In-Situ Combination of Bipolar Membrane Electrodialysis with Monovalent Selective Anion-Exchange Membrane for the Valorization of Mixed Salts into Relatively High-Purity Monoprotic and Diprotic Acids

Abstract

The crystalized mixed salts from the zero liquid discharge process are a hazardous threat to the environment. In this study, we developed a novel electrodialysis (SBMED) method by assembling the monovalent selective anion-exchange membrane (MSAEM) into the bipolar membrane electrodialysis (BMED) stack. By taking the advantages of water splitting in the bipolar membrane and high perm-selectivity of MSAEM for the Cl− ions against the SO42− ions, this combination allows the concurrent separation of Cl−/SO42− and conversion of mixed salts into relatively high-purity monoprotic and diprotic acids. The current density has a significant impact on the acid purity. Both the monoprotic and diprotic acid purities were higher than 80% at a low current density of 10 mA/cm2. The purities of the monoprotic acids decreased with an increase in the current density, indicating that the perm-selectivity of MSAEM decreases with increasing current density. An increase in the ratio of monovalent to divalent anions in the feed was beneficial to increase the purity of monoprotic acids. High-purity monoprotic acids in the range of 93.9–96.1% were obtained using this novel SBMED stack for treating simulated seawater. Therefore, it is feasible for SBMED to valorize the mixed salts into relatively high-purity monoprotic and diprotic acids in one step.

Electrodialytic Processes: Market Overview, Membrane Phenomena, Recent Developments and Sustainable Strategies

“…Similarly, a ZLD strategy involving novel selective bipolar-membrane electrodialysis (SBMED) was developed to remediate industrial wastewaters, leading to the generation of valuable products HCl, H 2 SO 4 , NaOH, purified water. Its ZLD feature and current efficiencies of 90% for NaOH and 50% for HCl make it a promising remediation process [ 315 ]. Other SED-based approaches were studied to generate acid and base using wastewaters from chemical or desalination plants which could then be resupplied in commodity chemicals.…”

Decreasing Seawater Desalination Footprint by Integrating Bipolar-Membrane Electrodialysis in a Single-Pass Reverse Osmosis Scheme

“…Depending upon their permeability through the AEMs and CEMs, the divalent ions (especially Ca 2+ , Mg 2+ ) that tend to precipitate can significantly influence the overall acid/base production rate, the SEC, and the product purity. ,,, Introducing alkali precipitation as a pretreatment step to BMED is therefore required, which invariably increases the overall process cost. Alternatively, using a monoselective CEM (PC MVK, Table S1) to prevent Ca 2+ /Mg 2+ from reaching the base compartment is a presumably attractive approach . We systematically explored this alternative by performing BMED experiments (exp.…”

“…Alternatively, using a monoselective CEM (PC MVK, Table S1) 35 to prevent Ca 2+ /Mg 2+ from reaching the base compartment is a presumably attractive approach. 36 We systematically explored this alternative by performing BMED experiments (exp. 3a−3f and 4b, 24 V, CSM stack, Tables 1 and 2) with varying concentrations of either Mg 2+ or SO 4 2− in 1 M NaCl feed solution.…”

Assessment of Graphical Methods for Determination of the Limiting Current Density in Complex Electrodialysis-Feed Solutions

“…When the ionic composition of SCS1 and SCS2 is compared (Table 2), it can be seen that SCS1 has higher PO 4 -P and Cl − concentrations, whereas SCS2 has around a double concentration of SO 4 2− ions. Yan et al [56] researched the competing transport of monovalent and multivalent ions based on their concentration ratios. In another study [57], lower LCDs were observed when some of the Cl − was substituted with SO 4 2− anions.…”