共查询到19条相似文献，搜索用时 187 毫秒
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pH值对羟基磷灰石除镉行为的影响 总被引：13，自引：1，他引：13
介质的pH值是影响羟基磷灰石(Hap)除镉行为最为复杂的因素之一,它决定了水溶液中Cd2+的赋存状态及Hap的溶解特性与表面性质等,而这些因素与Hap的除镉行为密切相关。实验研究表明,强酸(pH<3)条件下Cd2+的去除率随pH值的升高增加较快,但当pH≥3时这种增加变缓。在广泛的pH值范围内,Hap在含镉溶液和空白溶液中均表现为质子催化和非化学计量比的溶解机理。根据络合平衡计算,Cd2+在不同pH值时具有不同的型体及分布系数。Hap在空白溶液中的表面电动电势ζ为负值,且随pH值的增加其电负性增大。由此可知Hap除镉行为的作用机理是表面络合与表面电位吸附,而不存在溶解 沉淀作用。 相似文献
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巯基改性蒙脱石对Cd(Ⅱ)的吸附机理研究 总被引：3，自引：1，他引：2
蒙脱石对镉有良好的吸附性,但吸附力较弱,巯基改性蒙脱石可增强对镉的吸附,而关于蒙脱石的巯基改性及改性后对镉的吸附机理研究少见报道.本文以(3-巯丙基)三甲氧基硅烷作为改性剂,采用简单的溶液法对蒙脱石原土(简称MMT)进行巯基改性,并探讨了改性蒙脱石(简称MMT-SH)对镉的吸附机理.红外和X射线衍射表征显示MMT被成功接上巯基.吸附条件实验表明,MMT-SH对Cd(Ⅱ)的吸附效果显著优于原土,对Cd(Ⅱ)的饱和吸附容量是原土的39倍;吸附容量受pH值影响大,受离子强度的影响较大;MMT-SH对Cd(Ⅱ)的吸附作用除了静电吸附、离子交换吸附、羟基配位吸附,还主要存在巯基配位吸附.热力学及动力学实验表明,MMT-SH吸附Cd(Ⅱ)的反应符合Langmiur等温模型和Lagergren二级动力学方程,是易于发生的化学反应;吸附过程的热力学参数(△H、△G、AS)表明此吸附是一个自发的吸热过程. 相似文献
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以高比表面积活性炭作为吸附剂制备电容电极,研究电容去离子化（CDI）对地下水中镉的吸附性能。分别探讨了镉初始质量浓度、体系供电电压、地下水中常见阳离子种类对CDI去除镉的影响。结果表明,CDI吸附镉符合准二级吸附动力学、满足Langmuir等温吸附方程,CDI对镉的吸附为单分子层吸附。吸附量随镉初始质量浓度的升高而增加;在低质量浓度时,较高的供电电压会提高初始阶段的吸附速率,但对电极的最终吸附量无显著影响;地下水中主要阳离子的存在增加了体系的电导率,从而促进了CDI对镉的吸附,提高了镉的吸附速率和去除率。 相似文献
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淋洗剂EDTA 二钠和柠檬酸三钠与镉形成的络合物及镉本身在黏土上的吸附行为研究表明: 上述两种淋洗剂能有效提取表层土中的Cd,形成的络合物在迁移过程中又能较好地被黏土层吸附。黏土对Cd2 +、Cd--EDTA 和Cd--柠檬酸的吸附容量顺序为: Cd--柠檬酸＞ Cd2 + ＞ Cd － EDTA; 3 种形态的吸附过程均以离子交换吸附为主,并在15 min 内完成。黏土对Cd2 + 和Cd － 柠檬酸的吸附容量随溶液初始pH 的升高而增大,对Cd--EDTA 的吸附容量随pH 升高略有降低。 相似文献
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金属矿物的反应动力学与地球化学意义 总被引：8，自引：0，他引：8
概述了动力学实验的技术方法和金属矿物的反应动力学研究进展。动力学实验使用的三种基本化学反应装置是间歇反应器（ＢＲ）、活塞流反应器（ＰＦＲ）和混合流反应器（ＭＦＲ）,确定速率定律的数学方法包括积分法、微分法和混合法,以微分法中的初始速率法应用最广。目前主要研究了水溶液中黄铁矿氧化、黄铁矿和黄铜矿形成、晶质铀矿和磁铁矿溶解的速率定律和反应机理,发现：（１）酸性溶液中黄铁矿的氧化速率对Ｆｅ３＋和Ｏ２浓度呈分数依赖并受表面反应的控制;（２）低于３００℃时黄铁矿不能从溶液中直接成核,而需初始地通过ＦｅＳ先驱物的硫化生成,ＦｅＳ与Ｈ２Ｓ反应形成黄铁矿的速率方程为二级;（３）磁黄铁矿或黄铁矿与Ｃｕ２＋反应均可形成黄铜矿,前者经历了一系列准稳的Ｃｕ Ｆｅ硫化物的中间物,后者的速率方程为表观一级并受表面反应的控制;（４）酸性ｐＨ时磁铁矿的非线性溶解行为可采用表面反应扩散输运耦合的收缩核模型（ＳＣＭ）来描述。有关动力学实验成果完善和深化了对矿床中黄铁矿、黄铜矿的形成机理和风化壳中磁铁矿的稳定性等方面的认识。将来的实验研究将向更多的金属矿物和高温高压领域发展。 相似文献
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Apatite dissolution experiments were conducted using both a fluidized bed and stirred tank reactor over a range of pH, temperature, solution saturation state, and on non-carbonated and carbonated apatite compositions: igneous fluorapatite (FAP) and sedimentary carbonate fluorapatite (CFA), respectively. From 2 <pH <6, the rate of release from dissolution of all apatite components [calcium (Ca), phosphorus (P), and fluoride (F)] increased with decreasing pH for FAP. From 6 < pH < 8.5, the FAP dissolution rate is pH independent. Measuring apatite dissolution rates at pH > 8.5 were not possible due to detection limits of the analytical techniques used in this study and the high insolubility of FAP. For the CFA compositions studied, the dissolution rate decreased with increasing pH from 4 < pH < 7. During early stages of the dissolution reaction for both FAP and CFA, mineral components were released in non-stoichiometric ratios with reacted solution ratios of dissolved Ca:P and Ca:F being greater than mineral stoichiometric ratios, suggesting that Ca was preferentially released compared to P and F from the mineral structure during the early stages of dissolution. An increase in reacted solution pH accompanies this early elevated release of Ca. As the dissolution reaction proceeded to steady state, dissolution became