Selective cation substitution electrodialysis enables direct production of high-purity magnesium aspartate: quantification of ion transport

Abstract

Direct production of high-purity amino acid salts offers an efficient and sustainable solution to reduce fresh acid/base consumption and wastewater generation. In this study, we specifically designed a selective cation substitution electrodialysis (SCS-ED) with a novel configuration to enable the direct production of high-purity magnesium l-aspartate ($\text{Asp}‐\text{Mg}$) from monoammonium l-aspartate. To achieve this, we firstly established an ion transport model to quantify the ion transport including the competitive migration of ${\text{NH}}_4^{+}$ and ${\text{Mg}}^{2+}$ through the selective cation exchange membrane, and the co-ion transport of ${\text{NH}}_4^{+}$ through the anion exchange membrane. Then, effects of various parameters including stack voltage, feed concentration, and feed velocity on the ion transport as well as SCS-ED performance were investigated comprehensively. Results indicate that decreasing stack voltage acts as a significant role in obtaining a high selectivity ($S_{{{NH}_4^{+}/Mg}^{2+}}^{SCS-ED}$) and high purity ($P_{Asp-Mg}$), decreasing feed concentration acts as a significant role in obtaining a high current efficiency (${\eta }_{{NH}_4^{+}}^{{SCEM}^{\prime }}$) and $S_{{{NH}_4^{+}/Mg}^{2+}}^{SCS-ED}$, and increasing feed velocity acts as an important role in obtaining a relatively low total coat. Overall, considering the high $P_{Asp-Mg}$ for pharmaceutical application, a high $S_{{{NH}_4^{+}/Mg}^{2+}}^{SCS-ED}$ (32), $P_{Asp-Mg}$ (99.8 %), and ${\eta }_{{NH}_4^{+}}^{{SCEM}^{\prime }}$ (91.3 %), and a relatively low total cost (0.946 $ kg^-1) can be achieved in SCS-ED process at optimized parameters. The above findings give new insights into SCS-ED for directly producing high purity $\text{Asp}‐\text{Mg}$. Compared with traditional methods, this ion substitution approach provides a more efficient and streamlined process, showing strong potential in the production of high-purity divalent salt (e.g., amino acid divalent salt).