The influence of hydrating agents on the hydration of industrial magnesium oxide

BACKGROUND: The influence of different hydrating agents on the pH of the hydrating solutions, rate of hydration of MgO to Mg(OH)₂ and product surface area was studied as a function of temperature of hydration. Hydrating agents used were aqueous solutions of ammonium chloride, magnesium acetate, magnesium nitrate, nitric acid, acetic acid, magnesium chloride, sodium acetate and hydrochloric acid and distilled water as control. These were chosen to determine either the effect of addition of a common ion, the effect of changing the solution pH or due to the presence of an acetate ion, found earlier to have a beneficial effect on the hydration of MgO. RESULTS: There was no significant difference in the hydration behaviour of the hydrating agents up to 50 °C, where less than 10% of magnesium hydroxide was formed. The amount of hydroxide increased at temperatures above 60 °C. When compared with the hydration in water, all the hydrating agents, with the exception of sodium acetate, showed a significant increase in the degree of hydration. Sodium acetate formed the lowest amount of magnesium hydroxide, ranging between 1.2 and 12.2% magnesium hydroxide. The largest percentage (56.7%) of magnesium hydroxide was formed from hydration in magnesium acetate. CONCLUSION: It seems that MgO hydration is a dissolution‐precipitation process controlled by the dissolution of MgO. The increased degree of hydration in magnesium acetate is possibly due to the presence of acetate and Mg²⁺ ions. Copyright © 2010 Society of Chemical Industry     

Kinetics and mechanistic analysis of caustic magnesia hydration

The kinetics of magnesia hydration to produce magnesium hydroxide is crucial for process design and control, and for the production of an Mg(OH)₂ powder with desirable particle morphology. In this study, highly pure magnesia has been hydrated in a batch reactor. The effects of the following variables were evaluated experimentally: temperature (308–363 K), reaction time (0.5–5 h), initial slurry density (1–25%wt) and particle size in the ranges ?212 + 75 µm and ?45 + 38 µm. Experimental data indicate increasing magnesia hydration rates with increasing temperature, as expected. In addition, it has been observed that the hydration of magnesia increases significantly up to about 4–5%wt initial slurry density, stabilising afterwards. On the other hand, the reaction was almost unaffected when magnesia with different particle sizes were hydrated because of similar specific surface areas involved. A reaction mechanism to explain the oxide dissolution and the hydroxide precipitation has been proposed, assuming no significant change in the initial solids size and dissolution rate as the controlling step. The calculated activation energy value of 62.3 kJ mol^?1 corroborates the mechanism proposed in this study and compares well with values previously reported in the literature. Copyright © 2004 Society of Chemical Industry     

Influence of precursors of Li2O and MgO on surface and catalytic properties of Li‐promoted MgO in oxidative coupling of methane

The influence of the catalyst precursors (for Li₂O and MgO) used in the preparation of Li‐doped MgO (Li/Mg = 0.1) on its surface properties (viz basicity, CO₂ content and surface area) and activity/selectivity in the oxidative coupling of methane (OCM) process at 650–750 °C (CH₄/O₂ feed ratio = 3.0–8.0 and space velocity = 5140–20550 cm³ g⁻¹ h⁻¹) has been investigated. The surface and catalytic properties are found to be strongly affected by the precursor for Li₂O (viz lithium nitrate, lithium ethanoate and lithium carbonate) and MgO (viz magnesium nitrate, magnesium hydroxide prepared by different methods, magnesium carbonate, magnesium oxide and magnesium ethanoate). Among the Li–MgO (Li/MgO = 0.1) catalysts, the Li–MgO catalyst prepared using lithium carbonate and magnesium hydroxide (prepared by the precipitation from magnesium sulfate by ammonia solution) and lithium ethanoate and magnesium acetate shows high surface area and basicity, respectively. The catalysts prepared using lithium ethanoate and magnesium ethanoate, and lithium nitrate and magnesium nitrate have very high and almost no CO₂ contents, respectively. The catalysts prepared using lithium ethanoate or carbonate as precursor for Li₂O, and magnesium carbonate or ethanoate, as precursor for MgO, showed a good and comparable performance in the OCM process. The performance of the other catalysts was inferior. No direct relationship between the basicity of Li‐doped MgO or surface area and its catalytic activity/selectivity in the OCM process was, however, observed. © 2000 Society of Chemical Industry     

