Despite good rains in recent years across large parts of southern Australia, it is only a matter of time before drought returns to once again stress our farmers, graziers and irrigators. When that happens, the Murray Darling Basin, responsible for half of the nation’s rural produce, will again find its production limited by water. Towns and cities dependent on the system will again face restrictions, and all large users of water in such regions will be looking for ways to trim back their consumption for economic, social and environmental reasons.
The mining industry in Australia accounts for 2% of the nation’s total water use, and in some areas it is the largest consumer. Mineral processing in particular can use large volumes of water, and typically needs 500 litres (half a tonne) for every tonne of ore ground. As mined ores continue to trend towards lower and lower grades, finer grinding is likely to become more common, requiring more water per tonne of product.
It is widely recognised already that the processes used to separate liquids from solids are low in efficiency, with mineral tailings typically made up of 60–90% potentially reusable fresh water. Clearly any improvement in water-use efficiency in the minerals sector could lead to major savings in water and costs.
In standard mining operations, mineral tailings (waste materials that remain after mineral processing) are thickened in a process that uses large volumes of water. Mining companies are able to extract some of this water for reuse, but much is lost through evaporation. However, sonicCARE™ – a new technology developed at CRC CARE – increases the efficiency of the water recovery process by up to 4%. This saving represented more than 400 million litres in one mine alone in the Murray Darling Basin, and worth over $5 million per year to its operator.
Scanning electron microscope images showed that large amounts of water are locked in a minute honeycomb structure by the kaolinite clays in the crushed mineral mix. Even though traditional ‘raking’ was found to break down the honeycomb structure into smaller self-supporting structures, these still trapped a large amount of water. The breakthrough for this research and its new contribution to mineral processing was the finding that ultrasonics – high-frequency sound waves – could help release more water from these closed structures. Researchers liken the new process to shaking a jar full of flour, which causes the flour to compact down.
The world’s mines produce more than 10 billion tonnes of tailings waste every year, and being 60–90% water, a saving of 4% equates to a very large volume of water at this global scale. In practice in Australia this new development will be most valuable in regions where there is already strong demand for limited supplies, such as the Murray Darling Basin, or the southwest of WA. However, even where groundwater or surface water is abundant, a reduction of pumping and handling volumes by 4% represents a substantial efficiency gain in resources, infrastructure and energy use.
The research work was conducted by CRC CARE’s Dr Jianhua (Jason) Du at the University of South Australia.