congruent. When normalized to BET measured surface area, FAP dissolved faster from 4 < pH < 7 compared to CFA. The apparent Arrhenius activation energy (Ea) of FAP dissolution over the temperature range of 25-55°C at pH = 3.0, I = 0.1, and pCO2 = 0 is 8.3 ± 0.2 kcal mol−1. Both the apparent exchange of solution H+ for solid-bound Ca at low pH in the early stage of dissolution and the Ea of dissolution suggest a surface and not a diffusion controlled dissolution reaction for FAP and CFA. The degree of undersaturation of the solution, ΔGR, with respect to FAP was important in determining the dissolution rate. At pH = 3.0, I = 0.1, and pCO2 = 0, the dissolution rate of FAP was ∼ 5× greater in the far-from-equilibrium region compared to the near-equilibrium slope region.A simple apatite weathering model incorporating the experimental results from this study was constructed, and numerical calculations suggest that during the Phanerozoic both the surface area of igneous rock available for weathering and the average global temperature were important factors in determining the P weathering flux from apatite dissolution. It is possible that elevated global temperatures coupled with relatively high surface area of igneous rock during the early- to mid-Paleozoic resulted in elevated P weathering fluxes, which along with climatic evolutionary pressures of the Neoproterozoic, facilitated the radiation of multicellular organisms, large-scale phosphorite deposition, and abundance of calcium phosphate shelled organisms during the early Cambrian. 相似文献
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ZHANG Ronghu HU Shumin SU YanfengOpen Research Laboratory of Geochemical Kinetics Institute of Mineral Resources Chinese Academy of Geological Sciences Baiwanzhuang Ro Beijing China 《《地质学报》英文版》2002,76(3):351-366
This study reports the kinetic experimental results of albite in water and in KCI solution at 22 MPa in the temperature range of 25 to 400℃. Kinetic experiments have been carried out in an open flow-through reaction system (packed bed reactor). Albite dissolution is always incongruent in water at most temperatures, but becomes congruent at 300℃ (close to the critical point 374℃). At temperatures from 25 to 300℃, the incongruent dissolution of albite is reflected by the fact that sodium and aluminum are easily dissolved into water; from 300 to 400℃ it is reflected by silicon being more easily dissolved in water than Al and Na. Maximum albite dissolution rates in the flow hydrothermal systems have been repeatedly observed at 300℃, independent of flow rates.The kinetic experiments of albite dissolution in a KCl aqueous solution (0.1 mol KCl) indicate that the dissolution rate of albite increases with increasing temperature. Maximum silicon release rates of albite have been observed at 400℃, while ma 相似文献
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1INTRODUCTION BARITE(BASO4)ISANEXTREMELYINSOLUBLESALT;THISAROUSESPROBLEMSINPETROLEUMINDUSTRYBECAUSE BASO4ISAPARTICULARLYINTRACTABLESCALINGAGENT.BARITE PRECIPITATIONINTHEWELLBOREENVIRONMENTGENERALLYRE QUIRESMECHANICALREMOVAL,WITHCONSIDERABLEASSOCIAT EDEXPE… 相似文献
