Scientists are harnessing the power of plants to absorb certain materials, especially heavy metals. This could be to either provide an alternative to mining the metal, (Phytomining) particularly in areas where commercial mining would not be a viable option due to the low percentage of the ore present in the soil or to clear toxic heavy metals such as lead and cadmium from contaminated soil (Phytoremediation).
Plants such as Streptanthuspolygaloides are currently planted in areas in the USA with Nickel rich soil which is not quite viable enough for profitable conventional mining. The plants absorb the metal as they grow, are then harvested and burnt to an ash which contains around 1% of the metal (by mass). This is then smelted to extract the metal. The energy produced in the burning process is used to generate the electricity needed in the extraction process with any excess being available to sell to the national grid. The obvious environmental advantages of metal extraction using this method are clear. Firstly, the ability to extract metals from mineralised soils that would be uneconomical for mining. Secondly, the process is almost sulfur free. Thirdly, less energy is needed for smelting. Fourthly, far fewer gases causing acid rain are released and finally, destruction of habitat that is caused by opencast mining isn’t an issue.
Unfortunately, the main disadvantage is, as always financial. Making a profit from phytomining depends solely on the price of the metal and is only viable when the cost of the metal is high. Because the prices of metals can fluctuate with the markets, a farmer could plant a crop when the cost is high only to harvest it when the cost has reduced.
Phytoremediation, however, could be extremely useful in cleaning up areas of land which have become contaminated and can no longer be used to grow crops or graze animals. Plants, known as hyperaccumulators remove the toxic metal while growing and again these can be removed once harvested and disposed of correctly and safely.