Preparation and crystallization kinetics of micron-sized Mg(OH)2 in a mixed suspension mixed product removal crystallizer

Magnesium hydroxide is an important chemical, and is usually obtained from seawater or brine via precipitation process. The particle size distribution of magnesium hydroxide has great effects on the subsequent filtration and drying processes. In this paper, micron-sized magnesium hydroxide with high purity, large particle size and low water content in filter cake was synthesized via simple wet precipitation in a mixed suspension mixed product removal (MSMPR) crystallizer. The effects of reactant concentration, residence time and impurities on the properties of magnesium hydroxide were investigated by X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Malvern laser particle size analyzer. The results show that NaOH concentration and residence time have great effects on the water content and particle size of Mg(OH)₂. The spherical Mg(OH)₂ with uniform diameter of about 30 μm was obtained with purity higher than 99% and water content less than 31%. Furthermore, the crystallization kinetics based on the population balance theory was studied to provide the theoretical data for industrial enlargement, and the simulation coefficients (R²) based on ASL model and C-R model are 0.9962 and 0.9972, respectively, indicating that the crystal growth rate of magnesium hydroxide can be well simulated by the size-dependent growth models.     

纳米氢氧化镁简易制备

采用液相合成法,考察了水相、甲醇相、表面活性剂等因素对氢氧化镁粒径和粒径分布的影响.实验表明,甲醇作溶剂,回流反应,氢氧化钠作为沉淀剂,得氢氧化镁粒径D98为2.5 μm,粒径分布集中.     

均相沉淀法制备超细氢氧化镁

以氯化镁、氢氧化钠为原料,采用均相沉淀法制备超细氢氧化镁。研究了分散剂种类对氢氧化镁产率和粒径的影响,以及分散剂种类、氯化镁浓度、反应温度等因素对氢氧化镁沉降速率的影响,同时分别选择水、乙醇两种不同的反应介质,对氢氧化镁的粒径及产率进行对比。结果表明,以葡萄糖作为分散剂,氯化镁浓度为0.75 mol/L,反应温度为60 ℃,所得氢氧化镁产率较高,且粒径较小（约为6.4 μm）、粒度分布较均匀。     

不同制备方法对纳米氢氧化镁性能的影响

以六水氯化镁为原料,氢氧化钠为沉淀剂,分别采用正向沉淀法、反向沉淀法、双向沉淀法和超重力沉淀法制备了纳米氢氧化镁,以沉降速度为评价指标,考察了制备方法对氢氧化镁料浆沉降性能的影响.利用透射电子显微镜(TEM)、纳米激光粒度分布仪、X射线衍射仪(XRD)对产物的形貌、粒径、粒径分布和晶型进行表征.结果表明,采用超重力沉淀法,氢氧化镁料浆的沉降速度明显加快,分别是正向沉淀法、反向沉淀法、双向沉淀法的4.7倍、12.4倍、2.1倍;所得氢氧化镁的分散性好,纯度高,粒度分布均匀并呈六方片状晶体.     

从卤水制备耐火级高活性氧化镁影响因素探讨

特种耐火级氧化镁不但要有高的纯度,也要有很高的活性,但目前中国尚不能生产这样的优质产品。以卤水为原料,经过氢氧化镁途径制备高纯高活性氧化镁,重点考察了卤水浓度、反应时间等因素对中间体氢氧化镁粒径、分散状态、纯度的影响,并通过添加表面活性剂,得到了制备高纯度高分散中间体氢氧化镁的最佳工艺条件为：氯化镁的浓度为1-1.5 mol/L,反应时间为2-2.5 h。该工艺条件下可以得到粒径小、分散性好、纯度达99%以上的氢氧化镁,为高活性氧化镁的制备奠定了基础,具有重要的实际应用意义。     

高纯氧化镁的制备研究

以卤水为原料,经过氢氧化镁途径制备高纯氧化镁。采用共沉淀结合超滤法对卤水进行了精制,并重点考察了卤水浓度、反应温度、加料速率等因素对氧化镁纯度的影响,获得了纯度大于99%的氧化镁产品。     

Manufacturing of high quality hydrotalcite by computational fluid dynamics simulation of an impinging jet crystallizer

Hydrotalcite was produced by solid-state reaction with magnesium hydroxide particles as the precursor using the impinging stream method. Traditional impinging stream reactors are complex or prone to blockage during the reaction process. To solve this problem, computational fluid dynamics (CFD) simulation was used to optimize the operating conditions in 1 L and 10 L impinging jet crystallizers to produce hydrotalcite. The produced hydrotalcite had a uniform morphology, large particle size, narrow particle size distribution and high purity (>99%), which enabled the controlled reactive crystallization of high-quality hydrotalcite and provided theoretical support for industrial scale-up. Moreover, the solid-state reaction kinetics were analyzed and showed that the reactive crystallization of hydrotalcite could be explained by nucleation and nuclei growth mechanism.     

