Solid oxide membrane process for magnesium production directly from magnesium oxide

The solid oxide membrane (SOM) process is an emerging technology for the environmentally friendly extraction of high-energy-content metals such as magnesium, tantalum, and titanium directly from their respective oxides. This paper reports on the recent success of the SOM process for magnesium production from magnesium oxide dissolved in fluoride-based fluxes in the temperature range 1150 °C to 1300 °C. This process employs an inert oxygen-ion-conducting stabilized zirconia membrane to separate the inert cathode in the flux from the anode. When the applied electrical potential between the electrodes exceeds the dissociation potential of magnesium oxide, oxygen ions are pumped out of the melt and through the zirconia membrane to the anode where they are oxidized. Reduced magnesium evolves at the cathode as a vapor and is condensed in a separate chamber yielding a high-purity product. The SOM cell has been electrochemically characterized, and key concepts related to MgO dissociation, leakage current, and mass transfer relevant to the SOM process are explained.     

Chlorination and carbochlorination of magnesium oxide

Thermogravimetric technique and boat experiments were used to study the chlorination of MgO and its reactivity with respect to Cl₂ + air, Cl₂ + N₂, and Cl₂ + CO gas mixtures at temperatures lower than 1000°C. Oxychlorination of MgO occurs at temperatures higher than that of its carbochlorination. Effects of experimental parameters such as gas flow rate, temperature, and partial pressure of the carbochlorinating gas mixture on the reaction rate were examined. At 550 °C, the apparent reaction orders with respect to Cl₂ + CO, Cl₂, and CO were 2.37, 1.47, and 0.89, respectively. At this temperature, the maximum reaction rate was obtained using a Cl₂ + CO gas mixture having a Cl₂/CO molar ratio equal to about 0.6. The apparent activation energy of carbochlorination of MgO was calculated as 49 kJ/mol between 425 °C and 600 °C.     

Kinetics of oxychlorination of magnesium oxide

The kinetics of oxychlorination of MgO by Cl₂ + O₂ were studied in the temperature range from 850 °C to 1025 °C, using thermogravimetric analysis (TGA). The effects of Cl₂/O₂ ratio, gas velocity, temperature, and partial pressure of reactive gases on the reaction rate were investigated. The oxychlorination process was characterized by an apparent activation energy of about 214 kJ/mol. The reaction orders with respect to O₂, Cl₂, and Cl₂ + O₂ at 950 °C were about −0.37, 0.98, and 0.65, respectively. Data concerning oxychlorination of MgO, Cr₂O₃, and MgCr₂O₄ contained in chromite were compared. The effectiveness of using oxychlorination to extract iron oxides contained in magnesia was demonstrated.     

电位滴定法测定石灰中氧化钙和氧化镁

石灰以其优越的造渣性能而备受钢铁冶金行业青睐,石灰的主要成分为氧化钙和氧化镁,高效、准确测定石灰中氧化钙和氧化镁至关重要。采用国家标准GB/T 3286.1—2012中EDTA络合滴定法测定石灰中氧化钙和氧化镁,过程繁琐流程长,滴定终点通过肉眼判断容易产生视觉误差,因此不能满足冶炼过程工艺动态控制生产需求。实验使用盐酸溶解样品,在待测样品中加入三乙醇胺,掩蔽Fe³⁺、Al³⁺;加入糊精,抑制样品溶液中生成大量的氢氧化镁沉淀对Ca²⁺的吸附;用EDTA标准溶液在强碱介质下,电位滴定法测定氧化钙、氧化镁含量。对使用盐酸溶解石灰后的不溶物进行回收和不回收两种处理方法,并对氧化钙和氧化镁的测定结果进行t检验,结果无显著差异。按照实验方法测定3个石灰样品中氧化钙、氧化镁,结果的相对标准偏差(RSD,n=11)均小于0.5%。选择一批石灰试样,分别按照实验方法和GB/T 3286.1—2012测定氧化钙和氧化镁含量,两种方法测得的氧化钙和氧化镁差值分别小于±0.20%和±0.10%。通过电位突变来判断滴定终点,减少了人员判定滴定终点的视觉误差,能够满足冶炼过程工艺动态控制的测定需求。     

