Co-disposal Research of Red Mud and Aluminum Electrolysis Solid Waste Based on External Thermal Reduction and Smelting Separation

In large aluminum smelting enterprises, the solid wastes of red mud and waste cathodes are satisfied the basic elements requirements of the solid-solid direct reduction technology. Thus, it is proposed a solution to use waste cathodes and red mud under indirect heating supply to produce pellets and to utilize in situ. It has been studied the reduction mechanism of red mud and waste cathode, the influence of carbon allocation method on pellet reduction and the research of the smelting separation and product quality. Experiment shows that the iron of red mud can be successfully reduced by waste cathode and anode toner at high temperature. The metallization rate of iron in red mud can reach more than 95% and the quality of pellets is more suitable with the mode of external carbon mixing. In order to carry out effective melting and separation of slag and iron, the red mud pellets must to be briquetted or to reserve a molten pool before charging into the melting furnace. After separation, the content of iron and carbon in steel can reach about 98.85% and 0.13% respectively, and the yield of iron elements can reach more than 96%, the harmful components flow into the slag can be effectively solidified. Content of alumina in the slag reached about 37% which can be economically recycled to the alumina purification process as a matching.

Effect of catalyst on tail gas during reduction of vanadium-titanium magnetite carbon-containing pellet

Catalyst can enhance the reduction effect and promote the reduction of vanadium titanomagnetite. In this paper, the carbon-containing pellets of vanadium titanomagnetite were prepared by using highly volatile coal as the reducing agent under the background of a novel process of pre-reduction in the rotary kiln. The effects of CaO, CaCO3, B2O3 and borax (Na2B4O7·10H2O) on the tail gas characteristics of carbon-containing pellets in the prereduction process were studied by using a simulated rotary kiln and flue gas analyzer. The results showed that the enhanced reduction effect of boron catalysts was slightly stronger than that of calcium catalysts, among which CaO catalyzed the least and borax the best. With the increase of metallization rate, the CO utilization in the tail gas is generally reduced, while when using CaCO3 as the catalyst, the CO utilization is significantly increased. Due to different reduction mechanism, the boron catalysts have little effect on the tail gas, and the calcium catalysts have a great effect on the tail gas. Based on the experimental results and the characteristics of the tail gas from the reduction process, we put forward the idea of using CaCO3 as the best catalyst and using CaO to absorb CO2 in the tail gas to form CaCO3.

The effect of composite reducing agent on the reduction process and the tail gas of carbon-containing pellets

In order to explore a reasonable way for the efficient utilization of coal resources in the ironmaking process. In this paper, lignite and bituminous coal are used as reducing agents, and two types of vanadium-titanium magnetite composite reducing agent pellets are prepared for different content ratios and mixed forms of the two coal powders. Under the simulated rotary kiln pre-reduction conditions, the influence of the ratio and mixing of pulverized coal on the metallization rate and tail gas composition of the reduction process was explored. The results show that increasing the proportion of high volatile lignite is beneficial to the reduction of pellets and can obtain pellets with a higher metallization rate. Under the new pre-reduction process conditions of the rotary kiln, the vanadium-titanium magnetite double-layer pellet with 75wt% lignite inside and 25wt% bituminous coal outside has the highest metallization rate of about 76%. At the same time, this new type of composite reducing agent pellets reduced gas emissions. This pellet is of great significance to the coal-based ironmaking process.

Effects and mechanism of MgO on carbothermal reduction of Fe2TiO4

The effects of MgO on carbothermal reduction of Fe2TiO4 had been researched including the thermodynamic calculation in this paper. And, based on XRD and SEM-EDS, the effect mechanism of MgO on the direct reduction of Fe2TiO4 had been deeply dissected, systematically. The results showed that magnesium titanium phases including MgTi2O5, MgTiO3 and Mg2TiO4 were formatted after MgO added into Fe2TiO4, which was main reason to affect the reduction of Fe2TiO4. When the MgO content in Fe2TiO4 did not exceed 2%, there was the promoting effect on the reduction of Fe2TiO4. With the increase of MgO content from 2% to 8%, the magnesium titanium phases transformed from MgTi2O5, and through MgTiO3 to Mg2TiO4. The inhibition function appeared, and can be weaken in the high reduction temperature. When reduction temperature reaches to 1300 °C, the metallization rate of F-M-8 (the reduction sample of 8% MgO) can reach 80.62% from 56.43% at 1200 °C. However, the aggregation degree of iron particles became worse when MgO was added to the sample.

Influence of Parameters on the Pre-Reduction Process of Vanadium-Titanium Magnetite Carbon-Containing Composite Pellets in Rotary Kiln

A novel smelting reduction process called pre-reduction in rotary kiln and total oxygen melting pool is a promising route to reduce environmental pollution from the ironmaking industry. In this paper, the process parameters and appropriate efficiency of reduction in the pre-reduction process of the rotary kiln were investigated via the detection of the metallization rate, phase composition, and internal morphology of the product combining with the analysis of the off-gas. The results indicated that the parameters of reduction temperature, reduction holding time, and coal ratio have a remarkable influence on the metallization rate. The reduction temperature has the most significant effect, followed by the reduction time and the coal ratio. Furthermore, under the condition of reduction temperature 1000 °C, holding time 30 min, coal ratio = 1, a product with a metallization rate of more than 70% can be obtained, which meets the requirements of the rotary kiln process, and its CO2/CO value of the pre-reduction endpoint is appropriate. Continue to increase the temperature, holding time, and coal ratio can raise the metallization rate of the pellets, but only a little improvement and may cause reoxidation of the product.

