Guozhi Lu

Extraction of vanadium from vanadium slag by high pressure oxidative acid leaching

To extract vanadium in an environment friendly manner, this study focuses on the process of leaching vanadium from vanadium slag by high pressure oxidative acid leaching. Characterizations of the raw slag, mineralogy transformation, and the form of leach residues were made by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The result shows that the vanadium slag is composed of major phases of fayalite, titanomagnetite, and spinel. During the high pressure oxidative acid leaching process, the fayalite and spinel phases are gradually decomposed by sulfuric acid, causing the release of vanadium and iron in the solution. Meanwhile, unreacted silicon and titanium are enriched in the leach residues. With the initial concentration of sulfuric acid at 250 g·L−1, a leaching temperature of 140°C, a leaching time of 50 min, a liquid-solid ratio of 10:1 mL·g−1, and oxygen pressure at 0.2 MPa, the leaching rate of vanadium reaches 97.69%.

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.

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.

Preparation and properties of ultra-fine chromium carbonization of high performance mechanical activation

The preparation of hydroxyl chromium oxide by hydrogen reduction of disodium chromate and particulate hydroxyl mechanical activation features were studied. Then with self-made hydroxyl chromium as the raw material, a direct reduction and carburization process was used to prepare ultra-fine chromium carbonization. Through SEM and XRD, the high performance mechanical activation, key coefficients, microstructure, hardness and wear-resisting property were investigated. The results reveal that suitable mechanical activation and carbon reducing carbonization temperature, carbonization time, carbon content are beneficial to obtaining ultra-fine chromium carbonization. Typically, when the time of high performance grinding is 5 min, the carbon reducing temperature is 1 100 ℃, the carbon reducing time is 1 h, the carbon content is 28%, and finally the particle size of chromium carbide powder is 1 μm. Under this condition of preparation of ultra-fine chromium carbide, both the hardness and wear resistance are better than those in the industrialization of chromium carbide coating.

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.

Variation law of gas holdup in an autoclave during the pressure leaching process by using a mixed-flow agitator

The multiphase reaction process of pressure leaching is mainly carried out in the liquid phase. Therefore, gas holdup is essential for the gas–liquid–solid phase reaction and the extraction rate of valuable metals. In this paper, a transparent quartz autoclave, a six blades disc turbine-type agitator, and a high-speed camera were used to investigate the gas holdup of the pressure leaching process. Furthermore, experiments determining the effects of agitation rate, temperature, and oxygen partial pressure on gas holdup were carried out. The results showed that when the agitation rate increased from 350 to 600 r/min, the gas holdup increased from 0.10% to 0.64%. When the temperature increased from 363 to 423 K, the gas holdup increased from 0.14% to 0.20%. When the oxygen partial pressure increased from 0.1 to 0.8 MPa, the gas holdup increased from 0.13% to 0.19%. A similar criteria relationship was established by Homogeneous Principle and Buckingham’s theorem. Comprehensively, empirical equation of gas holdup was deduced on the basis of experimental data and the similarity theory, where the criterion equation was determined as ε = 4.54 × 10-11n3.65T2.08Pg0.18. It can be seen from the formula that agitation rate made the most important impact on gas holdup in the pressure leaching process using the mixed-flow agitator.