Solubility of magnesium oxide in calcium oxide-calcium chloride mixtures

Measurements and theoretical calculations of the solubility product of magnesium oxide in calcium chloride-calcium oxide mixtures at 1133 K are reported. A filtration technique in an inert atmosphere was used to obtain samples for analysis by atomic absorption for magnesium content. At low concentrations of O^-2, the data are in consonance with the very low solubility product of 10^-6.2 predicted by a simple thermodynamic cycle first proposed by Flood, Fϕrland and Grjotheim. Work performed under the auspices of the U.S. Energy Research and Development Administration.     

Internal friction peak associated with the enhanced re-orientation of split interstitials of magnesium atoms in close vicinity of the dislocation kinks in aluminium

A new internal friction peak has been observed around 125°C (| = 1 Hz) in AlMg specimens twisted and subsequently annealed at an elevated temperature. This peak appears only when internal friction measurements are taken at descending temperatures. It does not appear in the case of tensile deformation and the peak is suppressed by subsequent tensile deformation. The activation energy is found to be 0.7 ± 0.1 eV and τ₀ is 10⁻⁸ s. The peak is very sensitive to application of a small bias-stress. It is assumed that the mechanism of this peak is the stress-induced re-orientation of an <100 > split interstitials or dumbbell of MgMg atoms enhanced by the stress field of moving dislocation kinks in aluminium.     

Diffusion of dumb-bell interstitials in concentrated random alloys: An effective field approximation

By extending the notion of trapping of the dumb-bell interstitial on a solute atom to the case of a random concentrated alloy, we obtain five variants of the same simple basic model, which rest only on two parameters and which exhibit in general the following features: a rapid decrease of the interstitial diffusivity D₁ while increasing the solute content; this drop is all the more important that the trapping is deeper; a further increase of D₁ at higher solute content due to cluster percolation, which restores a value of D₁ comparable to the one observed in pure metals. It is shown that the problem can be satisfactorily solved by an effective field approximation and that D₁ is the solution of the self consistency equation which defines the effective field. The agreement with Monte-Carlo simulations is reasonable over the whole range of concentrations. No simple analytical solution could be worked out in all cases, but one, contrarily to the case of the transport via vacancies which is much less intricated. If this model proposes a simple and immediate interpretation for the low interstital diffusivities, which have been observed recently in several alloys, a more systematic set of experiments on solid solutions is still required to ground its validity.     

氧化镁的制备方法及发展趋势综述

介绍了以菱镁矿、白云石、蛇纹石、卤水及镁盐试剂为原料,采用不同的技术及工艺路线生产氧化镁的方法.对各种制备氧化镁的方法进行了分类、总结与评述,指出了不同制备方法的反应机理和优缺点.此外,由于纳米氧化镁的特殊性,专门总结了制备纳米氧化镁的方法,并指明其不同制备方法的反应机理和优缺点.最后,根据我国生产特种氧化镁(硅钢级氧...     

自动电位滴定法测定冶金辅料中氧化钙和氧化镁

利用自动电位滴定仪, 测定了冶金辅助材料中氧化钙和氧化镁的含量。考察了滴定参数的影响, 最终确定滴定波长为660 nm, 搅拌速度为1 250 r/min, 预搅拌时间为30 s, 每次加入滴定剂后, 仪器达到的电位差dE(set)为8 mV;平衡条件(dE/dt)设置为0.5 mV, 等待的最长时间间隔t(max)为15 s;测定氧化钙时, 设置阈值为100 mV/mL, 测定氧化钙、氧化镁合量时, 设定阈值为300 mV/mL。将方法应用于白云石标准样品、石灰石标准样品、炉渣标准样品耐火材料标准样品中氧化钙和氧化镁的测定, 结果与认定值一致, 相对标准偏差(RSD, n=7)为0.06%~0.77%, 加标回收率为99%~101%。