| At present, the industry of extracting vanadium from stone coal in China still has many problems such as tatty equipment, low recovery rate of vanadium, low utilization rate of stone coal, high producing cost, and serious environmental pollution. In this paper, the process of extracting vanadium by reburning and sulfuric acid leaching is raised in connection with characteristics of the stone coal from Shanglin region in Guangxi province, which route is reburning with compound additive-dilute sulfuric acid leaching-ion exchange-vanadium precipitation by ammonia. The process has a high vanadium recovery efficiency and low acid consumption.During this process, reburning in moving-bed is the key link to determine the vanadium recovery. In this paper, the reaction process in moving-bed was analyzed and studied thoroughly and systematically and mechanism research, industrial tests were aslo reported.Firstly, in order to determine the optimum conditions for roasting to maximize vanadium extraction from ash of stone coal, and to identify the mechanisms governing the transition of vanadium oxidation state during composite additives (NaCl-CaF2-CaCO3) roasting. X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and energy spectrum analysis (EDX) were used to study the mechanisms involved in transformation of vanadium during composite additives roasting.Secondly, based on the temperature conditions for roasting, stone coal was added to the samples containing ash and composite additives to supply heat. The effect of reducing substances in stone coal, such as organic carbon and pyrite, on the oxidization of vanadium was discussed based on oxidizing roasting system. According the reaction orders for multistep oxidation process, the two-stage oxidization technology was put forward. The first step of it is carbon oxidization during heating stage, and the second step is vanadium oxidization during insulation stage.The influence of the change of the temperature, roasting time, heating-rate and atmosphere on the transformation of vanadium and buring of fuel was discussed thoroughly. The analysis of crystal contents by XRD, pore structure by mercury porosimetry, surface forms by SEM and emission gas concentration by Gasmeter were used to illustrate the feasibility and validity of this heating method. Afterwards, TG-FTIR-DSC was employed to examine the effect of the composite additives on the characteristics of stone coal combustion which is closely related to transformation of vanadium and heat supply. The ignition temperature and the thermo-kinetic analysis were also used to investigate combustion behaviour of the samples. This recearch on burning technology of stone coal provide valuable data and theory foundation for the utility of this technologyAt last, the moving-bed was used to reburn the ash with stone coal to extract vanadium, considering the demand of vanadium conversion for temperature conditions and calcination atmosphere, the moving-bed was divided to five temperature zone. With the transformation of the roasting status, concentration of various compositions of emission gas, including HC1, HF, CO2and CO was measured. Optimal operating conditions were determined through lots of tests, including composite additives, proportion of stone coal, pellet size, location of temperature zone, material moving rate and the amount of input air. The test results show that compared to tube furnace roasting the reburing with moving-bed can achieve higher conversion rate of84.68%, lower concentration of pollutants in the flue gas. Because of its high efficiency, simple operation, low cost, environment-protecting and energy-saving, the technology has obvious benefits in society and economy and has wide foreground for industrial application. |
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