Sulfuric acid leaching kinetics of South African chromite

The sulfuric acid leaching kinetics of South African chromite was investigated. The negative influence of a solid product layer constituted of a silicon-rich phase and chromium-rich sulfate was eliminated by crushing the chromite and by selecting proper leaching con- ditions. The dimensionless change in specific surface area and the conversion rate of the chromite were observed to exhibit a proportional re- lationship. A modified shrinking particle model was developed to account for the change in reactive surface area, and the model was fitted to experimental data. The resulting model was observed to describe experimental findings very well. Kinetics analysis revealed that the leach- ing process is controlled by a chemical reaction under the employed experimental conditions and the activation energy of the reaction is 48 kJ.mol-1.

Leaching kinetics of fluorine during the aluminum removal from spent Li-ion battery cathode materials

The high content of aluminum(Al)impurity in the recycled cathode powder seriously affects the extraction efficiency of Nickel,Cobalt,Manganese,and Lithium resources and the actual commercial value of recycled materials,so Al removal is crucially important to conform to the industrial standard of spent Li-ion battery cathode materials.In this work,we systematically investigated the leaching process and optimum conditions associated with Al removal from the cathode powder materials collected in a wet cathode-powder peeling and recycling production line of spent Li-ion batteries(LIBs).Moreover,we specifically studied the leaching of fluorine(F)synergistically happened along with the removal process of Al,which was not concerned about in other studies,but one of the key factors affecting pollution prevention in the recovery process.The mechanism of the whole process including the leaching of Al and F from the cathode powder was indicated by using NMR,FTIR,and XPS,and a defluoridation process was preliminarily investigated in this study.The leaching kinetics of Al could be successfully described by the shrinking core model,controlled by the diffusion process and the activation energy was 11.14 kJ/mol.While,the leaching of F was attributed to the dissolution of LiPF6and decomposition of PVDF,and the kinetics associated was described by Avrami model.The interaction of Al and F is advantageous to realize the defluoridation to some degree.It is expected that our investigation will provide theoretical support for the large-scale recycling of spent LIBs.

Leaching kinetics of ionic rare-earth in ammonia-nitrogen wastewater system added with impurity inhibitors

Ammonia-nitrogen wastewater is produced during the dressing and smelting process of rare-earth ores.Such wastewater includes a very high concentration of NH4＋, as well as other ions（e.g., NH4＋, RE3＋, Al3＋, Fe3＋, Ca2＋, Cl–, and Si O32–） with a p H of 5.4–5.6.Its direct discharge will pollute, yet it can be recycled and used as a leaching reagent for ionic rare-earth ores.In this study, leaching kinetics studies of both rare earth ions and impurity ion Al3＋ were conducted in the ammonia-nitrogen wastewater system with the aid of impurity inhibitors.Results showed that the leaching process of rare-earth followed the internal diffusion kinetic model.When the temperature was 298 K and the concentration of NH4＋ was 0.3 mol/L, the leaching reaction rate constant of ionic rare-earth was 1.72 and the apparent activation energy was 9.619 k J/mol.The leaching rate was higher than that of conventional leaching system with ammonium sulfate, which indicated that ammonia-nitrogen wastewater system and the addition of impurity inhibitors could promote ionic rare-earth leaching.The leaching kinetic process of impurity Al3＋ did not follow either internal diffusion kinetic model or chemical reaction control, but the hybrid control model which was affected by a number of process factors.Thus, during the industrial production the leaching of impurity ions could be reduced by increasing the concentration of impurity inhibitors, reducing the leaching temperature to a proper range, accelerating the seepage velocity of leaching solution, or increasing the leaching rate of rare earths.

