Sodium sulfate splitting as zero brine process in a base metal refinery: Screening and optimization in batch mode

Abstract

In base metal refineries Na2SO4 is produced in large quantities as a neutralization salt and recovered via energy intensive evaporative crystallization. Splitting the Na2SO4 brine into its three components NaOH, H2SO4 and process water via electrodialysis using a bipolar membrane (EDBM) in combination with reverse osmosis (RO) was investigated as an alternative solution.Process phenomena such as non-ideal membrane behavior and electro-osmosis were investigated at the high concentration levels occurring in a metal refinery using synthetic Na2SO4 solutions. Subsequently, operating conditions were optimized. It was found that a determining factor in minimizing the splitting cost is the salt concentration that should be kept in the 100–150 g Na2SO4/L range to maintain a high current density. To maintain a high feed concentration, the EDBM was combined with a Disk Reverse Osmosis (DRO) unit to re-concentrate the partially depleted salt solution.The techno-economic analysis of a 100 kg Na2SO4/h demonstration plant shows that the production cost of NaOH, which is the most valuable of the three products, is in the range of the bulk NaOH price. All three products are reused in the metal refinery making the EDBM-DRO plant a Zero Brine solution to prevent salinization in in-land mining areas.