Wentang Xia

Kinetic and Thermodynamic Studies on the Phosphate Adsorption Removal by Dolomite Mineral

The efficiency of dolomite to remove phosphate from aqueous solutions was investigated. The experimental results showed that the removal of phosphate by dolomite was rapid (the removal rate over 95% in 60 min) when the initial phosphate concentration is at the range of 10–50 mg/L. Several kinetic models including intraparticle diffusion model, pseudo-first-order model, Elovich model, and pseudo-second-order model were employed to evaluate the kinetics data of phosphate adsorption onto dolomite and pseudo-second-order model was recommended to describe the adsorption kinetics characteristics. Further analysis of the adsorption kinetics indicated that the phosphate removal process was mainly controlled by chemical bonding or chemisorption. Moreover, both Freundlich and Langmuir adsorption isotherms were used to evaluate the experimental data. The results indicated that Langmuir isotherm was more suitable to describe the adsorption characteristics of dolomite. Maximum adsorption capacity of phosphate by dolomite was found to be 4.76 mg phosphorous/g dolomite. Thermodynamic studies showed that phosphate adsorption was exothermic. The study implies that dolomite is an excellent low cost material for phosphate removal in wastewater treatment process.

Resource Utilization of High-Sulfur Bauxite of Low-Median Grade in Chongqing China

Resource utilization of high-sulfur bauxite is one of the technical problems for alumina refineries in China. There are rich highsulfur bauxite ores of low-median grade in Chongqing China, which haven’t been utilized until now. Sulfur in bauxite will cause many negative effects on alumina production. There are still some disadvantages for current desulfurization technologies and it is difficult to make a breakthrough progress only from the view of application of these desulfurization technologies. So it is necessary to undertake fundamental theoretical studies on the occurrence of sulfur in high-sulfur bauxites, the reaction behavior and the impact of sulfur in the production process. Combining theoretical research with experiments, it is possible to develop a feasible desulfurization process. This will provide technical support and theoretical guidance for the utilization of high-sulfur bauxites in Chongqing, and is also advantageous for prolonging bauxite resource security for the Chinese alumina industry.

Roasting Pretreatment of High-Sulfur Bauxite with Low-Median Grade in Chongqing China

High-sulfur bauxite is being paid more and more attention due to the decreasing grade for traditional ore in China. There is rich high-sulfur bauxite with low-median grade in Chongqing, which is being treated with Bayer process with dressing. But there still exist excess impurities of sulfur and iron in the alumina product. The effect of surface density, particle size, temperature and time on the roasting desulfurization process was studied. The optimized roasting conditions are as follows: 750 °C, 60 minutes, the surface density of 7.6 kg / m2 and the particle size from 147 μm to 177 μm for the ore. Under these conditions, residual sulfur in the roasted ore is lower than 0.4%, which can meet the requirements of alumina production. Meanwhile, the digestion performance of the roasted ore improves. Roasting desulfurization might be one of methods for treating high-sulfur bauxite with low-median grade, and better technical and economic results might be attained when it is used to treat high-sulfur bauxite with organic and / or goethite impurites.

Leaching kinetics of cobalt from the scraps of spent aerospace magnetic materials

Based on physicochemical properties of the scraps of spent aerospace magnetic materials, a roasting - magnetic separation followed by sulfuric acid leaching process was proposed to extract cobalt. Roasting was performed at 500 °C to remove organic impurity. Non-magnetic impurities were reduced by magnetic separation and then the raw material was sieved into desired particle sizes. Acid leaching was carried out to extract cobalt from the scraps and experimental parameters included agitation speed, particle size, initial concentration of sulfuric acid and temperature. Agitation speed higher than 300 r/min had a relatively small impact on the cobalt extraction. As the particle size reduced, the content of cobalt in the raw material decreases and the extraction of cobalt by acid leaching increased at first and decreased afterwards. Raising the initial concentration of sulfuric acid and temperature contributed to improve the cobalt extraction and the influence of temperature was more remarkable. SEM image revealed that the spent aerospace magnetic materials mainly existed in the sliced strip flake with a loose surface and porous structure. Under the experimental condition, the leaching rate of cobalt from the scraps in sulfuric acid solution could be expressed as ln(-ln(1 - α)) = lnk + nlnt. The apparent activation energy was found to be 38.33 kJ/mol and it was mainly controlled by the surface chemical reaction.

Removal of Cd(II) Ion from Aqueous Solution by Adsorption on Wasted Low Grade Phosphorus-Containing Iron Ore

Low grade phosphorus-containing iron ore (LGPIO), a raw and wasted industrial solid material was used as an adsorbent to remove Cd(II) ion from wastewater. The effects of initial pH value, adsorptive time, initial Cd(II) ion concentration, adsorptive temperature and LGPIO dosage on the Cd(II) ion removal efficiency were studied. The results show that the Cd(II) ion removal efficiencies exceed 99.8% and Cd(II) ion concentrations are less than 0.10 mg/L under the pH value 6, temperature 20 °C, adsorptive time 90 min, initial Cd(II) ion concentration 50 mg/L, particle size <0.15 mm, adsorbent dosage 50 g/L and stirring speed 290 r/min. After Cd(II) ion removal reaction, the Cd(II) ion concentrations completely complies with the requirement of national discharge standard of water pollutants for cadmium and zinc industry (GB 20466-2010) (TCd(II) = 0.1 mg/L) in China. Therefore, it can be concluded that LGPIO is a new low-cost adsorbent which is suitable for the adsorption of Cd(II) ion from wastewater.

Effect of Crystal Growth Modifier on the Structure of Sodium Aluminate Liquors Analyzed by Raman Spectroscopy

It has been proved that crystal growth modifier (CGM) can improve particle size distribution (PSD) and the alumina production. However, few researches were reported on whether CGM has an effect on the structure of sodium aluminate liquors. In order to provide fundamental guidance to the application of CGM to seed precipitation, the effect of CGM on the structure of synthesized sodium aluminate liquors was studied. It is shown that there is no new characteristic peak and obvious shift in the Raman spectrum of the liquors after adding a certain amount of CGM. By constructing a comparison function and using calculation function of the software of Raman spectrometer, it is found that CGM might have micro effect on the structure of sodium aluminate liquors via changing the concentration of principal ion Al(OH)4-in the liquors.