含锂、钾硼酸盐水溶液体系固液相平衡研究

采用等温溶解平衡法测定了含锂、硼硼酸盐水溶液体系在35℃时的溶解度、密度和折光率,根据实验数据,绘制了相应的溶解度图、密度图、折光率图和pH值图。该体系溶解度相图包含一个共饱点,两个单盐结晶区,分别为结晶相区较大的（L+ Mg2B6O11·15H2O）和结晶相区较小的（L + K2B4O7·4H2O）,溶液体系中没有固溶体和复盐产生。溶液的密度、折光率和pH值随着硼酸钾溶液的浓度增大而呈现与规律的变化,并采用半经验公式对溶液的密度和折光率进行计算,计算值和实验值吻合较好。     

Recent Progress on Structure of Aqueous Polyborate Solutions

The crystal structure of metal borates has been extensively investigated by X-ray and neutron diffraction,but,the structure of aqueous polyborate solutions are still largely unknown.Over the last decade,our group has focused on studying the structure of complex aqueous polyborate solutions of Li,Na,K,Rb,Cs,and Mg using synchrotron radiation X-ray scattering(XRS),EXAFS,Raman,NMR,and DFT,as well as determining the density,conductivity and pH of such solutions.Polyborate species distributions were calculated using pH measurements,and the main species in the solution have been confirmed by NMR and Raman spectra.For alkali-metal metaborates,the dominant species is always B(OH)-₄in a wide range of concentration,while the presence of others species is negligible.For alkali metal tetraborates,when concentration is in the extreme low range,only B(OH)₃ and B(OH)-₄ are present in these solutions.As the total boron concentration increases,B(OH)₃ and B(OH)-₄ polycondensated to form more complex oligomers.Of them,while B₄O₅(OH)2-₄ in the tetraborate solutions is the main species,B(OH)₃,B(OH)-₄,and B₃O₃(OH)-₄ are minor species,and B₃O₃(OH)2-₅ and B₅O₆OH)-₄ are present only in negligible amounts.As solution continues to concentrate,B₄O₅(OH)2-₄ eventually becomes the dominant species,which is consistent with the congruent compound M₂B₄O₇·nH₂O(M=Li,Na,K,Rb,Cs) in the system M₂O-B₂O₃-H₂O(M=Li,Na,K,Rb,Cs).For alkali metal pentaborates,B(OH)₃ and B(OH)-₄ are the main species at low concentrations.The species distribution,Raman and NMR spectroscopy results verified that the dominant species in concentrated pentaborate solutions with Li and Na is pentaborate B₅O₆OH)-₄,but it is surprising that the main species with K,Rb,and Cs is always the triborate monoanion B₃O₃(OH)-₄.Although all M[B₅O₆OH)₄]·nH₂O(M=Li,Na,K,Rb,Cs) are all congruent compounds in the system M₂O-B₂O₃-H₂O(M=Li,Na,K,Rb,Cs) ,the main species in aqueous solutions are quite different because of various cation hydration distance(d),hydration number(CN),and configuration,especially charge(Z).For bivalent Mg²⁺,three borate minerals,namely,Inderite(2MgO·3B₂O₃·15H₂O),Hungchaoite(MgO·2B₂O₃·9H₂O),and Mcallisterite(MgO·3B₂O₃·7.5H₂O),exist in the system MgO-B₂O₃-H₂O at 298K.Inderite is a congruent compound,but Hungchaoite and Mcallisterite are incongruent compounds.The species distribution and Raman spectra demonstrat that the predominant species in all the solutions with magnesium borates is bivalent triborate B₃O₃(OH)2-₅,while the subordinate species are B(OH)-₄ at a low B₂O₃/MgO ratio and B(OH)₃at a high B₂O₃/MgO ratio,and the other anions are negligible,as the high Z of the borate anion must match that of Mg²⁺.The disappearance of divalent B₄O₅(OH)2-₄ is in agreement with its incongruent nature.The DFT and XRS results showed that tetrahedral Li(H₂O)⁺₄(d=0.20 nm,CN=4),octahedral Na(H₂O)₆⁺(d=0.236 nm,CN=6),and Mg(H₂O)²⁺₆(d=0.210 nm,CN=6) in the first hydration shell belong to Platonic polyhedra.However,K(H₂O)⁺₈(d=0.28 nm,CN=8,XRS and DFT),Rb(H₂O)⁺₈(d=0.293 nm,CN=7.7-8.2,EXAFS),and Cs(H₂O)⁺₈(d=0.320-0.326 nm,CN=7.6-7.9,EXAFS) are inclined Voronoi polyhedra.Therefore,the effects of cation Z and d on the structure of polyborates in aqueous solutions are deterministic,while the effect of hydrated-cation symmetry is secondary.Their hydrolysis order was:Mg＞Li＞Na＞K＞Rb＞Cs,in step with hydration power.Among them,Mg²⁺ and Li⁺have a strong tendency towards hydrolysis,but Na⁺ scarcely hydrolyzes,especially Rb⁺ and Cs⁺ have a little protonation.X-ray scattering of aqueous alkaline sodium borohydride solutions confirmed that dihydrogen bonds exist in an aqueous solution.The four distinct features of dihydrogen bonds in aqueous solution-unidirectionality,divaricativity,multicentricity,and multidentativity have been also described here in brief.     

