Mineral deposits (such as those containing copper.or tin) slowly release ions into the surrounding soils.  This release of ions occurs through chemical processes such as oxidation or through the activity of microbes.  Because of these processes, it is often the case that metals such as lead, cadmium, nickel and mercury can be found in plants.  Indeed, some are referred to as hyper accumulators. Such plants might be used in phytomining.  This would involve growing hyper-accumulator plants on a metal-rich soil, harvesting the plants and then burning the plant biomass down to an ash  from which the metal might be reclaimed.   This would make sense economically where the metals were rare or of high intrinsic value.  In Finland, two species of willow trees (Salix schwerini and Salix viminalis) have been studied as agents of phytoremediation.  These trees can grow in acidic soils and can cope with with copper, zinc, nickel, chromium or lead contamination.  Initial research indicates that willows can help reduce zinc levels withinin six years under favourable conditions, though nickel, copper and chromium take much longer. New research at the Finnish University of Oulu has indicated that even gold may move into certain plants.  The research team were studying Norway Spruce trees that were growing in the mineral deposit above a gold mine.  They took samples from a number of trees and analysed the leaves, and found that some had gold nanoparticles within the leaves. These minute particles were surrounded by bacterial films. It would seem that certain spruce associated bacteria can help transform soluble gold from the soil into solid particles within the leaves.   The ‘soluble gold’ enters from the soil and is transported up to the needle-like leaves, where it is precipitated into solid form. The size of the particles is indeed microscopic, being only about a millionth of a millimetre in size.  Far too small to be extracted for commercial use.   The process of biomineralisation is poorly understood, but it seems that certain endophytic bacteria (those that live within the plant) play a role in the process.  

An electric or hybrid car needs a rechargeable battery to power the electric motors of the vehicle. The batteries make use of oxides of lithium nickel manganese & cobalt. The battery of such vehicles makes up a significant portion of  the cost and  environmental impact  of an electric vehicle.  Growth in this market has created issues in securing ethical battery supply chains. The future supply of nickel, cobalt and lithium is problematical, presenting challenges both in environmental and geopolitical terms.  Much of the battery production is centred on China.  Mining of a metal such as Nickel generates significant quantities of carbon dioxide, which contributes to global warming.  The demand for Nickel is forecast to double. An alternative to traditional mining techniques for metallic ores is phyto-mining. This is possible where there is a significant quantity of the metal in the soil, and there is a plant that can take up and accumulate  the metal.  The absorption and accumulation of metals like Nickel, Cadmium and Copper is perhaps more problematic as they are toxic to many plants.  Worldwide some 450 different species can absorb and accumulate ‘toxic’ metals, growing in ‘poisoned’ or toxic soils, such as former mine workings.   Some of these plants are hyper-accumulators – noted for their ability to take up a metal to many times the level in the soil. In Albania, a project is underway to use a plant to ‘mine’ nickel.  The plant is a perennial herb with yellow flowers - Odontarrhena decipiens.  It is a member of the Brassica / cabbage family and is a hyperaccumulator.  It can take up into its stems and leaves about 2% of its dry weight as nickel.  The plant is being ‘farmed’ in Albania, where there are nickel-rich soils derived in part from the mineral Olivine.     Though olivine contains too little nickel for conventional mining, it has enough for hyper-accumulators to absorb and concentrate it.  When the olivine is ground up and spread on the field, it not only replenishes the soil with nickel [that the plants absorb] but it also reacts with carbon dioxide in the atmosphere locking the CO2 away.  This project is being developed by ‘Metalplant’ . Whether phytomining using this plant will prove to be a useful way of augmenting Nickel supplies remains to be seen.  

There are plants that we like, and some that we don’t.  In the latter category, there are weeds - the plants that grow in the ‘wrong places’.  The plants that we like include those that we eat (crops), those that we grow for timber, for pharmaceuticals or for aesthetics / pleasure.  However, we now can add other uses for certain plants - namely phytoremediation and phytomining. Phytoremediation involves the use of plants to ‘extract’ heavy metals from contaminated land.  Land can become contaminated with potentially harmful metals (lead, cadmium, mercury, copper) due to mining activities.  Read more...