Organic lixiviants for metal recovery from industrial process residues

Promovendus/a: Thupten Palden

Promotor(en): Prof. dr. Koen Binnemans, Mevrouw Mercedes Regadío

Rapid depletion of high-grade ores, stringent environmental regulations and global movement towards a circular economy has highlighted the importance of metal recovery from waste materials, including the residues generated by the metallurgical industry. Recovery of toxic and valuable metals from the industrial process residues is complex because the metals are often present in very low concentrations and often locked in complex matrices. Hence it is important to develop a process that can selectively recover the metal(s) of interest, while the undesired metals remain in the solid residue. In this PhD thesis, organic lixiviants were used to selectively recover valuable metals from industrial process residues. If the lixiviants are composed mainly of organic solvents with no or very limited water, the process can be referred to as a solvometallurgical process. Solvometallurgy is a new branch of extractive metallurgy that uses non-aqueous solvents instead of aqueous solutions.

The first part of this PhD thesis shows the development of novel solvometallurgical processes to selectively recover lead and zinc from jarosite of the zinc industry. Jarosite is a by-product of zinc hydrometallurgy plants. It contains iron, lead, zinc, and low concentrations of valuable metals such as indium, germanium and silver. Two processes were developed to recover valuable metals from the jarosite. In the first process, ionic liquids Aliquat 336 ([A336][Cl]) and Cyphos IL 101 ([C101][Cl]), equilibrated with 0.5 mol L−1 hydrochloric acid, were used to selectively leach lead and zinc from the iron-rich residue. In the second process, concentrated methanesulfonic acid (MSA) was used to leach lead and zinc from jarosite. In the second part of the PhD thesis, organic lixiviants were used to recover valuable metals from secondary lead smelter residues. Two processes were developed: one on iron-rich matte and slag, and the other on lead-rich dross. In the first process, EDTA was used as a lixiviant to recover lead from the matte and slag. These residues are composed mostly of iron and lead, with some amounts of tin, antimony, nickel and zinc. In the second process, antimony was selectively leached from a lead-rich dross, using 2 mol L−1 hydrochloric acid in ethanol as a lixiviant.

In conclusion, leaching by organic lixiviants exhibited high selectivity towards the metal(s) of interest with minimal co-dissolution of matrix metals. The high selectivity of the organic lixiviant was due to the selective reactivity of the organic lixiviant towards the target mineral, or the selective solubility of the dissolved metal in the organic lixiviants. The high cost of using organic lixiviants was offset by recycling and reusing them several times.