Economical silica removal

Leader

 

Challenge

The concentration of salts and other chemicals in brine affect solubility, leading to salt crystal formation and the generation of other solid particles that reduce desalination efficiency. The quantity of clean water that can be extracted (i.e. the water recovery) is limited by the types of salts and chemicals present in the water before treatment. The maximum achievable amount of water recovery in reverse osmosis (RO) treatment of groundwater is typically 70% to 80%, but can be as low as 50% for some bore waters, which results in up to 50% waste brine. High volumes of waste brine are a major impediment to bore water desalination due to the high construction and maintenance cost of evaporation ponds. Mining operations can be limited by the availability of water and improved recovery rates would be of significant benefit to the industry. A potential solution is the removal of scale precursor chemicals from the brine, such as silica, which could increase water recovery up to 95%, leaving a more manageable volume of waste brine.

Investigation

Investigate silica scale mitigation and the effect on water recovery and waste brine volumes from two different sources of groundwater. The mitigation techniques to be investigated are (1) silica removal by adsorption and (2) operation of a reverse osmosis process at low pH where silica is more soluble.

Outcomes

Silica adsorption and low pH operation are two promising options for silica scale mitigation that allow high water recovery and low waste brine volume to be achieved during RO treatment of groundwater. Removal of silica from two groundwater sources in Western Australia and Queensland using commercially available alumina absorbents demonstrated potential water recoveries of up to 96%. High temperatures and smaller absorbent particle size produced optimal absorption rates.

Regeneration of the absorbent was also possible and demonstrated continued effectiveness after three regeneration cycles. Scale mitigation was also successful by operating at a low pH, resulting in higher fluxes and water recoveries however, this was only effective for short batch mode operation.

Future Direction

A recommendation of the most economical silica removal process was made to the partners who are considering the implications of implementing the process. The possibility of operating the low pH silica mitigation process in continuous mode will be tested, which promises to make the process more economically viable and attractive for further trials. More detailed investigations will carried out on the absorption of silica using the activated alumina process and several novel anti-scaling agents were identified that will be followed up.

Partners

Sanciolo logos 2


 

Total Value: $497,559 (cash and in-kind contributions)

Principal Investigators: Dr Peter Sanciolo and Professor Stephen Gray

Title: Silica removal from groundwater for reverse osmosis water recovery enhancement and waste brine volume reduction

Length: 15 months

Personnel: 6 collaborators contributing 2.05 FTE

Further Information

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