On the kinetics of magnesia hydration in magnesium acetate solutions

High‐quality magnesium hydroxide powders can be produced by hydrating slow‐reacting magnesia in dilute magnesium acetate solutions. The kinetics of this process are very crucial for process design and control, and for the production of a powder with desirable particle morphology. In this work, industrial heavily‐burned magnesia powders were hydrated in 0.01–0.1 mol dm⁻³ magnesium acetate solutions at temperatures ranging between 333 and 363 K. Examination of the magnesium hydroxide produced and the analysis of the kinetic data suggest that the hydration of heavily burned magnesia in magnesium acetate solutions is a dissolution–precipitation process controlled by the dissolution of magnesia particles. The activation energy was estimated to be 60 kJ mol⁻¹, while the reaction order with respect to acetate concentration was found to be about one. © 1999 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     

醋酸镁合成工艺的研究

研究了采用镁、醋酸直接反应合成醋酸镁工艺的可行性和反应条件.实验得出,用镁与醋酸反应可以制得无水醋酸镁.在实验条件下,镁与醋酸反应合成醋酸镁的适宜操作条件为:镁与醋酸的质量比为1:8、反应温度为50～120℃、醋酸滴加速率为1.25 mL/min左右、反应时间为2 h,不需要加入催化剂,需要进行快速搅拌.此时,醋酸镁的收率达82%以上.     

用氯化镁生产氢氧化镁和氧化镁的方法

采用一种精制原料和两次煅烧工艺克服在Aman法分步精制原料和三次煅烧等现有工艺路线长、能耗高、生产成本高等不足，将煅烧温度分为：600－800℃轻烧，800－1200℃重烧，1200－1800℃死烧3个温度段，可以分别制得高纯的轻质、重质氧化镁和镁砂。大幅度缩短了工艺路线和生产周期并降低生产成本，成功解决了从原料直接生产氧化镁的技术难题，创造了氧化镁生产的又一方法。     

以活性氧化镁和氯化镁为原料合成氧化镁晶须

探讨了一种合成氧化镁晶须的新的工艺方法。首先以活性氧化镁和氯化镁为原料合成了前驱体碱式氯化镁晶须，接着将碱式氯化镁焙烧成氧化镁晶须。分别用X射线衍射仪（XRD）、扫描电镜（SEM）、热重分析仪（TGA）和化学分析，分析了中间体碱式氯化镁和产品氧化镁晶须的成分、形貌和热化学行为。探讨了各个工艺条件对产物的影响，探索出最佳的工艺条件：活性氧化镁与氯化镁的物质的量比在0．08左右，氯化镁溶液的浓度为3mol／L，反应温度40～50℃，陈化时间在48-72h，陈化温度50℃。在此条件下制得了形貌良好的前驱物碱式氯化镁晶须。将碱式氯化镁晶须焙烧，控制升温速率在2—5℃／min，采取分段升温方式升温至600℃，即可制得氧化镁晶须。制得的晶须长度在100μm左右，直径约0．5μm。     

氢氧化镁和氧化镁中酸不溶物的研究

产硝后的高镁卤水和硫氢化钡溶液进行反应，生成氢氧化镁，酸不溶物在0．3％（质量分数）左右，但将其煅烧成氧化镁后，酸不溶物高达1．2％-2．5％（质量分数），二者酸不溶物远不成比例关系。通过对样品在分析中穿滤对比、硫酸法测定酸不溶物、碘量法测定硫化物试验，确定在生产过程中，硫氢化钡被氢氧化镁吸附，经过高温煅烧，硫氢化钡被氧化成硫酸钡，成为氧化镁中的酸不溶物，这就是氧化镁和氢氧化镁中酸不溶物不成比例的主要原因。     

碱式氯化镁废渣生产氧化镁

由麦芽酚生产中的碱式氯化镁废渣为原料制取氧化镁。考察了温度及反应物用量对氧化镁产率和质量的影响。证明了该方法技术可行，能产生较好的经济效益，解决了废渣对环境的污染，产生了较好的社会效益。     