PRODUCTION OF COMPOSITE PELLETS FROM WASTE COFFEE GROUNDS, MILL SCALE AND WASTE PRIMARY BATTERY TO PRODUCE FERROMANGANESE; A ZERO WASTE APPROACH

This study was aimed to produce ferromanganese by using waste battery as manganese source, mill scale as iron source and waste coffee ground as reduction agent and carbon source. Waste batteries were collected from waste battery collection bins. Mill scale was collected from hot rolling workshop. Waste coffee grounds were household used coffee. All starting materials were characterized. Weighted raw materials blended with addition of bentonite as a binder. Pelletizing equipment was used to produce composite pellets. Produced pellets were dried then used for reduction experiments. Reduction experiments were conducted in Argon purged tube furnace for 1250 oC, 1300 oC and 1400 oC according to thermodynamic background. Produced ferromanganese samples were characterized for chemical compositions and metallization rate.

An Experimental Study on the Reduction Behavior of Dust Generated from Electric Arc Furnace

To improve the utilization value of electric arc furnace dust (EAFD) containing zinc, the reduction behavior of non-agglomerate dust was investigated with carbon and ferrosilicon in an induction furnace. The experimental results show that when the temperature increases, the zinc evaporation rate increases. When the reducing agent is carbon, zinc evaporation mainly occurs in the range of 900–1100 °C. When the reducing agent is ferrosilicon, zinc begins to evaporate at 800 °C, but the zinc evaporation rate is 90.47% at 1200 °C and lower than 99.80% with carbon used as a reducing agent at 1200 °C. For the carbon reduction, the iron metallization rate increases with a rise in the temperature. When the reducing agent is ferrosilicon, with an increase in temperature, the metallization rate first increases, then decreases, and finally, increases, which is mainly due to the reaction between the metallic iron and ZnO. In addition, the residual zinc in the EAFD is mainly dispersed in the form of a spinel solution near the metallic phase.

Performance simulation and optimization of COREX shaft furnace with central gas distribution

To improve the distribution of the reducing gas inside the shaft furnace, recently, a central gas distribution (CGD) device is installed at the bottom of the shaft furnace in Bayi Steel. In this work, a two-dimensional steady-state mathematical model, including momentum, heat and mass transfers and chemical reaction, is developed to study the performance of the furnace with CGD. The model is validated by industrial production data of COREX-3000, and then it is used to study the detailed phenomena in the furnace with CGD. The results show that, compared with the traditional COREX shaft furnace without CGD, the CGD device has a positive effect on improving the solid metallization rate (MR) and gas utilization rate (UR). The solid metallization rate (MR) increases from 0.601 to 0.628, the gas utilization rate (UR) increases from 0.3437 to 0.3519 and the standard deviation (STDEV) of solid MR decreases from 0.0820 to 0.0037, which means that the MR of the DRI from the furnace with CGD is more uniform than that without CGD. In addition, the effects of operation conditions and the CGD design on the solid MR, gas UR and STDEV of MR are discussed and the optimized conditions are suggested.

Study of the reduction mechanism of ironsands with addition of blast furnace bag dust

To improve the reduction properties of ironsands carbon-containing briquettes, the behavior of ironsand during reduction by the addition of blast furnace bag dust (BFBD) is studied using a high temperature resistance furnace, X-ray diffraction (XRD) analysis and scanning electron microscopy. Additionally, the reduction mechanism is discussed in this study. The results showed that the reduction level and compressive strength of ironsand carbon-containing briquettes could be promoted by increasing the proportion of BFBD. When the addition rate of BFBD was 31.25%, the metallization rate and compressive strength increased from 82.1% and 21.5 N/a to 91.4% and 172.5 N/a, respectively. Metallic iron reduced from BFBD particles favored the carbon gasification reaction, which enhanced the internal CO concentration, and then promoted the FeTiO3 reduction to Fe in ironsand. Meanwhile, a large amount of the liquid phase generated during the reduction process also favored Fe2+ diffusion, spread of iron joined crystals and the growth of crystals, which resulted in the improvement of the compressive strength of the ironsand carbon-containing briquettes.

Impact on the Reduction Process of Carbon Containing Pellets with Biomass Replacing Traditional Reducing Agent

Considering the rotary hearth furnaces (RHF) direct reduction process, using bamboo char, charcoal and straw fiber as reducing agents added into the carbon containing pellets, the experimental study on the impact of reduction effect has been conducted from metallization rate, compressive strength and volumetric shrinkage. Test results showed that biomass reducing agents can replace traditional reducing agents used in the RHF direct reduction process. Compared with traditional reducing agents, biomass has less of effect on metallization rate, but different biomass reducing agents have large impact on strength and volumetric shrinkage of pellets. The compressive strength of pellet with straw fiber is relatively higher, and the compressive strength of pellets with charcoal or bamboo charcoal is low, for reaching the production requirement, which will be improved at higher temperature (1300°C). Using bamboo charcoal as reducing agent will lead to the swell of pellets in the beginning stage, and this situation will make the volumetric shrinkage at high temperature lower, finally, all of these will affect the strength of pellets and the heat-transfer between different material layers, thus it should be used accompanying with other reducing agent.