【作者】 熊利芝；

【导师】 陈启元；

【作者基本信息】 中南大学 ， 冶金物理化学， 2011， 博士

【摘要】 随着锌用途范围的扩大,世界各国锌产品消耗量逐年增加,硫化锌矿日渐供应不足,氧化锌矿的开发利用已越来越受到重视。但由于氧化锌矿极易“泥化”和伴生元素Si等含量高,无论是湿法或火法处理,均受到一定的限制。为了在处理含锌氧化矿时,提高能效、提高金属回收率,缩短工艺流程,节约资源、环境友好并获得高品质的金属锌,本文以菱锌矿和异极矿两种含锌氧化矿为研究对象,较系统地研究了真空碳热还原分级冷凝处理含锌氧化矿的新工艺及相关的热力学和动力学,主要研究内容和取得成果如下：(1)对含锌氧化矿进行了热力学研究,结果表明：真空条件下碳还原含锌氧化物具有较大的优势,当系统压强不断降低时,所对应氧化锌、硅酸锌的碳还原反应临界温度不断降低,但碳还原硅酸锌的温度较氧化锌的高；真空碳热还原含锌氧化矿时,产物金属锌中的杂质Cd较难通过真空蒸馏与Zn分离,除Cd程度将直接影响产物锌的质量。(2)根据真空碳热还原含锌氧化矿的特征,设计了分级冷凝真空炉,利用余热分级冷凝蒸气。由于各物质的性质不同而将在分级冷凝器的不同部位冷凝,达到分离纯化产品的目的。实验研究表明：真空碳热还原分级冷凝处理含锌氧化矿时,反应温度降低,反应时间缩短,产品质量大大提高。(3)以煤作为还原剂,对菱锌矿进行真空碳热还原分级冷凝处理。实验考察了菱锌矿的热处理条件,包括烧结时间、烧结温度对试样强度、锌质量的影响,同时也考察了真空碳热还原温度、还原时间、碳矿比和系统压强等因素对锌产率和锌质量的影响。结果表明：试样烧结温度控制在823～873K,烧结时间不少于30min,试样落下强度较好；真空碳热还原菱锌矿时,较佳工艺条件为C/Zn总的物质的量比为3,还原蒸馏温度1173K,系统压强50～2000Pa,真空碳热还原蒸馏60min；在较佳工艺条件下,菱锌矿中约97%的锌被还原蒸馏出来；采用真空碳热还原分级冷凝的方法,可以将铅、砷、镉与锌分离,但镉与锌分离的程度较小；通过改变烧结条件,可将产物锌中杂质Cd含量降低；在适宜的条件下,真空碳热还原分级冷凝处理菱锌矿后,可获得纯度为99.995%的高纯锌。(4)对异极矿进行了真空碳热还原的实验研究。通过对异极矿进行热处理,实验考察烧结时间、烧结温度对原料强度、锌产率和锌质量的影响,同时考察真空碳热还原温度、碳矿比、系统压强等因素对锌产率和质量的影响,特别考察添加试剂及其添加量的作用。实验结果表明烧结温度控制在823～873K,烧结时间不少于30min,试样强度较高；真空碳热还原处理异极矿时,较佳工艺条件是：C/Zn总的物质的量比为2.5, CaF2的添加量约为10%,还原蒸馏温度1373K,系统压强50～20kPa,真空碳热还原蒸馏约40min；在较佳工艺条件下,异极矿中约93%的锌被还原蒸馏出来；在此过程中CaF2中的氟离子主要起催化作用；烧结条件的改变可以降低产物锌中杂质Cd的含量,改变系统压强可降低产物锌中杂质Pb的含量；在适宜的条件下,真空碳热还原分级冷凝处理异极矿后,可获得纯度为99.995%的高纯锌。(5)在对含锌氧化矿碳还原的动力学研究中,对真空炉进行科学的改造。重点对真空炉的送样器和产物收集器进行改造,使实验在准确的反应时间内在较恒定的温度、稳定的系统压强等的条件下进行。(6)在真空条件下,对ZnO-C体系在还原温度1073～1223K下进行研究,发现在真空条件下煤还原菱锌矿中氧化锌的还原反应为一级反应,其还原速率由扩散过程所控制,活化能为177.72～191.31KJ·mol-1。(7)对未添加CaF2的Zn2SiO4-C体系在还原温度为1323～1473K下进行研究,得出其反应为一级反应,界面化学反应为控制步骤,活化能为246.16kJ·mol-1；对添加10%CaF2的Zn2SiO4-C体系在还原温度为1273～1423K下进行研究,还原反应为一级反应,界面化学反应仍为控制步骤,但活化能降低至164.82kJ-mol-1;添加试剂CaF2中的氟离子在Zn2SiO4-C还原体系中起催化作用,氟离子能增大硅酸锌晶体的活性,促进硅酸锌中Zn-O键断裂,降低反应活化能。更多还原

