Selective Recovery of Zinc over Iron from Spent Pickling Wastes by Different Membrane-based Solvent Extraction Process Configurations

Abstract

This paper reports the selective separation of zinc over iron from spent pickling wastes or effluents using two different membrane-based solvent extraction process configurations, Nondispersive solvent extraction (NDSX) and emulsion pertraction technology (EPT). The process aims to obtain a highly concentrated zinc solution with a negligible content of iron to allow for Zn electrowinning. The effect of the following process variables on the kinetics and selectivity of zinc separation has been evaluated: (i) process configuration NDSX and EPT, (ii) extractant concentration, tributylphosphate (TBP) in the range of 20–100% v/v and (iii) stripping phase/feed phase volume ratio in the range V s/V a 0.2–2. The transport of iron, chloride and free acid has been also monitored to gain insight into the separation fundamentals. EPT configuration overcame NDSX in terms of zinc and iron separation kinetics, although separation selectivity (at 30 min) was higher for NDSX configuration, αZn/Fe = 22, compared to EPT process αZn/Fe = 15. The optimum TBP content in the extractant phase was found to be 50% v/v. A further increase did not improve the Zn recovery kinetics and reduced the Zn/Fe selectivity. The increase of the V s/V a ratio improved the process efficacy in terms of kinetics and zinc recovery.

Selective recovery of zinc from spent pickling baths by the combination of membrane-based solvent extraction and electrowinning technologies

“…Due to the dependence of zinc and iron extraction and back-extraction kinetics on the operation conditions [14] and with the aim of attaining stripping solutions with different concentrations of zinc and iron, EPT experiments were performed under different operation conditions namely the operation time in the range between 1 and 3 h and the concentration of the selective extractant TBP varying from 20% (v/v) and 50% (v/v). Table 2 summarizes the conditions of EPT and electrowinning (EW) experiments, and the pH and composition of the stripping solutions employed in electrolysis experiments.…”

“…This operation variable was modified according to the typical molar ratios observed in the stripping solutions obtained by the treatment of SPB by MBSX technology [14]. For this purpose different amounts of synthetic iron were added to the stripping solutions being the initial concentration of zinc kept constant as reported in experiments 5-8 present in Table 2.…”

“…As reported in Table 2, several EPT experiments were performed by increasing either the operation time or the TBP concentration in order to obtain stripping solutions with different initial concentrations of zinc in the range from 0.07 to 0.61 M (experiments 1-4). In addition, iron concentration and pH also varied in the ranges of 0.005-0.04 M and 1.67-0.8, respectively due to the unavoidable co-extraction of Fe and H + together with zinc species [14] and thus, the values of the initial molar ratio Zn/Fe varied from 14 to 20.…”

“…On the other hand, different membrane-based solvent extraction (MBSX) process configurations namely Emulsion Pertraction Technology (EPT) and Non-Dispersive Solvent Extraction (NDSX), which differ in the way of contacting the fluid phases and the number of the membrane contactors involved, have proved to be efficient alternatives to perform the selective separation of zinc over iron in HCl media employing tributylphosphate (TBP) and water as extraction and stripping agents, respectively [11][12][13][14]. In a previous work [14], the effect of several process variables on the kinetics http://dx.doi.org/10.1016/j.seppur.2015.07.051 1383-5866/Ó 2015 Elsevier B.V. All rights reserved.…”

“…In a previous work [14], the effect of several process variables on the kinetics http://dx.doi.org/10.1016/j.seppur.2015.07.051 1383-5866/Ó 2015 Elsevier B.V. All rights reserved. and selectivity of zinc over iron separation was analysed in order to obtain a highly concentrated zinc solution with a negligible content of iron to allow for further recovery of zinc by electrowinning.…”