Process Simulation And Optimization Of The Vanadium And Chromium Cleaner Production From Vanadium Slag Using Sub-Molten Salt Technology

Vanadium, an important element, has been widely used in metallurgy, aerospace,chemical, electrical and other industrial fields. The main vanadium extraction methodfrom vanadium slag is sodium salt roasting, which suffers from low vanadiumrecovery and ineffective recovery of chromium, creating serious resource waste andenvironmental pollution due to the presence of hexavalent chromium in the tailings.New processes using sub-molten salt (SMS) technology, therefore, are developed tosolve the above mentioned problems by the Institute of Process Engineering, CAS.The SMS processes can recovery vanadium and chromium simultaneously at a lowertemperature and pressure, exhibiting attractive industrialization prospect. In order toobtain conditions including mass balance, energy consumption, and heat utilizationefficiency, which are necessitated for the process scaling up, the SMS processes totreat vanadium slag have been simulated in this paper using METSIM. Based on thesimulation results, the mass and heat balances of every operation unit are obtained,providing valuable reference for the process design. Further, the heat exchangenetwork optimization using pinch technology is performed. The main contents are asfollows:(1) The thermodynamic study of the sub-molten salt medium. Based on the Pitzermodel, the thermodynamic properties of KOH medium are investigated, and the heatcapacity equation of KOH medium is obtained by nonlinear fitting. By adding theequation to the METSIM built-in database, the foundation is laid for energy balanceof the sub-molten salt processes.(2) Validation of METSIM feasibility and reliability of the sub-molten saltmedium thermodynamic data. Because a10,000tonnage scale chromate salt cleanerproduction demonstration plant using SMS technology has already been successfullyestablished, the existing process has been simulated using METSIM to verify thefeasibility of METSIM and reliability of KOH medium thermodynamic data.(3) Process simulation with respect to the vanadium extraction from vanadiumslag using sub-molten salt technology. Utilizing METSIM, the material and energybalances are conducted for the cleaner production processes for vanadium extraction from vanadium slag with potassium and sodium-based sub-molten salt methods.Based on the results, the energy consumptions of the heat exchanger network in theprocesses are optimized with pinch technology, providing a reference for futureprocess design and optimization.(4) Economic evaluation of the cleaner production processes for vanadiumextraction from vanadium slag using sub-molten salt technology. Economicevaluation is performed for the cleaner production processes for vanadium extractionfrom vanadium slag with potassium and sodium-based sub-molten salt methods, andthe optimal conditions for processes design are obtined.