As more of Australia’s accessible and high grade mineral reserves are depleted, Chris Vernon reports that our great challenge is to find ways to target and process our lower grade or more complex ores to maintain productivity and value for the nation.
Article from resourceful: Issue 7, June 2015
It’s an unfortunate fact that the majority of the easy to process, high quality ores in Australia seem to have been discovered and exploited. The following graph shows the trend of declining ore grades in Australia’s producing mines, and this is fairly typical internationally.
Australia has an ancient landscape and some exceptionally rich deposits are undoubtedly still to be discovered from under deep land cover or regolith. Such deep ore bodies could be technically and economically challenging to reach and extract.
In most situations we are faced with ores that are of declining quality, have difficult mineralogies, and are increasingly expensive to process.
To remain competitive, Australia must obviously produce ‘more from less’. This is true not only for existing ore types (where commercial and technical risks are comparatively well known), but especially so for the new lower grade ore types that are becoming necessary to consider.
CSIRO is playing a part in understanding how to improve the efficiency of existing processes, and also uncovering new processing routes for the more difficult ore types that have not yet been successfully exploited.
Activities within CSIRO include advanced geometallurgy techniques to quantify and qualify required processing parameters for an orebody, more efficient drilling and mining, at-face and at-rig instrumentation to rapidly assess ores, and an advanced understanding of processing technologies, from the unit operations of flotation and beneficiation, to value and gangue leach chemistry, impurity removal and separations technology such as solvent extraction and selective crystallization.
Significant efficiencies at the unit operations level can be made through understanding particle interactions, fluid flow phenomena, and how equipment design impacts on these. CSIRO scientists have developed excellent suites of tools for example to design hardware to increase throughput and efficiency in settling and dewatering, the design of pumps and pipes in order to reduce erosion and make slurry pumping more efficient, and in mixing efficiency.
One example of a new technology is the thiosulfate process for gold, developed collaboratively in CSIRO laboratories and now deployed commercially by Barrick Gold (see article page 8).
Thiosulfate is far less toxic than the commonly used cyanide and can be used in more environmentally sensitive areas, requiring less capital-intensive infrastructure. It can also be used on preg-robbing ores, that were previously impossible to treat economically.
Another example is a novel use of solvent extraction to turn weak acid streams into a strong acid stream plus a neutral stream, and yet another that avoids multiple pH changes, consuming lime, and using solvent extraction to directly strip metals from concentrated acid streams.
A process by Direct Nickel (developed for commercial implementation in conjunction with CSIRO) avoids the need for pressure leaching of nickel laterite ores in titanium autoclaves and instead uses stainless steel tanks, thus saving capital cost and energy.
we are playing a part in understanding how to improve the efficiency of existing processes, and also uncovering new processing routes for the more difficult ore types not yet successfully exploited.
Further, the technology consumes an order of magnitude less acid (saving operating costs and resources), and produces commercial grades of magnesia and iron oxide as byproducts, both of which are commercially saleable. This is a good example of resource efficiency – diverting materials that would become a mixed waste stream in a conventional process, to a useful product.
CSIRO is also working on the game-changing technology of in situ recovery. This involves drilling into an orebody and leaching valuable metals underground – avoiding the need to dig, and shift overburden. This is a technology particularly suited to deep, stranded orebodies.
Although already practiced in the uranium industry and to some extent in the copper industry, recovery of other metals is generally more difficult. Uranium is recovered from easily permeable sandstone and calcrete-hosted ores at shallow depths, and in situ copper, from gravelly deposits. But rich and therefore attractive copper, gold and other mineral deposits generally occur in hard rock, at great depth.
This initiative will potentially make ores that are too deep for conventional mining, and too low in grade to justify the cost of mining, accessible for processing. In situ recovery will require new reagents in order to safely extract metals without jeopardising the environment.
Thiosulfate is one example of a novel reagent (cyanide would be impossible to use safely), and in other CSIRO research, acids that occur naturally in nature have been used to extract metals.
In situ recovery isn’t just about chemistry, though – a successful implementation will require a holistic approach based on the ore body, rock physics, drilling, pumping and hydrology. The diversity of skills across CSIRO and in our industry partners, will be required to make this development possible.