低温条件下长石溶解模拟实验研究

为了研究有机酸和无机酸对长石的溶解能力以及不同有机酸对长石溶解能力的差异,笔者等在80℃条件下,在不同pH值（4、6和8）的分别含有盐酸、乙酸和草酸的溶液中,对碱性长石和斜长石进行了溶解模拟实验研究。实验结果表明：酸性(pH=4)和弱酸性(pH=6)条件下,乙酸对两种长石的溶解能力大于草酸,碱性条件(pH=8)下草酸的溶解能力最大,无论在酸性或碱性条件下,有机酸对长石的溶解能力均高于无机酸,酸性(pH=4)条件下,斜长石与碱性长石溶解量差别不大,在弱酸性(pH=6)和碱性(pH=8) 条件下,斜长石的溶解量高于碱性长石。     

长石溶解模拟实验研究综述

在综合分析前人研究成果基础上,对长石溶解模拟实验研究进行了综述.研究表明,长石溶解与其成分、结构、反应的温压条件以及流体性质等有关.在相同的温压条件下,3种长石的稳定性依次为:钾长石>钠长石>钙长石,且温度升高可加强长石的溶解能力,促进长石的溶解,而压力的变化对长石的溶解影响不大.长石的溶解速率在酸性区域随pH值增大而减小、在中性区域溶解速率低且受影响小、在碱性区域随pH值增大而增大.有机酸通过提供H+、络合金属元素来提高长石的溶解度.长石的溶蚀速率与颗粒的总表面积大小以及颗粒表面粗糙度有关,总表面积越大,表面越粗糙,则反应速率越快,而且溶液的矿化度越低越有利于长石的溶解.长石的溶解过程由表面反应和扩散反应所控制,描述长石溶蚀机理的模型主要包括:表面反应模型和淋滤层扩散模型.     

有机酸对长石溶解度影响的热力学研究

为明确认识有机酸（草酸、醋酸）对长石溶解度及储层次生孔隙发育的影响，本文利用热力学方法，计算了不同温度、酸度下钾长石在含有醋酸根0.05mol/L、草酸0.0055mol/L的溶液中的溶解度及草酸和醋酸对溶液酸度的影响，计算的结果表明醒酸根与铝的络合作用只发生在偏酸性的溶液体系中，并且随温度升高要求酸度增加，实际的络合能力降低，醋酸根的络合作用对长石溶解度的增加作用极及有限，最高时不足一倍；但醋酸能有效地缓冲溶液酸度，从而提高长石溶解度。草酸根与铝的络合作用发生在弱碱性至酸性条件下，温度升高，络合能力增加，络合效应对长石溶解度，草酸根上铝的络合作用发生在弱碱性至酸性条件下，温度升高，络合能力增加，络合效应对长石溶出量的增加最多可达2个数量级以上，草酸的浓度太低无法通过缓冲溶液在较高的酸度下来促进长石的溶解，草酸和醒酸能否促进储层次生孔隙的发育取决于盆地流体的酸度及组成流体的缓冲体系。     

低温碱性溶液中微纹长石溶解性质研究

对微纹长石在碱性溶液中的溶解过程及表面特征变化规律进行实验研究，温度为60℃，实验溶液分别为NaOH(pH≈8)、Na2CO3，[ρ(Na^ )=26μg／mL]和NaCl溶液，利用X射线光电子能谱(XPS)和ICP-MS测定实验前后微纹长石的表面特征及实验溶液成分变化，结果表明，随着pH值升高，微纹长石的溶解性增强；微纹长石的溶解不是被单一反应模式所控制，而是在表面控制(surface-conrtolled)、扩散控制(diffusion-controlled)和次生物相形成三种过程交替进行的结果。碱性溶液中长石表面反应分三个步骤：H^ 与长石表面碱性阳离子交换反应；OH^-联合已进入长石架状结构内部空隙，具较大结合能的Al-O键逐步破裂，并生成铝的水解产物而溶出；表面形成富Si的络合物。     

