• Resources Recycling
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• v.31 no.5
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• pp.3-19
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• 2022

Electro-membrane technology is a process for separating and purifying substances in aqueous solution by electric energy using an ion exchange membrane with selective permeability, such as electrodialysis (ED) and bipolar electrodialysis (BMED). Electro-membrane technology is attracting attention as an environmental friendly technology because it does not generate by-products during the process and the recovered base or acid can be reused during the process. In this paper, we investigate the principles of ED and BMED technologies and various characteristics and problems according to the cell configuration. In particular, by investigating and analyzing research cases related to the treatment of waste sodium sulfate (Na₂SO₄), which is generated in large amounts during the metal recovery process.

• Journal of Hydrogen and New Energy
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• v.21 no.6
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• pp.507-512
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• 2010

The effect of catholyte to anolyte amount ratio on the electrodialysis cell performance for HI concentration was investigated. For this purpose, the electrodialysis cell was assembled with Nafion 117 as PEM membrane and activated carbon fiber cloth as electrodes. The initial amount of catholyte was 310 g and that of anolyte varied from 1 to 3 of amount ratio. The calculated electro motive force (EMF) increased with time and the increment enhanced as the amount ratio of catholyte to anolyte decreased. The mole ratios of HI to $H_2O$ (HI molarity) in catholyte were almost the same and exceeded pseudo-azeotropic composition for all amount ratios after 2 h operation. The HI molarity continuously increased with time for 10 h operation. The mole ratio of $I_2$ to HI decreased in catholyte but increased in anolyte. The increment of mole ratio of $I_2$ to HI in anolyte rose as the amount ratio of catholyte to anolyte decreased. In case of 1:1 amount ratio, the cell operation was stopped for the safety at approximately 6 h operation, since the mole ratio of $I_2$ to HI reached solubility limit. The cell voltage of the electrodialysis cell increased with time and the rate of increase was high at low amount ratio. This suggests that the amount ratio of catholyte to anolyte not only crucially influences the cell voltage, but also cell operation condition.

• Journal of Hydrogen and New Energy
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• v.18 no.4
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• pp.458-463
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• 2007

An experimental study on scale-up of Electro-electrodialysis(EED) to increase the efficiency of HI decomposition section in the IS(Iodine-Sulfur) process was carried out. The EED stack extends the effective area of the membrane to 20 times of that formerly used in a single EED unit cell. The experiment was carried out using HIx solution($HI:H_2O:I_2=1:8.4{\sim}9:1.85{\sim}1.9$) at $100^{\circ}C$ and various solution flow rates of 20, 30, 40 and 50 cc/min. The increased HI molality in catholyte after one-pass throughout from the EED stack was 3 mol/kg-$H_2O$, 2.2 mol/kg-$H_2O$, 2 mol/kg-$H_2O$ and 1.37 mol/kg-$H_2O$ at 20, 30, 40 and 50 cc/min, respectively. These values satisfied the target of HI molality(the increase of HI molality: 2 mol/kg-$H_2O$) in the IS process for hydrogen production of 20 L/hr.

• Journal of Hydrogen and New Energy
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• v.22 no.6
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• pp.749-758
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• 2011

The present work explores the performance and operation limit of electrodialysis cell for HI concentration in sulfur iodine thermochemical hydrogen production process, For this purpose, the electrodialysis cell was assembled with Nafion 117 as a PEM membrane and two activated carbon papers as the electrodes. HIx solution was prepared with composition of HI: $I_2$: $H_2O$ = 1: 0.5~2.5: 5.2 in molar ratio. The cell and its peripheral apparatus were placed in the specially designed convective oven in order to uniformly maintain the operation temperature. As operation temperature increased, the amount of water transport from anode to cathode increased, thus reducing HI molarity in catholyte. Meanwhile, the current efficiency was constant as about 90 %, irrespective of temperature change. The cell voltage increased with initial $I_2$ mole ratio as well as anolyte to catholyte mole ratio. Moreover the cell voltage overshot took place within 10 h cell operation, which is due to the $I_2$ precipitation inside the cell. From the analysis of $I_2$ mole ratio in the anolyte, it is noted that operation limit (in $I_2$ mole ratio) of the electrodialysis cell, arising from was measured to be 3.2, which is much lower than bulk solubility limit of 4.7.