Simulation studies on metastable phase equilibria in the aqueous ternary systems (NaCl-MgCl2-H2O) and (KCl-MgCl2-H2O) at 308.15 K

The solubilities and densities of the aqueous metastable ternary systems (NaCl-MgCl₂-H₂O) and (KCl-MgCl₂-H₂O) at 308.15 K were determined by the isothermal evaporation method. On the basis of the experimental results, the phase diagrams for those systems were plotted. It was found that the former system belongs to the hydrate-I type with one invariant point of (NaCl + MgCl₂·6H₂O), two univariant curves, and two crystallization regions corresponding to halite (NaCl) and bischo.te (MgCl₂6H₂O); and the latter system belongs to the type of incongruent-double salts with two invariant points of (KCl + KCl·MgCl₂6H₂O) and (MgCl₂·6H₂O + KCl·MgCl₂·6H₂O), three univariant curves, and three crystallization regions corresponding to potassium chloride (KCl), carnallite (KCl·MgCl₂·6H₂O) and bischofite (MgCl₂·6H₂O). No solid solutions were found in both systems.     

Solubility measurement and prediction of phase equilibria in the quaternary system LiCl + NaCl + KCl + H_2O and ternary subsystem LiCl+ NaCl + H_2O at 288.15 K

Using isothermal dissolution method, the phase equilibrium relationship in quaternary system LiCl + NaCl + KCl+ H_2O and the ternary subsystem LiCl + NaCl + H_2O at 288.15 K were investigated. Each phase diagram of two systems was drawn. The phase diagram of LiCl + NaCl + H_2O system contains two solid phase regions of crystallization LiCl·2H_2O and NaCl. In the phase diagram of LiCl + NaCl + KCl + H_2O system, there are three crystallization regions: LiCl·2H_2O, NaCl and KCl respectively. In this paper, the solubilities of phase equilibria in two systems were calculated by Pitzer's model at 288.15 K. The predicted phase diagrams generally agree with the experimental phase diagrams.     

Solubility measurement and prediction of phase equilibria in the quaternary system LiCl + NaCl + KCl + H2O and ternary subsystem LiCl + NaCl + H2O at 288.15 K

Using isothermal dissolution method, the phase equilibrium relationship in quaternary system LiCl + NaCl + KCl + H₂O and the ternary subsystem LiCl + NaCl + H₂O at 288.15 K were investigated. Each phase diagram of two systems was drawn. The phase diagram of LiCl + NaCl + H₂O system contains two solid phase regions of crystallization LiCl·2H₂O and NaCl. In the phase diagram of LiCl + NaCl + KCl + H₂O system, there are three crystallization regions: LiCl·2H₂O, NaCl and KCl respectively. In this paper, the solubilities of phase equilibria in two systems were calculated by Pitzer's model at 288.15 K. The predicted phase diagrams generally agree with the experimental phase diagrams.     

四元体系Li+,K+//CO32-,B4O72- -H2O 273 K介稳相平衡研究

针对西藏扎布耶盐湖卤水组成,用等温蒸发平衡法研究了四元体系Li+,K+//CO23-,B4O27--H2O 273 K的相平衡,测定了平衡时各组分的溶解度及平衡液相的密度。四元体系Li+,K+//CO32-,B4O72--H2O273 K时的相图由5条溶解度单变量线、4个结晶区及2个共饱点组成。4个结晶区分别为对应于盐Li2CO3,K2CO3.1.5H2O,K2B4O7.4H2O及Li2B2O4.16H2O。2个共饱点中,一个为Li2CO3,K2CO3.1.5H2O及K2B4O7.4H2O三盐相称共饱点,另一个为Li2CO3,K2B4O7.4H2O和Li2B2O4.16H2O的三盐不相称共饱点。体系属四元水合物相图Ⅰ型,4种原始组分间未形成复盐或固溶体。对于该四元体系273 K和288 K下的介稳相图发现,碳酸锂盐的溶解度呈现较明显的负温度效应,它在273 K下的结晶相区比在288 K下的要小,且析出固相为偏硼酸锂;而碳酸钾、硼酸钾及硼酸锂结晶区则比288 K下的大。     

