硅酸盐体系的化学平衡:(2)反应热力学

通过具体的应用实例,系统介绍了在矿物材料学研究中硅酸盐体系的多相平衡反应热力学的基本原理。对硅酸盐体系的典型多相平衡反应进行了热力学计算,包括:(1)微晶玻璃制备过程中的硅酸盐熔融反应;(2)霞石正长岩和高铝粉煤灰利用技术中的硅酸盐烧结反应;(3)S iO2-CaO-H2O体系和KA lS i3O8-CaO-H2O体系雪硅钙石、硬硅钙石的水热晶化反应;(4)高铝粉煤灰和霞石正长岩烧结产物的溶解反应;(5)Na[A l(OH)4]-A l(OH)3-H2O体系和Na2SO4-Ca(OH)2-H2O体系中α-A l(OH)3和CaSO4.2H2O的析晶反应。研究成果可望对矿物材料制备实验方案设计、工业生产过程优化及改进产品性能提供理论指导,同时为同类材料学研究提供借鉴。     

硅酸盐体系的化学平衡:(1)物质平衡原理

通过具体应用实例,系统介绍了在硅酸盐体系的化学平衡研究中,依据物质平衡原理,求解“相混合方程”(PME)而进行物相定量分析的“相混合计算”(PMC)方法。应用实例包括矿物原料和结晶岩物相的定量分析,复杂固溶体矿物的端员组分计算,多组分硅酸盐陶瓷的配料比例计算,以及硅酸盐陶瓷制品物相的定量分析。物相定量分析结果是结晶岩和工业岩石原料分类命名的基础,可以为改进矿物原料预处理工艺提供依据,也是研究硅酸盐体系的化学平衡、对材料制备过程进行热力学分析的基础。实际计算中必须合理估计各种分析数据的累积误差。优化计算结果的理论依据主要有矿物晶体化学原理、矿物共生组合规律和次要组分分配的固溶体矿物相优先原则。     

铝酸钠溶液中Al(OH)3析晶反应的热力学分析与实验

随着中国原铝需求量不断增加,氧化铝工业的快速发展,导致国内铝土矿资源日益减少.因此,从上世纪中期起,研究者便把高铝粉煤灰作为一种新的铝资源,开始探索利用它来制备铝产品[1].     

硅酸盐-磷酸盐平衡反应对熔体中磷制约实验

目前，根据磷灰石溶解度模型、P在碱性长石与熔体相间的分配以及黑云母、锰铝榴石、透锂长石与对应的磷酸盐（包括斜磷锰铁矿、磷铝锂石-羟磷锂铝石）的平衡研究，已对过铝质岩浆中P的归宿进行了有效的平衡。但未见锰铝榴石-磷灰石的平衡研究。由于锰铝榴石-磷灰石矿物共生组合是花岗岩和LET型伟晶岩中最常见的矿物组合，直到岩浆演化晚期才出现锂辉石-磷铝锂石-羟磷锂铝石的组合。为此，本文实验研究锰铝榴石-磷灰石平衡反应，对过铝质岩浆体系中P溶解度起控制作用。     

利用高铝粉煤灰制备莫来石微晶玻璃的实验研究

以高铝粉煤灰为主要原料,采用粉末烧结法制备出莫来石微晶玻璃。X射线衍射分析显示,经1350~1550℃热处理后,制得的微晶玻璃的主晶相均为莫来石。扫描电镜分析表明,较高的温度下热处理有利于晶体的生长。微晶玻璃的理化性能如吸水率、气孔率、体积密度、抗折强度和化学稳定性,随热处理温度的不同而发生相应的变化。1500℃热处理2 h制得的微晶玻璃具有优良的理化性能,在工程和结构领域具有潜在的应用前景。     

矿物溶解—结晶的反应动力学分析

系统地探讨了矿物溶解－结晶的反应动力学特征,分析了制约矿物溶解－结晶的几上关键因素,并就矿物溶解－结晶作用的反应动力学研究的发展前景进行了预测。     

沉积CaCO3与金属离子界面反应动力学研究

金属离子与沉积碳酸盐之间２同反应动力学模拟实验表明,由于ＣａＣＯ３快速溶解和溶液ＰＨ急剧上升,大部分Ｐｂ＾２＋、Ｚｎ＾２＋离子与溶液中ＣＯ３＾２－和ＯＨ＾－离子反应生成白铅矿ＰｂＣＯ３、水白铅矿Ｐｂ３（ＯＨ）２（ＣＯ３）２,或Ｚｎ（ＯＨ）３和锌矿Ｚｎ（ＯＨ）６（ＣＯ３）２沉淀于体相溶液中,仅有少部分Ｐｂ＾２＋、Ｚｎ＾２＋通过扩散与ＣａＣＯ３表面发生离子交换反应。２５℃时,Ｐｂ＾２＋溶液中以白铅矿沉     

