Biogeotechnology for Industry and Land Management

Thermophilic heap bioleaching for copper extraction

In the mining industry, there are applications of biogeotechnology in the processes involved in metal production, as well as the treatment and rehabilitation of wastes and old mine sites.

The natural physiological capabilities of acidophilic microorganisms are exploited for the extraction of metals from mineral sulfide ores in a process known as bioleaching.

Crushed ore is stacked into large heaps, irrigated with low pH water. Colonies of bioleaching microorganisms then become established, the ore is oxidised and the target metals are released into the water, which is collected as it exits the heap.

The cycle is a closed loop that prevents the escape of potential contaminants off site. And, as the metal is in solution, smelting and refining are not required, so there are no gaseous emissions of sulfur dioxide, which has been associated with the lifetime prevalence of asthma. The process is also more energy efficient, and as it is invariably conducted at the mine site, there are also savings on transportation costs.

Bioleaching is currently used commercially for the recovery of base metals such as zinc, copper, nickel, and cobalt, and precious metals such as gold. For certain ores (e.g. chalcocite, Cu2S, a secondary mineral sulphide), bioleaching will occur readily at ambient or mesophilic temperatures (10-40°C). But it does not work so well for other ore types, due to their chemical structure.

One such example is the primary mineral sulphide ore chalcopyrite (CuFeS2), an important mineral sulphide ore. Approximately 80 per cent of global copper resources are trapped in this mineral form, although the ore is often of fairly low grade (i.e. low metal content). However, greater recovery of copper can be achieved through bioleaching at thermophilic temperatures (>55°C) using thermoacidophilic bacteria.

Extension into chalcopyrite would take advantage of existing equipment (e.g. solvent extraction and electro-winning circuits). The technology would extend the lives of mines, and ensure a much greater return on the original capital investments. Economic modelling of the potential associated with thermophilic heap bioleaching has shown that the economic return to a single mine operation over a five year period could be as high as $AUS100 million for a 30 megatonne chalcocite/chalcopyrite mixed resource (Strategic Technology Evaluation and Management, 2002).

Biogeochemistry of fertiliser and nutrients

For maximum agricultural production and profitability, the best use of fertiliser is essential. It is also important to minimise any undesirable impacts such as the accumulation of cadmium and zinc, which can result from repeated applications of fertiliser.

To optimise the application of fertiliser, an extensive understanding of biotechnology and geochemistry is required. Such an understanding would encompass the geochemical fate of fertiliser components, how they react with other components and nutreints in the soils, how they accumulate in (or leach from) the soil, how they interact with plant and microbial systems, and the likelihood of transport to waterways and ground waters. Specific objectives include:

• Predict fixation of Mn , Zn and P in soils
• Develop methods to assess nitrogen (N) availability, biological N transformation and chemistry (15N Nuclear Magnetic Resonance - NMR)
• Develop Mid Infra Red (MIR) technology as a real-time soil testing tool
• Understand fluid fertiliser (such as polyphosphate) chemistry
• Develop and use Diffusive Gradients in Thin-films (DGT) as an improved multi-nutrient assessment tool

Researchers are developing innovative solutions to the challenge of sustainable nutrient management in Australian soils: determining constraints to nutrient availability; developing improved techniques to assess soil fertility; and designing fertiliser technologies that enhance nutrient use efficiency. Their work will provide a greater understanding of macro- and micro- nutrient cycling in plant-based agricultural systems (including methods to measure different pools of nutrients), technologies for more efficient delivery of nutrients, and renewed understanding of the constraints to nutrient availability.

Technology for the treatment of wastes for the prevention of contamination

In many industries there is a preference for waste treatment at the site of production. This practice helps to prevent contamination due to the dissemination of waste products into the surrounding environment. Toxic emissions or odours can also hinder the establishment or expansion of companies, so the decision to perform waste treatment on-site may be driven by economic imperatives as well. And clean-up of disseminated wastes, by remediation for example, can be very costly.

New waste treatment processes are being developed all the time. There are bioreactors and novel applications of geochemical technology for specialised waste such as organic compounds, derivatives of cyanide, odour compounds, metals, and acidic waste products.

Bioreactors research is one area of activity in CSIRO Land and Water. Another area is the management of water bodies that receive waste. This involves manipulating elements of the ecosystem: altering the nutrient status to induce bacterial or algal growth, for example, or introducing fish. Researchers actively promote a particular part of the aquatic ecosystem, so that one element may flourish over and above another.

Biological treatment of potable water, and production of biologically stable water

The science of water quality and treatment is driven by economic, social, and environmental imperatives and when things go wrong, there are serious implications for health.

One problem faced by water companies is caused by the use of high concentrations of chlorine to control biofilms in the systems that distribute our water. High levels of dissolved organic carbon result in the production of trihalomethanes and other chlorinated and brominated organic compounds. These compounds have been implicated in the development of certain cancers.

Many water companies in Europe (especially Germany and The Netherlands) are moving to the production of biologically stable water: water with very low assimilable organic carbon (AOC) and biologically degradable organic carbon (BDOC), which, if rigorously produced, can be distributed with minimal or no chlorination.

The water companies that operate in Australia will also move in this direction, but they need access to scientific expertise. CSIRO Land and Water has now begun to research, optimise, validate and integrate these treatment options into the delivery of potable water. The Water Corporation of Western Australia has commissioned the first operational MIEX® plant in the world, and is evaluating biofiltration for incorporation into their treatment options. In addition, biofiltration is being investigated in small community water supplies for reduction of algal flavours, herbicide contamination, and halomethanes.

Environmental molecular diagnostics for biological function

Biological function is a key element of soil, sediment and aquatic health. It is essential for healthy ecosystems and critical for the development of sustainable agricultural production.

New technology, for the assessment of biological function, will assist growers and managers to better understand the biological health dynamics of their systems. CSIRO Land and Water is developing commercial molecular diagnostic tools that measure the functional status of microbial populations in soils, sediments and aquatic environments to determine their biological heath and ability of systems to perform key processes such as nutrient cycling, and maintenance of soil fertility.

Potential markets and applications include agricultural, mining, environmental consultancy (pollution risk assessment) industries, state and federal natural resource management agencies.

Allied to molecular technology is the development of interpretative, predictive tools that determine how a system will respond to management strategies and interventions, or contamination, based on molecular measurements.

The advantages of molecular diagnostics over existing products include:

• Rapid assessment (the current technique for assessing ammonia oxidising bacteria involves a 30 day incubation whereas molecular technology for the determination of population and activity requires just 24 hours).
• Potential for automation and rapid through-put analytical systems.
• Measures functional attributes of microbial populations, which are the determinants of system productivity and health, rather than population attributes. (There is no evidence of links between population diversity or size and system function).
• Captures all functional components, based on extracting genes from an environmental sample, not isolation of individual species, and is therefore more efficient and comprehensive.