Mining technology looks to a sustainable future

Sustainability and mining are two words that don’t quite seem to fit together. But with evolving social expectations, and under increasing public and media scrutiny, the past decade has seen the mining industry put in a huge effort into sustainable development in order to maintain its ‘social licence to operate’.

For the mining industry today, sustainable development means ensuring the benefits of mining operations balance out adverse social and environmental impact, while remaining economically viable. It’s a tough challenge but one where innovative Australian technology is playing a prominent role. The latest developments in the areas of emissions reduction, geosequestration, water usage and waste management are set to help shape the future of sustainable mining on a global basis.

Sustainable water use

According to Morrie Goodz, Conference Chair for the AusIMM Sustainable Mining 2010 conference held in Kalgoorlie in August, using water from ground and seawater and re-using water from the community and industry are important areas. “Our conference has a number of papers that are looking at processes for re-using water or using water that is considered of no use, such as hyper saline ground water,” he says.

“We’re also seeing opportunities to look at technologies that require less use of water. In a lot of processes the heating and cooling of water is very energy intensive. If you can filter out the water and dry it by some natural means before the process that involves energy then you reduce the quantity of energy required to heat or cool the material.”

Reducing greenhouse gas emissions

Reduced water consumption with a dry granulation process for molten slags in the steel industry is one of the benefits of another new area that is currently being investigated by the Australian CO₂ Breakthrough Program. The program is a collaboration between CSIRO’s Minerals Down Under National Research Flagship and the Australian steel industry (Bluescope Steel and OneSteel).

The Flagship’s Driving Sustainability Theme Leader, Dr Sharif Jahanshahi, says the program is focusing on two breakthrough technologies: waste heat recovery through dry granulation of slags and the use of biochar as a partial substitute for fossil carbon. “The combination of these two technologies could reduce greenhouse gas emissions from the steel industry by more than 50%,” says Jahanshahi.

Dry granulation uses much less water than wet granulation and has the potential to reduce water consumption by the steel industry by around 2-3 GL per year in Australia. There are considerable benefits in terms of reduced energy consumption and associated greenhouse gases (about 300,000 tonnes per year in Australia alone) through recovery and utilisation of high-grade heat from molten by-product from the smelting and refining process. The global impact will be up to two orders of magnitude higher. Other reductions from the cement industry are possible through the replacement of Portland cement with the granulated slag. “In two to three years we will have demonstrated this technology in a full-scale plant environment before the industry implements the technology,” says Jahanshahi. As these industries account for 3-4% of the total world greenhouse gas emissions, this represents a huge potential for a reduction in emissions.

The biochar process involves substituting biomass-derived carbon products, such as charcoal (biochar) and bio-oil, for the coal-based fuels and reductants currently used in the iron and steel industries. This reduces the net CO₂ emissions without extensive capital expenditures to replace existing iron and steel making plants. Around two million tonnes of charcoal, which is potentially a cleaner and more efficient fuel/reductant, could be used in Australia annually. This represents a net reduction of seven million tonnes of CO₂. There are also environmental and social benefits associated with the biomass/biochar, such as addressing the soil salinity issues in affected regions in Australia.

Biomass - cement value chain - Using biochar and dry slag granulation to reduce water usage, waste and GHG emissions. CSIRO.

Increasing operational energy efficiency

Increased labour costs, dwindling fuel supplies and the potential for a shortage of vehicle tyres all add to transportation costs. One method that is now being used to reduce these costs while providing environmental and economic benefits is in-pit crushing where the ore is separated while still underground or in the open pit. “If you don’t have to take that waste out of the mine then you impact on a much smaller footprint on the site,” says Goodz. “When you disturb less ground you need less permitting requirements from the government, which means fewer delays because permits require time to be processed. The waste material that you don’t need can be used as backfill while it’s still in the mine. This saves an enormous amount of energy and time - and mining becomes more sustainable and efficient.”

Carbon capture and storage

The Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) has just begun a new five-year research program following continued success at the CO2CRC Otway Project in Victoria. The project set out to demonstrate that carbon capture and storage (CCS), or geosequestration as it is also referred to, is technically and environmentally safe. It’s Australia’s first, and currently only, large-scale demonstration of the geological storage of carbon dioxide. (See Figure 1.)

Figure 1: The Otway operations showing extraction, injection and monitoring of Co2-rich gas.

According to Dr Peter Cook, Chief Executive of CO2CRC, the 65,000 tonnes of CO₂ that were injected behaved as the researchers anticipated. “We had no problems with leakage and the CO₂ migrated in the reservoir formation in the manner that we predicted. It’s provided us with a lot of confidence in the technology and this is very important in terms of taking this technology forward,” he says.

A new well has now been drilled in a shallower geological formation with more complex rocks - something that hasn’t been done before. “We’ll be injecting CO₂ into these rocks, leaving it down there to react with the saline ground water and the rocks, then taking that CO₂ back out again so we can understand how it’s trapped, how much is trapped and the chemical reactions that take place,” says Dr Cook.

The CO2CRC research will be used to support the commercial projects that will come on stream in the next few years, both overseas and in Australia through the Federal Government’s CCS Flagship initiative.

Towards zero waste

Tailings are the residue from the extraction of minerals and metals from ores, and are often considered to be a waste product. CSIRO is working to minimise the environmental impact of tailings and looking at ways to convert these wastes into saleable by-products. Recent progress includes a process to produce high-quality quartz from Victorian gold tailings. High-purity quartz can fetch up to $2000/tonne and be used for feedstock for silica crucibles and metallurgical and solar grade silicon.

Managing and minimising toxic elements

CSIRO has also developed a thermodynamic model to understand how to minimise the dispersion of heavy metals and NORMs (naturally occurring radioactive materials) in the biosphere and provide a more attractive option for safely storing such elements. This overcomes some of the key barriers to processing large ore deposits in Australia.

Investing in our greatest resource

An aspect of sustainable mining that Goodz is keen to highlight is people, and in particular women. Women make up 50% of the mining industry workforce, particularly in the areas of geology, environment and chemistry, and often struggle with juggling careers and families. Goodz says he would like to see this part of the mining workforce better catered for. “If we managed our communities better, all those women would have the opportunity to return to work part time. Mining communities should have well-developed nurseries, creches and primary schools. Although it goes beyond mining, I think that’s an important aspect of sustainability. We seem to forget that people are our greatest resource.”

The sustainable future

Maintaining its ‘social licence to operate’ depends on how the mining industry engages with people, and in particular with the communities impacted by its activities. Demonstrating an ability to make a sustainable contribution to the socioeconomic development of these communities is vital. The technology that is emerging now will facilitate this process and thus play an important part in the mining industry’s future.