Direct calculation of thermodynamic properties of the barite/celestite solid solution from molecular principles

 Thermodynamic properties of the barite–celestite solid solution were calculated using molecular principles. Cation–cation (Ba–Ba, Sr–Sr, and Ba–Sr) interaction energies were derived from a number of random and ordered cation distributions which were energy-optimized using force potentials as incorporated in the program package GULP. With these interaction energies, diagrams for the enthalpy and free energy of mixing could be computed for the entire range of the solid solution between the barite and celestite end members and for a number of annealing temperatures. These thermodynamic data show that the solid solution is nonideal. The system has a tendency for Ba²⁺ and Sr²⁺ cations to order onto alternating layers ||(100). However, this ordering scheme is thermodynamically only relevant for annealing temperatures below approximately 500 K and systems that are kinetically inhibited during crystal growth. For sufficiently long annealing times at room temperature, the solid solution tends to exsolve with barite–celestite interfaces ||(100). The cell parameters a and c were calculated to have almost linear behavior for the whole solid solution, suggesting close to ideal behavior according to Vegard's law. In contrast, b tends to deviate positively from linearity, in agreement with experimental values. Received: 6 April 1999 / Revised, accepted: 29 September 1999     

近地表温压条件下白云岩溶解过程的实验研究

与溶解作用有关的次生孔隙是碳酸盐岩最主要的油气储集空间,从实验模拟角度研究碳酸盐溶解机制具有重要的理论与应用价值。本文在近地表的温度和压力条件下,进行了具相同成分和结构的白云岩在CO2和乙酸介质中的对照溶解实验,两种类型的具相同成分和不同结构的白云岩在CO2介质中添加和不添加硬石膏的对照溶解实验,以及方解石含量50%的岩石在CO2介质中添加和不添加硬石膏的对照溶解实验。实验结果表明:(1)近地表温压条件的酸性环境中,乙酸对碳酸盐矿物的溶解能力显著大于CO2流体,乙酸对白云石的溶解是接近化学计量的,而CO2流体则是非化学计量的,白云石中Ca优先溶出而Mg滞留;(2)溶解CaSO4的加入会显著改善近地表温压条件下CO2流体对白云石的溶解效果,使得白云石溶解接近化学计量组成,该过程是通过抑制Ca的溶出和加速Mg的溶出来实现的;(3)对于白云石含量大于90%的较纯的白云岩来说,溶解CaSO4的加入会使得白云岩溶出离子的Ca、Mg合量增加,因而总体上有利于白云岩溶解,与之相反,溶液中CaSO4的沉淀可能导致白云石的沉淀。实验结果可以帮助我们更深刻理解近地表环境白云岩的溶解过程,尤其是与膏盐伴生的白云岩的溶解及相应岩溶过程和次生孔隙的形成机制。      

不同水流速度下温度对奥陶系碳酸盐岩溶蚀速度的影响

为了解不同水流速度下温度对碳酸盐岩溶蚀速度的影响,以自行设计、制造的能够模拟水流条件,并且可同时容纳24个样品的溶蚀试验装置为平台,以淮南张集矿、潞安漳村矿和兖州东滩矿奥陶系灰岩为代表性岩石试样,选取不同温度、水流速度及CO₂压力,进行了溶蚀试验。试验结果显示,在水流速度较低时(16.67 mL/min),环境温度的变化对溶蚀速度的影响比较微小(平均溶蚀变化量为0.000 6 g/cm²)。在水流速度较大时(60 mL/min),温度的改变对溶蚀速度影响较大(平均溶蚀变化量为0.0038 g/cm²)。也就是说在地下水的强径流带,温度对溶蚀速度的影响相对较大,溶蚀速度较快,所以岩溶较发育。     

第三系红层中石膏溶蚀特性及其对工程的影响

第三系红层中石膏分布比较广泛,大量的实验证明,石膏发生溶蚀的主要是含Ca2 的物质,并且溶蚀速率和与水接触的方式以及水头压力大小有直接关系。结合现场资料,将渗透系数K=10-5cm s作为石膏在第三系红层泥岩封闭下发生溶蚀的判据。同时针对水利工程中石膏溶蚀以及对砼的腐蚀性提出了相应的防治措施。     

