The Applicability of Debye-Hückel Model in NaAl(OH)4-NaOH-H2O System

Focusing on the most important NaAl(OH)4-NaOH-H2O system in the industry of alumina production, the feasibility of establishing a calculation model of activity coefficients according to Debye-Hückel theory via the equilibrium solubility data of sodium aluminate solution is discussed in this paper. Firstly, the hypotheses for applying Debye-Hückel theory into NaAl(OH)4-NaOH-H2O system are involved and the values of parameters are determined. Then the applicability of Debye-Hückel model in NaAl(OH)4-NaOH-H2O system is testified. The results indicate that Debye-Hückel model is applicable to the establishment of calculation model of activity coefficients in NaAl(OH)4-NaOH-H2O system and the value of ?NaAl(OH)4 is estimated as 0.3595 nm.     

The Applicability of Debye-Hückel Model in NaAl(OH)_4-NaOH-H_2O System

1 INTRODUCTION NaAl(OH)4-NaOH-H2O system plays a paramount role in the industry of alumina production, and the calculation of its activity coefficients can not only aid to perfect the theory of alumina production, but also accelerate the research and the development of new technology for reducing the production cost and energy consumption. However, the solution in alumina industry has high concentration with extremely complex structure, and the properties of the solution are easily affe…     

R2SO4-NaOH-H2O体系静力学的研究

本文分析了考察了ＮａＯＨ－Ｎａ２ＳＯ４－Ｈ２Ｏ体系的相律平衡和Ｒ２ＳＯ４－ＮａＯＨ－Ｈ２Ｏ体系的交换平衡的相互影响及再生碱液加工再用效果。     

Na2CrO4-NaOH-H2O体系中Na2CrO4 蒸发结晶工艺研究

以90 ℃的Na2CrO4-NaOH-H2O体系相图为依据,采用蒸发盐析结晶的方法从体系中分离铬酸钠晶体,研究了搅拌强度、蒸发速度、结晶温度、晶种添加等因素对工艺过程的影响规律,得到最优工艺操作条件：搅拌强度为能使晶体离底悬浮所需的最小转速;每1 050 g原料的蒸发速率约为140 mL/h;结晶温度为90 ℃;并添加一定量的晶种。在以上操作条件下制备出的铬酸钠晶体粒度较大,尺寸均一。同时研究了不同氢氧化钠浓度下体系压力与沸点间的关系,为铬酸钠结晶过程的温度控制提供了基础数据。     

CaSO_4-Ca(OH)_2-H_2O体系中硫酸根的平衡浓度

测定了25℃时不同pH值下CaSO4-Ca(OH)2-H2O三元体系中SO42-的平衡浓度,考察了Na+离子的影响. 结果表明,pH值在3.0~12.0范围内SO42-平衡浓度最小,为0.01235 mol/L,基本不受pH值的影响;Na+的存在使溶液中SO42-的平衡浓度增大,且二者呈线性关系. 应用Pitzer电解质溶液理论对体系进行了活度修正,计算结果与实验测定结果基本一致. 研究结果为含SO42-工业废水处理提供了一定的理论依据.     

(NH_4)_2SO_4-H_2O体系中CaSO_4·2H_2O溶解度模型

在25℃恒温水浴中,采用EDTA滴定、ICP-AES检测二水硫酸钙在0~2.50 mol/kg硫酸铵溶液中的溶解度,结果显示在同离子效应和盐效应影响下,二水硫酸钙的溶解度随硫酸铵浓度增加先降低后增大,突变点的硫酸铵质量摩尔浓度为0.07 mol/kg;建立二水硫酸钙在(NH_4)_2SO_4-H_2O体系中的溶解度模型,并利用建立的溶解度模型拟合实验数据,拟合效果较好,且平均相对误差为4.50%。研究结果为CO_2矿化磷石膏反应器的优化设计提供了基础数据和理论依据。     

煤矸石-Ca(OH)2-H2O体系反应动力学初探

通过测定不同龄期煤矸石地酸溶出量,对不同温度热激活下的煤矸石在煤矸石-Ca(OH)2-H2O体系中的反应速率进行了研究,并在此基础上建立了煤矸石火山灰反应动力学模型.该模型表明:煤矸石的反应速率(v)主要取决于煤矸石的火山灰活性(v),值大则煤矸石的火山灰活性高,反应速率常数k值大则煤矸石的火山灰反应活性高,最后采用Ca(OH)2的吸收实验来验证本模型的正确性.     

