(383am) Fabricating a Nano-Filtration Membrane for Separating Multivalent Cations from a Mine Tailing Water

Selective ion separation is one of the essential technologies for sustainable water treatment and resource recovery. It plays a crucial role in addressing water scarcity, pollution, and the efficient utilization of resources. Specifically, separating cations is crucial for sustainable processes like extracting Li⁺ from salt lake brines and seawater, as well as removing Ca²⁺, Mg²⁺, heavy metals, and harmful ions [1].

Nanofiltration (NF) based on thin-film composite (TFC) membrane is an excellent method for ion separation, because of selective ion separation based on Donnan exclusion and size sieving. Recent advances in NF membrane manufacturing have established diverse techniques for improving ion selectivity by modifying the structure of the polyamide (PA) active layer and electric charge property [1–4]. Studies show that the keys to enhance ion selectivity depends on the performance of membrane materials and the ability to control pore size and chemical properties, which improve size-sieving and ion-membrane interactions. The removal capacity for multivalent cations and the ion selectivity of NF membranes can be enhanced through the regulation of the structure and surface charge of the PA layer [1–4]. Introducing positive surface charges to the NF membrane represents a direct strategy for improving the rejection of multivalent cations through Donnan exclusion. This can be achieved by either modifying the PA layer through the grafting of positively charged chemicals or by preparing NF membranes with positive charges using alternative monomers [1–4].

In this work, commercial polyether sulfone (PES) membranes are modified via interfacial polymerization method to separate multivalent cations from a dilute mining tailing. This method consists of several steps, where initially a piperazine (PIP) solution is added to the PES membrane letting the excess dry, then trimesoyl chloride (TMC)/hexane is added to PES/PIP to make the PES/PIP/TMC membrane. Moreover, to positively charge the surface of the membrane an aqueous solution of 3,5-diamino benzoic acid is added to the surface of the membrane. This NF membrane is characterized by a scanning electron microscope (SEM) and atomic force microscope (AFM) to analyze the surface morphology and roughness. Later, the membrane is housed in the module to test the membrane performance in terms of selectivity and concentration of the rejected multivalent cations at room temperature, different pressures, and varying the cations concentration. Ion chromatography is used to investigate the concentration of cations in both permeate and retentate solutions.

References

[1] D. Lu, Z. Yao, L. Jiao, M. Waheed, Z. Sun, L. Zhang, Separation mechanism, selectivity enhancement strategies and advanced materials for mono-/multivalent ion-selective nanofiltration membrane, Advanced Membranes 2 (2022) 100032. https://doi.org/https://doi.org/10.1016/j.advmem.2022.100032.

[2] P. Hu, B. Yuan, Q.J. Niu, K. Chen, Z. Xu, B. Tian, X. Zhang, Modification of polyamide nanofiltration membrane with ultra-high multivalent cations rejections and mono-/divalent cation selectivity, Desalination 527 (2022) 115553. https://doi.org/https://doi.org/10.1016/j.desal.2022.115553.

[3] W. Li, C. Shi, A. Zhou, X. He, Y. Sun, J. Zhang, A positively charged composite nanofiltration membrane modified by EDTA for LiCl/MgCl2 separation, Sep Purif Technol 186 (2017) 233–242. https://doi.org/https://doi.org/10.1016/j.seppur.2017.05.044.

[4] Z. Zhao, S. Feng, C. Xiao, J. Luo, W. Song, Y. Wan, S. Li, Exploring ions selectivity of nanofiltration membranes for rare earth wastewater treatment, Sep Purif Technol 289 (2022) 120748. https://doi.org/https://doi.org/10.1016/j.seppur.2022.120748.