Yanxiu Wang

Recovery of alkali and alumina from Bayer red mud by the calcification–carbonation method

Red mud produced in the Bayer process is a hazardous solid waste because of its high alkalinity; however, it is rich in valuable components such as titanium, iron, and aluminum. In this study, a novel calcification–carbonation method was developed to recover alkali and alumina from Bayer red mud under mild reaction conditions. Batch experiments were performed to evaluate the potential effects of important parameters such as temperature, amount of CaO added, and CO2 partial pressure on the recovery of alkali and alumina. The results showed that 95.2% alkali and 75.0% alumina were recovered from red mud with decreases in the mass ratios of Na2O to Fe2O3 and of Al2O3 to Fe2O3 from 0.42 and 0.89 to 0.02 and 0.22, respectively. The processed red mud with less than 0.5wt% Na2O can potentially be used as a construction material.

Roasting Pretreatment-Low Temperature Digestion Method for Comprehensive Utilization of High-Sulfur Bauxite

The Roasting Pretreatment-Low temperature Digestion Method developed by the Northeastern University is presented in this paper, aiming for the comprehensive utilization of high-sulfur bauxite. Experimental results show that pre-roasting of the bauxite in a fluidized bed can effectively remove pyrite sulfur, and that the removal is increased with the increase of roasting temperature and roasting time. When the roasting temperature is 850 °C, the roasting time is 10 min the sulfur content in the bauxite can be reduced to below 0.2%. The digestion performance of the roasted ore was better than for the raw ore. This indicates that a low energy consumption production process with high-sulfur bauxite can be achieved by this method.

Processing Diasporic Red Mud by the Calcification-Carbonation Method

The novel calcification-carbonation method was proposed to process the diasporic red mud discharged from Bayer process alumina plant. In this study, Batch experiments were performed to evaluate the potential effects of important parameters such as temperature, amount of CaO added, CO2 partial pressure and carbonation cycles on the recovery of alkali and alumina. The results showed that 78.74% alumina was recovered from the diasporic red mud with decreases in the mass ratios of Al2O3 to SiO2 (A/S) from 1.27 to 0.27. The Na2O content in the processed red mud was less than 0.3 wt%, and it can be used as a construction material.

Comprehensive Utilization of Red Mud: Current Research Status and a Possible Way Forward for Non-hazardous Treatment

Red mud is an alkaline solid waste produced in the process of alumina extraction from bauxite. Presently, more than 3.0 billion tonnes of red mud are estimated to be stockpiled on land with an annual growth rate of approximately 120 million tonnes. The large amount of red mud has become a very real threat to the environment and human health because its high alkalinity presents a potential pollution to water, land and air. This article provides an overview of current research status for the options of comprehensive utilization of red mud and attempts to review their strengths and weaknesses. Ideally red mud is encouraged to be utilized as an industrial by-product for other applications, leading to a zero-discharge situation. On this basis the review recommends the Calcification-Carbonization Method, a promising technology for non-hazardous treatment, to recover the alkali and alumina and meanwhile transform the red mud into a non-hazardous material available for subsequent use.

Thermodynamics Analysis on Process of Pelletizing Chlorination of Fly Ash

Fly ash, generated during the combustion of coal for energy production, is an industrial by-product which is recognized as an environmental pollutant. In this paper, thermodynamic calculations and experiments in a tubular furnace reactor were conducted to investigate the process of pelletizing chlorination of fly ash. The thermodynamic calculations indicated that with the increase of the chlorination temperature, the Gibbs free energy of the chlorination reaction is negative, and this demonstrates the thermodynamics feasibility of pelletizing chlorination process. Experiments results show that the alumina chlorination efficiency was up to 70% when the pellet diameter was 8 mm and the C/Al was 3:1 at 1050 °C for 30 min. The effect of alumina chlorination efficiency in pelletizing chlorination process mainly depended on the temperature, chlorination time and pellet diameter. These findings provide useful information for understanding the pelletizing chlorination process, facilitating the development of pelletizing chlorination metallurgy in efficient clean utilization of fly ash.

Application of Tricalcium Aluminate Instead of Lime for the Recovery of Aluminum in Middle-Low Grade Bauxite in Calcification-Carbonization Process

In the process of calcification-carbonization, the alkali and aluminum in the mid-low grade bauxite and red mud can be recovered. Aluminum is obtained in the form of low-concentration sodium aluminate solution which is comparatively difficult to reuse. In this paper, the low-concentration sodium aluminate solution was reused to prepare tricalcium aluminate and went back to the Calcification-Carbonization process instead of lime. When processing gibbsite and diasporic bauxite with Calcification-Carbonization method, the effect of calcium aluminate on dealkalization and dealumination was investigated. The results show that the alumina-silica ratio of these two ores can be both reduced to 0.70, and the sodium alkali content can be reduce to less than 0.50%. It indicates that it’s feasible to use calcium aluminate replacing lime. The proposal well solved the problem that aluminum is difficult to recycle at low concentrations and enhances the effectiveness and cleanness of Calcification-Carbonization process which has an extensive prospect.

New Process Research on Aluminium Production from Non-Traditional Aluminum Resource by Microwave Chlorination

A novel method was developed to prepare aluminium via fluidizing chlorination with untraditional aluminum resources as raw materials. The main steps in this method were: alumina transformed into aluminium chloride through fluidizing chlorination; aluminium chloride reacted with NaOH solution for aluminium hydroxide and NaCl; NaOH and Cl2 were recycled from NaCl solution by electrolytic process. The new process for preparing aluminium resources by fluidizing chlorination method was proposed to realize efficient separation of the valuable components in non-traditional aluminum resources such as fly ash or low grade bauxite, silicon in untraditional aluminum changed into SiCl4 in fluidizing chlorination which could be used as raw materials for high purity Si products. Furthermore, the tailings emission of this process was quite lower than that of Bayer process. This paper mainly introduce the principle of this new process, the thermodynamics of fluidizing chlorination is analysis as well.

The effect of NaOH on the direct calcification–carbonation method for processing of Bayer process red mud

Abstract The Bayer red mud generated from the alumina industry is a hazardous solid waste. In our team, a green calcification–carbonation process is proposed for its disposal. Red mud is treated with lime to convert the silicon phase in solution into hydrogarnet, which is then decomposed by CO2 to recover alumina. In order to simplify the process flow, the direct carbonation process is employed, in which the NaOH-containing solution resulting from calcification is sent directly to carbonation without prior liquid–solid separation. The discrete and direct carbonation processes gave 34.9% and 35.5% alumina recoveries, respectively, with Na2O contents in the final red muds of 0.15%wt and 0.21%wt, respectively. The optimum NaOH concentration in the whole calcification–carbonation process liquor was 40 g/l. Under this alkali condition, alumina recovery reached 40.5% and the Na2O content in the processed red mud was reduced to <1 %wt.