Zinc containing wastes/secondaries viz. zinc ash, dross, flue dusts, sludge, residue etc. are generated in various chemical and metallurgical industries. The materials contain different level of impurities depending on the source. The hydrometallurgical processing is effective and flexible for treating such materials as it can control the different level of impurities. Depending on the nature and composition of the secondaries, a suitable lixiviant could be selected to dissolve the desired metals leaving gangue in the residue. In the present paper, the hydrometallurgical processes have been described for the recovery of zinc from the secondaries using sulphuric acid, hydrochloric acid, ammoniacal solution and sodium hydroxide etc. as lixiviants. The leach solution thus obtained has been purified with respect to dissolved impurities using precipitation, ion exchange or solvent extraction method. The metal or salt is produced from the purified solution by electrolysis or crystallization.

Review of hydrometallurgical recovery of zinc from industrial wastes

The search for more environmentally-friendly reaction media has prompted the development of a wide array of alternative systems that will sustain biphasic separations with aqueous solutions without the use of volatile organic compounds (VOCs). We have begun to employ Room Temperature Ionic Liquids (RTIL), specifically 1-alkyl-3-methylimidazolium hexafluorophosphate ([Cnmim][PF6]), as VOC replacements in liquid/liquid separations of metal ions from aqueous solutions. Here we show that the partitioning of metal ions in these novel biphasic systems is consistent with traditional liquid/liquid separations: the metal ion affinity for the hydrophobic phase necessitates the presence of an extractant. In this report we explore the application of wellknown organic (1-(pyridylazo)-2-napthol, PAN, and (1-thiazolylazo)- 2-napthol, TAN) and inorganic (CN−, OCN−, SCN−, and halides) extractants for partitioning a variety of metal cations between [C4mim][PF6] or [C6mim][PF6] and an aqueous phase. PAN and TAN show pH depe...

Liquid/liquid extraction of metal ions in room temperature ionic liquids

The revived interest and research on the development of novel energy storage systems with exceptional inherent safety, environmentally benign and low cost for integration in large scale electricity grid and electric vehicles is now driven by the global energy policies. Within various technical challenges yet to be resolved and despite extensive studies, the low cycle life of the zinc anode is still hindering the implementation of rechargeable zinc batteries at industrial scale. This review presents an extensive overview of electrolytes for rechargeable zinc batteries in relation to the anode issues which are closely affected by the electrolyte nature. Widely studied aqueous electrolytes, from alkaline to acidic pH, as well as non-aqueous systems including polymeric and room temperature ionic liquids are reported. References from early rechargeable Zn-air research to recent results on novel Zn hybrid systems have been analyzed. The ambition is to identify the challenges of the electrolyte system and to compile the proposed improvements and solutions. Ultimately, all the technologies based on zinc, including the more recently proposed novel zinc hybrid batteries combining the strong points of lithium-ion, redox-flow and metal-air systems, can benefit from this compilation in order to improve secondary zinc based batteries performance.

An overview of progress in electrolytes for secondary zinc-air batteries and other storage systems based on zinc

Neutral aqueous electrolytes have been shown to extend both the calendar life and cycling stability of secondary zinc-air batteries (ZABs). Despite this promise, there are currently no modeling studies investigating the performance of neutral ZABs. Traditional continuum models are numerically insufficient to simulate the dynamic behavior of these complex systems because of the rapid, orders-of-magnitude concentration shifts that occur. In this work, we present a novel framework for modeling the cell-level performance of pH-buffered aqueous electrolytes. We apply our model to conduct the first continuum-scale simulation of secondary ZABs using aqueous ZnCl2 -NH4 Cl as electrolyte. We first use our model to interpret the results of two recent experimental studies of neutral ZABs, showing that the stability of the pH value is a significant factor in cell performance. We then optimize the composition of the electrolyte and the design of the cell considering factors including pH stability, final discharge product, and overall energy density. Our simulations predict that the effectiveness of the pH buffer is limited by slow mass transport and that chlorine-containing solids may precipitate in addition to ZnO.

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J. L. Limpo

Papers

The CENIM-LNETI process: a new process for the hydrometallurgical treatment of complex sulphides in ammonium chloride solutions

Solubility of zinc chloride in ammoniacal ammonium chloride solutions

Hydrolysis of zinc chloride in aqueous ammoniacal ammonium chloride solutions

Reactions during the oxygen leaching of metallic sulphides in the CENIM-LNETI process

Hydrometallurgy of bulk concentrates of spanish complex sulphides: Chemical and bacterial leaching