Functionalized Nanoporous Ceramic Membranes for Electrodialysis Treatment of Harsh Wastewater
Authors: Rabe Emily , Candelaria Stephanie , Lenz Olivia , Malone Rachel , Newbloom Greg 
Published: February 2024

INTRODUCTION

Electrodialysis (ED) is a well-developed technology for electrochemical desalination. However, many industries generate harsh wastewater streams that are incompatible with traditional ion exchange membranes and thus limit the use of ED. Membrion® has developed novel ceramic-based ion exchange membranes which offer a number of advantages over traditional polymer membranes: high performance in low pH, chemical resistance to oxidizers, and a rigid structure which minimizes membrane swelling. This presentation will discuss these novel membranes and their performance in electrodialysis stacks.

EXPERIMENTAL

Novel ceramic ion exchange membranes (IEM) are synthesized with patented silane-based sol-gel techniques. These ceramic membranes have covalently bound charged moieties similar to polymer IEMs; however, they are attached to a tunable nanoporous structure. The pore size, shape, and network structure are engineered through a molecular self-assembly process where thermodynamic driving forces are used to direct where and how pores form. Either cation (e.g., SO3
-) or anion (e.g., NH4
+) groups can be added within the membrane nanopore structure to enhance ion selectivity. The ceramic IEMs are produced on a roll-to-roll manufacturing line with low temperature processing. Membrane performance is assessed by measuring permselectivity (PS), area-specific resistance (ASR), and batch electrodialysis tests.

RESULTS

Figure 1 shows that both cation exchange membranes (CEM) and anion exchange membranes (AEM) show a decreased ASR compared to traditional polymer membranes, while maintaining comparable PS (i.e., the ability to separate cations and anions). The lower ASR of ceramic membranes is advantageous, as this can improve the overall energy efficiency of electrodialysis desalination. We maintain good performance (i.e., comparable current efficiency and water recovery) when integrated into a 10-cell pair stack. Most significantly, the right plot of Figure 1 shows a stable dilute water recovery of ~90% achieved with ceramic membranes after being stored in solutions ranging from pH 3 to pH 0 for 30 days. We have also demonstrated this technology in the field with copper wastewater generated at a microelectronics manufacturing facility. On site bench and pilot testing showed that our membranes could be used to nearly eliminate the copper sent to single-use IEX resin.

DISCUSSION

Ceramic-based ion exchange membranes are able to achieve comparable performance to traditional polymer membranes and offer some unique advantages. Long exposure to very low pH has negligible impact on ceramic ED stack performance. Additionally, we have observed stable performance in the presence of strong oxidizing agents such as hydrogen peroxide. This stability is expected, as the silica backbone of these materials is already in a fully oxidized state, as opposed to traditional polystyrene-based membranes. This data suggests ceramic membranes could be an ideal solution for acidic and/or oxidizing wastewater streams found in industries such as semiconductor manufacturing and mining. In addition to offering chemical stability in harsh environments, the patented silica sol-gel process used to cast these membranes is extremely tunable. Through incorporating commercially available functionalized silanes, the pore size and chemical make-up can be easily altered to target specific waste streams.

CONCLUSIONS

Ceramic ion exchange membranes are shown to have similar performance attributes to traditional polymer IEMs when evaluated for electrodialysis water purification applications. The good stack-level performance combined with stability in harsh environments have the potential to dramatically broaden the use of ED/EDR for industrial wastewater treatment.

Figure 1