Silica removal technique boosts groundwater recovery

WATER recovery of between 90 and 95 per cent from mine groundwater could be possible using a technique involving silica removal in reverse osmosis (RO) desalination.

A studyfrom Victoria University's Institute for Sustainability and Innovation and Hatch Associates in Perth explored the feasibility of the process using WA mine groundwater supplies.Silica, often highly concentrated in groundwater, causes scaling of RO membranes which reduces water recovery.Here, researchers removed silica by adding a fine powder (activated alumina adsorbent) which is able to collect dissolved silica on its surface.After the powder is added, the brine is stirred for a period of time and filtered to remove the adsorbent powder with captured silica.

Study author Dr Peter Sanciolo believes there is enormous potential for the silica removal method, not only for groundwater in mining processes but also for associated water from the coal seam gas (CSG) industry."The data presented on mining groundwater in our recent publication is only part of the research we conducted," he says."We also tested silica-laden groundwaters produced in Queensland CSG operations and found it works on these as well."These waters are a by-product of CSG production and need to be desalted before discharge to the environment.

"The sheer quantity of this water being extracted, coupled with projected growth in the CSG industry, are powerful drivers for silica removal to allow sustainable management of the waste brine from desalting processes."The good thing about the application of silica removal by adsorption to CSG-produced water is that it promises to be less expensive than its application to mining groundwaters because less adsorbent is required."Preliminary costings in the study found high water recovery from groundwaterin mining processes was $5.6 perkilo litre.Dr Sanciolo says the silica removal method's potential depends on how well the challenges involved in its implementation are addressed in future research.

"One of the challenges to overcome will be the quantity of waste produced during regeneration of the adsorbent," he says."Conventional thinking is to try to remove the captured silica using large volumes of caustic soda solution, which must be discarded after a few uses—but we are developing new approaches to overcome this disposal problem.

"The process has not been widely used before because the time wasn't right but we believe it will be used in the near future because the economics will be more favourable."With finite groundwater resources, and the large volume of waste resulting from desalting groundwater limiting future economic activities, Dr Sanciolo says the value society puts on what is produced by the process - more clean water and less waste - will increase.

Notes:

The study was funded by the National Centre of Excellence in Desalination Australia, located at Murdoch University's Rockingham Campus.

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Taxonomy

• Water Resource Mapping
• Groundwater Recharge
• Groundwater Pollution