由白云石制备特种硅钢级氧化镁工艺研究

研究了由白云制备特种硅钢级氧化镁的原理及工艺条件，讨论了各工艺参数对产品性能的影响，制出了粒径细小，粒度分布均匀、分散性好，水化率低的氧化镁。     

A simplified mechanistic analysis of the hydration of magnesia

The kinetics of the hydration of magnesia to produce magnesium hydroxide is described by a kinetic model with no diffusive contribution, including an additional resistance to the reactive flux due to the transient variation of the porosity of the material during reaction. The proposed model has been applied to data from the literature and obtained by hydration of MgO samples with distinct physical characteristics. The model describes well the mechanism of hydration of powder and single crystal MgO in liquid and vapour water with temperatures varying from 35°C to 200°C.     

The influence of composition and temperature on hydrated phase assemblages in magnesium oxychloride cements

Due to their nonhydraulic nature, magnesium oxychloride cements (MOCs) are susceptible to degradation following contact with water. Improving the water resistance of these materials requires better understanding of hydrated phase relations and the sensitivity of hydrated phases to water. Toward this end, a series of targeted experiments and complementary thermodynamic calculations were carried out to assess hydrated phase assemblages in the system MgO‐MgCl₂‐H₂O across a range of compositions. Focus is placed on appraising the effects of composition and reaction temperature. In broad agreement with literature data, under ambient conditions, hydrated MOCs are noted to contain Phase 3 (P3), Phase 5 (P5), and brucite, but the mass partitioning of these phases is highly dependent on H₂O/MgCl₂ and MgO/MgCl₂ molar ratio as well as curing temperature and age. At room temperature, P3 is favored at lower water contents, however, P5 and/or brucite are favored to form as water availability increases. Thermodynamic calculations indicate that P3 is “more stable” than P5 at lower temperatures—an outcome which impacts the engineering properties, for example, strength and volume stability. The impacts of the accuracy and self‐consistency of currently available thermodynamic data and their implications on predicted phase assemblages are discussed.     

微波辐射煅烧碱式碳酸镁制备轻质活性氧化镁

以碱式碳酸镁为原料，采用微波辐射煅烧制备轻质活性氧化镁是可行的，正交实验结果表明，影响碱式碳酸镁分解的主要因素是微波功率，其次是煅烧时间，物料质量影响最小。确定了最佳实验工艺条件为：微波功率490W，煅烧时间12min，物料质量2g，碱式碳酸镁的分解率为93．81％，活性氧化镁的碘吸附值为72．56mg／g。     

超细氧化镁粉体的制备方法探讨

超细氧化镁粉体属于新型高功能精细无机材料。着重介绍了超细氧化镁粉体的制备方法(包括气相法、金属醇盐水解法、液相法、固相法、硬脂酸法)，对各方法的原理及优缺点作了详细的阐述。最后提出了硬脂酸法这一有前景的新工艺。     

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。     

以氯化镁为原料制备氧化镁晶须的工艺研究

以氯化镁和碳酸钠为原料,通过前驱体烧结法制备氧化镁晶须.首先以氯化镁和碳酸钠为原料合成了前驱体碳酸镁晶须,接着将碳酸镁焙烧成氧化镁晶须.探讨了各个工艺条件对产物的影响,探索出最佳的工艺条件:氯化镁溶液的浓度为0.6mol/L,氯化镁和碳酸钠的摩尔比为1:1,陈化时间2h.在此条件下制得了前驱物碳酸镁晶须,将碳酸镁晶须焙...     