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This investigation was carried out to assess the protective properties of the alteration film that develops during aqueous alteration of the French SON 68 (R7T7-type) nuclear glass, notably by examining the behavior of some network-forming cations in the presence of complexing anions. Glass alteration was studied here in the presence of orthophosphate ions. Comparisons were established between two series of tests performed with a solution containing orthophosphate ions and control tests performed under the same conditions but without phosphates. The first series of experiments was performed under initial rate conditions (i.e. in dilute media) to assess the effect of pH and phosphate concentration on the initial glass dissolution rate. Under these conditions, which ensure maximum chemical affinity of the glass dissolution reaction, phosphate adsorption occurs at the reaction interface only with acid pH values, at which the glass dissolution reaction is strongly inhibited. The elements that form complexes with the phosphates (Al, Fe, etc.) partially control glass dissolution in acidic media. Additional experiments carried out under saturated conditions — notably with respect to Si — in a solution enriched with phosphates showed that rare earth and Ca phosphates precipitated in the outer region of the alteration film, maintaining a glass dissolution rate significantly higher than in the control experiment. These observations have several implications. (1) Comparing the results obtained in the presence of phosphates and in the reference medium, the authors demonstrate deductively that glass dissolution is limited by the inner portion of the alteration film, i.e. the amorphous gel. (2) A kinetic law of SON 68 glass dissolution cannot be based on silica alone; the results of these experiments contradict Grambow’s model. (3) With regard to control of the glass dissolution kinetics by the protective properties of the gel, this type of experiment shows that the relation between the chemical composition and the microstructure of the gel is an important aspect in modeling the glass alteration kinetics, but that it is still poorly understood. 相似文献
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黏土质白云岩是新生代形成的弱固结沉积白云岩,具有丰富且开放的孔隙率及高化学反应活性,其作为环境工程材料的应用值得探讨。本文研究了黏土质白云岩去除溶液中铅的效果和作用机理,考察了黏土质白云岩除铅动力学以及初始浓度、固液比对除铅效果的影响。结果表明,黏土质白云岩与不同浓度的铅溶液反应达到平衡所需的时间不同,初始铅浓度越高反应平衡时间越长,与铅浓度100 mg/L溶液反应70 h才基本达到平衡;黏土质白云岩除铅效果主要受反应平衡后溶液的p H值控制,固液比也可影响溶液p H值;固液比越高,平衡p H值越高,铅去除越完全;黏土质白云岩去除溶液中铅离子的作用机制是其中的白云石诱导的铅沉淀,白云石溶解同时形成了碱式碳酸铅。 相似文献
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Thermodynamic equilibrium, kinetics, activation barriers, and reaction mechanisms for chemical reactions in Karst Terrains 总被引：2，自引：0，他引：2
W. B. White 《Environmental Geology》1997,30(1-2):46-58
Chemical reactions pertinent to karst systems divide broadly into (a) speciation reactions within aqueous solutions, (b) dissolution/precipitation and other acid/base reactions between aqueous solutions and solid minerals, and (c) redox reactions involving various carbon and sulfur-bearing species. As a backdrop against which other chemistry can be evaluated, selected phase diagrams and equilibrium speciation diagrams were calculated for the system Ca—Mg—O—H—C—S. The kinetics of reactions within this system span time scales from milliseconds for homogeneous reactions in solution through hundreds of hours for carbonate mineral dissolution reactions, to geologic time scales for reactions such as the aragonite/calcite inversion or the oxidation/reduction of native sulfur. In purely inorganic systems, kinetic barriers, typically on the order of tens of kJ/mole, are set by nucleation processes and by activated complex formation. Biological processes