利用高铝粉煤灰制备堇青石微晶玻璃的实验研究

以高铝粉煤灰为主要原料，制备了堇青石微晶玻璃。通过差热分析（DTA）和X射线粉末衍射分析（XRD）确定了合适的热处理条件：核化温度807℃，核化时间2h，晶化温度960℃，晶化时间3h。XRD分析显示，制得微晶玻璃的主晶相为堇青石。SEM分析表明，基础玻璃晶化完全，微晶玻璃中微晶体呈不规则柱状、棒状，微晶体长度为5～15μm，长径比为5～10。     

晋蒙边界富铝片麻岩的矿物演化序列及动力学意义

华北地台北缘早前寒武纪孔兹岩系的变质反应结构及矿物组合演化序列在晋蒙边界地区代表性岩石；夕线石榴黑云钾长（二长）片麻岩（Ａ）和石榴（紫苏）黑云斜长片麻岩（Ｂ）中保存的最为完整，以岩相学及显微组构特征为依据，可将其划分四个世代的矿物组合；（１）峰前以含蓝晶石残晶和包裹于平衡镶嵌，出现典型的麻粒岩相矿物组合；Ｋｙ±Ｇｔ＋Ｋｆ±ｐｌ＋Ｑｚ（Ａ），Ｂｉ±Ｇｔ＋Ｐｌ＋Ｑｚ（Ｂ）；（２）峰期以基质矿物平衡镶嵌     

硫化物矿物氧化反应动力学实验研究

硫化物矿床和含硫化物矿床（如中高硫煤）在开发过程中由于氧化作用向环境释放大量的酸、硫酸盐、重金属及其它有害物质,造成一定范围内的次生地球化学异常和环境污染;而中国大陆硫化物的排放量2010年将达到39．1×10 6 t。因此,人们对硫化物矿物在表生环境下的氧化行为日益重视。硫化物矿物的氧化速率受矿物本身物理化学特性（组成、结构、表面性质）和介质条件（溶解氧DO、Fe 3＋浓度、pH、Eh、温度及微生物）等多种因素的控制。在全面分析近年来国内外文献的基础上,系统介绍了硫化物矿物氧化动力学实验研究方法、实验参数的选择、反应机理、反应产物及反应速率等的研究现状。指出今后应加强对初始阶段的氧化反应速率、反应中间产物、多因素的综合作用、分子水平上的反应机理解释等方面的研究。     

环境矿物界面反应动力学

环境矿物界面反应动力学主要探讨地表中各种有毒、有害离子或分子与矿物表面之间的反应速率与反应机制。矿物表面存在一组化学活性很强的表面功能基，当它们与环境中毒害物质发生作用时，会因其极性、荷电性和Lewis酸碱性不同而表现出不同的作用力和反应速率，进而控制有毒、有害物质在大气、水体和沉积物中的赋存形态，稳定性及迁移转化速率。本文简要介绍了环境矿物界面反应动力学理论，并给出几个应用实例。     

Determination of Ge, As, Se and Te in Silicate Samples Using Isotope Dilution-Internal Standardisation Octopole Reaction Cell ICP-QMS by Normal Sample Nebulisation

A method for the determination of Ge, As, Se and Te in silicate samples using isotope dilution-internal standardisation (ID-IS) octopole reaction cell (ORC) ICP-QMS by normal sample nebulisation was developed. The method does not involve either hydride generation or ion exchange. Germanium, Se and Te were determined by isotope dilution (ID), and As was determined by ID-IS. A silicate sample with an added Ge-Se-Te spike was digested with an HF-HNO₃-HBr mixture, dried, re-dissolved with HF and the supernatant liquid was directly aspirated into an ORC-ICP-QMS instrument with He or H₂ gas. No matrix effects were observed down to a dilution factor (DF) of ∼ 70 for Ge, Se and Te and DF of ∼ 1000 for As, which resulted in 3s detection limits in silicates of 2, 1, 0.1 and 4 ng g⁻¹, respectively. Advantages of the method are the simple sample introduction as well as a capability of determining S, Ti, Zr, Nb, Mo, Sn, Sb, Hf and Ta by ID-IS-ICP-QMS/SFMS from the same solution. Furthermore, the total sample solution consumption was only 0.253 ml with DF = 2000. Therefore, only a 0.13 mg test portion was required. To demonstrate the applicability of this technique, Ge, As, Se and Te in eight silicate reference materials were determined, as well as S, Ti, Zr, Nb, Mo, Sn, Sb, Hf and Ta in four carbonaceous chondrites.     

