Abstract
High-chromium vanadium slag (HCVS) is an important by-product generated during the smelting process of high-chromium-vanadium-titanium-magnetite. Direct acid leaching and calcium-roasting acid leaching technology were applied to recover vanadium and chromium from HCVS. The effects of experimental parameters on the leaching process, including concentration of H2SO4, reaction temperature, reaction time, and liquid-to-solid ratio, were investigated. The XRD and UV-Vis DRS results showed that vanadium and chromium existed in low valence with a spinel structure in the HCVS. The Cr-spinel was too stable to leach out; no more than 8% of the chromium could be leached out both in the direct acid leaching process and calcium-roasting acid-leaching process. Most low valence vanadium could be oxidized to high valence with calcium-roasting technology, and the leaching efficiency could be increased from 33.89% to 89.12% at the selected reaction conditions: concentration of H2SO4 at 40 vt.%, reaction temperature of 90 °C, reaction time of 3 h, liquid-to-solid ratio of 4:1 mL/g, and stirring rate of 500 rpm. The kinetics analysis indicated that the leaching behavior of vanadium followed the shrinking core model well, and the leaching process was controlled by the surface chemical reaction, with an Ea of 58.95 kJ/mol and 62.98 kJ/mol for direct acid leaching and roasting acid leaching, respectively.
Highlights
Vanadium and chromium are strategic transition elements that have been widely used in some fields such as steel-making, energy-storage, catalysts, the petrochemical industry, and green chemistry owing to their excellence hardness, high corrosion resistance, and other excellent physicochemical properties [1,2,3,4,5]
High-chromium vanadium slag (HCVS) is a by-product generated during the smelting process of high-chromiumvanadium-titanium-magnetite, and it is an important vanadium source in China [6,7,8,9,10]
The roasting process is similar to the sodium-roasting process; the vanadium-containing ores are mixed with lime, limestone, and calcium salts at fixed mole ratios and roasted at high temperatures, which are higher than with sodium roasting
Summary
Vanadium and chromium are strategic transition elements that have been widely used in some fields such as steel-making, energy-storage, catalysts, the petrochemical industry, and green chemistry owing to their excellence hardness, high corrosion resistance, and other excellent physicochemical properties [1,2,3,4,5]. The basic recovery technology for vanadium has been sodium-roasting leaching technology, which was first proposed by Birck in 1912 and is widely used in the Chinese industries since the 1980s [12,13,14]. The vanadium-containing ores are mixed with the sodium salts (sodium carbonate (800–1000 ◦C), sodium sulfate (1200–1250 ◦C), sodium chloride (750–850 ◦C), and sodium hydroxide (400–800 ◦C)) at determined mole ratios and roasted in a vertical kiln under a high temperature atmosphere with O2 [13,15,16]. The vanadium spinel is decomposed and reacted with calcium salts to form different kinds of calciumvanadate, which are determined by the mole ratio of the vanadium to calcium salts [26,27,28,29,30]. Some leaching enhancing processes or multiple roasting processes accompany this process to achieve high recovery [16,31,32,33,34]
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