有机组分对长石溶解和次生孔隙发育的影响

在储层温度下，长石溶解于有机组分水溶液的模拟实验提示了许多重要事实，这些事实对于含长石砂岩中次生孔隙的形成具有重要的意义。实验采用油田水中两种最常见的羧酸，一种多元羧酸和一种酚（儿茶酚）。草酸盐溶液能显著提高长石的溶解速率。但这种疚在溶液中存在钙和镁时明显受到抑制。醋酸盐的存在能有效地缓冲地下流体的ｐＨ值，进控制长石的溶解速率。在醋酸盐缓冲溶液里，当ｐＨ值由中性降为酸性时，钾长石的溶解速率增大。然     

形成沥青铀矿的化学环境

有几种铀的络离子在pH值、温度和压力的广泛变化范围内是稳定的。在25℃和中性溶液中,铀酰的碳酸盐络合物、氟化物络合物和氢氧化物络合物在溶液中能保持的浓度值在10~(-5)M和10~(-3)M之间。在较高温度(215℃)下,当pH值为7时,这些离子的溶解度仍在10~(-5)M以上。温度为25℃,pH值为7时,上述离子将与还原剂(H_2S)起反应,形成沥青铀矿很小的雏晶。在温度升高(215℃)和pH值为7时,有相似的反应,但在这种情况下沉淀的沥青铀矿雏晶较大。铀的络离子比较不稳定。在25℃时,从氢氧化亚铀溶液中析出了少量的沥青铀矿。而在较高温度(215℃)下,溶液中全部的铀都转变为结晶良好的沥青铀矿。     

砂岩储层中有机酸对主要矿物的溶蚀作用及机理研究综述

砂岩储层中有机酸对矿物的溶解和沉淀在很大程度上影响着次生孔隙的发育。研究发现，有机酸之所以能提高石英的溶蚀速率和长石的溶解度，主要是由于在矿物的表面及溶液中形成络合物，有效地降低了矿物表面反应的活化能及溶液中硅、铝离子浓度的结果。有机酸与粘土矿物的吸附或催化反应可抑制长石等其他矿物的溶解。有机酸与CO2一起共同控制着体系中碳酸盐的溶解或沉淀。     

从HgS—NaCl—HCl—H_2O体系的热力学分析探讨辰砂以氯汞络合物运移成矿所需的物理化学条件

通过对HgS—NaCl—HCl—H2O体系的热力学分析,根据J.O.Nriagu和H.C.Helgeson提出的浓氯化钠溶液中重金属硫化物溶解度的近似计算公式,本文进行了25℃到200℃的有关条件下辰砂作为氯汞(Ⅱ)络合物的溶解度的近似计算。同时,根据笔者推导的反映热液Fh和重金属硫化物溶解度关系的类似公式。近似地计算了给定条件下,辰砂溶解度达成矿意义的浓度时的Eh下限。讨论了辰砂作为氯汞(Ⅱ)络合物运移和成矿所需的物理化学条件。进行了有关条件下辰砂溶解作用的初步试验,结果和热力学分析基本一致。     

锡石溶解度和锡迁移形式的实验研究

笔者用RA-2A-1型巴恩斯容量热液装置实验测定了锡石在H_2O,NaCl和KF溶液中的溶解度。实验结果显示,锡石在纯水和NaCl溶液中的溶解度是很低的,但锡石在KF溶液中的溶解度较高,且随KF的浓度增加和温度的升高而增大。在400℃时测得的溶解度达4.43mg/L,超过了成矿溶液所需的最低金属浓度。氟羟基络合物Sn(OH)_4F_2~(2-)是Sn(Ⅳ)在高温氟化物溶液中存在的主要形式,因此也是锡在热液成矿过程中主要的迁移形式。氟在锡的成矿过程中起着重要作用。     

