Ting-an Zhang

Phase transformation in reductive roasting of laterite ore with microwave heating

Abstract Selective reduction of laterite ores followed by acid leaching is a promising method to recover nickel and cobalt metal, leaving leaching residue as a suitable iron resource. The phase transformation in reduction process with microwave heating was investigated by XRD and the reduction degree of iron was analyzed by chemical method. The results show that the laterite samples mixed with active carbon couple well with microwave and the temperature can reach approximate 1 000 °C in 6.5 min. The reduction degree of iron is controlled by both the reductive agent content and the microwave heating time, and the reduction follows Fe2O3→ Fe3O4→ FeO→ Fe sequence. Sulphuric acid leaching test reveals that the recoveries of nickel and iron increase with the iron reduction degree. By properly controlling the reduction degree of iron at 60% around, the nickel recovery can reach about 90% and iron recovery is less than 30%.

Pressure acid leaching of zinc sulfide concentrate

Abstract Effects of particle size of the zinc sulfide concentrate, leaching temperature, solid-to-liquid ratio and additive amount on pressure acid leaching process of the zinc sulfide concentrate were studied. The results indicate that the additive can improve the reaction kinetics and the conversion rate. And sulfur can be successfully separated from the zinc sulfide concentrate as elemental sulfur. The reasonable experiment parameters are obtained as follows: the leaching temperature 150 °C, oxygen partial pressure 1 MPa, additive amount 1%, solid-to-liquid ratio 1:4, leaching time 2 h, initial sulfuric acid concentration 15%, and particle size less than 44 μm. Under the optimum conditions, the leaching rate of the zinc can reach 95% and the reduction rate of the sulfur can reach 90%.

Computational simulation of fluid dynamics in a tubular stirred reactor

Abstract The flow and concentration fields in a new style tubular stirred reactor were simulated by simulating the fluids dynamics(CFD), in which FLUENT software was used and the standard k—ɛ model and multiple reference frame(MRF) were adopted. The various values of initial rotating speed and inlet flow rate were adopted. Simulations were validated with experimental residence time distribution(RTD) determination. It is shown that the fluid flow is very turbulent and the flow pattern approaches to the plug flow. The velocity increases from shaft to the end of impeller, and the gradient is enlarged by increasing the rotating speed. Comparison between RTD curves shows that agitation can improve the performance of reactor. As the flow rate increases, the mean residence time decreases proportionally, and the variance of RTD lessens as well. When rotating speed increases to a certain value, the variance of RTD is enlarged by increasing rotating speed, but the mean residence time has no obvious change.

φ-pH diagram of V-Ti-H2O system during pressure acid leaching of converter slag containing vanadium and titanium

Abstract To analyze the thermodynamic characteristics of leaching process of converter slag, φ-pH diagram of V-Ti-H 2 O system at oxygen partial pressure of 0.5 MPa, ionic mass concentration of 0.1 mol/kg and temperatures ranging from 60 to 200 °C was obtained by recently published critically assessed standard Gibbs energies and activity coefficients of various species. When pH 3+ , VO 2+ and VO 2 + exist in the stable region of TiO 2 . The pH values of stable regions of vanadium and titanium decrease and redox potentials become more positive with the temperature increasing. Vanadium and titanium could be separated by one-step leaching based on thermodynamics. The experiment results of pressure acid leaching of converter slag show that leaching rates of vanadium and titanium are 96.87% and 8.76% respectively, at 140 °C of temperature, 0.5 MPa of oxygen partial pressure, 0.055-0.075mm of particle size, 15:1 of liquid to solid ratio, 120 min of leaching time, 500 r/min of stirring speed and 200 g/L of initial acid concentration. Vanadium and titanium could be selectively separated in the pressure acid leaching process, and the experiment result is in agreement with thermodynamic calculation result.

