Preparing Ultrafine Chromic Oxide Slag By Hydrogen Research Of Chromium Carbide

Chrome carbide powder has a lot of excellent properties, such as high chemical stability, high hardness, good wearing-resistance and corrosion-resistance, high melting point and good wettability with the metal of cobalt and nickel. Thus, it is now widely applied in metallurgy industry, electronic industry, high-temperature coating. In this thesis, the technique of ultra-fine chrome carbide preparation from the waste chromic hydroxide slags was proposed. The waste chromic hydroxide slags were produced from no-calcium roasting of chromite. The waste chromic hydroxide slags were treated by alkali-leaching to remove the element of aluminum and then roasted to produce chrome oxide which can be further reducted by carbothermic process. The main research contents are as follows:The alkali-leaching behavior as well as the leaching kinetics of aluminum in the waste chromic hydroxide slags was studied. The controlling step in the leaching was further determined. The experimental results show that the temperature has a great influence on the leaching of aluminum and the leaching of aluminum can be achieved as94.07%only when the temperature is raised to373K. The apparent activation energy for aluminum leaching is determined as62.38kJ/mol and the kinetic equation follows the unreacted shrinking core model under the temperature ranged from343K to373K.Based on single-factor experiment method, the effect of sodium hydroxide concentration, liquid to solid ratio, temperature, agitation speed and reaction time on the removal of aluminum and the chromium content in the alkali-leaching residue was studied. The experimental results show that92.69%of aluminum can be removed under the following conditions:the leaching temperature of373K, the initial concentration of sodium hydroxide of150g/L, the liquid to solid ratio of7/1(mL/g), the agitation speed of400r/min and the reaction time of3.5h. After alkali-leaching, three-stage countercurrent washing was carried out for the removal of the entrained alkali. After washing, the alkali-leaching residue was roasted at1223K for1.5h to produce the intermediate product of chrome oxide, in which the chrome content can arrive at97.23%.The lime precipitation method was adopted to remove the aluminum from the alkali-leaching solutions and improve the recycling of alkali-leaching solutions. Based on single-factor experiment method, the effects of dosage of lime, temperature and reaction time on the removal of aluminum were studied. The results show that96.93%of aluminum can be removed under room temperature and CaO/Al mass ratio of3:1and reaction time of3h.Based on the thermodynamic and kinetic analysis of carbothermic process, the effects of carbon source, blending of the reaction materials, temperature and reaction time on the preparation of ultra-fine chrome carbide from the intermediate product of chrome oxide were studied. The carbon black as the carbon source and the dosage of carbon black is2%over the theoretic reaction dose. The mixture of carbon black and chrome oxide after being mixed for5min by high-performance ball miller was sent in high-temperature tube furnace and then roasted at1373K for2h after the evacuation of oxygen in the tube by Argon gas with the flow rate of1L/min. By this means, ultra-fine chrome carbide powder can be finally produced. It can be seen that the properties of the chrome carbide product are superior to those of the commodities on the basis of scanning electron microscope and X-ray diffraction analysis.