Study On The Effect And Mechanism Of PVC On The Roasting Process Of Vanadium-Bearing Shale

The extraction of vanadium from vanadium shale is of great significance in promoting the comprehensive utilization of vanadium resources and the development of vanadium industry in China.Most of the vanadium in shale substitutes for Al（III）and exists stably in the structures of mica group minerals in the form of isomorphism,which is hard to be extracted.In general,the structure of vanadium containing minerals is destroyed by the combination of fire and wet methods.Adding additives in the roasting process is an effective method to strengthen the roasting effect and improve the leaching rate of vanadium while substantial Polyvinyl chloride（PVC）waste is not recycled well.Aiming at this situation,PVC was adopted as roasting additive in this paper and the effect of the addition of PVC on the vanadium extraction process of shale and the mechanism of strengthening vanadium leaching were studied.The main research conclusions are as follows:PVC as a roasting additive could produce HCl in the roasting stage which could effectively destroy vanadium mineral structure,and reduce the standard Gibbs free energy of mica decomposition reaction;Moreover,PVC was a kind of high value polymers which could also provide heat for the roasting process,so as to reduce energy consumption and promote vanadium oxidation roasting.On the other hand,HCl produced in roasting process could react with vanadium oxide and generate volatile VOCl₃.Hence,when PVC was selected as the roasting additive,the leaching rate of vanadium and the loss rate of vanadium should be both under the consideration.Adding 10%PVC of stone coal quality in the roasting process,under the roasting conditions of heat rate was 10℃/min,roasting temperature was 800℃,roasting time was 60 min and the leaching conditions of ratio of liquid to solid was 1.5 mL/g,concentration of sulfuric was 15 vol%,leaching temperature is 95℃,leaching time is 4h.the leaching rate of vanadium can be increased by 8.8%compared with the blank roasting.There was no solid ash if PVC was selected as roasting additive for vanadium extraction from shale after roasting process.The tail gas produced during roasting process could be absorbed by distilled water to produce hydrochloric acid.Moreover,no high salt wastewater was generated and no new impurity ions wer generated in the leaching solution after leaching.Therefore,the addition of PVC would not have adverse effects on the subsequent process.