Shaohua Yin

Extraction and separation of Ce(III) and Pr(III) in the system containing two complexing agents with di-(2-ethylhexyl) phosphoric acid

In order to develop a novel separation technology superior to the current extraction systems, the extraction behaviors of Ce(III) and Pr(III) from chloride medium with P204 in the presence of two complexing agents lactic acid (LA) and citric acid (H3cit) have been reported. The distribution ratios increase with the increase of the equilibrium pH and the ratio of [H3cit] : [LA] under certain conditions. The separation factors of Ce(III) and Pr(III) increase with the ratio of [H3cit] : [LA] at fixed pH, and the maximum value is as high as 5.78 in this complexing system. The maximum saturated extraction capacity is 27.08 g L−1 which is close to that in the current saponified P507 extraction system. The equilibrium constants and thermodynamic functions, ΔG, ΔH and ΔS have been calculated. Lactic acid and citric acid can be effectively recycled and enriched, providing possibilities for dissolving minerals in the circular process. By comparison with the experimental results, this complexing extraction method could be regarded as an effective strategy for separating REs.

The kinetics and mechanism of solvent extraction of Pr(III) from chloride medium in the presence of two complexing agents with di-(2-ethylhexyl) phosphoric acid

The extraction kinetics of Pr(III) from chloride medium containing two complexing agents lactic acid (HLac) and citric acid (H3cit) with di-(2-ethylhexyl)phosphoric acid (D2EHPA, H2A2) have been investigated by constant interfacial area cell with lamina flow. The influence of stirring speed, temperature, specific interfacial area, extractant and hydrogen ion concentrations on the extraction rate has been studied. It is concluded that the extraction of Pr(III) takes place at the liquid–liquid interface, while the extraction regime belongs to diffusion-controlled kinetics process. The extraction rate equation and the rate-determining step have been obtained under the experimental conditions, and the extraction rate constant is calculated. The interfacial reaction model is proposed based on the kinetic steps.

Solvent extraction of Nd(III) in a Y type microchannel with 2-ethylhexyl phosphoric acid-2-ethylhexyl ester

Abstract Conventional extraction equipment has many problems like a long mixing time, a large factory area occupation, a large amount of organic solvent consumption and so on. In this paper, a micro solvent extraction system for the extraction of Nd(III) was investigated to solve the above issues. The initial aqueous pH 4.0 and saponification rate 40% of 2-ethylhexyl phosphoric acid-2-ethylhexyl ester (P507) were selected as the optimal experimental conditions. The extraction equilibrium was quickly achieved within 1.5 s, without any mechanical mixing in a narrow channel (100 μm in width and 120 μm in depth) at a volumetric flow rate from 5.55×10-10 m3/s to 1.53×10-9 m3/s. The extraction behavior of Nd(III) in the microreactor is an interface chemical reaction or the diffusion rate of the Nd-complex in the organic phase at low pH and [P507], while the extraction rate is controlled by the rate of metal diffusion in the aqueous phase at high pH and [P507], and the apparent mass transfer rate is up to 3.29×10-5 mol/m2·s. The extracted complexes are determined by the infrared (IR) spectrum method, and confirm that the extraction is via a cation exchange mechanism in the microreactor.

Study on the aqueous solution behavior and extraction mechanism of Nd(III) in the presence of the complexing agent lactic acid with di-(2-ethylhexyl) phosphoric acid

The aqueous solution behavior and extraction mechanism of single Nd(III) from a chloride medium with di-(2-ethylhexyl) phosphoric acid (D2EHPA, H2A2) in the presence of the complexing agent lactic acid (HLac) have been reported. The analyses by FT-IR and UV of the aqueous solution indicate that there is a coordination mechanism between Nd3+ and Lac− in the form of the carboxyl oxygen bridge bidentate ligand. A cation extraction mechanism has been studied using the method of slope analysis and saturation loading capacities, and also confirmed by FT-IR and NMR. The equilibrium constants and thermodynamic functions have been calculated. The separation factors of La/Ce, Ce/Pr and Pr/Nd are 3.24, 2.04 and 1.58, indicating that this system is beneficial for separating light rare earths. The results could provide some reference value for complexing extraction systems.

Ultrasound augmented leaching of nickel sulfate in sulfuric acid and hydrogen peroxide media

A new method of preparation high purity nickel sulfate assisted by ultrasonic was studied. The process mechanism was analyzed by Inductively Coupled Plasma (ICP), X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Energy dispersive X-ray spectrometry (EDS).The reaction mechanisms of oxidizing leaching and ultrasonic leaching were explored, respectively. Results showed that ultrasonic treatment peel off the oxide film on the surface of nickel. The leachate under strongly agitated, the yield rate of nickel sulfate was accelerate. And the reaction area was increased by the cavitation effect, the liquid-solid reaction was promoted, and the activation energy was reduced. The leaching rate of nickel reached 46.29% by conventional leaching, which takes about 5h. Under the same conditions, the ultrasonic leaching rate reached 40%, only half of the conventional leaching time. Concentration of leaching agent, reaction temperature, ultrasonic power, leaching time had significant effect on the enhancement of the leaching reaction with ultrasonic radiation. The leaching rate of 60.41% under the optimum experiment conditions as follows: sulfuric acid concentration 30%, hydrogen peroxide 10%, leaching temperature 333K, ultrasonic power 200W and leaching time 4h. The kinetic study of the system was investigated, and the reaction rates of conventional leaching and ultrasonic leaching were controlled by diffusion, and the apparent activation energies were 16.2kJ/mol and 11.83kJ/mol.