【Abstract】 Consumption of zinc products has been increased each year with the wide application of zinc. As zinc sulphide is in a short supply, exploitation and utilization of zinc oxide ore have attracted more attention. There are some shortcomings in both hydrometallurgical and pyrometallurgical process when zinc oxide ore with clay and high content of silica is used as the starting material. The extraction process of zinc oxide ore was studied thermodynamically and dynamically by the vacuum carbothermic reduction with classification condensation in order to increase the energy efficiency, improve the recovery of metallic zinc, shorten the process flow, attain metal zinc with higher quality, meet the environmentally-friendly and resource-saving requirements. Two representative oxide ores were selected as the starting materials, one is smithsonite, the other is hemimorphite. The main contents studied and the important conclusions are as follows:(1)Thermodynamic studies indicate that there are specific advantages in vacuum carbothermic reduction. The critical temperature of zinc oxide or zinc silicate by carbothermic reduction is decreasing obviously, when the pressure of system is dropping, but that of zinc silicate is higher than that of zinc oxide. Cd can not be completely separated from Zn by vacuum distillation, the content of Cd in metal zinc will directly affact the quality of the zinc product.(2)The vacuum furnace with classification condensation was designed as experimental facility according to the characteristics of vacuum carbothermic reduction of zinc oxide ore and utilization of the waste heat for the condensation classification of Vapours. The vapour of different metallic products was condensed gradually at different position of the classification condenser with the decrease of temperature due to their different condensing temperature, and the products were therefore separated and purified. The experimental results show that the reaction temperature is decreased, the reduction time is shortened, and the quality of products are greatly improved by vacuum carbothermic reduction with classification condensation.(3) Smithsonite was processed by the vacuum carbothermic reduction with coal as the reductant. The effects of sintering time, sintering temperature on the strength of pellet samples and the quality of metallic zinc were investigated. The effects of the reduction temperature, reduction time, initial moles ratio of C/Zntotai and the pressure of system on the zinc yield and the quality of metallic zinc were also studied. It is found that the drop number of the pellets is greater when the suitable sintering temperature is from 823K to 873K and the sintering time is not shorter than 30 min. The optimal process condition for the vacuum carbothermic reduction is obtained as follows:the molar ratio of C/ZnTotal 3, the reaction temperature 1173K, the pressure of system 50～2000Pa, the reaction time around 60 min. At the optimal condition, the zinc yield is about 97%from smithsonite. Pb, As, Cd can be well separated from Zn, but the separation between Cd and Zn is not ideal enough. The content of Cd in metallic zinc could be decreased when the sintering conditions were changed. At suitable experimental conditions, high-purity zinc can be obtained with a purity of 99.995%.(4) The vacuum carbothermic reduction of hemimorphite was studied. The effects of sintering time, sintering temperature on the strength of pellet samples and on the quality of metallic zinc were investigated. The effects of reduction temperature, reduction time, initial moles ratio of C/Zntotal, the pressure of system, the mass of CaF2 additive on the zinc yield and the quality of metallic zinc were also studied. Results show that the drop number of the pellets is greater when the suitable sintering temperature is 823-873K and the sintering time is not shorter than 30 mins. CaF2 can catalyze the carbothermic reduction of zinc silicate. The optimal process condition is obtained as follows:the amount of CaF210%, the reaction temperature 1373K, the molar ratio of C/ZnTotal 2.5, the pressure of system lower than 20kPa, the reaction time about 40 min. At the optimal condition, the zinc yield is about 93%from hemimorphite. The content of impurity Cd in metallic zinc could be decreased when the sintering conditions were changed. The content of impurity Pb could be reduced as the pressure of system is raised within certain range. At suitable experimental conditions, the high-purity zinc can be abtained with a purity of 99.995%.(5) The vacuum furnace was improved to make the experiment conditions more accurately controlled for the kinetic study of zinc oxide ore by carbothermic reduction. The main designs are the sample transfer device and the collection equipment of the product to maintain a fairly constant temperature and pressure of system at the right reaction time.(6) The kinetics of the vacuum reduction of ZnO-C system was investigated. Experimental results indicate that the vacuum carbothermic reduction of zinc oxide from smithsonite is a first-order reaction. The diffusion is the rate-determining step of the overall reduction process, where the activation energy is estimated to be 177.72～-191.31 kJ-mol-1.(7) The kinetics of the vacuum reduction of Zn2SiO4-C without CaF2 at temperature 1323～1473K was investigated. Experimental results showed that the vacuum carbothermic reduction of zinc silicate from hemimorphite is a first-order reaction. The interface-chemical reaction is the rate-determining step of the overall reduction process, where the activation energy is estimated to be 246.16 kJ·mol-1. The kinetics of Zn2Si04-C with 10%CaF2 at reduction temperature 1273～1423K was also studied. It was found that the process is controlled by interface-chemical reaction, but the activation energy is decreased to 164.82kJ-mol-1. As F-ion can improve the activity of zinc silicate, the Zn-O bond is broken more easily and the activation energy is decreased. Therefore CaF2 could catalyze the carbothermic reduction of zinc silicate.更多还原