack aperture, the distance to the surface, and sealing by secondary phases account for these low alteration thicknesses. The agreement between simulations and observations thus validates the predictive capacity of this coupled geochemical model and increases more generally the robustness and confidence in glass alteration models to predict long-term behavior of nuclear waste in geological disposal or natural glass in the environment. 相似文献
15.
《Applied Geochemistry》1993,8(6):529-549
Changes in the distribution of inorganic solutes in a shallow ground water contaminated by crude oil document a series of geochemical reactions initiated by biodegradation of the oil. Upgradient of an oil body floating on the water table, oxidation of oil to carbonic acid dissolves carbonate minerals in the aquifer matrix. In this oxidized zone pH is depressed ∼1 pH unit, and the concentrations of Ca, Mg and HCO3− increase to more than twice that of the native ground water. In the anoxic zone beneath the oil body concentrations of dissolved SiO2, Sr, K, Fe and Mn increase significantly. Here, Fe is mobilized by microbial reduction, pH is buffered by the carbonate system, and silicates weather via hydrolysis and organic-acid-enhanced dissolution. Farther down-gradient the ground water is reoxygenated and Fe precipitates from solution, possibly as iron hydroxide or iron carbonates, while SiO2 precipitates as amorphous silica. Other solutes, such as Mg, are transported more conservatively down-gradient where contaminated and native ground water mix.The observed changes in inorganic aqueous chemistry document changes in water-mineral interactions caused by the presence of an organic contaminant. These organic-initiated interactions are likely present in many contaminated aquifers and may be analogous to interactions occurring in other organic-rich natural waters. 相似文献
16.
Leakage of highly saline and alkaline radioactive waste from storage tanks into underlying sediments is a serious environmental problem at the Hanford Site in Washington State. This study focuses on geochemical evolution of tank waste plumes resulting from interactions between the waste solution and sediment. A synthetic tank waste solution was infused into unsaturated Hanford sediment columns (0.2, 0.6, and 2 m) maintained at 70°C to simulate the field contamination process. Spatially and temporally resolved geochemical profiles of the waste plume were obtained. Thorough OH− neutralization (from an initial pH 14 down to 6.3) was observed. Three broad zones of pore solutions were identified to categorize the dominant geochemical reactions: the silicate dissolution zone (pH > 10), pH-neutralized zone (pH 10 to 6.5), and displaced native sediment pore water (pH 6.5 to 8). Elevated concentrations of Si, Fe, and K in plume fluids and their depleted concentrations in plume sediments reflected dissolution of primary minerals within the silicate dissolution zone. The very high Na concentrations in the waste solution resulted in rapid and complete cation exchange, reflected in high concentrations of Ca and Mg at the plume front. The plume-sediment profiles also showed deposition of hydrated solids and carbonates. Fair correspondence was obtained between these results and analyses of field borehole samples from a waste plume at the Hanford Site. Results of this study provide a well-defined framework for understanding waste plumes in the more complex field setting and for understanding geochemical factors controlling transport of contaminant species carried in waste solutions that leaked from single-shell storage tanks in the past. 相似文献
17.
CO2-water-basalt interaction. Numerical simulation of low temperature CO2 sequestration into basalts
The interaction between CO2-rich waters and basaltic glass was studied using reaction path modeling in order to get insight into the water-rock reaction process including secondary mineral composition, water chemistry and mass transfer as a function of CO2 concentration and reaction progress (ξ). The calculations were carried out at 25-90 °C and pCO2 to 30 bars and the results were compared to recent experimental observations and natural systems. A thermodynamic dataset was compiled from 25 to 300 °C in order to simulate mineral saturations relevant to basalt alteration in CO2-rich environment including revised key aqueous species for mineral dissolution reactions and apparent Gibbs energies for clay and carbonate solid solutions observed to form in nature. The dissolution of basaltic glass in CO2-rich waters was found to be incongruent with the overall water composition and secondary mineral formation depending on reaction progress and pH. Under mildly acid conditions in CO2 enriched waters (pH <6.5), SiO2 and simple Al-Si minerals, Ca-Mg-Fe smectites and Ca-Mg-Fe carbonates predominated. Iron, Al and Si were immobile whereas the Mg and Ca mobility depended on the mass of carbonate formed and water pH. Upon quantitative CO2 mineralization, the pH increased to >8 resulting in Ca-Mg-Fe smectite, zeolites and calcite formation, reducing the mobility of most dissolved elements. The dominant factor determining the reaction path of basalt alteration and the associated element mobility was the pH of the water. In turn, the pH value was determined by the concentration of CO2 and extent of reaction. The composition of the carbonates depended on the mobility of Ca, Mg and Fe. At pH <6.5, Fe was in the ferrous oxidation state resulting in the formation of Fe-rich carbonates with the incorporation of Ca and Mg. At pH >8, the mobility of Fe and Mg was limited due to the formation of clays whereas Ca was incorporated into calcite, zeolites and clays. Competing reactions between clays (Ca-Fe smectites) and carbonates at low pH, and zeolites and clays (Mg-Fe smectites) and carbonates at high pH, controlled the availability of Ca, Mg and Fe, playing a key role for low temperature CO2 mineralization and sequestration into basalts. Several problems of the present model point to the need of improvement in future work. The determinant factors linking time to low temperature reaction path modeling may not only be controlled by the primary dissolving phase, which presents challenges concerning non-stoichiometric dissolution, the leached layer model and reactive surface area, but may include secondary mineral precipitation kinetics as rate limiting step for specific reactions such as retrieved from the present reaction path study. 相似文献
18.
