铬为重要的战略资源，铬化合物及含铬材料具有广泛的应用领域。铬酸钠作为制备其它铬化工产品的重要中间体，目前主要采用铬铁矿钠化氧化焙烧法生产。由于焙烧过程中低熔点物质熔融会产生液相，通常需加入一定量的返渣对液相进行稀释，以保证回转窑的正常运行，但返渣的加入也在一定程度上降低了工艺过程的热利用率和生产效率。因此，在不影响焙烧设备正常运行的前提下，减少返渣加入量是目前铬铁矿钠化氧化焙烧工艺亟需解决的技术难题。本论文采用引入添加剂的方法，代替返渣的使用，提高铬铁矿钠化氧化焙烧过程中铬转化率，同时降低反应过程中熔融液相比例。论文以焙烧熟料中铬和铝的浸出率、熟料烧结特性为考察指标，探究了不同添加剂对铬铁矿钠化氧化焙烧过程的影响规律，遴选出了效果最佳的添加剂和工艺参数，并深入分析了该添加剂对铬铁矿钠化氧化焙烧过程的作用机理。本论文取得的主要进展如下：（1）研究了引入添加剂后铬铁矿在Na2CO3介质中氧化焙烧过程的热力学。通过计算不同添加剂Fe2O3、MnO2、TiO2、Co3O4、CuO以及NiO存在条件下，铬铁矿主要成分FeCr2O4、MgCr2O4、FeAl2O4和MgAl2O4与Na2CO3在氧化焙烧过程中可能发生化学反应的吉布斯自由能，明确各反应的热力学趋势，掌握相关反应路径及物相变化。根据热力学计算结果，加入添加剂后，将促进含铬尖晶石中的Cr3+转化为Na2CrO4，并阻碍含铝尖晶石中的铝转化为Na2O·Al2O3。（2）考察了不同添加剂的加入对850 ℃~1000 ℃焙烧温度条件下铬铁矿钠化氧化焙烧过程的影响。根据焙烧熟料浸出实验的结果，Fe2O3能促进铬的浸出，同时抑制铝的浸出；MnO2则同时抑制铝和铬的浸出；TiO2能够抑制铝的浸出，并在焙烧温度小于900 ℃时促进铬的浸出；Co3O4、CuO和NiO则在不同温度范围内对铬和铝的浸出产生不同影响。进一步研究表明，铬铁矿无钙焙烧工艺产出的铬渣和铬铁矿液相氧化工艺产出的铬渣虽然含有55%~70%的Fe2O3，但二者均不能完全代替Fe2O3添加剂在铬铁矿钠化氧化焙烧过程中所起的作用。（3）优化了采用Fe2O3添加剂的铬铁矿钠化氧化焙烧工艺参数，并深入研究了Fe2O3添加剂的作用机理。以熟料中铬和铝浸出率及熟料烧结特性为指标，通过单因素实验，获得的铬铁矿钠化氧化焙烧最佳工艺参数为：配碱率1.1、Fe2O3用量30%、焙烧温度900 ℃~950 ℃。在最优工艺条件下，经过2.5 h~3.0 h的反应，熟料中铬的浸出率达到97%、铝的浸出率约24%，铬渣中Cr2O3含量约1%，获得的熟料疏松无烧结。通过热重分析以及物相分析，研究了Fe2O3添加剂存在条件下铬铁矿钠化氧化焙烧过程的反应机理。在反应初期，铬铁矿和Fe2O3均未与Na2CO3发生反应，铬铁矿中的Fe2+发生氧化生成Fe3+，引起铁铬尖晶石的晶格畸变，增强了铬、铝、铁组分的活性。反应中期，铬铁矿中铬、铝、铁组分和Fe2O3添加剂与Na2CO3同时发生反应，分别生成Na2CrO4、Na2O·Al2O3和Na2O·Fe2O3，由于Na2O·Fe2O3生成量较多抑制了Na+的扩散，所以Na2CrO4和Na2O·Al2O3的生成受到阻碍。反应后期，Na2O·Al2O3和Na2O·Fe2O3与铬尖晶石反应生成Na2CrO4和铁铝等尖晶石，由于Na2O·Al2O3和Na2O·Fe2O3的快速分解及铁铝等尖晶石的生成提高了Na+和O2扩散速率，所以促进了Na2CrO4的生成。;Chromium is an important strategic resource. Chromium compounds and chromium bearing materials have been widely applied in extensive fields. As the primary intermediate product for preparing other chromium chemical products, sodium chromate is industrially manufactured through the oxidative roasting of chromite ore with sodium carbonate. During the roasting reaction, the low-melting-point materials will form the liquid phase. A remarkable amount of chromite ore processing residue (COPR) is recycled and mixed with the raw materials in order to dilute the proportion of liquid phase and ensure the steady operation of rotary kiln. However, the addition of COPR partly reduces the heat utilization and industrial production efficiencies. At present, it is a technical problem to keep the operation of roasting equipment with reduced amount of COPR during the oxidative roasting process of chromite ore with sodium chromate. In this thesis, additives were introduced instead of COPR in order to reduce the volume of reaction liquid phase and increase the chromium conversion rate. The leaching rates of chromium and aluminum, as well as the sintering characteristics of the roasted mixture, were taken as the key indexes for investigating the roasting process. Based on the study of the influence of different addtives on the roasting process, the best additive and the optimized processing parameters were selected. The effect and mechanism of the selected additive on the oxidative roasting process of chromite ore with sodium chromate were further investigated in detail.The main progress of this thesis was summarized as follow:(1) The thermodynamics of the oxidative roasting process of chromite ore in the medium of Na2CO3 with different additives were investigated. The values of the Gibbs free energy for the possible chemical reactions among the main