球形氧化镁的控制合成研究

以聚乙烯吡咯烷酮为控制剂,氯化镁、氢氧化钠和氨水为原料,经静态反应制备出球形氢氧化镁前驱体,再经煅烧得到球形氧化镁。研究了控制剂种类、控制剂用量、反应物浓度、反应时间等因素对球形氧化镁形貌的影响,并用XRD、SEM等分析手段对产物做了表征。结果表明：在控制剂为聚乙烯吡咯烷酮、添加量为1.0%（质量分数）、氯化镁浓度为1.0 mol/L、氢氧化钠浓度为0.25 mol/L、反应时间为24 h的条件下,获得球形氢氧化镁前驱物;前驱物氢氧化镁在600 ℃下煅烧2 h,制得的球形氧化镁颗粒大小均匀、分散性好、球形度高,平均粒径为4.53 μm。     

纳米氧化镁的制备

研究了制备纳米氧化镁的方法。以碳酸铵和氯化镁为主要原料,加入有机表面活性剂,经过反应、过滤、水洗、醇洗、干燥和灼烧制得纳米氧化镁。经堆积密度、比表面积、孔容积、粒径及透射电镜的测定,试验样品的粒子大小均在10 nm左右。试验结果证明,试验工艺路线及测定方法均适合纳米氧化镁制备。主要原料碳酸铵和氯化镁来源广泛,价格低廉,对纳米氧化镁的工业生产具有重要的意义。     

氧化锌和氧化镁对HNBR过氧化物硫化体系性能的影响

本文主要研究了氧化锌和氧化镁单用用量及并用对HNBR过氧化物硫化体系性能的影响,结果表明金属氧化物能对过氧化物硫化体系产生活化作用提高胶料的交联密度及耐热性能且氧化锌活性要高于氧化镁,并随其用量增加耐热性能变优;热重分析表明HNBR胶料热降解呈现两个阶段,且5份氧化锌能显著提高胶料的热稳定性能;氧化锌和氧化镁并用比例为7/3时对胶料的耐热性能产生协同作用,耐热性能最佳,但氧化镁对胶料的压缩永久变形性能产生不利影响。     

硫酸镁热解制氧化镁工艺初探

考察了不同还原介质在不同情性保护气体下由无水奠酸镁高温煅烧制取氧化镁的工艺条件及过程,确定了最优反应条件及还原介质,无水硫酸镁转化率达到90%.     

硼泥中氧化镁组分的盐酸浸出工艺研究

为解决硼泥带来的环境污染问题,充分利用其中的镁元素制备镁盐和其他镁化工产品,进行了硼泥的盐酸浸出实验研究。首先采取煅烧的方式对硼泥活化预处理,研究了煅烧温度、煅烧时间对工艺的影响,得到适宜的煅烧工艺条件：煅烧温度为600 ℃、煅烧时间为2 h;在盐酸浸出硼泥工艺过程中,研究了盐酸用量、酸浸温度、酸浸时间对硼泥中氧化镁浸出率的影响,得到适宜的酸浸工艺条件：盐酸用量为2.5 mL/g、酸浸温度为95 ℃、酸浸时间为1 h,在此条件下氧化镁的浸出率达到95.8%。硼泥浸出渣的XRD测试表明,硼泥主要含有的镁物相镁橄榄石和菱镁矿已被完全浸出。     

花瓣状纳米氢氧化镁及氧化镁的微波辅助合成

在微波辅助下,以硫酸镁、NH₃•H₂O-NH₄Cl缓冲溶液为原料,通过均相沉淀反应制备了纳米氢氧化镁,经煅烧又得到了纳米氧化镁。采用X射线衍射（XRD）、透射电镜（TEM）、扫描电镜（SEM）、热重分析（TG）等分别对纳米氢氧化镁和氧化镁的结构、形貌及热稳定性进行了分析测试。结果表明,纳米氢氧化镁的结晶性能较好,其形貌为由厚度约40 nm的纳米片团聚而成的花瓣状;纳米氧化镁亦保持了氢氧化镁花瓣状形貌。并对微波辅助下纳米氢氧化镁形成的可能机理进行了初步探讨。