Jingkui Qu

Removal of Ca(II) and Mg(II) from potassium chromate solution on Amberlite IRC 748 synthetic resin by ion exchange

Experimental measurements have been made on the batch ion exchange of Ca(II) and Mg(II) from potassium chromate solution using cation exchanger of Amberlite IRC 748 as K+ form. The ion exchange behavior of two alkaline-earth metals on the resin, depending on contact time, pH, temperature and resin dosage was studied. The adsorption isotherms were described by means of the Langmuir and Freundlich isotherms. For Ca(II) ion, the Langmuir model represented the adsorption process better than the Freundlich model. The maximum ion exchange capacity was found to be 47.21 mg g(-1) for Ca(II) and 27.70 mg g(-1) for Mg(II). The kinetic data were tested using Lagergren-first-order and pseudo-second-order kinetic models. Kinetic data correlated well with the pseudo-second-order kinetic model, indicating that the chemical adsorption was the rate-limiting step. Various thermodynamic parameters such as Gibbs free energy (DeltaG degrees ), enthalpy (DeltaH degrees ) and entropy (DeltaS degrees ) were also calculated. These parameters showed that the ion exchange of Ca(II) and Mg(II) from potassium chromate solution was feasible, spontaneous and endothermic process in nature. The activation energy of ion-exchange (E(a)) was determined as 12.34 kJ mol(-1) for Ca(II) and 9.865 kJ mol(-1) for Mg(II) according to the Arrhenius equation.

Activation pretreatment of limonitic laterite ores by alkali-roasting using NaOH

Activation pretreatment of Cr-containing limonitic laterite ores by NaOH roasting to remove Cr, Al, and Si, as well as its effect on Ni and Co extraction in the subsequent pressure acid leaching process was investigated. Characterization results of X-ray diffraction (XRD) and scanning electron microscopy/X-ray energy dispersive spectroscopy (SEM/XEDS) show that goethite is the major Ni-bearing mineral, and chromite is the minor one. Experimental results show that the leaching rates of Cr, Al, and Si are 95.6wt%, 83.8wt%, and 40.1wt%, respectively, under the optimal alkali-roasting conditions. Compared with the direct pressure acid leaching of laterite ores, the leaching rates of Ni and Co increase from 80.1wt% to 96.9wt% and 70.2wt% to 95.1wt% after pretreatment, respectively. Meanwhile, the grade of acid leaching iron residues increases from 54.4wt% to 62.5wt%, and these residues with low Cr content are more suitable raw materials for iron making.

Preparation of titanium dioxide from titania-rich slag by molten NaOH method

Preparing titanium dioxide from titania-rich slag (TiO2 73wt%) by molten NaOH method has been developed. The effects of temperature and reaction time on the titanium conversion were investigated. The results showed that temperature had significant influence on the titanium conversion as well as the structure of the product. About 92% of titanium in the titania-rich slag could be converted after reacting with NaOH at 500°C for 1 h. Metatitanic acid was formed through the steps of washing treatment, acid dissolution, and hydrolysis. Well-dispersed spherical titanium dioxide particles with an average size of 0.1–0.4 μm can be obtained by calcination of metatitanic acid. In addition, the content of titanium dioxide in the product is up to 98.6wt%, which can be used as pigments after further treatment of coating and crushing.

Preparation and Characterization of Titanium Tetrachloride-Based Ionic Liquids

A series of TiCl(4)-based ionic liquids (ILs) was synthesized by mixing TiCl(4) with quaternary ammonium, pyridinium, and imidazolium chlorogenated salt, respectively. The structure and composition of the ILs were studied with Fourier transform ion cyclotron resonance mass spectrometry. IR, and Raman spectra. The primary anions of the TiCl(4)-based ILs were TiCl(9)(-) and TiCl(6)(2-), whose amounts were different by variation of the molar ratio of TiCl(4) to organic halogenated salt. The physical properties such as the phase transition behavior, surface tension, density, viscosity, and conductivity of these ILs were also investigated. Temperature-dependent viscocity and conductivity of the ILs followed the Vogel-Tammann-Fulcher equation, and the best-fit parameters had been estimated, together with the lienar fitting parameters for the density. The conductivity and viscosity of the TiCl(4)-based ILs were controlled by the ion mobility and the availability of voids with suitable dimensions. Hole theory could well explain the physicochemical properties of the TiCl(4)-based ILs. (c) 2008 The Electrochemical Society. [DOI: 10.1149/1.3046160] All rights reserved.

