采用(NH_(4))_(2)SO_(4)焙烧-水浸工艺提高菱镁矿的利用效率

研究采用硫酸铵焙烧—水浸工艺提高菱镁矿的利用效率,结合XRD和TG-DTA分析以及对比硫酸铵焙烧MgO的物相变化得到焙烧过程中矿相的转化过程。实验结果表明,在菱镁矿粒度为~74μm、硫酸铵与菱镁矿物料摩尔比为1.6:1、焙烧温度为475℃和焙烧时间为2 h的条件下,镁的提取率达到98.7%。反应中物相转化过程可以概括如下:MgCO_(3)先转变为(NH_(4))_(2)Mg_(2)(SO_(4))_(3),再分解得到MgSO_(4)。反应遵循化学反应和扩散混合控制机理,其表观活化能为33.02 k J/mol。

Reaction mechanism of roasting Zn_2SiO_4 using NaOH

The reaction kinetics of roasting zinc silicate using NaOH was investigated.The orthogonal test was employed to optimize the reaction conditions and the optimized reaction conditions were as follows:molar ratio of NaOH to Zn2SiO4 of 16:1,reaction temperature of 550°C,and reaction time of 2.5 h.In order to ascertain the phases transformation and reaction processes of zinc oxide and silica,the XRD phase analysis was used to analyze the phases of these specimens roasted at different temperatures.The final phases of the specimen roasted at 600°C were Na2ZnO2,Na4SiO4,Na2ZnSiO4 and NaOH.The reaction kinetic equation of roasting was determined by the shrinking unreacted core model.Aiming to investigate the reaction mechanism,two control models of reaction rate were applied:chemical reaction at the particle surface and diffusion through the product layer.The results indicated that the diffusion through the product layer model described the reaction process well.The apparent activation energy of the roasting was 19.77 kJ/mol.

Zinc extraction from zinc oxidized ore using(NH4)2SO4 roasting−leaching process

An improved method of(NH4)2SO4 roasting followed by water leaching to utilize zinc oxidized ores was studied.The operating parameters were obtained by investigating the effects of the molar ratio of(NH4)2SO4 to zinc,roasting temperature,and holding time on zinc extraction.The roasting process followed the chemical reaction control mechanism with the apparent activation energy value of 41.74 kJ·mol^−1.The transformation of mineral phases in roasting was identified by X-ray diffraction analysis combined with thermogravimetry–differential thermal analysis curves.The water leaching conditions,including the leaching temperature,leaching time,stirring velocity,and liquid-to-solid ratio,were discussed,and the leaching kinetics was studied.The reaction rate was obtained under outer diffusion without product layer control;the values of the apparent activation energy for two stages were 4.12 and 8.19 kJ·mol^−1.The maximum zinc extraction ratio reached 96%while the efficiency of iron extraction was approximately 32%under appropriate conditions.This work offers an effective method for the comprehensive use of zinc oxidized ores.

Microstructure and properties of Al–7Si–0.6Mg alloys with different Ti contents deposited by wire arc additive manufacturing

Numerous studies have addressed the advantages of wire arc additive manufacturing for manufacturing aluminum alloys. However, the role of Ti content in aluminum alloys has rarely been discussed. Herein, the effect of Ti content on the microstructure and properties of Al–7 Si–0.6 Mg alloys was studied. The alloys were deposited via wire arc additive manufacturing and were examined through optical microscopy(OM), scanning electron microscopy(SEM), and electronic universal testing. The results show that the increase of Ti content gradually promotes the increase of the secondary dendrite arm spacing and also has an increasing tendency to form pores defect in the as-deposited alloys. The change of titanium content also affects the difference between horizontal and vertical direction properties of the alloy. The alloy with a Ti content of 0.112 wt% exhibits the best comprehensive properties. There is no difference in its horizontal and vertical direction properties. The tensile strengths, yield strengths, and elongation of this alloy(T6) along the vertical and horizontal axis are 356 and 355 MPa, 307 and308 MPa, and 8.5% and 8.0%, respectively.