微生物作用下玄武岩的溶解: 粘附作用和温度的影响

使用透析的方法,设计实验探讨了多粘芽孢杆菌(Paenibacillus polymyxa)的粘附对玄武岩中矿物溶解的影响,同时通过改变实验温度,探讨了岩石的微生物溶解与温度的关系.10 d的实验结果表明,在30 ℃条件下,细菌P. polymyxa及其代谢产物对玄武岩的溶解有显著促进作用,加速了橄榄石中Mg、Fe、Mn的溶出及辉石和长石中Ca、Al的溶出,而在5℃条件下,这种促进作用不明显.细菌及其代谢物的粘附能加速Mg、Fe、Mn的溶出,抑制Ca的溶出,这种不同的影响与两组元素的溶出机制不同,且粘附对各溶出机制的影响也不同有关,Al的溶出受粘附作用的影响较小.低温条件下,粘附作用对玄武岩中各元素的溶出基本无影响.     

Gneiss-Water Interaction and Water Evolution During the Early Stages of Dissolution Experiments at Room Temperature

Gneiss-distilled water interaction at room temperature was investigated with batch-reactors to study water-rock reaction and geochemical evolution of the aqueous phase with time. The ion concentrations in water were controlled not only by the dissolution of primary minerals, but also by the precipitation of secondary minerals. The decreasing fraction sizes of gneiss could favor dissolution and precipitation simultaneously. Ca^2 and K^ were the major cations, and HCO3^- was the major anion in water. All the ions except Ca^2 increased in concentration with time. The Ca^2 release from the rock to the aqueous phase was initially much faster than the release of K^ , Na^2 and Mg^2 . But after about 5 - 24 hours, the Ca^2 concentrations in water decreased very slowly with time and became relatively stable. During the experiment, the water varied from the Ca-( K)-HCO3-type water to the K-Ca-HCO3-type water, and then to the K-(Ca, Na)-HCO3-type water. The water-gneiss interaction was dominated by the dissolution of Kfeldspar in the solution. The remaining secondary minerals were mainly kaolinite, illite and K (Mg) -mica.     

四川盆地东南缘红花岭重晶石—萤石矿流体包裹体特征研究

正四川盆地东南缘重晶石—萤石成矿带是我国重要的重晶石、萤石成矿带之一,具有丰富的重晶石和萤石资源(邹灏,2013)。红花岭重晶石—萤石矿行政隶属于重庆彭水苗族土家族自治县南部的汉葭镇,距县城15 km,大地构造位置为郁山背斜的北西翼近轴部位置。矿区内出露地层包括毛田组(∈3m)灰色厚层细粒白云质灰岩,南津关组(O_1n)灰至深灰色中厚层—厚层灰岩,分乡组(O_1f)灰色巨厚层块状灰岩,红花园组(O_1h)灰色—深灰色厚层灰岩,鲕     

Computing Lippmann Diagrams from Direct Calculation of Mixing Properties of Solid Solutions: Application to the Barite-Celestite System

The Lippmann diagram for the system(Ba, Sr)SO₄-H₂O was computed at 25 °Cby determining the solid-phase activity coefficientsfrom first principles calculations. Directcalculations of the mixing properties of thebarite-celestite series indicate this solid solutionbehaves as non-ideal and non-regular. At 25 °C,the enthalpy of mixing shows a minimum around 50 mole% SrSO₄ due to an ordering tendency. Thefree energy of mixing shows two minima that delimit awide and symmetric miscibility gap (from 2.1 to 97.9 mole% SrSO₄) at this temperature. The excessfree energy of mixing requires a Guggenheim expansionseries of 5 terms to be described, where the termswith odd exponents are null as a consequence of thesymmetric distribution of the mixing properties withcomposition. The Lippmann diagram shows a peritecticpoint that corresponds to the composition of an aqueoussolution which is simultaneously at equilibrium withthe two extremes of the miscibility gap. The largedifference between the solubility products of theendmembers involves a strong preferential partitioningof the less soluble endmember towards the solid phase,which explains the extremely Ba-poor composition ofthe aqueous solution (aqueous activity fraction forBa²⁺ = 0.000446 ) at the peritectic point.     