A tetranuclear oxomolybdenum(V) complex with bridging squarate ligands, [MoV4O8(OH)2(H2O)2(C4O4)2]2−

The new tetranuclear polyoxomolybdate(V) ion [Mo^V₄O₈(OH)₂(H₂O)₂(C₄O₄)₂]²⁻ has been obtained in one step by the reaction of sodium molybdate, hydrazine and squaric acid in water and crystallized as a potassium salt. The structure has been solved by single-crystal X-ray diffraction showing the location of the hydroxo and water molecule ligands.     

H_2SO_4-Ca(OH)_2-H_2O体系中用脱硫石膏制备石膏晶须

在常压条件下,以脱硫石膏为原料,在H_2SO_4-Ca(OH)_2-H_2O体系中制备石膏晶须,考察了结晶过程的影响因素,表征了石膏相的组成和形貌.结果表明,脱硫石膏中有色杂质大幅度被脱除,白度由45.78%升至94.01%.在Ca(OH)_2用量0.037mol/L、H_2SO_4用量0.92 mol/L、反应温度130℃的条件下,所制样品为半水石膏晶须,长度为100~600μm,直径为3~6μm,收率为74.02%.添加微量盐酸后,生成的晶须平均长度提高1.67倍,且表面更光滑;母液反复循环3次后,产品的形貌和晶型与初次所得半水石膏晶须产品无明显差异.     

(NH_4)_2SO_4-H_2O体系中CaSO_4·2H_2O溶解度的突变现象

在25℃、搅拌转速180 r/min的条件下,通过实验和理论研究硫酸铵浓度(≤2.50 mol/L)对二水硫酸钙溶解度的影响。结果表明:在同离子效应与盐效应的协同作用下,硫酸铵浓度为0.07 mol/L时,二水硫酸钙的溶解度发生突变。当硫酸铵浓度小于0.07 mol/L时,二水硫酸钙的溶解度随着硫酸铵浓度的增加而减小;而当硫酸铵浓度在0.07~2.50 mol/L时,二水硫酸钙溶解度随着硫酸铵浓度的增加而增加。基于活度积公式和德拜休克尔公式,建立方程预测硫酸铵浓度对二水硫酸钙溶解度的影响,该方程计算值与实验值有很高的吻合度。研究结果为优化磷石膏矿化反应器提供了理论依据。     

分子动力学模拟水化硅酸钙Ca4Si6O14(OH)4·2H2O的结构

为了在原子水平上再现硅酸盐水泥的主要水化产物水化硅酸钙的结构,以Hamid模型为基础建立初始结构,采用分子动力学方法这一物质结构研究的新手段,模拟低钙比的Ⅰ型水化硅酸钙[Ca4Si6O14(OH)4·2H2O,C-S-H(Ⅰ)]的结构;根据模拟结果,比较分析水合硅酸钙晶体与无定形水化硅酸钙在结构上的异同,并且通过与实验数据的比较验证模拟结果的可靠性。模拟结果表明:水合硅酸钙晶体的结构长、短程确实都有序,而其无定形态的C-S-H(Ⅰ)只存在近程有序的结构特点,因为后者中Ca—O、Si—O、O—O及Si—Si等原子对的径向分布函数随着原子间距的增大而逐渐趋于1;C-S-H(Ⅰ)的基本结构单元为硅氧四面体,并且Si的最近邻Si数目为2,即硅氧四面体以Q2的形式连接而呈链状;模拟得到的Si与O、Ca与O的间距分别为0.162nm和0.264nm,Si的O配位数为4,这些结构参数基本与实验值相符合,说明模拟结果能够再现C-S-H(Ⅰ)的结构。     