成岩作用中的地下水碳酸体系与方解石溶解度

方解石在沉积岩成岩环境中的溶解度与地下水化学特征、温度等有着极为密切的关系。地下水碳酸体系中各碳酸组分的比例是溶液pH值的函数,可溶性CO2、HCO3-和CO32-分别在pH≤pK1的酸性介质、pK1≤pH≤pK2的弱酸至中性介质和pH≥pK2的碱性介质中具有绝对数量。而地下水体系中碳酸总量及各组分的变化受到pH值、气相CO2分压PCO2及固相方解石的溶解-沉淀效应的控制。通过限定溶液中离子的电价平衡和质量守恒约束条件可以确定各种温压环境中的地下水组成及方解石的溶解度特征。溶液pH值和温度是方解石溶解度的最直接的控制因素,且方解石的溶解随pH值不同分别在强酸、弱酸和碱性介质中表现出不同的反应方式。基于质量守恒条件,溶液中初始[ΣCO2]-[Ca2+]值对中性至碱性介质中的方解石溶解度带来很大的影响,当[ΣCO2]0<[ca2+]0有利于方解石的溶解,当[σco2]0>[Ca2+]0时有利于方解石的沉淀。如果CO2—H2O—CaCO3体系同时受到电价平衡和质量守恒条件的约束,则方解石只在酸性介质中溶解,碱性介质中沉淀。新疆塔里木盆地库车坳陷克拉2气田及相关储层中方解石分布特征表明,该区碎屑岩储层中方解石的大量沉淀发生于重碳酸钠型地下水环境中,而孔隙度极好、次生孔隙发育的储集段则出现于氯化型的地下水环境,从而验证了成岩作用中地下水类型对方解石溶解—沉淀的控制机制。      

Dissolution mechanisms of goethite in the presence of siderophores and organic acids

In dynamic natural systems such as soils and surface waters, transient biogeochemical processes can induce strong chemical non-steady-state conditions. In this paper, we investigate the effects of non-steady-state conditions on ligand-controlled iron oxide dissolution. The rates of goethite dissolution at pH 6 in the presence of low molecular weight organic acids (oxalate, citrate or malonate) were observed. Non-steady-state conditions were induced by rapid additions of fungal, bacterial or plant siderophores. In the presence of the low molecular weight organic acids, dissolved iron concentrations are below detection limit as predicted by equilibrium solubility calculations. The rapid addition of the siderophores triggered reproducible, fast dissolution of kinetically labile iron from the iron oxide surface. The same effect was observed upon rapid additions of high citrate concentrations to goethite-oxalate suspensions. The concentration of the labile iron pool at the mineral surface was a function of the surface concentration of the low molecular weight organic acids and of the reaction time before addition of the siderophores. Isotopic exchange with ⁵⁹Fe independently confirmed the existence of the labile iron pool before addition of the siderophore. A dissolution mechanism was elucidated that is consistent with these observations and with accepted models of ligand-controlled dissolution. We conclude that the fast dissolution reaction observed here is an important process in biological iron acquisition and that it is based on a general geochemical mechanism.     

Kinetics of feldspar and quartz dissolution at 70–80°C and near-neutral pH: effects of organic acids and NaCl

Effects of the organic acid (OA) anions, oxalate and citrate, on the solubility and dissolution kinetics of feldspars (labradorite, orthoclase, and albite) at 80°C and of quartz at 70°C were investigated at pH 6 in separate batch experiments and in media with different ionic strength (0.02–2.2 M NaCl). Although it has been shown that OAs can increase rates of feldspar dissolution, prior experiments have focused primarily on dilute, highly undersaturated and acidic conditions where feldspar dissolution kinetics are dominated by H⁺ adsorption and exchange reactions. Many natural waters, however, are only weakly acidic and have variable ionic strength and composition which would be expected to influence mineral surface properties and mechanisms of organic ligand-promoted reactions.Oxalate and citrate (2–20 mM) increased the rate of quartz dissolution by up to a factor of 2.5. Quartz solubility, however, was not increased appreciably by these OAs, suggesting that Si–OA complexation is not significant under these conditions. The lack of significant OA–SiO₂ interaction is important to understanding the effects of OAs on the release of both Si and Al from feldspars. In contrast to quartz, both the rates of dissolution and amounts of Si and Al released from the three feldspars studied increased regularly with increasing OA concentration. Feldspar dissolution was congruent at all but the lowest OA concentrations. Total dissolved Al concentrations increased by 1–2 orders of magnitude in the presence of oxalate and citrate, and reached values as high as 43 mg/l (1.6 mM). Si concentrations reached values up to 65 mg/l (2.3 mM) in feldspar–OA experiments. Precipitation of authigenic clays was observed only in experiments without or at very low concentrations of OAs. The high concentrations of dissolved Si attained during dissolution of feldspars in OA solutions, relative to Si concentrations in quartz–OA experiments, is attributed to concomitant release of Si driven by strong Al–OA interactions.Modeling of the dependence of feldspar dissolution rates on OA concentration in natural diagenetic environments is complicated by the competing effects of overall solution chemistry and ionic strength on the dissolution mechanism. Results of experiments using labradorite (An₇₀) indicate that in OA-free solutions, dissolution is progressively slower at increasing NaCl concentrations (up to 2.2 M), in agreement with prior experiments on the effects of alkali metals on feldspar dissolution. The combined effects of oxalate and NaCl on labradorite dissolution rates are such that the rate increase due to oxalate is suppressed by the addition of NaCl. Thus, feldspar dissolution kinetics should be most significantly affected by a given concentration of OAs in low ionic strength solutions.     