Hydration of a low‐grade magnesium oxide. Lab‐scale study

BACKGROUND: Low grade magnesium oxide (LG‐MgO) is a by‐product from the calcination of natural magnesite that is currently hydrated to magnesium hydroxide by storing it in the open for up to 6 months. It is eight to ten times cheaper than pure magnesium oxide and therefore the revalorization of this by‐product is very attractive for those applications requiring great quantities of magnesium hydroxide for which high purity is not required. Here the hydration of LG‐MgO is studied as a function of two parameters: hydrating agent and temperature. RESULTS: Addition of acetic acid during the hydration of LG‐MgO improved the effectiveness of treatment. At 50 °C, the maximum percentage hydration was 40% in pure water and increased to 65% and 70% using aqueous solutions of 0.5 and 1.0 mol L^?1 acetic acid. Increase of temperature also had a positive effect on the final degree of hydration. When the treatment was carried out with 0.5 mol L^?1 acetic acid, the hydration increased from 50 to 65 and 80% at 25, 50 and 90 °C respectively. Accordingly under the optimum conditions of 90 °C and 0.5 mol L^?1 acetic acid 80% hydration was achieved within 8 h. CONCLUSIONS: The results showed that much shorter hydration times are possible and therefore an industrial alternative to the spontaneous process could satisfy an increasing demand for magnesium hydroxide. Moreover, agitation is not needed as the reaction is chemically controlled. Copyright © 2012 Society of Chemical Industry     

卤水-白云石微波催化制取氢氧化镁和氧化镁

就卤水-白云石灰在微波作用下生成氢氧化镁沉淀，及有关因素对沉淀的影响进行了试验。试验表明：微波作用可加快钙的溶出，降低沉淀的钙含量和含水量，提高了氢氧化镁和镁砂的品质。该法为卤水-白云石法的实际应用做了有益的探索。     

硼酸母液综合利用研究

介绍几种回收硼酸母液的方法,并提出以硫酸镁作为回收重点的新工艺,在将其转化为轻质氧化镁的同时,副产含硼酸的硫酸钾和氯化铵。试验结果表明,硫酸镁收率在 ９０％ 以上,副产品硫酸钾收率在 ８５％ 以上。     

高分散氧化镁粉体的晶格畸变研究

以六水氯化镁为原料,氢氧化钠和氨水为沉淀剂,采用直接沉淀法合成出高分散氢氧化镁粉体;再将前驱物氢氧化镁煅烧后得到高分散氧化镁粉体产品。通过X射线衍射(XRD)和扫描电镜(SEM)对所得产品的分析表征结果表明,氧化镁粉体的微结构中存在晶格畸变,表现为晶格膨胀。随煅烧温度的升高,氧化镁粉体的晶格常数减小,晶格畸变量也减小。     

高分散氧化镁粉体的制备及反常红外特性

以六水氯化镁为原料,氢氧化钠和氨水为沉淀剂,采用直接沉淀法合成出前驱物氢氧化镁粉体;再将氢氧化镁煅烧后得到氧化镁粉体产品。通过X射线衍射(XRD)、扫描电镜(SEM)和红外吸收光谱(FT-IR)等对所得产品进行表征分析。结果表明,在煅烧温度为400℃,煅烧时间为3h的条件下,可以得到高分散性的颗粒状氧化镁;在400℃下煅烧8h得到的氧化镁粉体的红外吸收峰出现了红移和蓝移同时并存现象。     

Kinetics and Activation Energy of Magnesium Oxide Hydration

The kinetics of hydration of magnesium oxide (MgO) powder to form magnesium hydroxide (Mg(OH)₂) were measured using isothermal calorimetry at different temperatures, and the morphology of the powders before and after hydration were examined. The hydration kinetics of light‐burned MgO exhibit a hydration rate peak similar to that of portland cement hydration, whereas the hydration kinetics of hard‐burned MgO are comparatively slower at the same temperature, and exhibit a continuously declining hydration rate after the first several minutes of reaction. The hydration kinetics of both light‐burned and hard‐burned MgO can be fit using a boundary nucleation and growth model that has previously been applied to the hydration of portland cement and tricalcium silicate. Activation energy values for MgO hydration were determined from the fitted rate constants and were also measured directly using small temperature excursions according to a recently proposed method. For light‐burned MgO the resulting values are in good agreement and indicate a value of 77 kJ/mol. For the hard‐burned MgO the activation energy values vary considerably depending on temperature and how the activation energy is measured, but are always lower than the value obtained for the light‐burned MgO.     