Calcification–carbonation method for red mud processing

Red mud, the Bayer process residue, is generated from alumina industry and causes environmental problem. In this paper, a novel calcification-carbonation method that utilized a large amount of the Bayer process residue is proposed. Using this method, the red mud was calcified with lime to transform the silicon phase into hydrogarnet, and the alkali in red mud was recovered. Then, the resulting hydrogarnet was decomposed by CO2 carbonation, affording calcium silicate, calcium carbonate, and aluminum hydroxide. Alumina was recovered using an alkaline solution at a low temperature. The effects of the new process were analyzed by thermodynamics analysis and experiments. The extraction efficiency of the alumina and soda obtained from the red mud reached 49.4% and 96.8%, respectively. The new red mud with <0.3% alkali can be used in cement production. Using a combination of this method and cement production, the Bayer process red mud can be completely utilized.

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%.

The Most Probable Mechanism Function and Kinetic Parameters of Gibbsite Dissolution in NaOH

Determination of probable mechanism function and kinetic parameters is important to hydrometallurgical kinetics. In this work, the most probable mechanism function and kinetic parameters of gibbsite dissolution in NaOH solution are studied. The sample, the mixture of synthetic gibbsite and sodium hydroxide solution, was scanned in high-pressure differential scanning calorimetry (DSC) equipment with the heating rate of 10 K·min−1. Integral equation and differential equation of non-isothermal kinetics were solved to fit the data related to DSC curve. According to the calculation results, the most probable mechanism function for pure synthetic gibbsite dissolution in sodium hydroxide solution is presented based on the optimum procedure in the database of the mechanism function. The apparent activation energy obtained is (75±1) kJ·mol−1, the frequency factor is 108±1 mol·s−1, and the reaction is a second order reaction.

Experimental and CFD studies of solid–liquid slurry tank stirred with an improved Intermig impeller

Abstract The improved Intermig impeller has been used in the seed precipitation tank in China, which could enhance the mixing and suspension of Al(OH)3 particles and the power consumption declined largely. The flow field, solids hold-up, cloud height, just off-bottom speed and power consumptions were investigated in solid–liquid mixing system with this new type of impeller by CFD and water experiment methods. Compared with the standard Intermig impeller, the improved one coupled with specially sloped baffles could promote the fluid circulation, create better solids suspension and consume less power. Besides lower impeller off-bottom clearance is good for solid suspension and distribution. The just-off-bottom speed was also determined by a power number criterion. Meanwhile, the predicted results were in good agreement with the experimental data.

Thermodynamics study on leaching process of gibbsitic bauxite by hydrochloric acid

Abstract For the low-grade gibbsitic bauxite, the leaching rate of alumina is very low during the Bayer process. The acid leaching method is attracting more attention, and the hydrochloric acid leaching was developed rapidly. The mineral composition and chemical composition were investigated by X-ray diffraction analysis and semi-quantitative analysis. The thermodynamics of leaching process was analyzed. The results show that the major minerals in the bauxite are gibbsite, secondly goethite and quartz, anatase and so on. The acid leaching reactions of the bauxite would be thermodynamically easy and completed. Under the conditions that ore granularity is less than −55 μm, the L/S ratio is 100:7, and the leaching temperature is 373–383 K, the leaching time is 120 min and the concentration of HCl is 10%, both the leaching rates of Al and Fe are over 95%. The main composition of leaching slag is SiO 2 which is easy for comprehensive utilization.

Preparation and characterization of LaB6 ultra fine powder by combustion synthesis

Abstract High-purity, homogeneous and ultra fine LaB 6 powders were prepared by combustion synthesis. The effects of reactant ratio and molding pressure on the phase and morphology of the combustion products were studied. The combustion products and leached products were analyzed by XRD, SEM and EDS. The results indicate that the combustion product consists of LaB 6 , MgO and a little Mg 3 B 2 O 6 . The combustion product becomes denser and harder when the molding pressure increases. The purity of LaB 6 is higher than 99.0%. The LaB 6 particle size is in range of 1.92–3.00 μm and the lattice constant of LaB 6 is a =0.414 8 nm.