Investigation of key process parameters in acid recovery for diffusion dialysis using novel (MDMH-QPPO) anion exchange membranes

A simple method to prepare anion exchange membrane by PVA/EVOH/MIDA for acid recovery by diffusion dialysis

Given the substantial environmental pollution from industrial expansion, environmental protection has become particularly important. Nowadays, anion exchange membranes (AEMs) are widely used in wastewater treatment. With the use of polyvinyl alcohol (PVA), ethylene-vinyl alcohol (EVOH) copolymer, and methyl iminodiacetic acid (MIDA), a series of cross-linked AEMs were successfully prepared using the solvent casting technique, and the network structure was formed in the membranes due to the cross-linking reaction between PVA/EVOH and MIDA. Fourier transform infrared spectrometer, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy were used to analyze the prepared membranes. At the same time, its comprehensive properties which include water uptake, linear expansion rate, ion exchange capacity, thermal stability, chemical stability, and mechanical stability were thoroughly researched. In addition, diffusion dialysis performance in practical applications was also studied in detail. The acid dialysis coefficient (UH+) ranged from 10.2 to 35.6 × 10-3 m/h. Separation factor (S) value ranged from 25 to 38, which were all larger than that of the commercial membrane DF-120 (UH+: 8.5 × 10-3 m/h, S: 18.5). The prepared membranes had potential application value in acid recovery.

Heterogeneous Anion-Exchange Membranes with Enhanced Ion Conductivity for Continuous Electrodeionization

In this study, the optimal fabrication parameters of a heterogeneous anion-exchange membrane (AEM) using an ionomer binder are investigated to improve the performance of continuous electrodeionization (CEDI) for producing ultrapure water. Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) is selected as the base material for preparing the ionomer binder and quaternized to have various ion exchange capacities (IECs). The optimal content of ion-exchange resin (IER) powder according to the IEC of the ionomer binder is then determined through systematic analyses. In conclusion, it is revealed that a heterogeneous AEM with optimal performance can be fabricated when the IEC of the ionomer binder is lowered and the content of IER powder is also lower than that of conventional heterogeneous membranes. Moreover, crosslinked quaternized PPO (QPPO) nanofiber powder is used as an additive to improve ion conductivity without deteriorating the mechanical properties of the membrane. The membrane fabricated under optimal conditions exhibits significantly lower electrical resistance (4.6 Ω cm2) despite a low IER content (30 wt%) compared to the commercial membrane (IONAC MA-3475, 13.6 Ω cm2) while also demonstrating moderate tensile strength (9.7 MPa) and a high transport number (ca. 0.97). Furthermore, it is proven that the prepared membrane exhibits a superior ion removal rate (99.86%) and lower energy consumption (0.35 kWh) compared to the commercial membrane (99.76% and 0.4 kWh, respectively) in CEDI experiments.

Synthesis of Porous BPPO-Based Anion Exchange Membranes for Acid Recovery via Diffusion Dialysis

Diffusion dialysis (DD) is an anion exchange membrane-based functional separation process used for acid recovery. TMA (trimethylamine) and BPPO (brominated poly(2,6-dimethyl-1,4-phenylene oxide) were utilized in this manuscript to formulate AEMs (anion exchange membranes) for DD (diffusion dialysis) using the phase-inversion technique. FTIR (Fourier transfer infrared) analysis, proton NMR spectroscopy, morphology, IEC (ion exchange capacity), LER (linear expansion ratio), CR (fixed group concentration), WR (water uptake/adsorption), water contact angle, chemical, and thermal stability, were all used to evaluate the prepared membranes. The effect of TMA content within the membrane matrix on acid recovery was also briefly discussed. It was reported that porous AEMs have a WR of 149.6% to 233.8%, IEC (ion exchange capacity) of 0.71 to 1.43 mmol/g, CR (fixed group concentration) that ranged from 0.0046 mol/L to 0.0056 mol/L, LER of 3.88% to 9.23%, and a water contact angle of 33.10° to 78.58°. The UH (acid dialysis coefficients) for designed porous membranes were found to be 0.0043 to 0.012 m/h, with separation factors (S) ranging from 13.14 to 32.87 at the temperature of 25 °C. These observations are comparable to those found in the DF-120B commercial membrane with UH of 0.004 m/h and S of 24.3 m/h at the same temperature (25 °C). This porous membranes proposed in this paper are excellent choices for acid recovery through the diffusion dialysis process.

Diffusion Dialysis for Acid Recovery from Acidic Waste Solutions: Anion Exchange Membranes and Technology Integration

Inorganic acids are commonly used in mining, metallurgical, metal-processing, and nuclear-fuel-reprocessing industries in various processes, such as leaching, etching, electroplating, and metal-refining. Large amounts of spent acidic liquids containing toxic metal ion complexes are produced during these operations, which pose a serious hazard to the living and non-living environment. Developing economic and eco-friendly regeneration approaches to recover acid and valuable metals from these industrial effluents has focused the interest of the research community. Diffusion dialysis (DD) using anion exchange membranes (AEMs) driven by an activity gradient is considered an effective technology with a low energy consumption and little environmental contamination. In addition, the properties of AEMs have an important effect on the DD process. Hence, this paper gives a critical review of the properties of AEMs, including their acid permeability, membrane stability, and acid selectivity during the DD process for acid recovery. Furthermore, the DD processes using AEMs integrated with various technologies, such as pressure, an electric field, or continuous operation are discussed to enhance its potential for industrial applications. Finally, some directions are provided for the further development of AEMs in DD for acid recovery from acidic waste solutions.