新法铝热炼镁还原渣提取高白氢氧化铝

新法铝热炼镁工艺以白云石和菱镁石为原料、以铝粉为还原剂,在真空还原获得金属镁的同时得到富含CaO·2Al₂O₃的还原渣,该还原渣可通过氢氧化钠和碳酸钠的混合碱液溶出得到铝酸钠溶液,并通过碳酸化分解制备氢氧化铝。以该工艺所得还原渣为原料,系统地研究各溶出条件对氧化铝溶出率的影响,并对碳分所得氢氧化铝进行性能检测。结果表明,在氢氧化钠浓度80 g·L^-1、碳碱浓度110 g·L^-1、溶出时间120 min、溶出温度95℃、液固比为6的条件下,炼镁还原渣中氧化铝的溶出率在85%以上。氢氧化铝产品白度均大于98,平均粒径为26.98 μm,能够达到高白氢氧化铝的要求。     

Low‐temperature synthesis of Mg(OH)2 nanoparticles from MgO as halogen‐free flame retardant for polypropylene

Mg(OH)₂ (MH) nanoparticles were synthesized by hydration of the light‐burned MgO at low temperature (70°C). Effects of additives, such as magnesium nitrate and magnesium acetate, on the size, morphology and agglomeration of MH particles were investigated. MH nanoparticles have platelet‐like structure and approximately 20–40 nm in thicknesses. The supersaturation degree plays an important role in magnesia hydration and is defined. When magnesium acetate was used as the additive, the hydroxyl ion can be homogeneously introduced into the solution. The size and morphology of MH nanoparticles are more homogeneous. Modified by titanate coupling agent, MH nanoparticles were used as the flame retardant for polypropylene (PP). The combustibility, mechanical properties and thermal behaviors of the PP/MH composites were characterized. The mechanical properties of PP/MH composites are not seriously deteriorated with increasing MH content. When the amount of MH fraction reached 65, the limiting oxygen index (LOI) value and UL 94 testing result of MH65 are 33.8 and V‐0 grading, respectively. The onset temperature (T_10%) and the maximum thermal decomposition temperature (T_max) of MH65 separately increased by approximately 100°C and 77°C than those of neat PP. Copyright © 2012 John Wiley & Sons, Ltd.     

利用催化剂厂废水生产七水硫酸镁

以三氧化二铁为主体的中变催化剂生产中会产生含铬硫酸铵母液，利用轻烧镁粉与除铬后的硫酸铵母液反应生产七水硫酸镁，既能治理污染又有经济效益。     

高分散氢氧化镁粉体的制备

以六水氯化镁为原料,氢氧化钠和氨水为沉淀剂,乙醇和水的溶液为溶剂,聚乙二醇为分散剂,采用直接沉淀法合成出氢氧化镁粉体;通过X-射线衍射（XRD）、扫描电子显微镜（SEM）和红外光谱（FT—IR）等对产物进行表征与检测,研究了沉淀剂、溶剂和分散剂等因素对产物晶粒大小和分散性的影响,制备出分散性高、粒度分布窄、平均粒径约为2μm的氢氧化镁粉体。     

浓海水—钙法制取氢氧化镁工艺研究

浓海水—钙法(轻烧白云石、石灰)制取氢氧化镁具有生产成本低、资源丰富的优势,但传统钙法生产的氢氧化镁存在杂质含量高、产品纯度低等缺陷。本文以自主研发的专利技术为基础,从原料预处理、氢氧化镁合成、硫酸钙沉降、沉淀洗涤等方面对浓海水—钙法制取氢氧化镁的工艺进行改进,并在河北黄骅完成万吨级示范工程建设和试运行。结果表明,采用改进后的工艺制备的氢氧化镁质量符合行业标准要求,氧化钙含量明显降低,同时得到高质量的副产硫酸钙。     

镁资源、镁质化工材料现状与前景

对镁资源、镁质化工材料现状与前景作了评述。介绍了中国镁质资源诸如菱镁矿、水镁石、水菱镁石、白云石、斜方云石、盐湖卤水和海水制盐工业副产--苦卤等。对世界镁化学制品生产企业近期变化和发展情况以及轻烧氧化镁（CCM）与氢氧化镁生产和应用进行了探讨,并展望了其发展前景。     

Fast transient fluorescence technique (FTRT) for studying dissolution of polymer glasses

