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Study on Preparation of Cobalt Oxide by Precipitation-Thermolysis Process of Oxalic Acid without Ammonia and Recovery Utilization of the Mother Liquor

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Tutor: GuoXueYi
School: Central South University
Course: Non-ferrous metallurgy
Keywords: oxilic acid,cobalt oxide,thermodynamics,kinetics,extraction,P350
CLC: TF816
Type: PhD thesis
Year:  2009
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Cobalt oxide is one of the most important functional materials with excellent properties, which is the main raw material for producing the lithium cobalt oxide as lithium-ion batteries cathode material. Meanwhile it is widely used in areas of super capacitor, cemented carbide, varistor ceramics, inorganic pigment and catalyst. At present, precipitation-thermolysis process with ammonium oxalate as the precipitant is the main supporting techniques for producing the cobalt oxide in industry, which consumes a lot of ammonia. And a great deal of ammonia-containing wastewater will be produced in this process. The non-treatment wastewater is directly discharged, thereby not only bringing about material loss but also polluting the environment. In this research, the addition of ammonia was avoided from the origins. Preparation of Cobalt Oxide by Precipitation-Thermolysis Process of Oxalic Acid without Ammonia and Recovery Utilization of the Mother Liquor with a great of Oxalic Acid were systematically studied. Wastewater closed circulation and reused technological process were adopted to prevent pollution. Therefore, this technique has important theoretical significance and practical value.According to the principle of simultaneous equilibrium and mass conservation, a series of thermodynamic equilibrium equations of the complex system of Me2+-C2O42--Cl--H2O were systematically studied, and the equilibrium curves of lg[Me]-pH were drawn, which indicated the equilibrium area and composites of the solutions at different complex and pH. This paper presents the comprehensive Analysis of the effect of pH value and additive such as citric acid, tartaric acid and EDTA on this Equilibrium System. It was found that the impurities such as Ca2+, Ni2+, Pb2+, Cu2+ in the solution always precipitated before Co2+, but Mg2+, Fe2+, Mn2+, Zn2+ precipitated before Co2+ only at high pH values. Therefore, reducing impurities contents and maintaining low pH value can get higher precipitation rate and better quality of cobalt oxalate in manufacture.The main factors affecting the precipitation rate, the size and morphology of the precipitated particles were investigated comprehensively. The Results show that the cobalt chloride content, temperature and the feeding speed of H2C2O4 played a decisive role in the size and morphology of cobalt oxalate. And the excess coefficient of oxalic acid had great influence on the precipitation rate. Adding ultrasonic on the process can decrease agglomeration effectively with the decrease of the particle size. But ultrasonic cavitation will hinder grains further growth, and the shape of cobalt oxalate particle became tubby and square finally and the ratio of length to diameter decreased. The optimum technological conditions were obtained as follows:using cobalt chloride as the starting material with 1mol/L, oxalic acid as coprecipitated agent with the excess coefficient(molar ratio of oxalic acid to cobalt chloride)1.5:1, positive-feed method,5.5 of pH value at 60¡æ, the feeding speed lOmL/min. Under these conditions, the rod-like¦Â-CoC2O4-2H2O with D50 from 30¦Ìm to 50¦Ìm can be fabricated, the precipitation rate was above 95%.Washing, drying and thermal decomposition on Cobalt oxalate dehydrate (CoC2O4-2H2O) were studied. The thermal decomposition behavior of Cobalt oxalate dehydrate was studied in Ar or Air Atmosphere by Thermogravimetry analysis(TGA) and Differential Scanning Calorimetry(DSC) respectively. It was also analyzed and discussed from thermodynamics point of view in this paper. The result shows that the thermal decomposed products were mainly Cobalt Metal in Ar Atmosphere, and mainly Co3O4 with temperature below 700¡æ, mainly CoO with temperature above 900¡æin air atmosphere. DSC-TGA curves verified the effectiveness of the thermodynamics model.This paper made an overall analysis of kinetic mechanism of the thermal decomposition behavior of cobalt oxalate.The kinetic model function, the apparent activation energy and preexponential factor were obtained by Coats-Redefrn equations, Ozawa method and Kissinger method. The most possible kinetic model function was [-ln(1-a)]1/3 in both inert atmosphere and oxidizing atmosphere. The activation energy of decomposition which was estimated by Ozawa and Kissinger in inert atmosphere were 129.82 KJ/mol and 125.37kJ/mol, respectively. And preexponential factor was 3.0533¡Á109S-1. The activation energy of reaction from COC2O4 to Co3O4 by Ozawa and Kissinger in air atmosphere were 70.5 kJ/mol and 64.11kJ/mol, respectively. And preexponential factor was 1.2008¡Á105S-1. The activation energy of reaction from Co3O4 to CoO by Ozawa and Kissinger in air atmosphere were 1232.14kJ/mol and 1276.04kJ/mol, respectively. And preexponential factor was 2.2103¡Á1056S-1.A novel method of selective extraction of oxalic acid from hydrochloric acid solution by the complexing agent P350 was proposed, which was used in recycling of the mother-liquor after precipitating cobalt effectively. The oxalic acid separated from the mother-liquor can be reused in precipitation process, and the hydrochloric acid in extraction raffinate can be used for leaching of raw materials Containing cobalt. The organic Phase after back extraction can extract again. So, all the resources of this process can be recycling used.The mechanism of extraction was investigated by infrared, and there were hydrogen bond association reaction. The composition of extracted complex had been determined P350: H2C2O4=1 : 1 by means of the slope method. The influences by factors such as the extractant concentration, aqueous phase acidity, volumetric ratio of oil phase and aqueous phase on the distribution ratio were examined. The optimum technological conditions were obtained as follows:the P350 concentration in extractant 50% by volume, the concentration of hydrogen ion 1.7mol/L,the concentration of oxalic acid from 0.2mol/L to 0.4mol/L,the time of extraction equilibrium 5min. The pH swing effect was used to strip the oxalic acid from organic Phase, using pure water as stripping agent, and the reuse of oxalic acid was realized.Multi-stage countercurrent extraction, back extraction and washing were investigated in this paper. The volumetric ratio of oil phase and aqueous phase (O/A) and extraction stages were determined by the method of equilibria isotherm and the string class simulate experiment. The concentration of the oxalic acid in extraction raffinate was less than 0.0040mol/L with 6-stage extraction while O/A was 2.0.And the back extraction ratio was more than 95% with 10-stage extraction while O/A was 2.0.
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