Dissolution kinetics of a lunar glass simulant at 25 degrees C: the effect of pH and organic acids

The dissolution kinetics of a simulated lunar glass were examined at pH 3, 5, and 7. Additionally, the pH 7 experiments were conducted in the presence of citric and oxalic acid at concentrations of 2 and 20 mM. The organic acids were buffered at pH 7 to examine the effect of each molecule in their dissociated form. At pH 3, 5, and 7, the dissolution of the synthetic lunar glass was observed to proceed via a two-stage process. The first stage involved the parabolic release of Ca, Mg, Al, and Fe, and the linear release of Si. Dissolution was incongruent, creating a leached layer rich in Si and Ti which was verified by transmission electron microscopy (TEM). During the second stage the release of Ca, Mg, Al, and Fe was linear. A coupled diffusion/surface dissolution model was proposed for dissolution of the simulated lunar glass at pH 3, 5, and 7. During the first stage the initial release of mobile cations (i.e., Ca, Mg, Al, Fe) was limited by diffusion through the surface leached layer of the glass (parabolic release), while Si release was controlled by the hydrolysis of the Si-O-Al bonds at the glass surface (linear release). As dissolution continued, the mobile cations diffused from greater depths within the glass surface. A steady-state was then reached where the diffusion rate across the increased path lengths equalled the Si release rate from the surface. In the presence of the organic acids, the dissolution of the synthetic lunar glass proceeded by a one stage process. The release of Ca, Mg, Al, and Fe followed a parabolic relationship, while the release of Si was linear. The relative reactivity of the organic acids used in the experiments was citrate > oxalate. A thinner leached layer rich in Si/Ti, as compared to the pH experiments, was observed using TEM. Rate data suggest that the chemisorption of the organic anion to the surface silanol groups was responsible for enhanced dissolution in the presence of the organic acids. It is proposed that the increased rate of Si release is responsible for the one stage parabolic release of mobile cations and the relatively thin leached layer compared to experiments at pH 3 and 5.     

Dissolution kinetics of biogenic silica from the water column to the sediments

Stirred flow-through experiments were conducted for the first time with planktonic biogenic silica (BSi). We investigated the dissolution kinetics of uncleaned and chemically cleaned BSi collected in ocean surface water, sediment traps, and sediments from the Norwegian Sea, the Southern Ocean, and the Arabian Sea. The solubility at 2°C is rather constant (1000 to 1200 μM). The dissolution rates are, however, highly variable, declining with water depth, and phytoplankton reactivity is two to three orders of magnitude higher than pure siliceous oozes. The reactivity decrease correlates well with an increase in the integrated peak intensity ratios of Si-O-Si/Si-OH measured by Fourier transform infrared (FTIR) spectroscopy. The removal of organic or inorganic coatings enhance the reactivity by at least an order of magnitude. Atomic Al/Si ratios of 0.03 to 0.08 in sedimentary diatom frustules decrease significantly to 0.02 as a result of removal of inorganic coatings and detritals present. Near equilibrium, the dissolution rates exhibit a linear dependence on the degree of undersaturation. At higher degrees of undersaturation—that is, at low concentrations of dissolved silica—the dissolution rates of uncleaned samples define a nonlinear trend.The nonlinear kinetics imply that the dissolution of natural BSi is strongly accelerated in silica-depleted surface waters. The FTIR results suggest that internal condensation reactions reduce the amount of surface reaction sites and are partly responsible for the reactivity decrease with depth. The high content of Al in sedimentary BSi is likely caused by precipitation of dissolved silica with Al dissolved from minerals in sediment. Nonbiogenic silica as coatings or detritals are partly responsible for the solubility and reactivity decrease of BSi in sediments. One order of magnitude different rate constants measured in Norwegian Sea and Southern Ocean sediment trap material support the so-called opal paradox—that is, high BSi accumulation rates in sediments in spite of low BSi production rates in surface waters of the Southern Ocean.     