Franziska D.H. Wilke Mónica Vásquez Thomas Wiersberg Rudolf Naumann Jörg Erzinger 《Applied Geochemistry》2012
The aim of this experimental study was to evaluate and compare the geochemical impact of pure and impure CO2 on rock forming minerals of possible CO2 storage reservoirs. This geochemical approach takes into account the incomplete purification of industrial captured CO2 and the related effects during injection, and provides relevant data for long-term storage simulations of this specific greenhouse gas. Batch experiments were conducted to investigate the interactions of supercritical CO2, brine and rock-forming mineral concentrates (albite, microcline, kaolinite, biotite, muscovite, calcite, dolomite and anhydrite) using a newly developed experimental setup. After up to 42 day (1000 h) experiments using pure and impure supercritical CO2 the dissolution and solution characteristics were examined by XRD, XRF, SEM and EDS for the solid, and ICP–MS and IC for the fluid reactants, respectively. Experiments with mixtures of supercritical CO2 (99.5 vol.%) and SO2 or NO2 impurities (0.5 vol.%) suggest the formation of H2SO4 and HNO3, reflected in pH values between 1 and 4 for experiments with silicates and anhydrite and between 5 and 6 for experiments with carbonates. These acids should be responsible for the general larger amount of cations dissolved from the mineral phases compared to experiments using pure CO2. For pure CO2 a pH of around 4 was obtained using silicates and anhydrite, and 7–8 for carbonates. Dissolution of carbonates was observed after both pure and impure CO2 experiments. Anhydrite was corroded by approximately 50 wt.% and gypsum precipitated during experiments with supercritical CO2 + NO2. Silicates do not exhibit visible alterations during all experiments but released an increasing amount of cations in the reaction fluid during experiments with impure CO2. Nonetheless, precipitated secondary carbonates could not be identified. 相似文献
19.
The present study aimed at identifying the salinity source in the groundwater of Lenjanat Plain. To do so, non-isotopic geochemical methods were employed: groundwater samples were collected seasonally from 33 wells widespread in the area, and physicochemical parameters as well as major and minor elements were measured in the 132 samples. The data collected from the field and laboratory measurements were interpreted through statistical and hydrogeochemical graphs, mass ratios and saturation indexes obtained from modeling. The results revealed that hydrogeochemical properties of the study aquifer were controlled by rock/water interactions including ion exchange, dissolution of evaporation deposits (halite and gypsum) and precipitation/dissolution of carbonates. Based on the values of Cl/Br ratio in Lenjanat groundwater (329–4,492), dissolution of evaporation deposits in aquifer was the main cause for groundwater salinity. Considering the Lenjanat groundwater geochemical properties, the data confirm the reported Cl/Br ratios for groundwater affected by the dissolution of evaporation deposits (Cl/Br > 300) and overlaps with the range of Cl/Br ratios for domestic sewage effluent groundwater. Selecting the best chemical components and their ratios in non-isotopic geochemical methods provides an accurate distinction between sources of groundwater salinity. 相似文献
20.
The net result of acid-generating and-neutralizing reactions within mining wastes is termed acid rock drainage (ARD). The oxidation of sulfide minerals is the major contributor to acid generation. Dissolution and alteration of various minerals can contribute to the neutralization of acid. Definitions of alkalinity, acidity, and buffer capacity are reviewed, and a detailed discussion of the dissolution and neutralizing capacity of carbonate and silicate minerals related to equilibium conditions, dissolution mechanism, and kinetics is provided. Factors that determine neutralization rate by carbonate and silicate minerals include: pH, PCO
2, equilibrium conditions, temperature, mineral composition and structure, redox conditions, and the presence of foreign ions. Similar factors affect sulfide oxidation. Comparison of rates shows sulfides react fastest, followed by carbonates and silicates. The differences in the reaction mechanisms and kinetics of neutralization have important implications in the prediction, control, and regulation of ARD. Current static and kinetic prediction methods upon which mine permitting, ARD control, and mine closure plans are based do not consider sample mineralogy or the kinetics of the acid-generating and-neutralizing reactions. Erroneous test interpretations and predictions can result. The importance of considering mineralogy for site-specific interpretation is highlighted. Uncertainty in prediction leads to difficulties for the mine operator in developing satisfactory and cost-effective control and remediation measures. Thus, the application of regulations and guidelines for waste management planning need to beflexible. 相似文献