The industry consumes only 2% of Australia’s water, much of it unsuitable for other uses. Despite this, the minerals industry is beginning research into new techniques and sources to further increase its efficiency in the use of water.
At an average value of $80 per cubic metre, the economic value of water used by the minerals industry is higher than that of the industrial (averaging about $40/cu.m) and agriculture (averaging about $5/cu.m) sectors, the latter which consumes nearly two thirds of water resources.
The economic comparisons were calculated using life cycle assessment (LCA), a method of analysing the environmental impacts of a process or product from “the cradle to grave” to optimise environmental performance.
By using LCA methodology, CSIRO Minerals researcher Terry Norgate was able to assess variations in water use associated with different metal production and processing routes and also provide insights into the value derived from water consumption.
Reporting in a recent CSIRO publication, Norgate says the LCA work shows it is worthwhile to allocate water to the minerals industry. “By showing the value in water consumption, we can discuss the demands all industries have for water and the ability to meet these needs.”
Norgate told Australia’s Mining Monthly much of the water used in mining and processing was found locally, often too saline for other uses or inaccessible for manufacturing or other uses. There were, however, some situations in which it might compete with agriculture.
The minerals industry is already researching alternative processes and water sources to deal with any changes to water allocations.
Norgate said this was where LCA work was crucial. “Without knowing how much water is used at each step of a process, the industry has no way of understanding and minimising that use.”
He said using “fit for purpose” and recycled water and dry processing were areas being researched by the industry and CSIRO.
“Water recycling is an obvious candidate to help reduce water consumption, but issues such as organic and inorganic matter build-up, microbial species and flotation collectors will influence the extent to which this will be achieved,” Norgate said.
He said although many operations already used water that was unfit for agricultural use, a flexible “fit for purpose” water strategy that accounted for local conditions and synergies needed to be more broadly adopted by mining, mineral processing and metal production operations.
The LCA work found that water consumption for producing various metals ranged from 3cu.m of water per tonne of steel up to about 250,000cu.m/t for gold, with results largely reflecting the grade of the initial ore.
The minerals industry uses about 80% groundwater, 15% surface water and 5% mains infrastructure water, with the majority sourced from purpose-built dams, rivers, lakes and groundwater sources.
Norgate explained that the minerals sector used relatively little water during mining, with the majority used in processing and refining operations such as grinding, flotation, gravity concentration, dense medium separation and hydrometallurgical processes, all of which consume big volumes.
Indirect consumption – in particular that due to electricity generation – can also make a significant contribution to the embodied water value, he said.
“With increasing competition for water, the minerals industry, along with others, can be expected to come under increasing pressure to reduce fresh or raw water use and integrate water use from across sectors,” Norgate said.
The LCA work shows it is worthwhile to allocate water to the minerals industry. “By showing the value in water consumption, we can discuss the demands all industries have for water and the ability to meet these needs,” he said.
“LCAs can drive the environmental debate by replacing emotion with objectivity and information, allowing groups with different objectives to find common ground in approaching a problem like increasing demand for water.”
University of Queensland Professor Chris Moran, the founding director of the Centre for Water in the Minerals Industry, agrees saying LCA is important in helping the industry better understand its environmental footprint.
“Because LCA considers direct and indirect implications, you gain a much
broader understanding of issues such as water use and greenhouse gas emissions.”
However, he believes there are challenges in terms of overall sustainability: “Just because a producer reduces their energy consumption in a bid to take better account of the upstream water used in energy generation, for example, does not mean that energy is being saved overall.
“Only if this results in less energy being generated is the water actually saved. Most institutions would not consider that their responsibility goes beyond their operation but one thing LCA teaches us is that this is not true.”
Norgate said any assessment of alternative metal production processes must take into consideration other impacts – such as greenhouse gases, community capacity and economics, not just water consumption.