Effects of roasting pretreatment on zinc leaching from complicated zinc ores

Abstract Roasting pretreatment and ammonia leaching were performed to extract zinc from complicated zinc ores. The residue of the unroasted ore showed that the zinc containing phase ZnCO3 cannot be effectively leached in the ammonia leaching system. Mineral phase transformation of ZnCO3 takes place at a roasting temperature of 673 K, and this is the reason for the improvement of zinc leaching recovery. Additionally, the parameters that can influence the leaching rate of zinc such as the calcined temperature, the total ammonia concentration, the ratio of liquid to solid, the stirring speed and the leaching time were also investigated. Zinc leaching recovery from the complicated zinc ores could reach 84.7% under the following optimized experiment conditions: roasting temperature of 673 K, leaching temperature of 298 K, stirring speed of 500 rpm, total ammonia concentration of 6 mol/l, liquid to solid ratio of 11:1 and leaching time of 60 min. Compared to the zinc leaching recovery from unroasted ore (49.7%, ammonia concentration 6 mol/l), roasting pretreatment and optimization of process parameters can increase the zinc leaching recovery by 70.4%.

Study on the calcination experiments of rare earth carbonates using microwave heating

Abstract The heating behavior and effect of experimental parameters like holding time, calcination temperature and microwave power on the weight loss of the mixed rare earth carbonate using microwave heating have been studied, also characterized by X-ray diffraction, thermogravimetry-differential scanning calorimetry, scanning electron microscopy (SEM), particle analysis and Fourier transform infrared (FT-IR). The results show the following: rare earth oxides are obtained at 850°C for holding 1 h; FT-IR analysis indicates that the vibration absorption peak of carbonate disappears after calcination using microwave, confirming the feasibility of microwave calcination for the rare earth carbonates; SEM shows that the rare earth oxides have the characteristics of better and finer particles, have better dispersion and have surface that is more loose and porous than that of products using conventional calcination; particle analysis indicates that average size (D50) of microwave heating is 1.52 μm, which is smaller than conventional calcination of 7.6 μm.

Ultrasound-assisted leaching of rare earths from the weathered crust elution-deposited ore using magnesium sulfate without ammonia-nitrogen pollution

The in situ leaching process of Chinas unique ion-adsorption rare earth ores has caused severe environmental damages due to the use of (NH4)2SO4 solution. This study reports that magnesium sulfate (MgSO4) as a leaching agent would replace (NH4)2SO4 by ultrasonically assisted leaching to deal with the ammonia-nitrogen pollution problem and enhance leaching process. At leaching conditions of 3wt% MgSO4 concentration, 3:1L/S ratio and 30min, the total rare earth leaching efficiency reaches 75.5%. Ultrasound-assisted leaching experiments show that the leaching efficiency of rare earths is substantially increased by introducing ultrasound, and nearly completely leached out after two stage leaching process. Thus, ultrasonic-assisted leaching process with MgSO4 is not only effective but also environmentally friendly, and beneficial to leach rare earths at laboratory scale.

Extraction of gold and silver in the selective chlorination roasting process of cyanidation tailing

ABSTRACT The selective chlorination of cyanidation tailing (CT) for the extraction of gold and silver has been investigated. The reaction operated at different conditions and their effect on the extraction of Au and Ag was studied. The mineral samples were characterized by fire assay, X-ray diffraction (XRD), X-ray fluorescence (XRF) and scanning electronic microscopy (SEM). The best recovery values were 95.32% of Au and 85.32% of Ag at 1373 K and 1.5 h with 5% KCl. The results show that gold chlorination reaction was controlled by the interfacial chemical reaction, and the apparent activation energy was 40.05 kJ/mol. Silver has an activation energy of about 8.97 kJ/mol, and silver removal is performed by diffusion control.

Impacts of ultrasound on leaching recovery of zinc from low grade zinc oxide ore

Abstract On the basis of an experiment on ultrasonic enhanced ammonia leaching of low grade zinc oxide ores, the effects of the total ammonia concentration, the ratio between the NH3 concentration (CNH3) and that of ammonium sulfate (NH4)2SO4 (C(NH4)2SO4), and the ultrasound power on zinc leaching rate were studied. The results showed that the leaching efficiency of zinc observably increased with the increase of the total ammonia concentration, and that the ratios between CNH3 and C(NH4)2SO4 can remarkably affect the zinc extraction from the low grade zinc oxide ores. When the ratio between CNH3 and C(NH4)2SO4 is 2 to 1, the leaching rates of zinc are observably improved. The ultrasound can improve the leaching efficiency of zinc, and its effect was especially pronounced when the NH3 concentrations were low. The higher ultrasound power cannot sensibly improve the leaching rate of zinc, but it can improve the leaching speed and shorten the leaching time. Under the optimized conditions - total ammonia concentration of 8 mol/l, ratio between CNH3 and C(NH4)2SO4 of 2 to 1, and ultrasound power of 600 W – 83.33% of zinc is recovered.