Kinetics of chemical leaching of chalcopyrite from low grade copper ore: behavior of different size fractions

The kinetics of the chemical leaching of copper from low grade ore in ferric sulfate media was investigated using the constrained least square optimization technique. The experiments were carried out for different particle sizes in both the reactor and column at constant oxidation-reduction potential （Eh）, pH values, and temperature. The main copper mineral was chalcopyrite. About 40% of Cu recovery is obtained after 7 d of reactor leaching at 85℃ using -0.5 mm size fraction, while the same recovery is obtained at 75℃ after 24 d. Also, about 23% of Cu recovery is obtained after 60 d of column leaching for ＋4--8 mm size fraction whereas the Cu recovery is as low as about 15% for ＋8--12.7 and ＋12.7--25 mm size fractions. A 4-stage model for chalcopyrite dissolution was used to explain the observed dissolution behaviors. The results show that thick over-layers of sulphur components cause the parabolic behavior of chalcopyrite dissolution and the precipitation of Fe3＋ plays the main role in chalcopyrite passivation. In the case of coarse particles, transformation from one stage to another takes a longer time, thus only two stages including the initial reaction on fresh surfaces and S0 deposition are observed.

Process and kinetics of the selective extraction of cobalt from high-silicon low-grade cobalt ores using ammonia leaching

An ammonia-based system was used to selectively leach cobalt(Co)from an African high-silicon low-grade Co ore,and the other elemental impurities were inhibited from leaching in this process.This process was simple and environmentally friendly.The results revealed that the leaching ratio of Co can reach up to 95.61%using(NH_(4))_(2)SO_(4)as a leaching agent under the following materials and conditions:(NH_(4))_(2)SO_(4)concentration 300 g/L,reductant dosage 0.7 g,leaching temperature 353 K,reaction time 4 h,and liquid-solid ratio 6 mL/g.The leaching kinetics of Co showed that the apparent activation energy of Co leaching was 76.07 kJ/mol(i.e.,in the range of 40-300 kJ/mol).This indicated that the leaching of Co from the Co ore was controlled by an interfacial chemical reaction,and then the developed leaching kinetics model of the Co can be expressed as 1-(1-α)^(1/3)=28.01×10~3×r_0^(-1)×C_((NH_(4))_(2)SO_(4))^(1.5)×exp(-76073/8.314 T)×t,whereαis the leaching ratio(%)of Co,r_0 is the average radius(m)of the Co ore particles,T is the temperature(K),and C_((NH_(4))_(2)SO_(4))is the initial reactant concentration(kg/m^(3)).

Kinetics of Magnesium Slag Leaching by NH_(4)Cl

The leaching kinetics of magnesium slag in ammonium chloride solutions was investigated.The effects of initial ammonium chloride concentration,liquid-solid ratio and reaction temperature on the leaching rate of calcium were determined.The results showed that the leaching rate increased with the increase in initial ammonium chloride concentration,reaction temperature and liquid-solid ratio.It was determined that the leaching rate fit the Avrami equation,and the leaching process was controlled by diffusion.The activation energy was 13.22 kJ/mol.

THE KINETICS OF FERRIC CHLORIDE LEACHING OF SPHALERITE IN THE MICROWAVE FIELD

The kinetics of ferric chloride leaching of sphalerite in the microwave field has being studied in this paper.According to the experimental data,the rate of dissolution of sphalerite microwave irradiation heating is faster than that with conventional heating.The dissolution of sphalerite in the microwave field was investigated in different condition of temperature,concentration of FeCl,and particle size and a nonisothermal kinetic equation has being obtained.

Preparation of manganese sulfate from low-grade manganese carbonate ores by sulfuric acid leaching

In this study, a method for preparing pure manganese sulfate from low-grade ores with a granule mean size of 0.47 mm by direct acid leaching was developed. The effects of the types of leaching agents, sulfitric acid concentration, reaction temperature, and agitation rate on the leaching efficiency of manganese were investigated. We observed that sulfuric acid used as a leaching agent provides a similar leach- ing efficiency of manganese and superior selectivity against calcium compared to hydrochloric acid. The optimal leaching conditions in sul- furic acid media were determined; under the optimal conditions, the leaching efficiencies of Mn and Ca were 92.42% and 9.61%, respec- tively. Moreover, the kinetics of manganese leaching indicated that the leaching follows the diffusion-controlled model with an apparent ac- tivation energy of 12.28 kJ·mol-l. The purification conditions of the leaching solution were also discussed. The results show that manganese dioxide is a suitable oxidant of ferrous ions and sodium dimethyldithiocarbamate is an effective precipitant of heavy metals. Finally, through chemical analysis and X-ray diffraction analysis, the obtained product was determined to contain 98% of MnSOa4·H20.