盐湖溶液热化学(Ⅳ) Li_2B_4O_7—Li_2SO_4—LiCl—H_2O体系298.15K时稀释热、热容和表观摩尔热焓的研究

用连续滴定量热法测定了四元体系Li_2B_4O_7—Li_2SO_4—LiCl—H_2O及其次级体系Li_2B_4O_7—Li_2SO_4—H_2O和Li_2B_4O_7—LiCl—H_2O 298.15K时的稀释热,并结合Debye-Hückel热焓极限公式研究了该体系的平均表观摩尔热焓。     

五硼酸钾水溶液的差示FT-IR和Raman光谱研究

研究了KB5O8·4H2O水溶液20℃时的差示FT-IR光谱和Raman光谱,对振动频率进行了归属。探讨了KB5O8·4H2O水溶液中硼氧配阴离子的存在形式(主要是B(OH)3、[B3O3(OH)4]-和[B5O6(OH)4]-)和相互作用。     

A Raman Investigation on the Boron form Occurring in Salt Lake Brine during Evaporation

Boron resources are abundant in the Da Qaidam Salt Lake of the Qaidamu basin in China,which has generated significant attention due to the presence of polyborate species in brine from this lake. In this study,Raman spectroscopy was used to investigate the existing form of boron in brine during evaporation. MgO·2 B_2 O_3-H_2 O,MgO·2 B_2 O_3-MgCl_2-H_2 O,and MgO·2 B_2 O_3-MgSO_4~-H_2 O solutions were also studied to determine the influence of boron concentration,pH,and electrolytes on the borate speciation from brine. The mononborates B( OH)_3 and B( OH)_4~-were found to be the only forms present in natural salt lake brine. Brine evaporation promoted the formation of the polyborate anions B_3 O_3( OH)_4~-,B_5 O_6( OH)_4~-,and B_6 O_7( OH)_6~(2-)and also promoted the disappearance of the B( OH)_4~-ion from brine at boron concentrations of more than 11 g/L B_2 O_3. The pentaborate ion B_5 O_6( OH)_4~-was sensitive to the solution pH and appeared only at p H values less than 8. 0. Meanwhile,the hexaborate ion B_6 O_7( OH)_6~(2-)was observed to be more dependent on the electrolyte magnesium chloride due to its special properties,such as promoting boron accumulation,lowering solution pH,and also its strong affinity for water molecules,which were all beneficial for the polymerization of borate ions in brine. Interaction mechanisms between polyborate anions during evaporation are also proposed herein. ake; evaporation; polyborate species; interaction mechanism.     

