Xuheng Liu

The microanalysis of the bonding condition between coated diamond and matrix

Abstract Ti, Mo, and Cu were plated on the diamond surface by magnetron sputtering method. The compression strength of Ti-coated diamond was measured; the structure of the diamond surface after vacuum heat treatment was analyzed by XPS. By the SEM analysis and the bending stress testing experiments, the authors researched the interface bonding condition of the coated diamond. The research revealed that the coatings on the diamond surface can protect the diamond well, and they also avoided or decreased the erosion of the diamond by matrix. The bonding strength between the diamond and the matrix was improved after plated Ti and Mo, but it was greatly influenced by the matrix composition and the hot-pressing technics. The plated metal and diamond could form local chemical union at the hot-pressing temperature of 830–840 °C.

Thermodynamic study on phosphorus removal from tungstate solution via magnesium salt precipitation method

Abstract The thermodynamic equilibrium diagrams of Mg 2 + − PO 4 3 − − NH 4 + − H 2 O system at 298 K were established based on the thermodynamic calculation. From the diagram, the thermodynamic conditions for removing phosphorus from the tungstate solution by magnesium salt precipitation were obtained. The results show that when the concentration of total magnesium increases from 0.01 mol/L to 1.0 mol/L, the optimal pH for the phosphorus removal by magnesium phosphate decreases from 9.8 to 8.8. The residual concentration of total phosphorus almost keeps the level of 4.0×10−6 mol/L in the system. MgHPO4, Mg3(PO4)2 and the mixture of Mg3(PO4)2 and Mg(OH)2 are stabilized in these system, respectively. However, increasing the total concentration of magnesium has little effect on phosphorus removal by magnesium ammonium phosphate, while it is helpful for phosphorus removal by increasing the total ammonia concentration. The calculated results demonstrate that the residual concentration of total phosphorus can decrease to 5.0×10−7 mol/L as the total concentration of ammonia reaches 5.0 mol/L and the optimal pH value is 9–10. Finally, verification experiments were conducted with home-made ammonium tungstate solution containing 50 g/L WO3 and 13 g/L P. The results show that when the dosage of MgCl2 is 1.1 times of the theoretical amount, the optimum pH for removing phosphorus is 9.5, which matches with the results of the theoretical calculation exactly.

Thermodynamics and kinetics of adsorption of molybdenum blue with D301 ion exchange resin

Abstract The adsorption behavior of D301 for molybdenum blue was investigated. The thermodynamics parameters in adsorption process were calculated and the adsorption kinetics was studied. The experimental results show that the adsorption characteristic of D301 for molybdenum blue fits well with the Freundlich adsorption isotherm equation. In the adsorption process of D301 for molybdenum blue, both the enthalpy change Δ H and entropy change Δ S are positive, while the free energy change Δ G is negative when temperatures are in the range of 303-333 K. It is indicated that the adsorption is a spontaneous and endothermic process, and the elevated temperatures benefit to the adsorption. Kinetic studies show that the kinetic data are well described by double driving-force model, and the adsorption rate of molybdenum blue on D301 is controlled by the intraparticle diffusion during the adsorption process. The total kinetic equation is determined.

Electrochemical behavior of Li+, Mg2+, Na+ and K+ in LiFePO4/ FePO4 structures

Abstract Besides Li + and Mg 2+ , the electrochemical behavior of Na + and K + in LiFePO 4 / FePO 4 structures was studied since they naturally coexist with Li + and Mg 2+ in brine. The cyclic voltammogram (CV) results indicated that Na + exhibits some reversibility in LiFePO 4 /FePO 4 structures. Its reduction peak appears at −0.511 V, more negative than that of Li + (−0.197 V), meaning that a relatively positive potential is beneficial for decreasing Na + insertion. The reduction peak of K + could not be found clearly, indicating that K + is difficult to insert into the FePO 4 structure. Furthermore, technical experiments using real brine with a super high Mg/Li ratio (493) at a cell voltage of 0.7V showed that the final extracted capacity of Li + , Mg 2+ and Na + that can be attained in 1 g LiFePO 4 is 24.1 mg, 7.32 mg and 4.61 mg, respectively. The Mg/Li ratio can be reduced to 0.30 from 493, and the Na/Li ratio to 0.19 from 16.7, which proves that, even in super high Mg/Li ratio brine, if a cell voltage is appropriately controlled, it is possible to separate Li + and other impurities effectively.

Effect of Mg doping on electrochemical performance of Li3V2(PO4)3/C cathode material for lithium ion batteries

Abstract Li 3 Mg 2 x V 2–2 x (PO 4 ) 3 /C ( x =0, 0.05, 0.1, 0.2) composites were synthesized by carbothermic reduction, using a self-made MgNH 4 PO 4 /MgHPO 4 compound as Mg-doping agent. X-ray diffraction (XRD), scanning electron microscope (SEM), electrochemical performance tests were employed to investigate the effect of Mg doping on Li 3 V 2 (PO 4 ) 3 /C samples. The results showed that a proper quantity of Mg doping was beneficial to the reduction of charge transfer resistance of Li 3 V 2 (PO 4 ) 3 /C compound without changing the lattice structure, which led to larger charge/discharge capacity and better cycle performance especially at high current density. Li 3 Mg 2 x V 2–2 x (PO 4 ) 3 /C sample with x =0.05 exhibited a better performance with initial charge/discharge capacity of 146/128 mA·h/g and discharge capacity of 115 mA·h/g at 5 C , while these two figures were 142/118 mA·h/g and 90 mA·h/g respectively for samples without Mg doping, indicating that a proper amount of doped Mg can improve the electrochemical performance of LVP sample. All of these proved that, as a trial Mg dopant, the synthesized MgNH 4 PO 4 /MgHPO 4 compound exhibited well doping effect.

