Humans produce a lot of waste, from flushing toilets to mining metals, like the copper in electrical wires that power computers, phones and tablets. To clean up our act, a new way to purify contaminated wastewater from mines has been developed by CSIRO scientists.
At a copper mining site in Queensland, the first demonstration of the new 'Virtual Curtain' treatment turned 50 million litres of acidic waste into rainwater quality water, which was safely discharged into a river.
“Since Roman times, lime has been the material of choice for neutralising acid waste,” says Grant Douglas from CSIRO. “This is a new technique to make a mineral from the contamination in solution. We can remove a wide range of contaminants in a single step.”
The Virtual Curtain treatment separates contaminated wastewater into two products – cleaner water and a fine sludge. This is not unique: sludge-producing lime treatments are used in mines around the world. The big advantage of the Virtual Curtain treatment is that it removes more contaminants. It also produces a much more concentrated sludge. So each litre of Virtual Curtain sludge contains much more metal and other contaminants than a litre of lime sludge.
“The concentration of contaminants in the material is so rich, it can form an ore and can be re-mined,” says Grant. Companies can turn their waste into wealth, money back for the cost of environmental treatment.
The Virtual Curtain treatment works by carefully balancing the conditions of the water. Scientists analyse the waste, and then add one or two chemicals and neutralise the acid, raising the pH to around 10. Once the conditions are just right, minerals in the water form hydrotalcites. Hydrotalcites are crystals that can incorporate a wide range of contaminants. Plus, they’re solid, so they drop out of the water and fall to the bottom, taking the trapped contaminants with them.
Grant says mining companies in Australia, Europe and the USA have contacted him and are interested in using the technique. It’s Australian research, made commercial by an Australian company, and taken to the world.
The Virtual Curtain treatment turns mining wastewater into rainwater quality water. Image: CSIRO
Quiz questions
What is the pH of Coca-Cola?
Is vanilla harvested from a type of a) wattle, b) orchid or c) jonquil?
Who was the second person to walk on the Moon?
What do you call a device that measures temperature?
In which year was the first Macintosh computer released?
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Make up solutions of washing soda and Epsom salts according to the instructions. Stir well.
Add a drop of food dye to the Epsom salt solution.Pick up some of the Epsom salt solution using the straw.Add the Epsom salt solution to the washing soda solution, and watch what happens!Keep adding more Epsom salt solution. Look at your results!
You will need
Epsom salts
Washing soda (also known as sodium carbonate)
Food dye
Warm water
Clear glass
Two small glasses
Measuring cups and measuring spoons
A straw
Spoon for stirring
What to do
Put half a cup of water and a teaspoon of washing soda into the clear glass. Stir well until dissolved.
Put two tablespoons of water and one tablespoon of Epsom salts into the small glass. Stir well until most has dissolved. Let it sit until it becomes clear. If some Epsom salts will not dissolve, gently pour most of the Epsom salt solution into the second small glass and leave the solids behind.
Add a drop of food dye to the Epsom salt solution.
Put the straw in the Epsom salt solution and place your thumb over the other end. Lift the straw up (some of the solution should stay in the straw) and drip the Epsom salt solution into the washing soda solution.
Look through the side of the glass while you keep dripping more liquid and watch what happens!
To clean up, dispose of all liquids down the sink, and run water through to flush it down the drain. Make sure all materials are cleaned well with detergent, and wash your hands.
What’s happening?
A chemical reaction has taken place. The washing soda solution reacted with the Epsom salt solution to produce a solid. This solid settles to the bottom of the cup, and is called a precipitate. Let’s look at the chemicals involved:
Washing soda, or sodium carbonate, has the formula Na2CO3. Epsom salts, or magnesium sulfate, has the formula MgSO4.
In this reaction, the carbonate and sulfate swap partners and we produce magnesium carbonate, MgCO3, and sodium sulfate, Na2SO4. Magnesium carbonate is not very soluble in water, so it falls down to the bottom of the glass as a solid, or precipitate.
Using chemical formulas, we can write:
Na2CO3(aq) + MgSO4(aq) = MgCO3(s) + Na2SO4(aq)
The (aq) means aqueous, or ‘in water’ and (s) means solid.
Applications
Humans make a lot of wastewater, from mining waste to sewage. This water needs to be treated to remove contaminants before we can release it safely. Using chemical reactions, we can make the contaminants form a solid so they precipitate out of the wastewater. The solids can be collected, leaving the water that much cleaner.
Want to extend this activity? You can collect the solid using a cup, a funnel and coffee filter paper. Just open the coffee filter paper in the funnel, and place the funnel in an empty cup to catch the liquid. Slowly pour your results from the activity through the filter paper. Some of the solid will collect in the filter paper, some will pass through and that's okay. Once the liquid has dripped out, scrape the solid onto a plate and let it dry overnight. You’ve separated solid magnesium carbonate!
Watch it! How small can technology get? Find out with A Week in Science by the RiAus.
Quiz answers
The pH of Coca-Cola is around 2.5.
Vanilla is harvested from an orchid.
Edwin “Buzz” Aldrin was the second person to walk on the Moon.
A thermometer measures temperature.
The first Macintosh computer was released 30 years ago, in 1984.
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