盐卤硼酸盐化学ⅩⅤⅢ·MgO·3B_2O_3-MgCl_2-H_2O浓溶液中六硼酸镁盐结晶动力学

人工模拟合成B_2O_3/MgO=3的过饱和氯化镁溶液,分别在20～60℃恒温条件下,在密封、无外界扰动条件下进行水合六硼酸镁盐结晶动力学实验测定。最后分离固相,经处理后,用化学分析和物理分析法进行物相鉴定。采用计算机对实验数据进行处理,给出相应的结晶动力学方程。根据硼在水盐溶液中是以多粒子形式共存这一结论,提出不同水合六硼酸镁盐的结晶反应机制。     

三元体系K+,Mg2+/B4O2-7-H2O 25℃相关系研究

对三元体系K+,Mg2+/B4O2-7-H2O25℃的溶解度进行了研究,该体系属简单共饱型,两段溶解度曲线对应于体系的两种原始组分K2B4O7·4H2O、MgB4O7·9H2O的结晶区,共饱点组成为K2B4O713 96%,MgB4O70 53%。     

298.15K下LiCl-Li2B4O7-H2O体系热力学性质的等压研究

用等压法研究了LiCl-Li2 B4O7-H2 O体系离子强度范围为 0 1 5 3 0～ 3 0 75 8mol kg-1不同质量摩尔浓度分数的等压平衡浓度 ,水活度 ;计算了LiCl和Li2 B4O7,混合盐溶液的饱和蒸汽压 ,渗透系数等热力学性质。以总硼浓度 0 0 8mol·kg-1为界 ,把所有混合盐的实验数据分为高浓度和低浓度两部分 ,按照不同的物种生成转化反应 ,考虑溶液中H3 BO3 和硼氧配阴离子B(OH) 4 -,B3 O3 (OH) 4 -和B4O5(OH) 4 2 -的存在形式。由实验数据用最小二乘法和迭代法求取了LiB(OH) 4 离子对的缔合平衡常数Km1,B3 O3 ,(OH) 4 离子的生成转化反应的化学计量平衡常数Km2 ,以及Pitzer模型的离子相互作用参数。用该模型计算的渗透系数值与实验结果取得合理的一致。对完善含锂、硼盐湖卤水体系的热力学模型和盐湖资源的综合开发具有重要意义     

盐卤硼酸盐化学 ⅩⅪ.MgO-B_2O_3-MgCl_2(8％)-H_2O体系20℃热力学非平衡态液固相关系

用动力学方法对标题体系过饱和溶液的结晶过程进行了研究,MgO:B_2O_3(mol比)为1:2、1:5和1:7时的结晶固相分别为多水硼镁石、三方硼镁石和硼酸,与MgCl_2浓度为28％时的结果对比表明,MgCl_2浓度越低,该四元体系溶液过饱和度越小,因此,液固相关系也变得比较简单,在本文研究的浓度条件下出现了多水硼镁石固相,而MgCl_2浓度为28％时却没有,拟合出结晶动力学方程,对结晶机制进行了探讨。     

盐卤硼酸盐化学ⅩⅨ——氯柱硼镁石溶解及相转化研究

本文研究了温度、盐效应、晶体用量和搅拌速度对氯柱硼镁石在水中溶解过程及相转化的影响。实验结果表明,该复盐属不同步溶解,先溶脱MgCl·6H_2O,生成中间产物MgO·B_2O_3·4H_2O,随后发生相转化和结晶过程。最终产物在10—50℃时是多水硼镁石,在60℃时是柱硼镁石。提出了相转化机理,计算了溶解度、溶解热等热力学函数。     

