Fundamental froth flotation research maximises mineral processing quality and quantity
Associate Professor Seher Ata is Postgraduate Director for Mining (coursework), at the School of Mineral Energy Resources Engineering. The majority of her work revolves around a separation process called froth flotation, of which she is an expert of some renown.
Although froth flotation has been around for over 100 years, in 2016 UNSW Associate Professor Seher Ata developed an innovative technique that enables researchers to directly observe, manipulate and tune particle-stabilised air bubbles and liquid droplets to discover improved applications for particle-stabilised interfaces. This fundamental research has multidisciplinary applications that include the food and oil industries.
In mineral processing, froth flotation is a major separation process used in the beneficiation of mineral particles and occurs when crushed and ground-up ore is treated with a reagent to make the mineral surface water repellent and causes the valuable mineral to stick to the bubbles. “These bubbles then rise to the surface and create what’s called a froth layer – much like the foam on top of a cappuccino – which can then be skimmed to easily recover the minerals you want,” says Ata.
Apart from minerals, froth flotation is also used in the separation of pyrite and other ash-forming minerals from fine coal particles. Since 2015, Ata has been involved in a world-first, two-stage project supported by the Australian Coal Industry Research Program (ACARP) which is examining the effect of floatation water chemistry on coal thermoplastic behaviour and coke quality.
“In the Australian coal industry water is a big issue. If you look at metallurgical coals, for example, they are invariably washed prior to use and this consumes huge volumes of water,” says Ata.
The scientific understanding gained from this project enables us to develop techniques to optimise the parameters for the coal washing process in order to maximise the quantity and quality of the metallurgical products produced.
Associate Professor Seher Ata, UNSW Mineral Energy Resources Engineering
“Most coal preparation plants are located in remote areas where there isn’t much water, so to minimise the use of fresh water, recycled, dam water or saline water are used instead. However, these alternative resources tend to contain a variety of dissolved inorganic compounds which can negatively impact the coke quality.”
According to Ata, significant work has already been carried out on the role of alternative water sources on flotation performance, but this is the first study to systematically examine the impact of water chemistry on the modification of coal and coke characteristics.
“Our research involved measuring the water quality in several coal preparation plants for two years. We found that water quality was highly variable over the days and months of the study,” Ata continues.
One of the major outcomes of the project has been the establishment of an association between the chemical characteristics of water and the particle sizes of coal, and the resultant modification of coal surface chemistry and fluidity parameters. “This information is important because it can give us insights into how changes in water quality can impact the end product,” she continues.
In 2016, Ata was awarded further ACARP funding to extend the project and has been working to assess the influence of the harmful chemical species on flotation performance as well as developing strategies to selectively remove the identified chemical constituents from water streams to improve coal fluidity.
As a result, Ata and her colleagues have been able to shed much needed light on the behaviour of coal that has been washed with low-quality water recycled from various sources. They have also been able to provide critical information on the interaction between the reused water composition and flotation performance and coal fluidity.
“The scientific understanding gained from this project enables us to develop techniques to optimise the parameters for the coal washing process in order to maximise the quantity and quality of the metallurgical products produced,” she says.
Written by: Penny Jones