Mechanism of kaolinite dissolution at room temperature and pressure Part II: kinetic study

Studies on the dissolution kinetics of kaolinite were performed using batch reactors at 25°C and in the pH range from 1 to 13. A rapid initial dissolution step was first observed, followed by a linear kinetic stage reached after approximately 600 hr of reaction during which the kaolinite dissolves congruently at pH < 4 and pH > 11. The apparent incongruency between pH 5 and 10 was due to the precipitation of an Al–hydroxide phase. The true dissolution rates were computed from the amount of Si released into solution. The rate dependence on pH can be described by: r = 10−12.19aH+0.55 + 10−14.36 + 10−10.71aOH−0.75Between pH 5 and 10, the rate is approximately constant, although a smooth minimum was observed at pH close to 9. mAn attempt was made to obtain a general rate law based on the coordination theory, which was first applied to the mineral dissolution studies by Stumm and co-workers. The kinetic data were combined with the results obtained for the surface speciation by Huertas et al. (1998). It is possible to express the linear dissolution rate as a simple power function of the concentration of the surface sites active in various pH ranges: r = 10−8.25 [>Al2OH2+] + 10−10.82 [>AlOH2+]0.5 + 10−9.1 [>Al2OH + >AlOH + >SiOH] + 103.78 [>Al2O− + >AlO−]3This equation assumes that the dissolution mechanism is mainly controlled by the two Al surface sites (external and internal structural hydroxyls, and aluminol at the crystal edges) under both acidic and alkaline conditions. The model reflects well the important contribution of the crystal basal planes to the dissolution of kaolinite.     

振动荷载及温度对白云岩和石灰岩溶蚀影响试验研究

在岩溶地区,列车运行期间的振动会对白云岩和石灰岩的水岩作用过程产生影响,再加上复杂的外界条件,这一影响会更加显著。以桂北岩溶石山地区白云岩和石灰岩为研究对象,利用自主设计的试验装置进行室内模拟试验,分别研究振动荷载及不同温度条件对白云岩和石灰岩的溶蚀的影响规律。研究发现：①常温常压条件下,在静止的酸性溶液中,白云岩的溶蚀速率小于石灰岩;②在H⁺充足的条件下,随着温度（0~45 ℃）的升高,石灰岩和白云岩的溶蚀速率都会增大,温度变化对于白云岩溶蚀影响更为显著;③白云岩和石灰岩的溶蚀受振动条件的强烈影响,二者的溶蚀量都随着振动次数的增加而增大,且在相同振动条件下石灰岩的溶蚀速率始终大于白云岩。该研究可为桂北岩溶石山地区的工程设计和建设提供理论依据。     

扬子板块北缘下志留统龙马溪组重晶石结核特征及其成因机制分析

在扬子板块北缘城口明中剖面及巫溪徐家坝剖面下志留统龙马溪组底部的硅质岩、泥岩中发现椭球状重晶石结核。其矿物组成主要为重晶石颗粒与作为"基质"的黄铁矿、粘土矿物和石英。通过重晶石岩石学、矿物学及锶同位素分析表明,重晶石结核形成于早期成岩阶段松软沉积物的孔隙水中。上升洋流带来丰富的营养及富钡物质,表层海水的高初始生产力促使生物繁盛,海水中的钡通过生物作用富集形成生物钡,生物钡(bio-barite)在埋藏过程中的硫酸盐耗竭区(sulfate depleted zones)通过硫酸盐细菌作用(BSR)溶解被激活提供了钡的来源。围岩岩性(黑色泥岩和硅质泥岩)表明重晶石结核形成于缺氧的环境中。上述研究对深入理解早志留世时期扬子板块北缘古海洋环境有一定的启示作用。     

