For vanadium-containing leach solution, solvent extraction method is usually used for purification and enrichment at present, but the conditions of solvent extraction method are harsh, usually after extraction and reverse extraction of more than 6 ~ 7 grades, and the extraction process is easy to form a third phase resulting in the failure of the extraction agent, and the organic extraction agent is volatile, poor working conditions. Relatively speaking, the ion-exchange rule can greatly simplify the process, reduce the production cost, improve the working environment, and obtain the enrichment solution with lower impurity content. The leaching solution containing vanadium is pretreated by oxidation, and the pH value range is adjusted to form polyvanadate ions. The exchange potential of polyvanadate ion groups is far greater than that of other anions. Therefore, the polyvanadate ions can be separated from other anion groups and metal cations in the solution by using ion exchange resin, so as to provide better vanadium precipitation solution for the subsequent process.
The process steps are as follows:
(1) Direct acid leaching
Vanadium titanium slag was crushed and ball milled to 38μm~250μm, and then leached directly with low concentration sulfuric acid (mass concentration 5% ~ 30%) in autoclave without oxidant, so that vanadium in the form of vanadyl sulfate into the leaching solution, titanium enriched in the leaching slag, leaching process conditions are: sulfuric acid mass concentration of 5% ~ 30%, according to the volume of sulfuric acid: The mass of vanadium and titanium slag, the ratio of sulfuric acid to vanadium and titanium slag is (2 ~ 40) :1, the leaching temperature is 50℃ ~ 200℃, the leaching time is 30min~300min, and the stirring speed is 50 RPM ~ 1000 RPM. After leaching, the leaching solution containing vanadyl sulfate and titanium-enriched slag were obtained by liquid-solid separation.
(2) Purification and separation of vanadium-containing leaching solution
NaClO was added to the leaching solution for oxidation pretreatment, and the amount of NaClO was 0.1%~0.5% of the mass of vanadium titanium slag. Weak basic anion exchange resin (type D301, type D201, type D311, type 717 or 312) transformed by sulfuric acid was used to purify and separate the leaching solution by ion exchange. The leaching solution after ion exchange (vanadium filtrate after extraction) was returned to the leaching process section for recycling. NaOH solution was used as desorption agent to obtain vanadium-containing desorption solution. Ion exchange separation conditions: adjust the pH of the leaching solution to 2 ~ 4, exchange adsorption contact time 30min ~ 90min; Resin desorption process conditions: the concentration of NaOH solution used was 1mol/L ~ 5mol/L, desorption contact time was 30min ~ 90min.
(3) Preparation of vanadium pentoxide
The pH value of the vanadium-enriched desorption solution was adjusted to 6-8, and ammonium chloride was added into the desorption solution for vanadium precipitation. According to the mass ratio, the amount of ammonium chloride was 1.1 ~ 1.4 times that of vanadium in vanadium-titanium slag. After stirring for 30min ~ 90min and aging for 3h ~ 12h, ammonium metadadate filter cake and filtrate were obtained by filtration. The powder vanadium pentahydrate was obtained by calcining ammonium metadadate filter cake at 500℃~700℃ for 60min~180min.
The filtrate after vanadium deposition was preheated to 50℃~90℃ in the multi-effect evaporator, held for 30min~60min, evaporation and concentration were carried out at 75℃~130℃, and sodium chloride crystals were centrifuged and recovered in the insulated tank. After salt separation, the filtrate was cooled to room temperature and ammonium chloride crystals were recovered for recycling in the vanadium deposition process.
