Higher efficiency of triethanolamine-grafted anion exchange membranes for acidic wastewater treatment

Abstract

Acidic wastewaters are major industrial effluents that must be cleaned before release in natural waters, yet classical treatment methods are limited. Diffusion dialysis through anion exchange membranes (AEM) appears as a sustainable alternative because those membranes are cheap and highly selective, yet there is a need for improved membranes. Here we synthesized AEMs from brominated poly(2,6-dimethyl-1,4-phenylene oxide) using triethanolamine as an ion-exchange group for acid recovery. The prepared membranes were characterized by Fourier-transform infra-red spectroscopy, scanning electron microscopy, and atomic force microscopy. Acid recovery was tested with a mixture of HCl and FeCl2. Results show that increasing triethanolamine content into the membrane polymer matrix led to an increase of water uptake from 12% to 117%, ion exchange capacity from 1.28 to 2.29 mmol/g, and linear swelling ratio from 3.52% to 32.70%. The diffusion dialysis coefficient of acid (U H +) reached 23 × 10-3 m/h, which is higher than that actual membranes, of 0.37-20 × 10-3 m/h. U H + increased with membrane triethanolamine content, which is explained by increasing H bonding of aqueous protons with membrane hydroxyl groups. U H + also increased from 23 × 10-3 m/h at 25°C to 71 × 10-3 m/h at 55°C due to easier ion flow. Moreover, the separation factor (S) reached 495 at 25°C, which is higher than that of actual membranes, of 73-351. The diffusion dialysis coefficient of metal (U Fe 2+) ranged from 0.0025 to 61 10-3 m/h. Membranes also showed excellent thermal, chemical and mechanical stability.