The fast transient fluorescence technique (FTRT) was used for studying the swelling and dissolution of a glassy polymer formed by free‐radical polymerization of methyl methacrylate (MMA). Anthracene (An) was introduced during polymerization as a fluorescence probe to monitor swelling and dissolution. Swelling and dissolution processes of disc‐shaped poly(methyl methacrylate) (PMMA) glasses in a chloroform–heptane mixture were monitored by measuring the fluorescence lifetimes of An from its decay traces. A method is developed for low quenching efficiencies for measuring lifetimes, τ, of An, and it was observed that τ values decreased as the dissolution process proceeded. Desorption, D, and mutual diffusion, D_m, coefficients of An molecules were measured during dissolution of PMMA and found to be around 5.4 × 10⁻⁶ (cm²/s) and 2.2 × 10⁻⁵ (cm²/s), respectively. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 948–957, 1999     

以轻烧氧化镁制备六角片状氢氧化镁的研究

以盐湖产不同粒径轻烧氧化镁为原料,通过水化水热法制备六角片状氢氧化镁。考察了不同的反应温度、反应时间、搅拌速度和固液比对氧化镁水化率、制得氢氧化镁形貌、粒径的影响。采用X射线衍射仪、扫描电子显微镜、激光粒度仪等对所制得的氢氧化镁颗粒的物相、形貌和粒度进行了分析,同时把不同原料所得氢氧化镁用在聚乙烯（PE）中检测其阻燃性能。结果表明通过控制反应温度、反应时间、搅拌速度和固液比,氧化镁原粉的水化率可以达到95%,氧化镁细磨粉的水化率可达到100%,得到的氢氧化镁均呈现六角片状,但粒径尺寸存在差异。用在PE中,细粒径的氢氧化镁分散性更好,阻燃效果更明显。     

Selective removal of magnesium from lithium-rich brine for lithium purification by synergic solvent extraction using β-diketones and Cyanex 923

In the production of battery-grade and high-purity Li₂CO₃, it is essential to remove magnesium impurities. The state-of-the-art solvent extraction (SX) process using Versatic Acid 10 and D2EHPA co-extracts 3.3–5.5% lithium, while removing 86–98% magnesium. Here, we demonstrate that synergic SX systems containing a β-diketone (HPMBP, HTTA or HDBM) and Cyanex 923 are highly selective for magnesium extraction over lithium (separation factor α > 1,000). The extracted magnesium and lithium complexes have the stoichiometry of [Mg∙A₂∙(C923)₂] and [Li∙A _x∙(C923)₂] (x = 1, 2), respectively (A represents deprotonated β-diketone). The three β-diketone synergic SX systems all considerably outperformed the Versatic Acid 10 system for magnesium removal from a synthetic solution containing 24 g L⁻¹ Li and 0.24 g L⁻¹ Mg. In a three-stage batch counter-current extraction, the HPMBP and Cyanex 923 synergic SX system removed 100% magnesium with only 0.6% co-extraction of lithium. This excellent Mg/Li separation is the best result reported so far.     

The crystallization of magnesium hydroxide

The thermodynamic association constant for the formation of the ion-pair MgOH⁺ in solutions of magnesium hydroxide has been studied by potentiometric and conductometric methods.The growth of magnesium hydroxide seed crystals in supersaturated solutions over a range of concentrations of magnesium and hydroxide ions and in the presence of phosphonate additives has been investigated by a precision conductance method. After a rapid initial surge of growth, an equation first order with respect to supersaturation can be used to explain the experimental data. A surface diffusion process is proposed as the controlling step in the crystallization process.     

A new phosphate pretreatment process for adhesive bonding of magnesium AZ31 sheets

An economic, high efficiency sodium dihydric phosphate surface pretreatment process (SDPT) was developed to improve the adhesive bond performance of 2 mm thick hot-rolled wrought magnesium AZ31 sheets. A phosphating solution with sodium dihydric phosphate (NaH₂PO₄), additive sodium fluoride (NaF), and accelerator sodium molybdate (Na₂MoO₄), sodium tungstate (Na₂WO₄) and potassium nitrate (KNO₃) were developed to pretreat the magnesium alloys. The content of sodium dihydric phosphate in the phosphating solution was strictly controlled to insure it supplied sufficient acid radical HPO₄ ^2? to phosphate magnesium AZ31 alloy. Furthermore, a suitable H⁺ content to keep the pH values in the range of 5–6 for a phosphating solution was necessary. With this SDPT pretreatment process, a coating consisting of the magnesium phosphate, magnesia (MgO), magnesium hydroxide (Mg(OH)₂), magnesium fluoride (MgF₂) and a minor amount of molybdenum oxide(MoO₃) was formed on the surface of the magnesium AZ31. While the SDPT pretreated adhesive-bonded joints had better initial bond strength than phosphate–permanganate process pretreated joints, the corrosion resistance of SDPT pretreated joints was slightly inferior.