Recovery of Spent Sulphuric Acid by Diffusion Dialysis Using a Spiral Wound Module.

Arthur Merkel,Ladislav Čopák,Daniil Golubenko,Libor Šeda,Lukáš Dvořák

doi:10.3390/ijms222111819

Abstract

In this study, we assess the effects of volumetric flow and feed temperature on the performance of a spiral-wound module for the recovery of free acid using diffusion dialysis. Performance was evaluated using a set of equations based on mass balance under steady-state conditions that describe the free acid yield, rejection factors of metal ions and stream purity, along with chemical analysis of the outlet streams. The results indicated that an increase in the volumetric flow rate of water increased free acid yield from 88% to 93%, but decreased Cu2+ and Fe2+ ion rejection from 95% to 90% and 91% to 86%, respectively. Increasing feed temperature up to 40 °C resulted in an increase in acid flux of 9%, and a reduction in Cu2+ and Fe2+ ion rejection by 2–3%. Following diffusion dialysis, the only evidence of membrane degradation was a slight drop in permselectivity and an increase in diffusion acid and salt permeability. Results obtained from the laboratory tests used in a basic economic study showed that the payback time of the membrane-based regeneration unit is approximately one year.

Highlights

Industrial processes often generate wastewaters characterized by high acidity or high alkalinity with pH lower than 1 and above 14 respectively in some cases and/or a high metal content [1,2]
We investigate impact of volumetric flow and feed temperature on module performance and assess membrane degradation through characterization of ion-exchange capacity and mechanical and transport properties before and after diffusion dialysis (DD) operation
Electrical conductivity of the outlet streams increases over time for Test 1.1. This behaviour is caused by the fact that diluted acidic solutions have higher conductivity than demineralized water which was present in the module before its run-up

Summary

Introduction

Industrial processes often generate wastewaters characterized by high acidity or high alkalinity with pH lower than 1 and above 14 respectively in some cases and/or a high metal content [1,2]. Membrane technologies facilitate the recovery of valuable dissolved components such as metals and allow the reuse of acids or alkalis. It is widely believed that DD represents the optimal process for recovery of acids at high concentrations (i.e., >0.5 M) [3]. DD has a number of advantages [5,6], including low energy consumption (due to spontaneous processes driven by activity gradients), low installation costs, simple operation and maintenance, and high product quality (due to the high selectivity of anion-exchange membranes (AEMs) for acids). The process is considered environmentally friendly due to the lack of post-processing and chemical agents used [3,4,7]

Methods

Results

Conclusion