Selective separation of Fe and Ga from al-containing HNO3 leach liquor using cupferron: Efficiency, mechanism, and regeneration

Coal gangue and fly ash are typical coal-based solid waste and can be considered as Al and Ga resources. The HNO3 leaching technology was proposed by our team for the economical and efficient co-extraction of Al and Ga, whereas the separation and recovery of metal elements became a challenge due to the variety of co-existing ions in the leach liquor. In this work, a Ga-Fe iso precipitation strategy with cupferron (C6H9N3O2) as a selective precipitant followed by regeneration and circulation of cupferron was proposed. The feasibility of the technique was assessed by thermodynamic analysis. The systematic precipitation experiments showed that 99.05 % of Ga, 99.89 % of Fe, and 4.74 % of Al were transferred into the complex precipitation product at optimal conditions. And the separation factor of Ga vs. Al and Fe vs. Al were as high as 2101.74 and 17713.93, respectively. The precipitation mechanism was revealed via a suite of characterization methods to be the chelation of metal ions and cupferron, with the terminal oxygen (N = O) and hydroxyl oxygen (O–H) as ligating atoms. The regeneration rate of cupferron reached 81.28 % with an ammonium hydroxide (NH3·H2O) concentration of 8 mol/L. And the circulation experiment demonstrated the excellent performance of the regenerated cupferron. This work provides a new insight into the deep removal of Fe and the enrichment of Ga from the acidic solution.