Vanadium recovery by electrodialysis using polymer inclusion membranes

Enhanced separation of monovalent and divalent ions in high salinity wastewater by selective electrodialysis: Experimental investigation and performance prediction

To fulfill the industrial requirements of salt fractionation and recovery from saline wastewater, a two-chamber selective electrodialysis (SED) stack incorporating commercial monovalent selective anion exchange membranes was employed and investigated in this study. Three different initial concentration ratios of NaCl/Na2SO4, namely 1:1 (10 g/L:10 g/L), 3:1 (30 g/L:10 g/L), and 5:1 (50 g/L:10 g/L) were examined to simulate various scenarios of saline wastewater. The influence of applied current density on membrane selectivity and overall system efficiency was further evaluated. The results indicated that an increase in the NaCl fraction within the feed solution directly correlates with enhanced concentration and purity of Na2SO4 in the product, achieving purities exceeding 92 %. A lower current density contributed to improved concentration and purity of Na2SO4, whereas higher current densities were conducive to augmenting the concentration and purity of NaCl. Additionally, a linear correlation was observed between the volumetric water transport and NaCl migration. Through numerical simulations, the concentrations of Na2SO4 and NaCl in the effluent were predicted, facilitating a comparative analysis with the salt fractionation efficiency of commercial nanofiltration membranes. Subsequent assessments of energy consumption and current efficiency revealed that the SED system ensured high product concentration and purity at reasonably low energy consumption (0.22-0.28 kWh per kg NaCl) alongside a high current efficiency (83-89 %). These findings offer critical insights into the optimization of salt fractionation process and highlight its economic and technical feasibility for the sustainable management of industrial saline wastewater.

Mechanistic investigation of intensified separation of molybdenum(VI) and vanadium(V) using polymer inclusion membrane electrodialysis

The main challenge in separating molybdenum(VI) and vanadium(V) which have similar properties results in great difficulties in the green recycling of hazardous spent catalysts. Here, selective facilitating transport and stripping are integrated into the polymer inclusion membrane electrodialysis process (PIMED) to separate Mo(VI) and V(V) to overcome the complicated co-extraction and stepwise-stripping in conventional solvent extraction. The influences of various parameters, the selective transport mechanism, and respective activation parameters were systematically investigated. Results revealed that the affinity of the Aliquat 36 as the carrier and PVDF-HFP as the base polymer of PIM towards Mo(VI) is stronger than that of V(V), while the strong interaction between Mo(VI) and carrier caused low migration through the membrane. By the combination of adjusting and controlling the electric density and strip acidity, the interaction was destroyed and the transport was facilitated. After optimization, stripping efficiencies of Mo(VI) and V (V) increased from 44.4% to 93.1% and reduced from 31.9% to 1.8%, respectively, while their separation coefficient increased 16.3 times to 333.4. The activation energy, enthalpy and entropy for the transport of Mo(VI) were determined to be 4.846 kJ mol^-1, 6.745 kJ mol^-1 and - 310.838 J mol^-1 K^-1, respectively. The present work demonstrates that the separation of similar metal ions could be improved by fine tuning the affinity and interaction between metal ions and the PIM, thus providing new insights into the recycling of similar metal ions from secondary resources.