Zhihe Dou

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%.

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.

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.

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.

Preparation of CeB6 nano-powders by self-propagating high-temperature synthesis (SHS)

CeB6 powders were prepared by high-temperature self-propagating synthesis (SHS) in which CeO2, B2O3 and Mg were taken as reactants. The adiabatic temperature and dynamics of SHS reactions were investigated. The SHS reaction products and leached products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicated that the adiabatic temperature of Mg-B2O3-CeO2 reaction system was rather higher than 1800 K to make the reaction propagate by itself, and the apparent activation energy (Ea) and reaction order (n) of exothermic peak on Mg-B2O3-CeO2 differential scanning calorimetry (DSC) curve were 23.03 kJ/mol and 1.31, respectively. The apparent activation energy was lower, so the reaction occurred easily. The SHS products consisted of MgO, CeB6 and little Mg3B2O6. The leached products consisted of single CeB6 phase and its purity was higher than 99.0%, and the average particle sizes of CeB6 were smaller than 150 nm.

Decomposition of the mixed rare earth concentrate by microwave-assisted method

Abstract A novel process was proposed to strengthen the decomposition of the mixed rare earth concentrate by utilizing the microwave radiation. Mineralogical information on the mechanisms by which microwave heating improved the leaching behavior of rare earth elements (REEs), and an interpretation of the interrelationship between mineralogy, decomposition process, and leaching process were provided in this study. The influences of the temperature, time of microwave heating and contents of NaOH (mass ratio of NaOH to mixed rare earth concentrate) on the decomposition of mixed rare earth concentrate were investigated. The results revealed that the temperature was the main factor affecting the decomposition process. The recovery of REEs by hydrochloric acid leaching reached 93.28% under the microwave heating conditions: 140 °C, 30 min and 35.35% NaOH. The BET specific surface area and SEM analysis indicated that the particles of mixed rare earth concentrate were non-hole, while the particles presented a porous structure after heating the concentrate by microwave radiation. For the microwave treated sample after water leaching, the BET specific surface area was 11.04 m2/g, which was higher than the corresponding values (6.94 m2/g) for the mixed rare earth concentrate. This result could be attributed to the phase changes of bastnaesite and monazite, and a number of cracks induced by thermal stress. The increase of BET specific surface area resulted in an increase of the recovery of REEs by promoting interaction within the system of acid leaching.

Study on leaching rare earths from bastnaesite treated by calcification transition

Extracting rare earths from bastnaesite concentrate treated by calcification transition was studied through the single factor test and XRD patterns of bastnaesite after calcification and slags after leaching in HCl solution. And the effects of the main calcified parameters such as temperature, liquid/solid and calcified time on transition performance of bastnaesite were investigated. It was found that under the optimal conditions of calcification temperature of 250 °C, liquid/solid of 20 mL/g, calcification time of 180 min, the highest leaching rate of rare earth were obtained, with the leaching ratio of rare earths 83.70% and Ce 77.01%, La 90.55%, Nd 92.03%, respectively; loss rates of fluorine with different calcification conditions were always less than 1% and XRD patterns of calcification slags and leaching slags showed that fluorine existed in the form of CaF2.

Kinetics of AlOOH dissolving in caustic solution studied by high-pressure DSC

Mechanism functions and kinetic parameters of AlOOH (boehmite or diaspore) dissolving in sodium hydroxide solution were researched. The mixture of boehmite or diaspore and caustic solution was scanned by high-pressure differential scanning calorimetry (DSC) instrument with heating rate of 10℃/min, and differential equation method was used to analyse the DSC curves, combining with iterative method and linear least square method. The most probable mechanism functions for both boehmite or diaspore and caustic solution reactions were logically selected from 30 types of non-isothermal kinetics differential equations, according to the calculated results obtained by Matlab program. The most probable differential mechanism function of boehmite dissolving in caustic solution is f(α)=1-α, which reveals the first-order reaction with apparent activation energy of 79.178 kJ/mol and the preexponential constant 1.031×10^8 s^(-1). The function, f(α)=2(1-α)(superscript 3/2), can describe the dissolution of diaspore sample in sodium hydroxide solution. The calculated results of kinetic parameters are apparent activation energy of 73.858 kJ/mol, preexponential constant of 5.752×10^7 s^(-1) and reaction order of 1.5.

Preparation and characterization of amorphous boron powder with high activity

Abstract The amorphous boron powders with high activity were prepared by the high-energy ball milling–combustion synthesis method. The effects of the milling rate and milling time on the crystallinity, microscopic morphology and reactivity of amorphous boron powder were studied. The results show that the crystallinity of amorphous nano-boron powder is only 22.5%, and its purity reaches 92.86%. The high-energy ball milling can significantly refine boron powder particle sizes, whose average particle sizes are smaller than 50 nm, and specific surface areas are of up to 70.03 m2/g. When the transmission electron beam irradiates the samples, they rapidly melt. It can be seen that the monomer amorphous boron size is less than 30 nm from the specimen melting traces, which indicates that the samples have high reactivity.