Experimental investigation of aqueous corrosion of R7T7 nuclear glass at 90°C in the presence of organic species

The initial dissolution kinetics of the French “R7T7” inactive LWR reference glass was investigated in organic media at 90°C by static experiments at imposed pH values. Tests were conducted with various organic acids or acid salts (formic acid, citric acid, humic acids, sodium citrate and sodium formate) at different concentrations and at pH values ranging from 3 to 9. The leachates were submitted to ICP-AES analysis, and the alteration films on the glass specimens were examined by SEM (equipped with an energy-dispersive chemical analysis systm) and XRD. Results are discussed for the following areas.Effect of pH: different mechanisms are involved at pH 2.5 and pH 9, but in both cases, the R7T7 glass dissolution kinetics are always controlled by a surface reaction mechanism. The most significant effects of the organic acids on the glass dissolution kinetics were observed at pH 3, which was not unexpected.Nature of the acid (or acid salt): this is an essential parameter. Formic acid (monoacid) and sodium formate had no effect on the initial glass dissolution rate nor on the nature of the alteration film; conversely, citric acid (triacid) and sodium citrate significantly affected glass dissolution. The role of citric acid in the surface reaction mechanism has been demonstrated experimentally at pH 2.5; it is also known to favor that extraction of Si (directly or indirectly) and Zr and probably of Fe. The humic acids are strong catalysts of the R7T7 glass dissolution reaction. The conclusions drawn from these observations corroborate other published findings, suggesting that the catalytic effect is appreciable only for species with at least two carboxylic acid functions.Effect of concentration: the effect of the concentration was observed at basic pH values in the presence of sodium citrate and humic acids. This parameter may thus be quantified and incorporated in the glass dissolution kinetic law.     

Oilfield waters and sandstone diagenesis

The evolution of the organic geochemistry and carbonate alkalinity of oilfield waters is apparently regular and predictable; this evolution can be typified by five generalizations (1) at or near 80°C there appears to be an exponential rise in the concentration of organic acid anions; (2) the maximum concentration of organic acid anions occurs over approximately the 80–100°C temperature interval; (3) the highest concentrations of difunctional acid anions are associated with the other organic species maxima; (4) difunctional acid anions are the first to be decarboxylated, typically at temperatures of 100–110°C; (5) with increasing temperature (110–130°C) monofunctional acid anions begin to become decarboxylated, resulting in a fluid alkalinity dominated by bicarbonate. Dissolution experiments using artificial and natural oilfield waters demonstrate that mono- and difunctional carboxylic acid anions and hydroxybenzoic acid anions (present in both oilfield waters and the aqueous phase of hydrous pyrolysates) are capable of greatly enhancing Al, Si, Fe and Ca concentrations in solutions from dissolution of minerals by organometallic complexation. This enhancement of mineral solubility has been called upon to explain aluminosilicate dissolution porosity which is quantitatively important in many subsurface reservoirs; certainly, no other viable mechanism has been proposed to explain aluminum transport in the subsurface. When integrated into basin models, the regular evolution of organic and carbonate alkalinity in oilfield waters and the changing mineral stabilities that accompany that evolution help explain commonly observed diagenetic sequences in clastic systems.     

烃源岩的有机酸生成及其影响因素的模拟实验研究

不同温度下地层水—烃源岩相互作用模拟实验结果表明:（1）在整个实验温度范围内（60～300℃），均有有机酸的生成，有机酸的总浓度在35.4 mg/l至153.9 mg/l之间，其中在100℃和140℃的温度下浓度最大，其它温度下浓度相对较低；（2）在低温（60℃）条件下，成熟度相对较高、有机碳含量较大的烃源岩，有利于生成有机酸，但是在中温（140℃）和高温（180℃、220℃和300℃）条件下，有机酸的生成受有机碳含量、成熟度和碳酸盐含量的多重影响；（3）中低温（60℃和140℃）时，随着碳酸盐含量的增加，有机酸浓度表现为逐渐降低的趋势，表明在60～140℃，有机酸对碳酸盐的溶解和沉淀起主要的控制作用，而高温（180℃、220℃和300℃）条件下，碳酸盐的溶解和沉淀作用受有机酸和CO2的共同控制，从而导致有机酸浓度与碳酸盐的关系变化复杂。     