四元交互体系Li+,K+//Cl-,B4O72--H2O 323 K相关系研究

采用等温溶解平衡法研究了四元交互体系L i+,K+//C l-,B4O72--H2O 323 K时的相关系。该四元交互体系323 K下的溶解度等温图含有4个盐类结晶相区、5条单变量线和2个无变量点。4个结晶相区分别对应于盐L i C.lH2O、KC、lL i2B4O7.3H2O和K2B4O7.4H2O的结晶区。2个无变量点标注为E和F。E点平衡固相为L iC l.H2O+KC l+L i2B4O7.3H2O,对应的平衡液相组成为w(L i+)6.55%,w(K+)2.16%,w(C l-)34.57%,w(B4O72-)1.89%;F点平衡固相为KC l+L i2B4O7.3H2O+K2B4O7.4H2O,对应的平衡液组成为w(L i+)2.35%,w(K+)2.37%,w(C l-)12.08%,w(B4O72-)4.56%。研究结果表明,该四元交互体系为简单共饱和型,体系中没有复盐和固溶体的形成。     

Modification of poly(vinyl alcohol) films by the addition of magnesium chloride hexahydrate

Poly(vinyl alcohol) (PVA) films modified with Magnesium chloride hexahydrate (MgCl₂·6H₂O) were prepared by casting method. The prepared films were characterized by X‐ray diffraction measurements (XRD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and mechanical testing. It was found that the presence of MgCl₂·6H₂O had considerable effects on the crystallinity, thermal, and mechanical properties of PVA films. The crystallization of PVA film was interrupted and the degree of crystallinity of PVA film decreased with the addition of MgCl₂·6H₂O. The glass transition temperature of PVA film decreased with the addition of MgCl₂·6H₂O. After modifying with MgCl₂·6H₂O, PVA film became soft, with lower tensile strength and higher elongation at break. The presence of MgCl₂·6H₂O could significantly increase the moisture content of PVA films and this may be the cause of the plasticizing. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Carnallite decomposition into magnesia,hydrochloric acid and potassium chloride: A thermal analysis study; formation of pure periclase

A thermal analysis study of the one-stage decomposition of small (mg) quantities of carnallite, KCl. MgCl₂, 6H₂O → KCl + MgO + 5H₂O ↑ + 2HCl ↓, showed that dehydration and hydrolysis require temperatures above 300 °C. Decomposition of greater amounts, and analysis of the products, showed that at 450 °C, 88 to 90% of the magnesium occurs as chloride-free high-purity periclase. At higher temperatures increasing amounts of chlorides remain in the periclase and are difficult to separate. Unglazed porcelain is a suitable material for the decomposition vessel.     

Modeling solid–liquid equilibrium of NH4Cl‐MgCl2‐H2O system and its application to recovery of NH4Cl in MgO production

A new method to recover NH₄Cl from NH₄Cl‐rich aqueous solutions generated in the magnesia (MgO) production is developed on the basis of modeling the solid–liquid equilibrium (SLE) for the NH₄Cl‐MgCl₂‐H₂O system with the Pitzer model embedded in Aspen Plus? platform. The SLE values for the ternary system were determined from 278.15 to 348.15 K. The new standard‐state chemical potentials of NH₄Cl and MgCl₂·6H₂O were judicially obtained. The resulting equilibrium constants were used to determine new interaction parameters for the NH₄Cl‐H₂O and MgCl₂‐H₂O systems. These new parameters, together with the mixing parameters determined from correlating the experimental values, were used to correlate the equilibrium constant for NH₄MgCl₃·6H₂O, which plays a key role in NH₄Cl recovery. The results could extend SLE calculation for the NH₄Cl‐MgCl₂‐H₂O system from 278.15 to 388.15 K, satisfying the process identification and simulation requirement involved in the recovery process. The phase‐equilibrium diagram generated by modeling was illustrated to identify the process alternatives for recovering NH₄Cl. The resulting course to recover NH₄Cl by three fractional crystallization operations was finally proved feasible. © 2010 American Institute of Chemical Engineers AIChE J, 2011.     