Gold-leaching performance and mechanism of sodium dicyanamide

In this work,sodium dicyanamide(SD)was used as a leaching reagent for gold recovery,and the effects of the SD dosage and solution pH on the gold-leaching performance were investigated.A gold recovery of 34.8%was obtained when SD was used as the sole leaching reagent at a dosage of 15 kg/t.In the presence of a certain amount of potassium ferrocyanide(PF)in the SD solution,the gold recovery was found to increase from 34.8%to 57.08%.Using the quartz crystal microbalance with dissipation(QCM-D)technique,the leaching kinetics of SD with and without PF were studied.The QCM-D results indicate that the gold-leaching rate increased from 4.03 to 39.99 ng·cm^(–2)·min^(–1) when the SD concentration was increased from 0 to 0.17 mol/L,and increased from 39.99 to 272.62 ng·cm^(–2)·min^(–1) when 0.1 mol/L of PF was used in combination with SD.The pregnant solution in the leaching tests was characterized by X-ray photoelectron spectroscopy and electrospray mass spectrometry,which indicated that Au and(N(CN)2)–in the SD solution formed a series of metal complex ions,[AuNax(N(CN)2)x+2]–(x=1,2,3,or 4).

Leaching of vanadium,sodium,and silicon from molten V?Ti-bearing slag obtained from low-grade vanadium-bearing titanomagnetite

The water leaching process of vanadium, sodium, and silicon from molten vanadium-titanium-bearing（V-Ti-bearing） slag obtained from low-grade vanadium-bearing titanomagnetite was investigated systematically. The results show that calcium titanate, sodium aluminosilicate, sodium oxide, silicon dioxide and sodium vanadate are the major components of the molten V-Ti-bearing slag. The experimental results indicate that the liquid-solid（L/S） mass ratio significantly affects the leaching process because of the respective solubilities and diffusion rates of the components. A total of 83.8% of vanadium, 72.8% of sodium, and 16.1% of silicon can be leached out via a triple counter-current leaching process under the optimal conditions of a particle size below 0.074 mm, a temperature of 90°C, a leaching time of 20 min, an L/S mass ratio of 4：1, and a stirring speed of 300 r/min. The kinetics of vanadium leaching is well described by an internal diffusion-controlled model and the apparent activation energy is 11.1 kJ/mol. The leaching mechanism of vanadium was also analyzed.

Leaching process of germanium oxide dust

A thermodynamic analysis on the acid leaching process of germanium oxide dust and discussion on the behaviors of main substances of the dust in the leaching process were carried out. The effects of temperature, acid concentration, leaching time and stirring speed on the leaching rate of germanium were investigated. Based on the characteristic of the dust, the kinetics and reactive mechanism of acid leaching were studied. The results show that the leaching of the dust by acid belonged to ＂the unreacted core shrinking model＂ of producing solid outgrowth layer. The chemical reaction was controlled by inner diffusion process. The apparent activation energy of leaching process was 12.60 kJ/mol. The leaching reaction of germanium was determined to be mainly second order reaction. The optimum conditions were the reaction temperature of 363 K, the leaching time of 2.5 h, the stirring speed of 120 r/min, the solid-to-liquid ratio of 1/8 and the acid concentration of 120 g/L. Under these conditions, the leaching rate of germanium can come up to more than 87%.

