Alkaline selective separation of silicon/vanadium from vanadium-bearing shale and recovery of silica

Abstract

To overcome the lack of effective separation driving force in traditional physical pre-concentration methods for vanadium hosted in mica-type minerals, an alkaline selective pre-desilication route for silicon/vanadium separation was proposed based on the differences in reactivity and structural stability of various mineral phases in alkaline systems. By controlling the reaction conditions, preferential dissolution of SiO₂ and relative retention of vanadium in the solid phase were achieved. To quantitatively evaluate the separation behavior, the selectivity coefficient α(Si/V) was introduced to characterize the relative dissolution differences between SiO₂ and V₂O₅, and the effective selective separation window was subsequently determined. The results showed that under the conditions of NaOH concentration of 160 g/L, liquid-to-solid ratio of 4 mL/g, temperature of 190 °C, and reaction time of 20 min, the leaching rate of SiO₂ reached 62.29%, while that of V₂O₅ was only 10.56%, corresponding to an α(Si/V) value of 5.9. The V₂O₅ grade in the solid phase was enriched from 1.09% to 1.87% after desilication. Under the studied conditions, the apparent leaching processes of both SiO₂ and V₂O₅ could be described by the unreacted shrinking core model. The dissolved silicon in the desilication liquor was recovered as precipitated silica via carbonation reaction, achieving an SiO₂ recovery rate exceeding 97% and a product purity higher than 99%. The carbonate system after carbonation could be further regenerated into NaOH through causticizing treatment.