察尔汗盐湖盐田工艺相图分析及计算

以察尔汗盐湖卤水滩晒含钠光卤石的盐田工艺为研究对象,以Na+、K+、Mg2+∥Cl-—H2O四元水盐体系相图理论为依据,对察尔汗盐田工艺分别做了25 ℃等温相图和多温相图分析。结果表明：察尔汗盐湖卤水在15~ 25 ℃时的结晶路线为NaCl→NaCl+Car→NaCl+Car+Bis,-5~15 ℃时的结晶路线为NaCl→NaCl+KCl→NaCl+Car→ NaCl+Car+Bis。物料衡算结果表明：分段蒸发使原矿的钠质量分数由37.046%降至12.353%,钾质量分数由16.899%提升至23.525%,分段蒸发可有效降低光卤石矿中杂质氯化钠的含量,提高含钠光卤石的品位,KCl收率高达97.90%。该研究可为盐田生产和工艺计算提供理论指导。     

海盐苦卤提制光卤石的研究

本文对从一般盐田苦卤（30°Be,MgCl_2/KCl8,MgSO_4/MgCl_20.4）提制光卤石的过程进行了相图分析与实驗测定。 为了避免蒸发过程中在光卤石饱和以前钾盐的析出,苦卤必须掺兌光卤石母液,使混合卤的MgCl_2/KCl比值在10以上（同时MgSO_4/MgCl_2比值在0.4以下）。但兌卤过多则在工业生产上既不经济又无必要。 本文提出了澄清液中光卤石饱和点的相图计算方法,并进行了实驗测定,为保温分离条件提供了依据。 为了制得质量稳定、产量最大的光卤石,必须使原料卤组成、蒸发终止沸点、保温分离温度和冷却温度互相适应。 对冷却析取光卤石过程的固、液相组成进行了相图分析,实驗结果与理论分析是符合的。提出了冷却过程光卤石析出量的计算方法,得出了兌卤法生产氯化钾的理论最大提取率及生产上提高提取率的途径。 最后,进行了工业性现场扩大试驗,结果证明上述分析是正确的。在工厂中从苦卤提取氯化钾总提取率可达87.13％。     

低品位含钾卤水蒸发结晶制备光卤石工艺研究

随着氯化钾生产规模的扩大,高品位含钾卤水资源过量消耗,而低品位含钾卤水采用传统的溶采-盐田晒制光卤石工艺因成矿周期长、成本高、操作复杂使盐湖企业难以为继。以低品位盐湖卤水为研究对象,以相图为指导,通过真空蒸发控速结晶工艺制备光卤石,研究快速结晶成矿技术。实验结果表明,采用蒸发结晶工艺可以制得氯化钾质量分数为13.82%~14.90%的光卤石产品,成矿周期较原工艺加快近1倍。实验考察了镁钾比例、蒸发水量等因素对光卤石产量和品位的影响,结果证实运用真空蒸发控速结晶技术制备光卤石是可行的。     

西台吉乃尔盐湖析钾老卤及冻卤25 ℃等温蒸发实验研究

为了有效利用西台吉乃尔盐湖析钾后老卤及冻卤中的锂、硼等元素,对西台吉乃尔盐湖析钾后老卤和冻卤展开了25 ℃等温蒸发实验,采用化学分析、X射线粉晶衍射等方法对析出固体矿物的含量及物相进行了分析,并依据Li⁺,Mg²⁺∥Cl^-,SO₄^2-—H₂O四元体系25 ℃介稳相图对盐类析盐路线进行了理论分析。结果表明,析钾老卤蒸发过程主要析出钠石盐、光卤石、水氯镁石、四水泻盐和一水硫酸锂,其中Li⁺富集到5.4 g/L左右时开始析出锂盐,而硼富集到46.73 g/L时仍无明显析出;冷冻后老卤蒸发过程中可获得较高品质的水氯镁石,冷冻脱硫后可以提高Li⁺的富集浓度,但最终仍有一水硫酸锂析出。该老卤25 ℃的蒸发析盐规律与Li⁺,Mg²⁺∥Cl^-,SO₄^2-—H₂O四元体系25 ℃介稳相图基本一致。     

Study of the Crystallization and Melting Behavior of a Latent Heat Storage by Computed Tomography

Thermal energy storage based on phase changes is a promising technology. However, heat transfer can often be problematic. A latent heat storage based on the single tube design is analyzed in a computer tomograph. The different densities of the solid and liquid phase change material (PCM) MgCl₂·6H₂O enable a clear identification of the phases in the computer tomographic images. No supercooling or phase segregation of water from the PCM was observed during melting or crystallization. The volume change, though often neglected, seems to be the biggest issue of the design of latent heat storage systems.     

