Science has solved a waste problem for a burgeoning mining company which has developed a unique technique to extract nickel from low grade ore.
Perth CSIRO scientist Grant Douglas says the eagerness of Direct Nickel to find innovative scientific solutions to treat waste at its Bentley pilot plant before going into full-scale production, is a great example of mining in the twenty-first century.
Direct Nickel's extraction process (DNi) is an atmospheric hydrometallurgic process using nitric acid rather than sulphuric acid. While the company reuses the bulk of that acid, the remainder is a nitrate-rich waste which can't be discharged into the environment.
Dr Douglas, who specialises in waste water remediation, has been developing hydrotalcites over a number of years to clean pollutants from waste, primarily from mines. He says this latest work broadens their stable of uses.
However, he says treating the extremely nitrate-rich DNi wastewater is not a simple process.
It uses a complex two-step method to neutralise it; the first absorbs some of the nitrate into hydrotalcite which is efficient in taking up anions or negatively-charged molecules. It acts as a sponge for the nitrate.
Once the high nitrate concentration is lowered sufficiently, the second step uses a de-nitrifying bacteria biofilm to 'polish' what's left.
"If we didn't do the first step, the de-nitrification step would probably be overwhelmed," Dr Douglas says.
"But under this process you end up with nitrogen gas from the de-nitrifcation step which is released into the atmosphere and water with very little nitrate in it, which can then be discharged.
"In addition, the nitrate-loaded hydrotalcite has potential agronomic applications as a slow release fertiliser and soil conditioner."
The process has been tested successfully on effluent from the pilot plant.
Dr Douglas says he expects the same "excellent" result from a full scale plant.
"We are very happy with the outcome and I think we've presented a very viable treatment method to Direct Nickel," he says
Direct Nickel's test plant produced its first marketable nickel and cobalt concentrate in July 2013, which the company describes as a culmination of several years work and $40 million investment.
A feasibility study is investigating a commercial plant in Halmahera, Indonesia with partner company PT Antam, capable of producing between 10,000 and 20,000 tonnes of nickel concentrate a year.
Direct Nickel CEO Russell Debney says the company will target the stainless steel sector because the DNi process has potential to reduce prices globally.
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