Thermodynamics analysis of LiFePO4 pecipitation from Li–Fe(II)–P–H2O system at 298 K

Abstract Thermodynamics of the precipitation from Li–Fe(II)–P–H2O system at 298 K was investigated. The results demonstrate that LiFePO4 can be formed at room temperature under pH value of 0–11.3, and the impurities Li3PO4 and Fe(OH)2 will be yielded at pH value above 11.3 and 12.9, respectively. The optimum pH value for LiFePO4 precipitation is 8–10.5. Considering the low rate of phase transformation kinetics, metastable Li–Fe(II)–P–H2O system was also studied. The results indicate that equimolar ratio of co-precipitation precursor Fe3(PO4)2·8H2O and Li3PO4 cannot be obtained at the initial molar ratio 1:1:1 and 1:1:3 of Li:Fe:P. In contrast, equimolar ratio of the co-precipitation precursor can be yielded by adjusting the pH value to 7–9.2, matching the molar ratio 3:1:1 of Li:Fe:P, meaning that Li+-excess is one of the essential conditions for LiFePO4 preparation by co-precipitation method.

New Insights into the Application of Lithium-Ion Battery Materials: Selective Extraction of Lithium from Brines via a Rocking-Chair Lithium-Ion Battery System

Abstract Lithium extraction from high Mg/Li ratio brine is a key technical problem in the world. Based on the principle of rocking‐chair lithium‐ion batteries, cathode material LiFePO4 is applied to extract lithium from brine, and a novel lithium‐ion battery system of LiFePO4 | NaCl solution | anion‐exchange membrane | brine | FePO4 is constructed. In this method, Li+ is selectively absorbed from the brine by FePO4 (Li+ + e + FePO4 = LiFePO4); meanwhile, Li+ is desorbed from LiFePO4 (LiFePO4 − e = Li+ + FePO4) and enriched efficiently. To treat a raw brine solution, the Mg/Li ratio decreases from the initial 134.4 in the brine to 1.2 in the obtained anolyte and 83% lithium is extracted. For the treatment of an old brine solution, the Mg/Li ratio decreases from the initial 48.4 in the brine to 0.5 and the concentration of lithium in the anolyte is accumulated about six times (from the initial 0.51 g L−1 in the brine to 3.2 g L−1 in the anolyte), with the absorption capacity of about 25 mg (Li) g (LiFePO4)−1. Additionally, it displays a great perspective on the application in light of its high selectively, good cycling performance, effective lithium enrichment, environmental friendliness, low cost, and avoidance of poisonous organic reagents and harmful acid or oxidant.

Extracting Vanadium from Stone Coal by a Cyclic Alkaline Leaching Method

In order to achieve an efficient and economical approach on extracting vanadium from stone coal, a cyclic alkaline leaching method was studied in this work. The effects of operating parameters, including the NaOH concentration, temperature, reaction time, and liquid–solid ratio, on vanadium leaching efficiency were investigated. Also, we studied the influence of caustic soda dosage on the cyclic leaching process as well as the effect of increasing ionic strength in leachates and wash water. The results show that this method achieved a 51 pct decrease of the dosage of caustic soda under the optimized conditions compared with the single-step alkaline leaching. The average leaching yield of vanadium reached 82.28 pct. The leachates and wash water in each leaching cycle were utilized for the next leaching cycle, achieving the recycling of alkali as well as waste water. During the cyclic process, the volume of water was not increased, which markedly reduces the discharge of waste water and is also beneficial in terms of cost reduction.

Measurement of binary phase diagram of Cu2S–MoS2 system

Abstract A novel method, bath smelting process, was developed to treat molybdenite concentrate aiming at the existing problems of traditional process. To understand the dissolving behavior of MoS 2 in white matte, the binary phase diagram of Cu 2 S–Mo 2 S was measured by the cooling curve method. The result shows that this system is a simple binary eutectic with a eutectic temperature of (1117.0±3.0) °C and a eutectic composition of (1.70±0.20)% MoS 2 in mass fraction. When the MoS 2 addition exceeds 4.48%, MoS 2 and Cu 2 S can form the ternary compound containing CuMo 2 S 3 or Cu 2 Mo 6 S 8 . In the temperature range of copper smelting, 1200–1300 °C, molybdenite can dissolve in the cuprous sulfide. At 1200 °C, the solubility of molybdenite can reach 14.8%.

Extraction of lithium from salt lake brine by aluminum-based alloys

Abstract Salt lake brine was reacted with activated aluminum-based alloys and lithium was precipitated. The effects of aluminum-based alloys on precipitating lithium were investigated and the reasonable alloy used to extract lithium from brine was obtained. The effects of the mole ratio of Al to Li and Ca content of Al–Ca alloy, the initial concentration of lithiumion ion in solution, reaction temperature and reaction time on the adsorption rate of lithium were studied, and the optimized process parameters were determined. The results show that the mole ratio of Al to Li and Ca content of Al–Ca alloy and reaction temperature have great influences on the precipitation rate of lithium. The precipitation rate of lithium reaches 94.6% under the optimal condition, indicating that Al–Ca alloy is suitable for the extraction of lithium from salt lake brine.