Easy-care properties of simultaneously grafted and crosslinked cotton fabrics

The Concurrent grafting of acrylic acid (AA) and crosslinking of dimethylodihydroxyethyleneurea (DMDHEU) with cotton fabric in the presence of ammonium persulfate [(NH₄)₂S₂O₈)], magnesium chloride hexahydrate (MgCl₂ · 6H₂O), and ammonium chloride (NH₄Cl) catalysts were studied. These salts were separately used or as a binary mixture of (NH₄)₂S₂O₈/MgCl₂ · 6H₂O or (NH₄)₂S₂O₈/NH₄Cl. The pad–dry–cure method was employed for the fabric treatment under a variety of conditions. The latter include the nature and kind of the single catalyst as well as pair-mixed catalysts, the concentrations of the catalyst and AA, and temperature and duration of curing. The effects of these conditions on the values of the carboxyl content and crease recovery angle (CRA) of the treated fabrics were evaluted. The tensile strength, elongation at break, dyeability, aqueous and nonaqueous oily soiling, and soil-release properties of the treated fabrics were also examined. Results obtained indicated that all treated fabrics have superior properties, except tensile strength and elongation at break, as compared with the untreated fabric (control). However, beside the AA-grafting and DMDHEU-crosslinking reactions, there are other types of reactions catalyzed by the salts used, viz., the addition reactions between AA molecules and the cellulosic hydroxyls The tentative mechanisms for these reactions are suggested. © 1996 John Wiley & Sons, Inc.     

A practical approach to produce Mg‐Al spinel based on the modeling of phase equilibria for NH4Cl‐MgCl2‐AlCl3‐H2O system

Based on chemical modeling of phase equilibria for the NH₄Cl‐MgCl₂‐AlCl₃‐H₂O system, a practical approach to produce Mg‐Al spinel (MgAl₂O₄) (widely used as refractory brick, supports in catalysts, and inert material for oxygen carriers) is proposed and proven feasible. This novel process includes coprecipitation of Mg₄Al₂(OH)₁₄·3H₂O from the NH₃‐MgCl₂‐AlCl₃‐H₂O system; calcination of Mg₄Al₂(OH)₁₄·3H₂O to obtain Mg‐Al spinel and recovery of NH₄Cl from NH₄Cl‐rich solutions by feeding MgCl₂‐AlCl₃. A MSMPR reactor was applied to investigate the effect of temperature, feed concentration, and NH₄Cl addition on coprecipitation of precursor Mg₄Al₂(OH)₁₄·3H₂O from MgCl₂‐AlCl₃ solutions with Mg/Al ratio = 2 through gradual addition of NH₄OH. The phase equilibria of the NH₄Cl‐MgCl₂‐AlCl₃‐H₂O system were determined over the temperature range 283.2 to 363.2 K using dynamic method. The experimental solubilities were regressed to obtain new Bromley‐Zemaitis model parameters. These newly obtained parameters were verified by predicting the quaternary system. A chemical model for the NH₄Cl‐MgCl₂‐AlCl₃‐H₂O system has been established with the OLI platform. All the results generated from this study will provide the theoretical basis for Mg‐Al spinel production. The high quality Mg‐Al spinel was prepared by calcination of precursor from 773.2 to 1273.2 K, and the NH₄Cl was successfully recovered through the common ion effect of MgCl₂‐AlCl₃ addition. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1855–1867, 2013     

Melt processing of poly(vinyl alcohol) through adding magnesium chloride hexahydrate and ethylene glycol as a complex plasticizer

