Scale-Up of Membrane-Based Zinc Recovery from Spent Pickling Acids of Hot-Dip Galvanizing

Abstract

Zinc recovery from spent pickling acids (SPAs) can play an important role in achieving a circular economy in the galvanizing industry. This work evaluates the scale-up of membrane-based solvent extraction technology aimed at the selective separation of zinc from industrial SPAs as a purification step prior to zinc electrowinning (EW). The experiments were carried out at a pilot scale treating SPAs batches of 57 to 91 L in a non-dispersive solvent extraction (NDSX) configuration that simultaneously performed the extraction and backextraction steps. The pilot plant was equipped with four hollow fiber contactors and 80 m2 of total membrane area, which was approximately 30 times higher than previous bench-scale studies. Tributylphosphate diluted in Shellsol D70 and tap water were used as organic and stripping agents, respectively. Starting with SPAs with high Zn (71.7 ± 4.3 g·L−1) and Fe (82.9 ± 5.0 g·L−1) content, the NDSX process achieved a stripping phase with 55.7 g Zn·L−1 and only 3.2 g Fe·L−1. Other minor metals were not transferred, providing the purified zinc stripping with better quality for the next EW step. A series of five consecutive pilot-scale experiments showed the reproducibility of results, which is an indicator of the stability of the organic extractant and its adequate regeneration in the NDSX operation. Zinc mass transfer fluxes were successfully correlated to zinc concentration in the feed SPA phase, together with data extracted from previous laboratory-scale experiments, allowing us to obtain the design parameter that will enable the leap to the industrial scale. Therefore, the results herein presented demonstrate the NDSX technology in an industrially relevant environment equivalent to TRL 6, which is an essential progress to increase zinc metal resources in the galvanizing sector.

Circular economy in hot-dip galvanizing with zinc and iron recovery from spent pickling acids

“…Fig. 6a shows the comparison between experimental data of the kinetic evolution of zinc in the SPA feed tank and in the stripping tank working in batch mode (data previously reported in 7 ), and the simulation results achieved with the model reported in the present study, in the conditions referred in the gure caption. The good match of simulated and experimental data conrms that the model predicts satisfactorily the pilot plant performance.…”

“…2− and ZnCl solvating agents such as tributyl phosphate (TBP). 7,20 Besides, TBP achieves high selectivity of zinc over iron and high loading capacity. 21 About the back-extraction process, tap water has proved an optimal performance for the stripping of zinc and TBP regeneration.…”

Past, Present and Future of Membrane Technology in Spain

“…The size growth of the research groups on membrane science and development has led to the subdivision of the former departments into subgroups specialized in a certain approach of membrane research and the type of publications and journals their members divulgate their results on, belonging to a wide range of applications and membrane materials and module fabrication methods. See, for instance in the directory, the IEC and PROMETEO groups of the Polytechnic University of Valencia, distinguish themselves between electrochemical applications and membrane processes for water treatment [62][63][64], the subgroups of the GIQA group at Rey Juan Carlos University, one devoted to polymeric membranes for wastewater treatment, the other on inorganic membranes for gas separation [65][66][67], or the division of the Chemical and Biomolecular Engineering Department at the University of Cantabria into four subgroups covering almost all the membrane topics [68][69][70][71][72][73][74][75][76]. Likewise, the CREG group at the University of Zaragoza has been divided by the results obtained in the later years in two subgroups, one devoted to membrane reactors and inorganic membranes, and the other on the synthesis and characterization of mixed matrix membranes for molecular separations [77][78][79], while the consolidation of membranes in health issues such as bone regeneration, grows in groups similar to that from the University of Seville here [80][81][82].…”

Anion exchange separations to produce a suitable electrolyte for the electrodeposition of pure zinc

“…The proposed method is anion exchange separation applying the differences in the formation and the sorption characteristics of the main metals contained in the SPL. This method has been applied mostly for the separation of small amounts of impurities for the purpose of ultra-purification (Kekesi and Isshiki, 2003; Kekesi et al 2002), but here the main task is to separate an unwanted element (Fe) which is usually of comparable concentration than the main element (Zn) (Arguillarena et al, 2020). A low Zn/Fe concentration ratio means challenges to the recovery process of a satisfactorily pure Zn product by electrodeposition.…”

“…The spent pickling liquor coming from the galvanizing industries usuallyon the global averagecontains 25 -125 g/dm 3 zinc, 90 -200 g/ dm 3 iron, and 70 -100 g/dm 3 free HCl, which means approximately 7 to 10 M total Clion concentration (Regel-Rosocka, 2010; Arguillarena et al, 2020;Lum et al, 2014;Kerney, 1994;Csicsovszki et al, 2005;Ortiz et al, 2004). Before the electrodeposition of Zn, it is imperative to purify the electrolyte from iron and the rest of the practically important contaminants, whereas the acidity also requires attention prior to separation and to electrodeposition.…”