About three years ago this column mentioned that phytomining was being used in the mining industry, and others, to extract left-over minerals from the ground and as a long-term effort to clean up a degraded area of contamination.
Phytomining is described by one company as the cultivation of a crop where the specific purpose is to process metals out of the harvested biomass for sale to the international market.
This process was first described for nickel in 1994 and after much experimentation it was predicted that the nickel yield would be about 100kg of metal per hectare.
Although in Queensland at the Sustainable Metals Institute a research team have discovered that one type of hyperaccumulator planted across a nickel-rich site, like a mine tailings dam, could yield up to 300kg of nickel per hectare every year.
That means that critical metals used in batteries and stainless steel manufacturing could be harvested rather than mined.
Phytomining make use of some plants that grow naturally and accumulate metals in their structure.
When harvested and burnt, the metals are extracted without the danger of using other chemicals for extraction.
There are over 400 different varieties of plants that can take up the minerals, however there are some that are unsuitable for various metals because they are insoluble in soil. However this can be corrected by special chemicals that can be used to force the take-up of the minerals by these plants.
The take-up is completed when the plant dies and is then harvested.
When gold is recovered in rock, cyanide is used to leach or free the gold from the rock and the now soluble gold can then be recovered as pure metal. This is why gold mines, especially in poor countries, need to be tightly managed.
There are numerous countries around the world actively participating in research and development of ways to go about the extraction of precious metals and as costs rise the idea of harvesting plants to help keep costs down become more viable.
Mercury, gold, nickel, palladium and platinum are just some of the metals being studied as a better environmental and social outcome.
The mining industry is still investigating the uses of phytomining as to whether widespread farming of hyperaccumulators could provide an alternative to some destructive mining methods, while also helping to rehabilitate former mine sites.
The Queensland Government has funded a “world first” study to assess the ability of native plants like selenium weed and macadamia trees to become these hyperaccumulators. All looks rosy for the future.
Till next time.