The melt processing of poly(vinyl alcohol) (PVA) was achieved using magnesium chloride hexahydrate (MgCl₂·6H₂O) and ethylene glycol as a complex plasticizer. The interaction between the complex plasticizer and PVA was studied by Fourier transform infrared spectroscopy (FT‐IR). The PVA films were characterized using X‐ray diffraction (XRD), differential scanning calorimetry, thermogravimetric analysis (TGA), scanning electron microscope, and dynamic thermomechanical analysis (DMA) techniques. The band shift of the observed peak around 3335 cm^?1 in the FT‐IR spectra indicates that the complex plasticizer MgCl₂·6H₂O and ethylene glycol could form strong interactions with PVA and thus interrupt the intermolecular and intramolecular hydrogen bonding in PVA. The XRD results show that the addition of the complex plasticizer would significantly destroy the crystallites of PVA and result to the decrease of the degree of crystallinity of PVA. The melting point was reduced from 229°C of pure PVA to around 170°C after the plasticization. The TGA studies show that with the complex plasticizer, the thermal stability of PVA is improved. PVA plasticized by 30 wt% MgCl₂·6H₂O and 10 wt% ethylene glycol shows the tensile strength of 33 MPa and the elongation at break of 362%. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Na~+,K~+//Br~-,B_4O_7~(2-)-H_2O交互四元体系348K相平衡研究

采用等温溶解平衡法研究了348 K时交互四元体系Na+,K+//Br-,B4O27--H2O的相平衡及平衡液相,测定了平衡液相的溶解度以及密度,补充了该体系在348 K下的溶解度和密度数据。研究结果发现,该体系属于简单共饱和体系,无复盐和固溶体生成。根据实验数据绘制了相应的相图、密度-质量分数图和含水量图,相图中有2个共饱点,5条单变量曲线,4个结晶区。4个结晶区的平衡固相分别为:Na2B4O7.5H2O,K2B4O7.4H2O,KBr和NaBr。从相图上可以看出,该体系在348 K时Na2B4O7.5H2O的结晶区最大,NaBr的结晶区最小。     

15℃时K~+、Na~+、Mg~(2+)//Cl~-、SO_4~(2-)-H_2O五元体系介稳相平衡研究

模拟青海察尔汉盐湖的自然气候条件,测定了K~(+)、Na~(+)、Mg~(2+)//Cl~-、SO_4~(2-)-H_2O五元体系在温度15±0.1℃、风速3.5～4.0m/s、空气相对湿度35%～40%以及蒸发速率2～4mm/d条件下的介稳相平衡数据,绘出了该五元体系的介稳相图.利用HW公式计算了该五元体系在15℃时的介稳相平衡数据,计算值同实验值吻合较好.     

高镁溶液对光卤石分解影响的初步研究

光卤石分解过程中,氯化钠在最初低镁的溶液中溶解很快,但随着分解过程的进行,由于氯化镁的溶解速率很快,从而使分解液中氯化钠的饱和度减小,最终使先前溶解的氯化钠又重新结晶析出,这对氯化钾从溶液中结晶析出产生影响。针对这个问题,通过相图计算和分析,加入不同浓度的氯化镁溶液,研究高镁溶液对光卤石分解的影响。结果表明：高镁溶液的加入使钾收率提高近1.1%,分解完后细粒氯化钠的质量分数降低近30%,光卤石分解转化收率提高约1.2%。     

Influence of molar ratios on properties of magnesium oxychloride cement

A parametric study has been conducted to investigate the influences of the molar ratios of MgO/MgCl₂ and H₂O/MgCl₂ on the properties of magnesium oxychloride (MOC) cement. By an integrated assessment of the experimental studies of strength development and X-ray diffractograms, together with application of the relevant phase diagram, it is recognized that the molar ratios of MgO/MgCl₂ and H₂O/MgCl₂ can significantly affect the properties of MOC cement. For a MOC cement paste possessing a dominance of 5MgO·MgCl₂·8H₂O (phase 5) crystals, the molar ratios of MgO/MgCl₂ of 11-17 and H₂O/MgCl₂ of 12-18 are found to be the most favorite ranges for design purpose. The choose of the molar ratio of H₂O/MgCl₂ is, however, largely depends on the molar ratio of MgO/MgCl₂ mainly for controlling workability of paste. Therefore, the most critical parameter to be selected in the design process is the molar ratio of MgO/MgCl₂, although the reactivity of the MgO powder is also important. Besides, the molar ratio can also be affected by the reactivity of the MgO powder to be employed. It is believed that a molar ratio of MgO/MgCl₂ of 13, the most suitable one shown in this study, can be used as a starting point in the normal practice.