High-pressure behavior and phase stability of Na2B4O6(OH)2·3H2O (kernite)

The high-pressure behavior of kernite [ideally Na₂B₄O₆(OH)₂·3H₂O, a ~ 7.02 Å, b ~ 9.16 Å, c ~ 15.68 Å, β = 108.9°, Sp Gr P2₁/c, at ambient conditions], an important B-bearing raw material (with B₂O₃ ≈ 51 wt%) and a potential B-rich aggregate in radiation shielding materials, has been studied by single-crystal synchrotron X-ray diffraction up to 14.6 GPa. Kernite undergoes an iso-symmetric phase transition at 1.6-2.0 GPa (to kernite-II). Between 6.6-7.5 GPa, kernite undergoes a second phase transition, possibly iso-symmetric in character (to kernite-III). The crystal structure of kernite-II was solved and refined. The isothermal bulk modulus (K_V0 = β^-1_P0,T0, where β_P0,T0 is the volume compressibility coefficient) of the ambient-pressure polymorph of kernite was found to be K_V0 = 29(1) GPa and a marked anisotropic compressional pattern, with K(a)₀: K(b)₀: K(c)₀~1:3:1.5., was observed. In kernite-II, the K_V0 increases to 43.3(9) GPa and the anisotropic compressional pattern increases pronouncedly. The mechanisms, at the atomic scale, which govern the structure deformation, have been described.     

Production of sodium metaborate tetrahydrate (NaB(OH)4·2H2O) using ultrasonic irradiation

Sodium metaborate, a derivative of the borax compound, has a wide range of industrial applications. Recently, it is used as a source of boron in the production of sodium borohydride (NaBH₄), which is a medium for hydrogen storage. In the present study, sodium metaborate tetrahydrate (SMT, NaB(OH)₄·2H₂O) was produced by the reaction of borax (B) with the sodium hydroxide (SH) solution under ultrasonic irradiation. The effect of the reaction parameters (amount of water, temperature, particle size, and time) on the production of sodium metaborate tetrahydrate was investigated in the present study. It was shown that the reaction parameters (amount of water, temperature, and time) played a significant role in the synthesis of sodium metaborate tetrahydrate. In addition, the concentration of characteristic B–O group in the reaction solution was quantitatively determined by Fourier Transform Infrared Spectroscopy (FTIR). The optimum condition for the production process included 26% water by weight, borax particles of size ?250+150 μm and irradiation time of 60 min at 80 °C.     

Al3(SO4)2(OH)5H2O与α-Al2O3晶须的制备及其生长机制

采用液相沉淀及烧结方法制备了Al3(SO4)2(OH)5H2O与α-Al2O3晶须,样品采用XRD、SEM及G-DTA等对样品物相、形貌及热行为进行了表征,结果表明晶须样品的分散性好,粒度分布均匀、表面光滑,Al3(SO4)2(OH)5H2O与α-Al2O3晶须品质优良.又从“生长基元”角度出发,讨论了Al3(SO4)2(OH)5H2O晶须的形成机制,其生长过程是生长基元是八面体[Al-(OH)6]3-与HSO4-往某一晶面稳定叠合生长的结果,Al3(SO4)2(OH)5H2O晶须经热分解后,其形貌不变,最终变为α-Al2O3晶须.     

298 K 时(NH4)2S2O3-(NH4)2SO4-H2O三元体系相平衡研究

通过改良合成复体法对(NH4)2S2O3-(NH4)2SO4-H2O三元体系在298 K下的溶液相平衡进行研究。利用X-射线粉末衍射法(XRD)表征平衡固相组成。结果证实:该方法能很好地用于(NH4)2S2O3-(NH4)2SO4-H2O三元体系平衡固相组成的分析。依据水、硫酸铵及硫代硫酸铵组成的饱和溶液各组分的质量分数绘制了(NH4)2S2O3-(NH4)2SO4-H2O在298 K下的三元体系相图。依据三元体系相图,结果显示:硫代硫酸铵的结晶区远远大于硫酸铵的结晶区,同时在该温度下,硫代硫酸铵、硫酸铵及水形成简单三元体系,体系中没有水合物形成。     

