The feasibility of silica removal in reverse osmosis (RO) treatment of groundwater from a Western Australian mining and processing operation has been investigated, to prevent scaling and enhance water recovery.
This study shows that it is possible to reduce the silica concentration in RO concentrate to levels that would allow an overall water recovery of 90–95% using 10 g/L of regenerable activated alumina adsorbent. Regeneration of the adsorbent using 2% NaOH was found to be effective for at least three regeneration cycles.
A preliminary costing of the high water recovery RO process using silica removal by adsorption indicates a product water (permeate) cost of A$5.6/kL (US$5.2/kL), and savings due to a reduction in brine volume from the current 40% of feed volume to 5–10% of feed volume.
This approach also allows better utilisation of a scarce groundwater resource, allowing the production of up to 1.6 times more low-salt water from a given volume of groundwater.
These results warrant larger-scale investigation of silica removal and adsorbent regeneration for high-recovery RO processing for mining operations, and the application of silica removal to RO treatment of other silica-laden waters such as coal seam gas produced water.