Environmental win for Alcoa

Using bacteria for Oxalate removal

Reductions in carbon dioxide emissions and energy use, thanks to innovative technology, have secured Alcoa a win at the 2010 WA Engineering Excellence Awards.

The process, which took out top honours under the environment category, uses naturally occurring bacteria to consume oxalate - an impurity in the alumina refining process.

Oxalate is a natural product found in soil and some plants. When decaying plant matter is carried underground via water, some of it sticks to bauxite ore and enters the alumina refining process, where it degrades into oxalate. Considered an impurity, oxalate must be removed for the process to work efficiently and for the alumina to meet specification.

The process, known as continuous biological oxalate destruction, is an environmentally friendly solution to the oxalate challenge. Development, by Alcoa’s global refining research and development division (Technology Delivery Group - TDG) based in Western Australia, was more than 10 years in the making. The process uses a series of tanks containing warm liquid and bacteria growing on plastic carriers. Oxygen and nutrients are added, and oxalate is introduced as a feed source. The bacteria consume the oxalate.

Alcoa Vice President of Technology and Manufacturing Laurie Stonehouse said: “The biological destruction process has proven to be extremely robust technology, delivering well above design expectations.

The biological destruction process is currently in operation at Alcoa’s Kwinana Refinery saving around 8000 tonnes of carbon dioxide from going into the atmosphere each year, compared with alternative oxalate-destruction techniques.

Alcoa is expected to rollout the process to its other WA refineries at Pinjarra and Wagerup and then, potentially, to its refineries around the world.

Long term, the process has the potential to consume all of the nearly 200 metric tonnes of oxalate removed each day by Alcoa’s nine refineries around the world, while reducing both greenhouse gas emissions and energy usage.

As a category winner Alcoa is now eligible to enter the Engineers Australia National Awards, with the winners announced at Parliament House in Canberra on 24 November 2010.