The Novel Strategy for Increasing the Efficiency and Yield of the Bipolar Membrane Electrodialysis by the Double Conjugate Salts Stress.

Dong Wang,Wenjuan Qu,Jiaji Cheng,Chunxu Li,Wenqiao Meng,Meng Zhang,Guohui Wang,Shaoxiang Li,Yunna Lei

doi:10.3390/polym12020343

Abstract

To improve sulfuric acid recovery from sodium sulfate wastewater, a lab-scale bipolar membrane electrodialysis (BMED) process was used for the treatment of simulated sodium sulfate wastewater. In order to increase the concentration of sulfuric acid (H2SO4) generated during the process, a certain concentration of ammonium sulfate solution was added into the feed compartment. To study the influencing factors of sulfuric acid yield, we prepared different concentrations of ammonium sulfate solution, different feed solution volumes, and different membrane configurations in this experiment. As it can be seen from the results, when adding 8% (NH4)2SO4 into 15% Na2SO4 under the experimental conditions where the current density was 50 mA/cm2, the concentration of H2SO4 increased from 0.89 to 1.215 mol/L, and the current efficiency and energy consumption could be up to 60.12% and 2.59 kWh/kg, respectively. Furthermore, with the increase of the volume of the feed compartment, the concentration of H2SO4 also increased. At the same time, the configuration also affects the final concentration of the sulfuric acid; in the BP-A-C-BP (“BP” means bipolar membrane, “A” means anion exchange membrane, and “C” means cation exchange membrane; “BP-A-C-BP” means that two bipolar membranes, an anion exchange membrane, and a cation exchange membrane are alternately arranged to form a repeating unit of the membrane stack) configuration, a higher H2SO4 concentration was generated and less energy was consumed. The results show that the addition of the double conjugate salt is an effective method to increase the concentration of acid produced in the BMED process.

Highlights

With the development of economy and industrialization, a great deal of wastewater is generated during industrial development
In order to explore the influence of current density on the current efficiency, energy consumption, and the concentration of acid before and after the addition of ammonium sulfate, the experiments were performed with 15 wt % Na2 SO4 and 5 wt % (NH4 )2 SO4 at different current densities (30–70 mA/cm2 )
During the whole experiment at constant current, it can be found that whether (NH4 )2 SO4 was added or not, the applied voltage declined sharply at the start of the experiment procedure. This was mainly related to the increase of the conductivity of the acid/base compartment caused by the splitting of water molecules and the migration of the hydrate ions, reducing the electrical resistance of the stack

Summary

Introduction

With the development of economy and industrialization, a great deal of wastewater is generated during industrial development. As a commonly used industrial raw material, is one of the main components of most industrial wastewater. Polymers 2020, 12, 343 industrial wastewater that contains sodium sulfate pollutes water sources, and causes salinization of the soil and damages the ecological environment. Environmental protection has been the focus of attention, and the development of effective technologies for the treatment of sodium sulfate wastewater has become a top priority. Acid and base solutions will be produced at the corresponding compartment of a BMED stack. For this case, BMED has been widely used for organic and inorganic acid/base production, environmental protection, and resources isolation, especially for the industrial development of zero emissions [1,2]

Methods

Results

Conclusion