Plants accumulating valuable metals, like nickel, can be farmed

This shrub oozes a green sap rich in nickel (Source: New Scientist)

Mining for metals is very destructive and expensive. For example, New Caledonia in the Pacific has rich deposits of nickel and its land has been ravaged by strip mining of the metal. However, some plants accumulate high concentrations of metals, such as nickel, possibly as a defence against pests. These plants are called hyperaccumulators and can be used to produce metals, perhaps reducing the need for mining. 

Nickel is an important metal for the making of steel and is used in many lithium-ion batteries in electric vehicles, phones and other consumer items. Demand for nickel and other metallic elements is expected to surge as they are needed for electric vehicles, wind turbines, magnets, lasers and other crucial technologies.

Hyperaccumlators have been found in areas where volcanic eruptions have brought the softened Earth's mantle, rich in metals, to the surface as ultramafic rock. The resulting soils have produced plants that accumulate metals such as cobalt, arsenic, manganese, zinc, nickel and other rare earth elements. 

As a result of finding these plants, farming has commenced and it is called agromining. Metal farms are now springing up in China, Europe and Malaysia. The ultramafic soils are poor for other crops, so are now given a more profitable use. In Europe, the nickel hyperaccumulator plant is related to kale. It is harvested, baled and burnt to release a nickel rich ash. The heat from burning is used to heat surrounding homes. The return per hectare is much greater than that for wheat.

Hyperaccumulator plants can also be used to rehabilitate old mining sites, such as in New Caledonia, as it is difficult to grow other plants there. Also field trials have been set up to test agromining production on old mining sites in China.

For more information see: How to grow metal. New Scientist, January 9, 2021, No3316, pp42-5.