Synergetic strengthening mechanism of ultrasound combined with calcium fluoride towards vanadium extraction from low-grade vanadium-bearing shale

The effect and mechanism of ultrasound and CaF_(2) on vanadium leaching from vanadium-bearing shale were investigated systematically.In consideration of the enhancement for vanadium recovery,the combination of ultrasound and CaF_(2)(66.28%) exerts more evident effects than ultrasound(26.97%) and CaF_(2)(60.35%) alone,demonstrating the synergetic effect of ultrasound and CaF_(2).Kinetic analysis manifests that the product layer diffusion controls vanadium leaching in ultrasound system without CaF_(2),however product layer diffusion and interfacial reaction is the rate-controlling step for vanadium leaching in other three leaching systems.The combination of ultrasound and CaF_(2) notably decreases the activation energy(E_(a)) from 62.03 to 27.61 kJ/mol,nevertheless individual CaF_(2) only reduces the E_(a) to 50.70 kj/mol.X-ray diffraction and fourier transform infrared spectrometer analyses show that the decomposition degree of the vanadium-bearing mica structure is the most significant in ultrasound and CaF_(2) system,proving the highest release degree of vanadium.Specific surface area and pore distribution combined with scanning electron microscope analyses reveal that the action of ultrasound and CaF_(2) would provide higher specific surface area,more abundant pores structure and cracks for the particles,which further prompts the rapid diffusion of H^(+),F^(-)and HF,and achieves the conspicuous improvement of vanadium leaching recovery.

Effects of mechanical activation on the kinetics of terbium leaching from waste phosphors using hydrochloric acid

The effect of mechanical activation （MA） on the kinetics of terbium （Tb） leaching from waste phosphors using hydrochloric acid was investigated. Leaching kinetics, such as apparent reaction rate, activation energy and reaction order, were determined using the shrinking-core model and the Arrhenius equation. Results obtained from experiments with different concentrations of HC1 and under different leaching temperatures were used for the determinations. The impacts of factors such as rotational speed, HC1 concen- tration and leaching temperature on the leaching rate of Tb were also discussed. The results showed that MA could dramatically increase the leaching rate of Tb from waste phosphors, and the apparent reaction rate （kap） of leaching was accelerated as well. For inactivated waste phosphors, the apparent activation energy （Eap） was 52.82±3.95 kJ/mol, indicating that the rate-controlling step of the leaching process was the chemical reaction. The Eap dropped to 25.96 ±3.90 kJ/mol and 10.96±2.79 k J/tool when the waste phosphors were mechanically activated at rotational speeds of 400 and 600 r/min, respectively; the leaching process transformed to a hybrid （chemical-reaction and diffusion） control process, and even a reagent-diffusion （through the product layer） control process. The apparent reaction order for Tb leaching from 400 r/min-activated waste phosphors was 2.49±0.11, and it decreased to 1. 16±0.17 when the rotational speed of 600 r/min was used. Kinetics results indicated that MA could make Tb leaching occur spontaneously, and thc activation intensity of waste phosphors was strengthened with higher rotational speed.

High-efficiency simultaneous extraction of rare earth elements and iron from NdFeB waste by oxalic acid leaching

Iron can not be recovered at high value because only rare earth elements are effectively recovered from NdFeB waste via oxidation roasting-hydrochloric acid leaching process.In this study,a new method for leaching NdFeB waste with oxalic acid was developed.The high-efficiency,simultaneous and high-value recovery of rare earth elements and iron was realized to simplify the process and improve the economic benefit.Results of the oxalic acid leaching experiments show that under the optimum leaching conditions at 90℃ for 6 h in the aqueous solution of oxalic acid(2 mol/L) with a liquid-solid ratio of60 mL/g,the iron leaching efficiency and precipitation rate of rare earth oxalate reach 93.89% and 93.17%,respectively.Rare earth oxalate and Fe(C_(2)O_(4))3^(3-) were left in the residue and the leaching solution,respectively.The leaching mechanism was further analyzed by characterising the leach residues obtained through X-ray powder diffraction(XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy(SEM-EDS).Results of the leaching kinetics study indicate that the process of oxalic acid leaching follows the shrinking nucleus model,and the leaching kinetics model is controlled by the mixed factors of diffusion and chemical reaction.The leaching residue was calcined at 850℃ for 3 h and then decomposed into rare earth oxide,which can be directly used to prepare rare earth alloy via molten salt electrolysis.For the leaching solution,ferric oxalate solution was reduced using Fe powder to prepare the ferrous oxalate(FeC_(2)O_(4)-2H_(2)O).