333.15K K~+,NH_4~+//Cl~-,SO_4~(2-)-H_2O和K~+,NH_4~+//Cl~-,SO_4~(2-)-(CH_2OH)_2-H_2O体系固液相平衡

采用等温溶解法研究333.15 K体系(K~+,NH_4~+//Cl~-,SO_4~(2-)-H_2O)和(K~+,NH_4~+//Cl~-,SO_4~(2-)-(CH_2OH)_2-H_2O)[w((CH_2OH)_2)=30%]的固液相平衡关系。测定了平衡溶液的溶解度数据及物化性质,包括密度、黏度、折射率、pH。根据实验数据,绘制了相应的干盐相图、水图及物化性质-组成图。实验中的物化性质(黏度、密度、折射率、pH)随J(2NH_4+)的变化呈现相似性规律。实验结果表明:在333.15 K下,体系(K~+,NH_4~+//Cl~-,SO_4~(2-)-H_2O)和(K~+,NH_4~+//Cl~-,SO_4~(2-)-(CH_2OH)_2-H_2O)[w((CH_2OH)_2)=30%]的相图相似,均含有一个四元共饱和点,四条单变曲线及四个固相结晶区域。这两个体系均为复杂体系,存在(K,NH_4)Cl、(NH_4,K)Cl、(K,NH_4)_2SO_4、(NH_4,K)_2SO_4四种固溶体。实验所获数据和结论,可优化以硫酸盐型固体废弃物为硫酸根来源,转化法生产硫酸钾工艺。     

Fe2(SO4)3-ZnSO4-H2O体系中Fe3+水热水解赤铁矿

研究了Fe2(SO4)3?ZnSO4?H2O体系中Fe3+水热水解赤铁矿过程中反应温度、时间、初始Fe3+浓度、Zn2+浓度、晶种用量等对除铁率、赤铁矿沉铁渣物相组成及化学组成的影响规律. 结果表明,升高反应温度、延长反应时间、降低初始Fe3+浓度、增加Zn2+浓度有利于提高除铁率和赤铁矿渣的品质,添加晶种有助于赤铁矿形核并提高赤铁矿纯度. 在反应温度200℃、反应时间4 h、初始Fe3+浓度15 g/L及Zn2+浓度80 g/L、搅拌转速400 r/min的条件下,除铁率可达97.1%,获得了以赤铁矿为主要物相的沉铁渣,其含铁64.73%,含杂质硫1.41%,锌入渣率约为0.2%.     

Crystallization of aluminium hydroxide from the reactive NaAl(OH)4–NaHCO3 solution: Experiment and modeling

The crystallization kinetics of aluminium hydroxide from the sodium aluminate solution reacted with sodium bicarbonate were systematically investigated in a steady-state MSMPR (mixed-suspension mixed-product removal) crystallizer for the first time, and the expressions of the nucleation rate, growth rate and the agglomeration kernel of aluminium hydroxide were successfully regressed. The aluminium hydroxide particles precipitated from the reactive system are identified as gibbsite by XRD and SEM examinations. The volume growth rate order of gibbsite with respect to the relative supersaturation of the solution is above the linear growth rate order, and the spiral growth mechanism for the growth of the basal face of gibbsite in the reactive system was further identified by the growth rate, morphology analysis as well as the calculated surface entropy factor. The secondary nucleation rate of gibbsite from the reactive system is three to four orders of magnitude larger than that from seeded process reported in the only available literature reference. The agglomeration kernel of gibbsite in the reactive system increases linearly with growth rate and residence time, and the positive order about 0.55 of magma density is thoroughly different from the negative order of magma density for gibbsite agglomeration in seeded process presented in the literature.     

(NH4)2C2O4·H2O和NH4HC2O4·0.5H2O 单晶的培养研究

利用六次甲基四胺缓慢水解产生的NH3和草酸反应,扩散法培养出(NH4)2C2O4·H2O和NH4HC2O4·0.5H2O两种单晶.