Factors controlling the solubility of aerosol trace metals in the atmosphere and on mixing into seawater

Previous work has shown that the type and pH history of an aerosol governs trace metal solubility in rainwater. This study concentrates on the crustal elements Al, Fe and Mn and identifies additional processes which affect dissolution not only in the atmosphere but also on mixing into seawater. Aerosol dissolution experiments (at aerosol concentrations of about 30 mg 1^–1) show manganese exhibiting high solubility at the low pH values typical of clouds (54±2.5% at pH 2, with results expressed in mole percent units) with 85% of this increase occurring within 6 hours of acidification. The percentage dissolution decreases to 50% at pH values representative of rainwater (pH 5.5) and to 26±4% at pH 8, typical of seawater. No such dramatic solution phase removal occurs at pH 8 in the presence of inorganic anions (to a final solubility of 44±2%). Thus the extent of manganese dissolution depends strongly on whether aerosols are cycled through acidic environments and on subsequent inorganic complexation once rainwater mixes into sea. Aluminium shows highest dissolution (7.1±0.6%) at low pH with 78% of this increase occurring within 6 hours of acidification. Rapid solution phase removal occurs on increasing the pH to that representative of rainwater (to 0.9±0.4% with 87% of this decrease occurring within 15 min). As a consequence of acid cycling and aluminium's amphoteric nature, solubility is enhanced at seawater pH (2.3±0.3%) over that in rain. Iron shows a strong pH-solubility relationship with highest solubility at low pH (4.7±0.2%), 70% of this value being reached within 6 hours of acidification, and decreasing rapidly to 0.17% as pH is raised to 8. Addition of inorganic anions at pH 8 to simulate mixing into seawater causes a further decrease in solubility, perhaps due to anion induced colloid destabilisation. Photochemical reduction also effects solubility under low pH conditions with Fe(II) comprising 1% of the total iron in the Saharan Aerosol used and 8.4% in an Urban material at a pH of 2. This element shows rapid solution phase removal with increasing particulate load which is tentatively rationalised in terms of a simple Kd approach.     

Speciation and solubility relationships of Al, Cu and Fe in solutions associated with sulfuric acid leached mine waste rock

 Solutions from oxidized waste rock originating from an acid-leached waste dump were studied. The dissolution data suggest that after the majority of the soluble solid phases are removed, remaining solid phases continued to buffer the solutions in the acidic pH range. Incorporating the solution data into MINTEQA2 identified controls on the solubility of Al, Cu and Fe at pH values from about 2.5 to slightly over 5. Sulfate appears to play a significant role in the formation of solubility controlling solid phases for Al and Cu. This is not the case for Fe, and is suggested that Fe and Cu solubility may be controlled by cupric ferrite at low pH values. Received: 5 April 1998 · Accepted: 27 July 1998     

The products of the interaction of feldspars with aqueous solutions at 25°C

Chemical analyses of 300 solutions produced by the artificial weathering of eight different feldspars in fourteen experiments of up to 1200hr duration were used to study the evolution of water during weathering. The range of pH was between 4 and 5·5. Within 4 hr of dissolution, the activity of Al was controlled by the pH and the solubility of microcrystalline gibbsite. After 100 hr of dissolution, the pH and microcrystalline halloysite controlled the activities of Al and silicic acid in all of the solutions.Microcrystalline halloysite was the only phase identified in the weathering of plagioclases in distilled water and 1 atm CO₂ partial pressure. Montmorillonites, halloysite and other clay minerals were produced from oligoclase in aqueous solutions containing high initial concentrations of Ca. Mg, K and SiO₂.The experimentally determined log solubility product of microcrystalline gibbsite was ?32·78 ± 0·04 and log $\text{K}$ for the hydrolysis of microcrystalline halloysite was 11.58 ± 0·05. The results suggest that very poorly crystalline metastable phases may control the initial compositions of some waters in contact with rocks containing feldspar minerals.