三元体系Mg~(2 )/Cl~-,Borate—H_2O25℃相关系和溶液性质的研究

用等温溶解法测定了Mg2+／Cl-，Borate-H2O三元体系25℃时的溶解度．此三元体系等温溶解度图为简单共饱型，它的平衡固相分别为三方硼镁石（Mg2B12O20·15H2O）和MgCl2·6H2O，未产生新的复盐或固溶体。拟合了MgB6O10随MgCl2浓度变化的溶解度曲线方程，并且对平稳溶液的物化性质（密度、粘度、折光率、电导、pH值）进行了测定，用半经验公式描述了一些物化性质随浓度的变化规律，结果令人满意。     

Isothermal Evaporating Phase Equilibria in the Quaternary System (LiCl+NaCl+Li2SO4+Na2SO4+H2O)at 348.15 K and 0.1 MPa:An Experimental and Theoretical Study

The gradient solar pond technique is an economic separating process employed in the inorganic chemical industrial production of salt lake chemical engineering processes. In this paper,a novel isothermal evaporation experimental method was employed to simulate the evaporation phase equilibrium for the reciprocal quaternary system( LiCl + NaCl + Li_2 SO_4+ Na_2 SO_4+ H_2 O) at 348. 15 K to serve as a useful guide for lithium salt production via the depth solar ponds. The isothermal evaporation equilibrium solubilities and physicochemical properties,including the densities and pH values,were experimentally investigated. The dry-salt phase diagram,water-phase diagram,and the diagram of the physicochemical properties versus composition were plotted with respect to the experimental data. The drysalt phase diagram consists of three invariant points,seven univariant solubility curves,and five crystallization regions,specifically halite( NaCl,Ha),thenardite( Na_2 SO_4,Th),double salt( Li_2 SO_4·Na_2 SO_4,Db_2),lithium sulfate monohydrate( Li_2 SO_4·H_2 O,Ls),and lithium chloride monohydrate( LiCl·H_2 O,Lc). Based on Pitzer and its extended HMW model,the Pitzer single salt parameters,mixing ion interaction parameters,and thermodynamic stable equilibrium constants for the quaternary system at 348. 15 K were obtained. The calculated phase diagram and experimental isothermal phase diagram at 348. 15 K exhibited a great difference. Based on these results,the isothermal evaporation phase diagram can truly reflect the salt sedimentary in salt lakes and can be applied as a useful guide for the solar pond process.     

三元体系Li~+,Mg~(2+)∥SO_4~(2-)—H_2O 25℃相关系及溶液物化性质的研究

研究了三元体系Li~+,Mg~(2+)∥SO_4~(2-)—H_2O在25℃时的相关系和平衡液相的密度、粘度、折光率、电导等物化性质,该体系为简单共饱型,两段溶解度曲线对应于体系的两种原始组份Li_2SO_4·H_2O和MgSO_4·7H_2O的结晶区,无复盐和固溶体形成,亦无脱水作用发生,应用电解质溶液Pitzer模型检测该体系25C的溶解度,并用经验或半经验公式对平衡液相的密度和折光率进行了理论计算,计算值与实验值非常接近。     

三水合五氧化二钒纳米棒合成、结构表征和热稳定性研究

以NH4VO3为原料,在盐酸水溶液中采用水热法制备V2O5.3H2O纳米棒。利用X-ray diffraction (XRD)、Raman、扫描电子显微镜(SEM),透射电子显微镜(TEM)、热失重分析(TGA)表征手段,研究了V2O5.3H2O纳米棒结构、形貌和热稳定性。     

五元交互体系Li~＋，K~＋，Mg~（2＋）／Cl~－，SO_4~（2－）－H_2O25℃相关系和溶液物化性质的研究

用等温溶解平衡法研究了Ｌｉ＋，Ｋ＋，Ｍｇ（２＋）／Ｃｌ－，—Ｈ２Ｏ五元交互体系２５℃的溶解度。该体系相图由十五个盐或复盐的结晶区构成，饱和溶液的某些物化性质的测定结果与经验公式计算结果吻合，用现代电解质溶液理论—Ｐｉｔｚｅｒ模型预测了该体系的溶解度，实验测定值与理论预测结果非常一致。     

