Study on the synergistic mechanism of sulfuric acid and ammonium sulfate on the extraction of metals from ferronickel slag by roasting

Abstract

Due to the complex occurrence state of valuable metals in ferronickel slag, the metal extraction rate of the ammonium sulfate roasting process is insufficient. This study proposes a more cost-effective strategy to extract ferronickel slag valuable metals by mixed roasting with sulfuric acid and ammonium sulfate. The effects of the reagent dosage, roasting temperature and roasting time on the metal extraction rate of (NH4)2SO4 roasting, H2SO4 roasting and (NH4)2SO4 and H2SO4 mixed roasting were compared and analyzed. XRD, SEM and TG-DSC were used to reveal the mechanism of mixed roasting to optimize the metal extraction effect from ferronickel slag. The results showed that mixed roasting with a mass ratio of ammonium sulfate to sulfuric acid of 1:1 could reduce the dosage of ammonium sulfate roasting by 2.5 times, and the leaching rates of valuable metals Mg, Fe, Al and Cr increased by 17.46%, 42.8%, 26.06% and 24.89%, respectively. Likewise, comparing to sulfuric acid roasting, the acid consumption of mixed roasting was reduced by two-thirds, and the metal leaching rate was increased by 10.08%, 12.98%, 18.76% and 45.18%, respectively. The “synergistic” mechanism of sulfuric acid and ammonium sulfate on metal extraction by roasting is as follows: ① Before roasting, sulfuric acid partially destroys the surface structure of ferronickel slag particles, forming more pores and channels, creating conditions for the rapid diffusion of ammonium sulfate and sulfuric acid into the slag particles. ② Sulfuric acid reacts with ammonium sulfate to form NH4HSO4, which is more acidic and can accelerate conversion to soluble metal complexes. ③ The addition of sulfuric acid greatly advances the initial temperature of the reaction between ammonium sulfate and metals, widening the temperature range of sulfation roasting and reducing the difficulty of the reaction between ammonium sulfate and metals in ferronickel slag. ④ The liquid–solid reaction increases the reaction interface, improves the mass and heat transfer efficiency and enhances the degree of metal acidification.