对福建李坊重晶石矿床成因的新认识——来自矿石构造、矿物学和流体包裹体的证据

福建李坊重晶石矿床是东南沿海地区发现的一个大型独立重晶石矿床,已有30余年的开采历史,在沉积重晶石矿床中占有重要地位,然而对该矿床的成因和成矿时代仍众说纷纭。本文通过对福建李坊重晶石矿床中矿石组构的野外调查、电子探针分析和重晶石的流体包裹体测温,取得如下发现和认识:①首次在重晶石矿石中发现了管孔状构造、角砾状构造、蜂窝状构造等热水喷流通道相沉积构造;②首次在重晶石矿石中发现具有热水成因指示意义的同生钡冰长石矿物;③140个重晶石的流体包裹体均一温度值为89.3～208.5℃,均值为162.7℃,表明李坊重晶石矿床属于低温热水沉积矿床;综合矿石构造、矿物学和流体包裹体测温等证据,提出李坊重晶石矿床为"白烟囱型"热水沉积矿床的新认识,为华南地区早古生代热水沉积矿床的研究和找矿勘探提供了重要新资料。     

The influence of Fe-rich coatings on the dissolution of anorthite at pH 2.6

Surface coatings are very common on mineral grains in soils but most laboratory dissolution experiments are carried out on pristine, uncoated mineral grains. An experiment designed to unambiguously isolate the effect of surface coatings on mineral dissolution from any influence of solution saturation state is reported. Two aliquots of 53 to 63 μm anorthite feldspar powder were used. One was dissolved in pH 2.6 HCl, the other in pH 2.6 FeCl₃ solution, both for ∼6000 h in flow-through reactors. An amorphous Fe-rich, Al-, Ca- and Si-free orange precipitate coated the anorthite dissolved in the FeCl₃ solution. BET surface area of the anorthite increased from 0.16 to 1.65 m² g⁻¹ in the HCl experiment and to 3.89 m² g⁻¹ in the FeCl₃ experiment. The increase in surface area in the HCl experiment was due to the formation of etch pits on the anorthite grain surface whilst the additional increase in the FeCl₃ experiment was due to the micro- and meso-porous nature of the orange precipitate. This precipitate did not inhibit or slow the dissolution of the anorthite. Steady state dissolution rates for the anorthite dissolved in the HCl and FeCl₃ were ∼2.5 and 3.2 × 10⁻¹⁰ mol_feldspar m⁻² s⁻¹ respectively. These rates are not significantly different after the cumulative uncertainty of 17% in their value due to uncertainty in the inputs parameters used in their calculation is taken into account. Results from this experiment support previous theoretical and inference-based conclusions that porous coatings should not inhibit mineral dissolution.     

塔中北斜坡鹰山组碳酸盐岩溶蚀的模拟实验研究

为了研究碳酸盐岩的微观溶蚀机理,本文采用溶蚀实验和镜像观察的方法,研究了塔中北斜坡鹰山组3种类型碳酸盐岩的溶蚀过程及微观溶蚀特征。结果表明:在相同实验条件下,亮晶生屑灰岩、云质灰岩和泥晶颗粒灰岩的溶蚀量基本一致。由于对物质成分和岩石微结构的选择性溶蚀,它们的微观溶蚀特征存在明显差异。亮晶生屑灰岩和泥晶颗粒灰岩样表面整体被溶蚀降低。云质灰岩样表面方解石部分整体被溶蚀降低,形成铸模孔,白云石溶蚀成蜂窝状溶蚀孔,并突出岩石表面,白云石晶间缝溶蚀加大且相互连通,这对油、气和地下水储渗具有重要意义。      

The effect of Fe-oxidizing bacteria on Fe-silicate mineral dissolution

Acidithiobacillus ferrooxidans are commonly present in acid mine drainage (AMD). A. ferrooxidans derive metabolic energy from oxidation of Fe²⁺ present in natural acid solutions and also may be able to utilize Fe²⁺ released by dissolution of silicate minerals during acid neutralization reactions. Natural and synthetic fayalites were reacted in solutions with initial pH values of 2.0, 3.0 and 4.0 in the presence of A. ferrooxidans and in abiotic solutions in order to determine whether these chemolithotrophic bacteria can be sustained by acid-promoted fayalite dissolution and to measure the impact of their metabolism on acid neutralization rates. The production of almost the maximum Fe³⁺ from the available Fe in solution in microbial experiments (compared to no production of Fe³⁺ in abiotic controls) confirms A. ferrooxidans metabolism. Furthermore, cell division was detected and the total cell numbers increased over the duration of experiments. Thus, over the pH range 2–4, fayalite dissolution can sustain growth of A. ferrooxidans. However, ferric iron released by A. ferrooxidans metabolism dramatically inhibited dissolution rates by 50–98% compared to the abiotic controls.

