Research On The Extraction Technology Of Vanadium From Chizhou Stone Coal

Vanadium is one kind of very important strategic resource which is used to make ferrovanadium and superalloy. China is one of the major countries with the large vanadium reserve in the world and stone coal is an important raw material for extracting vanadium in our country.There are some disadvantages with traditional process such as the low recovery of vanadium, the badly polluted environment and wasted resources. In this thesis, two non-pollution roasting technologies of extracting vanadium from stone coal of Chizhou City were researched. One techno1ogy inc1udes such processes as roasting with calcium additives￣acid leaching￣impurity removing￣ion exchange￣precipitation￣calcine to obtain vanadium pentoxide, and the other techno1ogy includes processes as non-salt roasting￣alkaline leaching￣impurity removing￣ion exchange￣precipitation￣calcine to obtain vanadium pentoxide. The optimum conditions of roasting and leaching stage were studied. The structure of stone coal before and after roasting was characterized by XRD. The economic benefit analysis and environmental analysis were taken. The kinetics of leaching vanadium with alkaline from stone coal was also studied.The results of experiments are as follows:(1) The optimum conditions of the roasting with calcium additives￣acid leaching process have been established. The roasting temperature, roasting time, CaCO3 additives, mass concentration of H2SO4, the solid to liquid ratio, the retention temperature, retention time, the size of particle are at 1000℃, 2h, 8%, 5~7%, 2:1, 30~50℃, 30min, less than 100μm respectively, and based on these conditions the leaching rate of vanadium reaches up to 65%. The ultimate recovery of vanadium is 60%.(2) The optimum conditions of the calcining-alkaline leaching process have been established. The roasting temperature, roasting time, mass concentration of c(NaOH), the solid to liquid ratio, retention temperature, retention time, the size of particle, stirring speed are at 800℃, 2h, 2~2.5mol·L-1, 3:1, 90~100℃, 3~3.5h, less than 100μm, over 500rpm respectively, and based on these conditions the leaching rate of vanadium reaches up to 85%. The ultimate recovery of vanadium is 80%.(3) The structural transformation of stone coal before and after roasting was characterized by XRD. According to the results, the structure of stone coal is almost destroyed after roast.(4) The results show that the roasting￣alkaline leaching process can be modeled with shrinking core model. The leaching kinetics equation is 1-(1-X(V2O5))1/3=kt. The kinetic apparent activation energy E was calculated to be 58.5kJ·mol-1, which indicates that the leaching process is controlled by surface chemical reaction.(5) The equipment choice, economic benefit analysis and environmental analysis in the processes of extrating vanadium were also considered in this thesis. According to the leaching rate of vanadium and economic benefits, non-salt roasting￣alkaline leaching process is better than the roasting with calcium additives￣acid leaching process. According to the environmental point of view, the two processes will cause little environmental pollution.