【作者】 王俊娥；

【导师】 周秋生； 刘桂华；

【作者基本信息】 中南大学 ， 有色金属冶金， 2011， 硕士

【摘要】 无钙焙烧法是以铬铁矿为原料生产铬盐的技术发展方向,但目前在我国95%以上的铬盐产能采用落后的有钙焙烧工艺,极少数采用无钙焙烧法的工厂在实际生产过程中又遇到许多问题：铬氧化慢(～2h)、铬氧化率低(<76%)以及容易出现结圈现象等。为了强化铬铁矿无钙氧化焙烧过程,本文进一步完善了铬铁矿无钙焙烧体系的反应机理,并在理论指导下寻找出一种添加剂来促进氧化焙烧反应过程,同时,通过实验研究确定了最佳反应条件。本文以实验室合成的尖晶石型化合物为原料,较系统地研究了铬铁矿无钙焙烧体系中杂质铁、铝和硅对矿石中Cr(Ⅲ)氧化率的影响规律及其机理。结果表明：铬铁矿中杂质铁对Cr(Ⅲ)的氧化率无明显影响。焙烧过程中FeO被氧化后得到的Fe2O3先与Na2CO3反应生成中间产物NaFeO2,它在体系中仍起着碱的作用,使铬的氧化反应继续进行,整个Cr(Ⅲ)氧化过程的反应速率均较快；杂质铝能明显抑制Cr(Ⅲ)的氧化。其主要原因是：在焙烧过程中Al2O3与Cr2O3和MgO反应生成相对稳定、难溶的多元复杂氧化物MgO·(Cr203)0.5·(Al203)0.5。此外,A12O3与Na2CO3反应生成Na2O·Al2O3,但Na2O·Al203难以进一步与MgO·(Cr203)0.5·(Al203)0.5反应生成Na2CrO4;杂质硅可阻碍Cr(Ⅲ)的氧化过程,这主要是由于当温度高于1173K时,Na2SiO3和Cr2O3发生的氧化反应可逆向进行,使生成的Na2CrO4部分发生分解,从而导致铬的氧化率降低。基于铬铁矿无钙焙烧体系的氧化反应机理,本文开展了较系统的铬铁矿氧化焙烧实验研究。结果表明：焙烧反应的最佳条件是配碱量为理论量的110%-120%,焙烧温度为1323K,反应时间为30min-60min;向体系添加物质A可明显提高铬氧化率,其主要原因是：添加剂A的加入可使氧化焙烧体系的液相量明显降低；在1223K～1323K温度范围内,随着焙烧温度的升高,焙烧体系中的液相量基本保持不变,有利于氧气向焙烧体系的扩散,此时物质A对Cr(Ⅲ)的氧化反应有最大程度的促进作用,铬的氧化率可达98%以上更多还原

【Abstract】 Calcium-free oxidative roasting process is the technological direction of the production of chromate salts extracted from the chromite ore home and abroad. However, more than 95% of industrial chromates in China was produced by the traditional soda-lime oxidative roasting process, and minor factories employing the calcium-free oxidative roasting process also encountered many problems in the actual production process, such as slow oxidation rate of Cr(Ⅲ) (-2h), low oxidation ratio (<76%) and prone to ring-forming phenomena. To intensify the oxidative roasting process, the oxidation mechanism was investigated in this paper, and a kind of additive was selected to promote the roasting process based on the oxidation mechanism. In addition, the optimal reaction conditions were determined by series of experiments.The separate influence of the impurities of ferrous oxide and aluminum oxide on the oxidation rate of trivalent chromium and its mechanism were systematically studied using the spinal compounds synthesized in the laboratory as the starting materials in the calcium-free oxidative roasting process of chromite ore in this paper. The results show that the impurity of ferrous oxide has almost no effect on the oxidation rate of the trivalent chromium. Ferrous oxide is first oxidized to form ferric oxide, and NaFeO2 formed by the preferential reaction of ferric oxide and sodium carbonate, can further act as alkali and thus maintain a relatively rapid oxidation rate of trivalent chromium during the whole roasting process of chromite ore. The results show that the impurity of aluminum oxide obviously hinders the oxidation of trivalent chromium. This is mainly attributed to the formation of the complicated insoluble compound of MgO·(Cr203)0.5·(Al203)0.5. In addition, aluminum oxide readily reacts with sodium carbonate to form sodium aluminate which is difficult to further react with MgO·(Cr203)0.5·(Al2O3)0.5 to form Na2CrO4, resulting in the decrease in the oxidaton rate of trivalent chromium. And the results also show that the impurity of silicon oxide obviously hinders the oxidation of trivalent chromium. The main reason may be that the oxidation reaction of Na2SiO3 with Cr2O3 with the temperature higher than 1173K is reversible and thus Na2CrO4 generated would be decomposed, lowing the oxidation rate of Cr(III).Systematic oxidative roasting experiments were carried out based on the oxidation mechanism of calcium-free oxidative roasting process. The results show that, the optimized conditions are as following:the amount of alkali is 110%～120% of the theoretical value of alkali, the roasting temperature is around 1323K and the roasting time varies from 30～60min. Adding substance A to the furnace charge can greatly increase the chromium oxidation rate, the main reason is that additive A can obviously reduce the quantity of the liquid phase formed in the oxidative roasting process of chromite ore, promoting the mass-transfer process of oxygen. In the temperature range of 1223K to 1323K, with the increasing of temperature, the liquid quantity is almost unchanged facilitating the oxygen diffusion in the roasting system, and additive A has obvious positive effect on oxidation reaction of Cr(Ⅲ) with the oxidation rate of Ci(Ⅲ) of more than 98%.更多还原