Two sets of abiotic experiments were conducted to determine why microbial iron oxidation suppressed fayalite dissolution. Firstly, fayalite was dissolved at pH 2 in fully oxygenated and anoxic solutions. No significant difference was observed between rates in these experiments, as expected, due to extremely slow inorganic ferrous iron oxidation rates at pH 2. Experiments were also carried out to determine the effects of the concentrations of Fe²⁺, Mg²⁺ and Fe³⁺ on fayalite dissolution. Neither Fe²⁺ nor Mg²⁺ had an effect on the dissolution reaction. However, Fe³⁺, in the solution, inhibited both silica and iron release in the control, very similar to the biologically mediated fayalite dissolution reaction. Because ferric iron produced in microbial experiments was partitioned into nanocrystalline goethite (with very low Si) that was loosely associated with fayalite surfaces or coated the A. ferrooxidans cells, the decreased rates of accumulation of Fe and Si in solution cannot be attributed to diffusion inhibition by goethite or to precipitation of Fe–Si-rich minerals. The magnitude of the effect of Fe³⁺ addition (or enzymatic iron oxidation) on fayalite dissolution rates, especially at low extents of fayalite reaction, is most consistent with suppression of dissolution by interaction between Fe³⁺ and surface sites. These results suggest that microorganisms can significantly reduce the rate at which silicate hydrolysis reactions can neutralize acidic solutions in the environment.     

Transformation of magnetite to hematite and its influence on the dissolution of iron oxide minerals

Deformed rocks of the Itabira Iron Formation (itabirites) in Brazil show microstructural evidence of pressure solution of quartz and iron oxides; it appears that magnetite was dissolved and hematite precipitated. The dissolution of magnetite seems to be related to its transformation to hematite by oxidation of Fe²⁺ to Fe³⁺. The transformation of magnetite to hematite occurs along {111} planes, and results in the development of hematite domains along {111} that are parallel to the foliation. The difference in volume created by the transformation of magnetite to hematite and the shear stress acting on the interphase boundaries allow fluids to migrate along these planes. The dissolution of magnetite involves the hydrolyzation of the Fe²⁺—O bonds at interphase boundaries of high normal stress. The high fugacity of oxygen in the fluid phase promotes the reaction of Fe²⁺ (in solution) with oxygen. Fe²⁺ ions oxidize to Fe³⁺ and precipitate as hematite platelets with their longest axes oriented parallel to the direction of maximum stretching. The transformation of magnetite to hematite during deformation plays an important role in the fabric evolution of the iron formation rocks. The transformation along {111} creates planes of weakness that facilitate fracturing. The fracturing plus the dissolution result in a reduction of magnetite grain size, and the oriented precipitation results in layers of hematite platelets. These processes produce a new fabric characterized by a penetrative foliation and lineation.     

大河边—新晃超大型重晶石矿床地球化学特征及形成的地质背景

本文从矿物岩石学、地球化学和沉积盆地分析角度，研究贵州天柱大河边－湖南贡溪两个超大型重晶石矿床中重晶石（矿）岩及其共生岩石的地球化学特征及构造地质背景。天柱－新晃－玉屏寒武纪热水沉积成矿盆地是发育在大陆斜坡上的断陷型热水沉积成矿盆地，由于同生断层作用将盆地切割成一系列次级盆地，大河边－碧林及龙背－铜盆盖三级热水沉积成矿盆地是大型重晶石矿床的构造定位空间。重晶石矿层主要赋存于下寒武统牛蹄塘组第一岩性段的黑色岩系中。 重晶石矿层是由海底低温热水同生沉积作用形成（105－192℃），古热水场的地球化学类型为硫酸盐型热水。硫酸盐型热水发生大规模同生沉积成岩成矿作用形成超大型重晶石矿床，重晶石矿层之上的黑色碳质粘土岩可能形成于封闭、还原、滞流的深水沉积环境，黑色碳质粘土岩构成矿层的封闭保存条件。     