中地壳的地球化学动力学和矿石成因

笔者重点进行了大于300℃——在近临界区至超临界区条件下的硅酸盐矿物与水反应动力学实验。矿物(钠长石Ab、透辉石Di、阳起石Act和磁铁矿Mt)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,在跨越水临界点时出现反应速率的涨落。各种多金属氧化物硅酸盐与水反应时,各个元素溶解到溶液里的释放速率一般不一样,常称为一致溶解作用。但是,在近300℃变为一致溶解作用。实验发现在22MPa时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。确切地说,金属与氧之间的键的性质决定了它们(金属氧化物)与水之间反应速率。在一般情况下,Na-Obr,Ca-Obr,Mg-Obr,Al-Obr和Si-Obr的键桥(br),它们之间相对地由具有离子键性质逐步变为具有极性键的性质。由常温常压到亚临界区(300～374℃22MPa),再到大于临界点374℃、22MPa进入超临界区,水的性质随温度、压力变化。水由容易溶解离子键逐渐变为容易打破极性键。笔者还研究了黑钨矿、锡石(玄武岩、花岗闪长岩)与水在250～400℃条件下的反应动力学过程,得出了相同的结果。实验均发现在跨越水临界点时矿物(或岩石)与水反应的动力学涨落。这些实验结果可以用于说明中地壳上部的水/岩相互作用的特征。发生于中地壳的水、岩相互作用大多是在300～450℃和20～50MPa条件下进行的。各地区的地壳厚度不一,中地壳温度压力并不完全相同。模拟中地壳条件下水/岩相互作用实验,目的主要是研究矿物(或岩石)在300～450℃条件下反应动力学过程。已有热液矿床矿物流体包体数据表明:有一批矿床的主要矿石形成于300～500℃,低于NaCl H2O溶液临界线的条件。中地壳的流体处于由亚临界态跨越临界态,进入超临界流体太的演化过程。这种流体的性质变化会引起水/岩相互作用的反应动力学涨落和矿石大量沉淀。     

靖宇县玄武岩区矿泉水特征组分H2SiO3成因实验——以王大山泉为例

以靖宇县典型泉岩样为实验材料,结合野外实际情况,考虑pH值和CO₂影响因素设计了矿泉水中H₂SiO₃实验,对实验结果进行了化学动力学分析,并利用matlab建立数学模型分析了矿物反应的机理。结果表明:1)仅考虑pH值的情况下:初始pH值近中性(pH=7.25)时,实验溶液中H₂SiO₃释放量较小,反应难以发生;初始pH值为碱性(pH=8.10)时,实验溶液中H₂SiO₃缓慢增加,平均释放速率为3.08 mg/(kg·d)。2)在考虑pH值和CO₂情况下:初始pH值为碱性条件时,通入CO₂能够较快促进H₂SiO₃产生,平均释放速率可由4.29 mg/(kg·d)升高为12.00 mg/(kg·d);初始pH值为弱酸性(pH=6.64)时,实验溶液中H₂SiO₃增加较快,通入CO₂,溶液中H₂SiO₃释放速率稍微增加。3)实验溶液中H₂SiO₃释放规律符合Stanford一阶反应动力学模型。靖宇县矿泉水中H₂SiO₃主要来自偏硅酸矿物(斜长石、镁橄榄石、辉石)的反应。在中性条件下,玄武岩矿物很难反应;在碱性条件时,主要是玄武岩矿物的水解,反应缓慢;在弱酸性条件下,主要是玄武岩矿物与H⁺和CO₂的反应,反应强度较大。     

Oxygen Isotope Exchange Kinetics Between Coexisting Minerals and Water in the Aral Granite Pliiton of the Altay Mountains,Northern Xinjiang

Abstract Coexisting quartz, feldspar and biotite vary widely in their δ¹⁸O values and display a remarkable ¹⁸O / ¹⁶O disequilibrium relation; especially, a quartz–feldspar reversal (Δ ¹⁸O_{Quartz?feldspar}<0) exsists in the Aral granite pluton of the Altay Mountains, northern Xinjiang. The ¹⁸O / ¹⁶O exchange reaction definitely occurred between granite and water. Initial δ¹⁸O values of the granite and exotic fluid are evaluated by the mass balance consideration. The conventional method of discrimination between various magma derivations simply with δ¹⁸O values of either whole rock or separate minerals is misleading and unreliable. Experiments carried out by the authors show that the ¹⁸O / ¹⁶O exchange reaction is not accompanied by what geologists describe as petrological and mineralogical alteration effect. This decoupling relation implies that exchange reaction occurs at a relatively high temperature during subsolidus–postmagmatic cooling of magmas. The exchange mechanism is mainly diffusion–controlled. It is demonstrated through quantitative modelling that the hydrothermal system associated with the Aral pluton is long–lived (0.8—6 Ma), with a relatively high fluid flow rate (3 x 10^?14 mol. s^?1) and high W/ R ratio (0.79-6.14). This means that an intense flow and convection may exist at the midcrustal level of orogenic magmatic arcs.     