Preparation of Cr2O3 precursors by hydrothermal reduction in the abundant Na2CO3 and Na2CrO4 solution

Precursors of chromium oxide (p-Cr2O3) were prepared by reducing hexavalent chromium in the presence of sodium carbonate solution under hydrothermal conditions. Methanal was used as the reductant, and carbon dioxide was the acidulating agent. The influences of reaction temperature, initial pressure of carbon dioxide, isothermal time and methanal coefficient on Cr(VI) reduction were investigated. Experimental results showed that Cr(VI) was reduced to Cr(III) with a yield of 99%. Chemical titration, thermogravimetry (TG), X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM) were used to characterize the p-Cr2O3 and Cr2O3. The series of p-Cr2O3 were found to be multiphase even if they presented different colors, from gray green to lavender. After these p-Cr2O3 samples were calcined, the product of rhombohedral Cr2O3 with a purity of 99.5wt% was obtained.

Synthesis of submicron spherical Fe–MCM-48 with actual gyroid like structure

Highly ordered submicron spherical Fe-MCM-48 was successfully synthesized by a mixed surfactant method using cheap water glass as silica source. The gyroid like structure of MCM-48 was captured by a TEM image for the first time, and it was corresponded well to the previous simulated gyroid model. A tentative mechanism of homogenization cooperative process involving the Helmholtz double electrical layer was purposed. After the loading of metal Ag, the resulting Ag/Fe-MCM-48 catalyst showed good catalytic performance in the catalytic combustion of benzene.

Dechromization Kinetics of Limonitic Laterite Ores by Alkali-roasting Method Using Sodium Hydroxide

A novel process was proposed for the activation pretreatment of Cr-containing limonitic laterite ores by NaOH roasting. The dechromization kinetics of the laterite ores and the effect of particle size, NaOH-ore ratio, and roasting temperature on Cr extraction were studied in detail. Experimental results indicate that decreasing the particle size and increasing the NaOH-ore ratio and roasting temperature increase the Cr extraction rate. Approximately 96% Cr in the laterite ores could be extracted under the optimal alkali-roasting conditions. The results also indicate that the Avrami model is suitable for the dechromization process and that the apparent activation energy is calculated 11.12 kJ·mol-1. The 99.5% Cr2O3 was obtained from Na2CrO4 leached in the alkali solution by liquid-phase reduction and then calcining at high temperature.

Synthesis and characterization of Co3O4 prepared from atmospheric pressure acid leach liquors of nickel laterite ores

A chemical precipitation–thermal decomposition method was developed to synthesize Co3O4 nanoparticles using cobalt liquor obtained from the atmospheric pressure acid leaching process of nickel laterite ores. The effects of the precursor reaction temperature, the concentration of Co2+, and the calcination temperature on the specific surface area, morphology, and the electrochemical behavior of the obtained Co3O4 particles were investigated. The precursor basic cobaltous carbonate and cobaltosic oxide products were characterized and analyzed by Fourier transform infrared spectroscopy, thermogravimetric differential thermal analysis, X-ray diffraction, field-emission scanning electron microscopy, specific surface area analysis, and electrochemical analysis. The results indicate that the specific surface area of the Co3O4 particles with a diameter of 30 nm, which were obtained under the optimum conditions of a precursor reaction temperature of 30°C, 0.25 mol/L Co2+, and a calcination temperature of 350°C, was 48.89 m2/g. Electrodes fabricated using Co3O4 nanoparticles exhibited good electrochemical properties, with a specific capacitance of 216.3 F/g at a scan rate of 100 mV/s.

Preparation of Alumina from NaOH-NaAlO2-Na2CrO4-H2O Solutions by Carbonization Process

Alumina was prepared from NaOH-NaAlO2-Na2CrO4-H2O solutions (chromate alkali solutions) by carbonization process. The effect of seed ratio, carbon dioxide (CO2) volume fraction, reaction temperature, and initial sodium hydroxide (NaOH) concentration on the removal efficiency of Al was investigated in detail. High removal efficiency of Al was obtained following the increase of CO2 volume fraction and temperature. While, initial NaOH concentration increases the stability of solution and reduces the removal efficiency of Al. Bayerite (Al (OH)3) with small content of Cr (VI) and Na2O was obtained from alkali metal chromate solutions at 50 °C with no seed. Particle size of bayerite (d50) was about 24 μm. Al2O3 was obtained after calcination at 1050 °C for 1.5 h.

Molecular Design of Solvents for Extractive Distillation

This paper presents an optimization technology for the molecular design of environmentally friendly solvents for extractive distillation. The approach based on the concept of group contribution methods (GCM). To decrease the complexity and random of design problem, a set of functional groups are pre-selected based on the modified UNIFAC method. Combination of groups can produce different molecule, once the molecule is generated, the properties are evaluated to determine if it satisfy the criteria. The criteria include separation performance and environmental performance. Simulated annealing algorithm is used to search feasible molecular structures. The molecule transition strategies and parameters of algorithm are described detailedly. Finally, the method is demonstrated with two examples, and the design results show that the proposed technology is a valid technology to design the desirable solvents.