KCl掺杂高纯度方钠石的合成

在硅铝酸盐胶体中掺杂KCl,采用水热法合成了高纯度的方钠石。考察了KCl掺杂量对合成方钠石的影响,研究表明:在不同含水量的硅铝酸盐胶体中掺杂KCl可以合成高纯度的方钠石,合成的方钠石均为球形颗粒,胶体中含水量越高,球形颗粒的粒径越大。为工业合成方钠石提供了一种新方法。     

Optimization of Parameters for Synthesis of MFI Nanoparticles by Taguchi Robust Design

MFI‐type zeolite was successfully synthesized by hydrothermal crystallization of clear synthesis mixtures. A statistical experimental design method (the Taguchi method with an L8 orthogonal array) was implemented to optimize the experimental conditions for the preparation of MFI nanocrystals with respect to particle size and distribution as the desirable properties. In the Taguchi experimental design, crystallization temperature, water content, template/silica molar ratio, aluminum content, as well as the presence of alkaline cations were chosen as significant parameters affecting the properties. It was shown that water and aluminum content of the synthesis solution were the most important parameters affecting particle size and distribution. The MFI nanocrystals with an average particle size of 95 nm and the narrow particle size distribution of ± 8.5 nm were synthesized under optimum conditions.     

工业生产氟硅酸镁工艺探究

为了寻求工业生产氟硅酸镁的最佳工艺条件,降低能耗并提高产品质量,系统研究并优化了利用磷肥工业副产氟硅酸和氧化镁粉生产氟硅酸镁晶体颗粒产品的工艺参数。列举了氟硅酸镁产品的粒径以及粒度分布等物化性能指标,得到了氟硅酸镁产品最大产率的最佳工艺参数：直接将氧化镁粉计量加入合成槽,并确定其加入的顺序,氟硅酸质量分数为16%,m（氧化镁）/m（氟硅酸）为0.244~0.260,合成温度控制在40~50 ℃,得到浓度较高的产品溶液;蒸发温度为35~45 ℃,蒸发浓缩的晶浆进入MSMPR冷却结晶槽;冷却结晶温度控制在30 ℃,结晶槽搅拌器的转动频率控制在20~40 Hz,产品粒径可以控制在0.16~0.37 mm,该研究可为相关生产企业提供工艺技术方面的借鉴。     

添加剂EDTA对氢氧化镁反应结晶过程的影响(英文)

The effects of additive ethylenediaminetetraacetic acid (EDTA) on crystallization process were investigated by the induc-tion time of MgSO4-NaOH system. Nucleation and growth rates, growth mechanism and particle size distribution of magne-sium hydroxide precipitation were involved with. The induction time in unseeded and seeded precipitation of magnesium hydroxide with and without additive EDTA was measured. The conductivity method was used to determine the induction period. Theoretical relations of the induction time and supersaturation ratio for different growth mechanisms and a combined analysis on the induction time were applied to determine nucleation and growth rates. The growth mechanism of magnesium hydroxide precipitation was dis-closed by analyzing the experimental data with and without additive. The analysis on induction time indicated that additive EDTA had a significant influence on both nucleation and growth of magnesium hydroxide precipitation. The mechanism underlying the effect of EDTA on crystal growth was 2-dimension nucleation-mediated growth model.     

The Influence of Spray Drying on the Dispersive and Physicochemical Properties of Magnesium Oxide

Magnesium hydroxide was obtained in a precipitation reaction with the use of magnesium nitrate or magnesium sulphate and sodium hydroxide. The influence of the temperature of the process, the mode and rate of substrate supply, as well as the concentration and ratio of the substrates on the product's properties, were tested. The intermediate product Mg(OH)₂ was subjected to drying by static and spray techniques followed by calcination to obtain magnesium oxide. To establish the effect of the synthesis conditions and drying techniques on the dispersive and physicochemical properties of the magnesium oxide obtained, this product was characterized using a number of experimental methods to obtain the bulk density, polydispersity index, and particle size distribution in the nano- and micrometric ranges. Moreover, the wettability profiles in water system were examined. For selected magnesium oxide samples the crystalline structure was determined by the WAXS method, and adsorptive properties (surface area, volume, and size of pores) as well as electrical properties (dielectric permittivity and electrical conductivity) were measured. Application of all the above-mentioned methods enabled a comprehensive characterization of the products and revealed a significant effect of spray drying on their properties, in particular on their dispersion and morphology.     

直接沉淀法制备超细氢氧化镁的实验研究

设计了以内水为主要原料的直接沉淀法生产超细氢氧化镁的工艺。首先考察了分散剂的种类和用量对产品性能的影响。在此基础上,系统研究了反应温度和反应时间对产品的收率、纯度、粒径及颗粒形态等影响,获得了直接沉淀法制备超细氢氧化镁的较佳反应条件。     

激光粒度仪测试阻燃剂级氢氧化镁粒度分布

建立了实用、准确和快速的阻燃剂级氢氧化镁粉体粒度分布的测试方法。采用MS2000激光粒度分析仪研究了待测样品质量、泵转速、分散时间、分散介质、分散剂种类以及分散剂质量浓度等因素对阻燃剂级氢氧化镁粉体粒度分布测试结果的影响。适宜条件:以700 mL水为分散介质,洗洁精为分散剂,分散剂质量浓度控制在0.1~0.3 g/L,氢氧化镁粉体样品质量范围为0.020~0.035 g,泵转速为1 400~2 000 r/min,超声波分散时间为2~5 min,超声波分散后立即测量。     