PEG400 - NaCl/KCl - H2O三元体系298 K溶解度、密度、折光率研究

采用等温溶解平衡法研究了 298 K下三元体系NaCl/KCl - PEG400 - H2O的相平衡关系,绘制了相应的相图、密度-组成图和折光率-组成图。研究发现：298 K下,两个三元体系均无分层现象,只存在固液相平衡关系,其平衡相图由不饱和液相区(L)和一固一液区(S+L)构成。PEG400对NaCl、KCl有一定的盐析作用,随着溶液中PEG400含量不断增加单盐溶解度减小。     

差示FT-Raman和11B NMR方法研究过饱和镁硼酸盐的溶液结构

用差示FT -Raman和11BNMR光谱研究了MgB6O10 ·7 5H2 O、MgB4O7·9H2 O、Mg2 B6O10 ·1 5H2 O三种镁硼酸盐饱和和过饱和溶液的结构机理 ,其结果表明饱和溶液和过饱和溶液中均存在B(OH) 3 、B(OH) -4、B3 O3 (OH) -4、B5O6(OH) 4 -粒子。镁硼酸盐的结晶过程是一个复杂的动力学平衡过程     

Solubilities,Densities,Refractive Indices of Aqueous Ternary Systems PEG400-NaCl/KCl-H2O at 298 K

Phase equilibria for the NaCl/KCl-PEG400-H_2 O aqueous ternary systems at 298 K were studied using an isothermal dissolution method. In addition,the densities and refractive indices were determined. The corresponding phase diagrams,as well as the density vs. composition and refractive index vs.composition diagrams,were plotted. Results revealed that over the entire PEG400 composition range studied at 298 K only 1 liquid phase was obtained,without the formation of a biphase region. The phase diagrams of these 2 systems consist of 1 homogeneous area with unsaturated liquid( L) and an equilibrium area containing the solid phase of NaCl/KCl and the saturated liquid phase( S + L). The solubility of NaCl/KCl decreases with the addition of PEG400 at 298 K.     

273.15K下LiCl-Li2B4O7-H2O体系热力学性质的等压研究

用等压法研究了273 15K下LiCl-Li2B4O7-H2O体系中纯盐水溶液(离子强度范围为LiCl0 2046～2 5055mol·kg-1,Li2B4O70 1295～0 3700mol·kg-1)以及混合盐水溶液(离子强度范围为0 0931～2 4911mol·kg-1)渗透系数和水活度;计算了LiCl-Li2B4O7-H2O体系的饱和蒸汽压,获得饱和蒸汽压、渗透系数随离子强度的变化规律。用实验数据以最小二乘法求取了LiCl和Li2B4O7纯盐参数及体系的混合盐参数,拟合的标准偏差分别为0 0077和0 026。用该模型计算的渗透系数值与实验结果取得合理的一致。同时研究结果与273 15K下LiCl-Li2SO4-H2O体系的渗透系数随离子强度变化的规律作了比较。本研究对完善低温下含锂、硼盐湖卤水体系的热力学模型和盐湖资源的综合开发利用具有重要意义。     

K2B4O7和KBO2溶液pH和拉曼光谱研究

用合成的水合四硼酸钾和偏硼酸钾晶体,配制一系列溶液,研究了pH与浓度变化的关系,并计算硼酸根离子的摩尔分数-浓度(δ-c)关系图。用拉曼光谱方法研究四硼酸钾和偏硼酸钾溶液,给出其拉曼光谱图,并对各峰进行了归属。研究表明,四硼酸钾溶液中存在的物种主要有[B4O5(OH)4]2-、[B3O3(OH)4]-和[B(OH)4]-,而其它物种所占摩尔分数很小;在偏硼酸钾水溶液中,[B(OH)4]-占绝大多数,有很少量H3BO3、[B4O5(OH)4]2-和[B3O3(OH)4]3-。硼酸盐离子浓度越低,越容易水解为聚合度较低的简单物种。