耿庄金矿含FeS2晶须环带重晶石巨晶的特征及成因意义

在山西耿庄金矿区含金隐爆角砾岩体的晶洞内,发现了含FeS2晶须环带重晶石巨晶,用扫描电镜、电子探针、Ｘ射线粉晶衍射等手段系统研究了重晶石及其所含FeS2晶须的矿物特征。结果表明,重晶石化学成分单一;晶体结构标准;发育完好;晶须为FeS2 Fe(Ni, Co)S2的类质同象系列。根据地质背景,结合包裹体研究成果,运用晶体生长和地球化学理论,讨论了重晶石巨晶及所含晶须的成因。认为重晶石巨晶是该区燕山期花岗岩浆活动的期后热液演化到后期阶段时,SO2-4与围岩中的钡反应而形成;所含的FeS2晶须是持续进行的火山隐爆作用所产生的大量H2S、SO2等与热液中分解出的Fe2+、Ni2+、Co2+反应而形成的;富碱、H2S溶解度增大,S2-增高有利于晶须的生长;重晶石和晶须生长的地质环境具有宏观上的一致性和具体条件的差异性。当pH值为1~8.5、lgfO2为-31~-38时,优先进入FeS2生长的优势场,形成FeS2晶须矿物。当pH值为5.5~10、lgfO2在-25~-36时形成重晶石;FeS2环带和重晶石的共生现象是两者共结晶交互生长的结果;重晶石的套叠生长和晶须环带特征,是耿庄地区隐爆作用脉动性和周期性作用的结果。耿庄含晶须重晶石巨晶,明确标示出所形成的地质条件和地质作用过程,为深入研究隐爆作用和理解该区成矿作用提供了矿物学证据。     

天柱大河边重晶石矿床铅同位素特征及来源探讨

对取自天柱大河边重晶石矿床的重晶石样品和含方铅矿黑色页岩样品进行了铅同位素测定与研究.结果表明,在 Zartman铅构造模式图中,重晶石矿石、含方铅矿黑色页岩和黑色页岩有大致相同的铅同位素分布区,均沿上地壳铅演化线分布,表明它们之间具有同源关系;重晶石矿石及其赋矿黑色页岩的铅同位素组成与基底地层的铅同位素组成在 Zartman铅构造模式图中具有完全不同的分布范围,表明重晶石矿石中的铅不大可能来源于基底地层;结合重晶石矿石及其赋矿黑色页岩的铅同位素组成在 Zartman铅构造模式图和Δγ-Δβ铅来源分类图的分布,天柱大河边重晶石矿床的铅主要具上地壳铅、壳幔混合的俯冲带铅和热水沉积作用铅的混合来源特点,这为天柱大河边重晶石矿床的热水沉积成因提供了铅同位素证据.     

青海马海盐湖低品位固体钾矿室内溶矿实验研究

柴达木盆地马海盐湖浅部赋存有储量可观的低品位固体钾盐资源,通过水溶开采即固液转化的方法为企业10万吨/年的钾肥生产提供了资源保障。随着水溶开采工作的持续进行,目前马海钾矿区北部浅部固体钾矿的品位进一步降低,给盐田和选矿工艺的调整带来极大挑战。为使这部分资源得以充分利用,本文以马海盐湖钻孔9-13和9-3附近埋深0～3m的固体钾矿样品为研究对象,系统开展了室内溶矿模拟实验。实验结果表明:(1)在固体钾矿KCl品位较低时,适当提高溶剂的波美度,有利于K⁺的溶出,提高溶出液中K⁺的浓度。(2)溶剂中Na⁺的浓度太低会溶解盐层骨架,而Na⁺的浓度太高会导致结盐,生产中应根据钾矿层的实际情况,以满足溶出液K⁺浓度含量达标为准调整溶剂的波美度。(3)随着马海矿区固体钾矿品位持续降低,当K⁺的浓度达到盐田生产要求时,钠盐池卤水中Na⁺的浓度会明显增加,卤水中SO₄^2-相对浓度也相应增加,钠盐池阶段析出的石...