impact the purely inorganic chemistry by the following mechanisms: (a) Secretions and waste products from biological activity or consumption of CO2 by organisms changes the chemistry in the microenvironments of reaction surfaces. Oxidation potentials, pH, and ion activities may be modified, thus shifting equilibria. (b) Reaction rates may be increased due to modification of activated complexes and thus the activation barriers to reaction. (c) Organic compounds or microorganisms may act as substrates, thus lowering nucleation barriers. The preservation of microorganisms in cave deposits does not necessarily prove a cause and effect relationship. 相似文献
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ZHANG Xuetong ZHANG Ronghu HU Shumin YU WenbinOpen Research Laboratory of Geochemical Kinetics Chinese Academy of GeologicalSciences Baiwanzhuang Ro Beijing 《《地质学报》英文版》2000,74(2):406-411
This work presents new experimental results on surface chemistry of reacting minerals and interface kinetics between mineral and aqueous solutions. These experiments were carried out using a flow reactor (packed bed reactor) of an open system as well as a continuous stirred tank reactor, CSTR. The authors measured reaction rates of such minerals as zeolite, albite and carbonate (rhodochrosite, dolomite) in various solutions, and tested corresponding mineral surface by using SEM, XPS, SIMS, etc. This paper mainly presents the experimental results of zeolite dissolution in water and in low pH solutions at room temperature, and dolomite dissolution at elevated temperatures. The results show that the release rates of Si, Al and Na of zeolite are different in most cases. The incongruent dissolution of zeolite is related to surface chemical modifications. The Na, Al and Si release rates for dissolution of albite and zeolite in water and various solutions were measured as a function of temperature, flow veloci 相似文献
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Kirill Aldushin Guntram Jordan Werner Rammensee Hans-Werner Becker 《Geochimica et cosmochimica acta》2004,68(2):217-226
Depending on pH and temperature, two different types of surface reactions occur on the apophyllite (001) surface in aqueous HCl-solutions at temperatures from 20 to 130 °C. At low pH, laterally spreading hillocks cover the surface. The hillocks are softer than the pristine surface, chemical analysis shows a depletion in Ca + K, and the spreading velocity of hillocks depends on pH. This indicates a change in chemical bond strength, non-stoichiometric dissolution and a mechanism involving protons. External disturbances such as the AFM scanning tip cause the upper surface layers to peel off revealing that the active sites of hillock formation are between the silicate layers of apophyllite. The observed process can therefore be described by a penetrative ion-replacement reaction which proceeds well below the surface monolayer. By this ion-replacement, the silicate layers eventually become destabilised. The observed reaction, therefore, is equivalent to an incongruent dissolution process. Despite structural similarities, this process is only superficially similar to the ion-exchange occurring in clay minerals or zeolites. In these minerals, the structural backbone is not destabilized. At a more neutral pH and high temperatures, step retreat and etch pit formation can be observed on the apophyllite (001) surface thus indicating a more congruent dissolution mechanism. 相似文献