components, including FeCr2O4, MgCr2O4, FeAl2O4 and MgAl2O4, of the chromite ore and Na2CO3 were calculated with different additives, including Fe2O3, MnO2, TiO2, Co3O4, CuO and NiO, during the roasting process. According to the results of calculation, the thermodynamic trends of reactions were definited, and the possible reaction paths and phase changes of the roasting process with additives were clarified. Moreover, the introduction of additives would promote the conversion of Cr3+ from Cr-bearing spinel to Na2CrO4 and hinder the formation of Na2O·Al2O3 from Al-bearing spinel. (2) The effects of different additives on the oxidative roasting of chromite ore with sodium carbonate were studied in the temperature range from 850 ℃ to 1000 ℃. The results showed that Fe2O3 could promote the leaching process of chromium and inhibit the leaching process of aluminum. MnO2 would simultaneously impede the leaching process of chromium and aluminum. TiO2 can block the leaching process of aluminum and enhance the leaching process of chromium at the roasting temperature below 900 ℃. Co3O4, CuO and NiO exhibited different effects on the leaching process of chromium and aluminum depending on the temperature. As for the COPRs obtained from both the calcium-free roasting process of chromite ore with sodium carbonate and the aqueous solution oxidation process of chromite ore with caustic alkali, although their Fe2O3 content is as high as 55% to 70%, their addition can not substitute for the addition of the Fe2O3 additive in the oxidative roasting process of chromite ore with sodium carbonate. (3) After adding the Fe2O3 additive, the processing parameters of oxidative roasing process of chromite ore with sodium carbonate was optimized and the related mechanism was also studied in details. Based on the leaching rates of chromium and aluminum as well as the sintering characteristics of the roasted mixture in the single factor experiment, the optimal operation parameters were found as: alkali ratio of 1.1, additive dosage of 30%, and roasting temperature range from 900 ℃ to 950 ℃. After a roasting time period of 2.5 hours to 3.0 hours, the leaching rates of chromium and aluminum were 97% and 24%, respectively; the content of Cr2O3 in the COPR was as low as 1%; a loose and unsintered roasted mixture was obtained under the optimal conditions. The reaction mechanism of the roasting process with the Fe2O3 additive was investigated by thermogravimetric analysis and phase analysis. In the initial stage, no reaction occurred between chromite ore, Fe2O3 additive and Na2CO3. However, Fe2+ in the chromite ore was converted to Fe3+ resulting in the lattice distortion of spinel and then enhanced the activity of chromium, aluminum, iron components. In the middle stage, Na2CrO4, Na2O·Al2O3 and Na2O·Fe2O3 formed in the reaction among chromium, aluminum, iron components in spinel, Fe2O3 additive and Na2CO3. Because Na2O·Fe2O3 could reduce the diffusion of Na+, the formation of Na2CrO4 and Na2O·Al2O3 was impeded. In the final stage, Na2O·Al2O3 and Na2O·Fe2O3 reacted with Cr-bearing spinel to form Na2CrO4 and ferroaluminite spinel. Fast decomposition of Na2O·Al2O3 and Na2O·Fe2O3 and quick generation of ferroaluminite spinel increased the diffusion of Na+ and O2, thereby improving the formation of Na2CrO4