# Dewatering Hypersaline Na2SO4 and NaCl via Commercial Forward Osmosis Module

## TL;DR

This paper explores using forward osmosis to efficiently dewater highly salty industrial wastewater, showing it can concentrate solutions to saturation without evaporation.

## Contribution

The study experimentally demonstrates FO membrane performance with hypersaline Na2SO4 and NaCl, identifying key operational thresholds for industrial use.

## Key findings

- The Aquaporin HFFO2 membrane can concentrate Na2SO4 to saturation under mildly acidic conditions.
- Maintaining a minimum water flux is critical to prevent salt rejection loss or draw solute leakage.
- A minimum osmotic differential is proposed to parameterize water flux in FO systems.

## Abstract

Efficient water recycling in the hydrometallurgical industry requires the dewatering of hypersaline Na2SO4 or similar brines via non-evaporative methods. Unfortunately, many non-evaporative methods require the use of specific solutes and are not compatible with complex hydrometallurgical effluents. Forward Osmosis (FO) uses a draw solution to link known non-evaporative water recycling methods with feed solutions that are otherwise incompatible. There is minimal experimental data on the dewatering performance of today’s available commercial FO membranes, especially with hypersaline concentrations (>70,000 mg/L total dissolved solids). This study tests the commercially available Aquaporin HFFO2 hollow fibre FO membrane module with hypersaline Na2SO4 or NaCl feed solutions versus a MgCl2 draw solution. It identifies a key requirement to maintain water flux above a certain threshold to prevent a decrease in Na Rejection or an increase in Mg reverse flux. It also defines a minimum osmotic differential that can be used to parameterize water flux, similar to the temperature of approach in heat exchangers, but to determine the extent of water removal in FO. We demonstrate that even under mildly acidic conditions, existing FO membranes can concentrate Na2SO4 to saturation, paving the way for their use in the hydrometallurgical industry.