CSIRO is investigating ways of turning the large volumes of hyper-saline brine generated during the desalination process into value-added products.
A growing population coupled with changing rainfall patterns is placing increasing stress on Australia's industrial, agricultural and domestic water resources.
The desalination of seawater and inland saline waters is one method being suggested as a means to help current and future water needs.
Australia is now paying more attention to desalination and the number of desalination plants in Australia is increasing. There are however a number of drawbacks, including:
CSIRO is searching for alternative energy sources to run these plants and developing methods to avoid discharging the hyper-saline waters into the sea.
Improving the desalination process
Reverse osmosis and multi-stage flash distillation are the most widely used methods in desalination plants.
Both of these methods generate large volumes of hyper-saline brine (highly concentrated salty water) which is generally discharged to the sea.
In reverse osmosis of seawater only half of the feed water is converted to potable (drinking) water and the other half is discharged into the sea. The brine is twice as salty as the initial feed seawater.
CSIRO’s is conducting research into methods to provide fresh water with minimal impact on the environment.
CSIRO’s research and development work focuses on:
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developing clever membrane technologies to improve the efficiency of desalination
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identifying major industrial waste heat sources and developing symbiotic technologies to recover heat and electricity needed for the desalination plants
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extracting mineral salts and extra water from the hyper-saline discharge waters.
Hyper-saline brine
CSIRO Minerals through the Water for a Healthy Country (WfHC) National Research Flagship is investigating the economic potential of hyper-saline discharge waters of desalination plants.
“Potentially desalination plants could use energy harnessed from waste heat and the chemical processing plants could use products from brine.”
Dr Hal Aral
Research Scientist, CSIRO Minerals
Studies showed the theoretical value of the discharged brines is up to six-times higher than the value gained from the production of potable water.
Only 45-50 per cent of seawater passing through a plant is converted into potable water.
In the desalination plant studied, potable water generated A$30 million per year revenue.
Theoretically the salt mineral value of the discharge brine is up to A$250 million per year.
The hyper-saline brine returned to the sea contains valuable salts including:
Value-added products from waste brine
Salts extracted from seawater are widely used across many industries, including the minerals and chemical processing industries.
Australia produces ten million tonnes of common salt from seawater for export per annum.
Potentially salt may be extracted from the hyper-saline brine left after desalination. This could significantly reduce the area of land required for salt evaporation pans.
Hyper-saline waters can be converted into higher value products such as:
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caustic soda – for the alumina industry
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sodium cyanide – for the gold industry
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sodium hypochlorite – bleach
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polyvinyl chloride – PVC
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titanium tetrachloride – for titanium pigment and titanium metal production
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hydrochloric acid – a common minerals acid widely used by all industries.
Bitterns – the liquid remaining after the salt has been removed from the sea water – can also be converted into valuable products for use in:
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waste water and sewage treatment
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scrubbing sulfur dioxide and sulfur trioxide
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making light-weight flame retardant panels and boards
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Epsom salt production for horticulture
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refractory bricks for industrial furnaces
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magnesium metal production.
Bitterns also contain valuable potassium, bromine and lithium salts.
Bromines are essential feedstock for many fumigating agents, petroleum products and medicine whereas lithium is mostly used in the making of lithium batteries.
‘Australia has the potential to co-establish a brine processing industry with chemical industries around desalination plants,’ says Dr Aral, ‘which may lead to zero brine discharge back into the sea and increase the value of the salt industry.’
Investigating opportunities for symbiotic relationships
Desalination plants require large amounts of energy and industries such as chemical processing plants require large quantities of products derived from salts.
CSIRO Minerals through the WfHC Flagship is investigating ways these industries can work together for economic and environmental benefits.
A recent project conducted through the Energy Transformed National Research Flagship reviewed various technologies used for capturing waste-heat. It also investigated methods for the mapping of waste-heat hot spots.
Another research team has been investigating novel dry granulation technology to derive value from waste heat generated by the minerals, cement, petrochemical industries and power generation plants.
Pyrometallurgical industries such as steel mills generate waste-heat which can potentially be harvested for energy production.
‘The recycling of waste heat means less costly desalination plants and less greenhouse gas emissions,’ says Dr Aral.
‘By choosing site locations carefully the plants may be able to use each others waste products. Potentially desalination plants could use energy harnessed from industrial waste heat to run the desalination as well as the hyper-saline brine processing plants.’
Read more about CSIRO's research on Identifying and recovering heat energy.
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