OptimalParameters of Response Surface Methodology for Preparation of Magnesium Hydroxide Flame Retardant

The yield of magnesium hydroxide was investigated via response surface methodology using bischofite and aqueous ammonia as raw materials. The experimental results indicated that the effects of reaction temperature, magnesium ion and aqueous ammonia concentrations on the yield of magnesium hydroxide gradually decreased. In particular, reaction temperature and magnesium ion concentration had a significant influence on the yield. After the regression and fitting of the response value and each factor, the regression equation was obtained. As proven by experiments, the predicted value and actual value showed a good fit. The products of the center experiment were characterized by particle size analysis, scanning electron microscopy, and X-ray diffraction. The results show that the morphology is irregular and shows a lamellar structure. The particles have a narrow size distribution ranging from 0.64 to 0.68 mm of D50 size. The difference in particle size of D10 and D90 is less than 0.91 mm, and the purity very high.     

复合改性制备超细球形氢氧化镁的研究

以氨水为沉淀剂与硫酸镁反应,直接沉淀法制备氢氧化镁,研究原料浓度、反应温度、反应时间、表面活性剂对产品粒径与形貌的影响,采用单因素实验确定最佳反应条件(Mg2+浓度1.5 mol/L,OH-浓度7 mol/L,水/乙醇比为5∶1,SDBS+明胶质量分数1.5%,温度70℃,时间40 min)下,得到平均粒径约为2.5μm的近似球形的氢氧化镁颗粒。通过XRD,SEM,FT-IR等手段表征了产品的属性及形貌特征,结果表明产品粒子呈球形,粒度分布均匀,分散性好,晶形好。     

新法合成碱式碳酸铝镁

对合成碱式碳酸铝镁的新方法进行了研究,以硫酸铝为铝源,用固相反应法成功合成得到碱式碳酸铝镁。在试验中优化控制了碱式碳酸铝镁的组成及粒度,得到比较纯净的碱式碳酸铝镁纳米晶体。     

Effect of Ultrasound Frequency on the Precipitation Process of Supersaturated Sodium Aluminate Solution

The effects of frequency of ultrasound on the precipitation process of prepared supersaturated sodium aluminate solutions of practical concentration were studied experimentally under seeded, isothermal, batch crystallization conditions at various temperatures and initial ak(mole ratio of Na2O/Al2O3). The decomposition and the particle number percentage for size below 2 mm at time of 15 h were compared, particle size distribution and SEM photos of the product aluminum hydroxide were also analyzed. The results indicate that the ultrasonic treatment at 16 kHz can enhance the decomposition rate of sodium aluminate solutions, and also has effects on particle morphology and particle size distribution of aluminum hydroxide precipitated.     

氨基酸调控无水碳酸镁晶体结晶试验研究

无水碳酸镁晶体作为一种新型无机功能材料引起了研究者们的广泛关注。以氯化镁为原料,碳酸钠为沉淀剂,合成了无水碳酸镁晶体,再以甘氨酸、组氨酸、丙氨酸及L-天门冬氨酸四种不同种类氨基酸作为添加剂,调控其结晶的粒度及形貌。采用X射线衍射仪、扫描电子显微镜、激光粒度分析仪对合成产物进行表征,分析不同种类氨基酸对合成的无水碳酸镁晶体物相结构和形貌的影响。结果表明:在组氨酸调控下合成的无水碳酸镁结晶纯度高,生成的产物中n(Mg²⁺)∶n(CO^2-₃)为1∶0.94;L-天门冬氨酸调控合成的晶体纯度次之;甘氨酸和丙氨酸调控合成的晶体中掺杂大量碱式碳酸镁晶体。在组氨酸、L-天门冬氨酸、甘氨酸及丙氨酸四种氨基酸调控作用下,晶体结晶形貌依次呈凸面球三角形状、近球状、球状及不规则状,且无水碳酸镁晶体粒径分布均呈先上升后振荡下降最后小粒径拖尾的趋势。以上研究结果为无水碳酸镁晶体的仿生合成提供了参考。     

工业硫酸镁制备高纯氧化镁的合成研究

以工业硫酸镁和氢氧化钠为原料,合成氢氧化镁前驱物经煅烧制备高纯氧化镁。研究了净化工业硫酸镁溶液时的pH值大小以及沉镁时氢氧化钠浓度对产品纯度的影响。在确定了精制硫酸镁与氢氧化钠摩尔计量比、陈化时间、煅烧时间的条件下,通过单因素实验和正交试验确定了反应的较佳工艺条件为：硫酸镁的浓度2mol／L,反应温度40℃,反应时间35min,煅烧温度900℃,产物氧化镁的纯度达到99％以上。采用x射线衍射仪和透射电镜对样品进行表征,结果表明：样品粒子平均粒径约为40nm,形貌为类球形,分布较均匀。