Oxygen Isotope Exchange Kinetics Between Coexisting Minerals and Water in the Aral Granite Pluton of the Altay Mountains, Northern Xinjiang

Coexisting quartz, feldspar and biotite vary widely in their δ18O values and display a remarkable 18O/16O disequilibrium relation; especially, a quartz-feldspar reversal (△ 18OQUartz_feldspar< 0) exsists in the Aral granite pluton of the Altay Mountains, northern Xinjiang. The 18O / 16O exchange reaction definitely occurred between granite and water. Initial δ18O values of the granite and exotic fluid are evaluated by the mass balance consideration. The conventional method of discrimination between various magma derivations simply with δ18O values of either whole rock or separate minerals is misleading and unreliable. Experiments carried out by the authors show that the 18O / 16O exchange reaction is not accompanied by what geologists describe as petrological and mineralogical alteration effect. This decoupling relation implies that exchange reaction occurs at a relatively high temperature during subsolidus-postmagmatic cooling of magmas. The exchange mechanism is mainly diffusion-controlled. It is     

Thorium sorption in the marine environment: Equilibrium partitioning at the hematite/water interface,sorption/desorption kinetics and particle tracing

Thorium(IV) sorption onto hematite (-Fe₂O₃) was examined as a function of pH and ionic strength. Sorption behaved Langmuirian over an eleven order of magnitude range in adsorption densities, : 10^–12 to 10^–1 moles Th sorbed per mole hematite sites, indicating that the overall free energy of Th adsorption is independent of adsorption density. Modeling of Th sorption was conducted with the Triple Layer Model of Davis and Leckie; reactions considered included solution-phase hydroxy and carbonato complexes of thorium, and carbonate/hematite surface complexes. The entire Th sorption isotherm can be modeled with a single surface complex formation reaction

Interplay between equilibrium and kinetics in prograde metamorphism of pelites: an example from the Nelson aureole, British Columbia

The distribution of metapelitic mineral assemblages in the Nelson aureole, British Columbia, generally conforms to what is predicted from phase equilibria. However, in detail, the sequence and spacing of isograds, mineral textures and mineral compositions and mineral chemical zoning do not. Two of the main disequilibrium features in the aureole are: (i) delay in the onset and progress of several reactions, i.e. overstepping in temperature; and (ii) unreactivity of staurolite and especially garnet porphyroblasts when they are reactants in prograde reactions. The thermal overstepping is ascribed to difficulty of nucleation of the product porphyroblasts and sluggishness of dissolution of porphyroblasts when they are reactants. The extent to which these kinetic barriers delay the onset of reaction is related to the reaction affinity of each reaction, defined herein as the Gibbs free‐energy difference between the thermodynamically stable, but not‐yet‐crystallized, products and the metastable reactants. For oversteps in temperature (ΔT), reaction affinity is, in turn, related to the difference in entropy (ΔS) between these two states through the relation A = ΔT * ΔS. Mineral reactions which release large quantities of H₂O, such as chlorite‐consuming reactions, have a higher entropy change per unit of temperature overstep, and therefore a higher reaction affinity, than those which release little or no H₂O, such as the chlorite‐free staurolite‐consuming reaction. Thermal overstepping is consequently expected to be less for the former than for the latter, as was estimated in the aureole where 0 to 30 °C overstepping was required for garnet, staurolite and andalusite growth from a muscovite + chlorite‐bearing precursor rock and ～70 °C overstepping was required for the growth of Al₂SiO₅ from a staurolite‐bearing, chlorite‐free precursor. In all cases, reaction progress was strongly influenced by the presence or absence of fluid, with presence of fluid lowering kinetic barriers to nucleation and growth and therefore the degree of thermal overstepping. Textural features of rocks from the nearly coincident garnet, staurolite and andalusite isograds are suggestive of a fluid‐catalysed ‘cascade effect’ in which reaction took place in a narrow temperature interval; several competing muscovite + chlorite‐consuming reactions, some metastable, appear to have occurred in parallel. Metamorphic reaction, fluid release and possibly fluid presence in general in the aureole were episodic rather than continuous, and in several cases well removed from equilibrium conditions. The extent to which these findings apply to regional metamorphism depends on several factors, a major one being enhanced deformation, which is expected to lower kinetic barriers to nucleation and growth.