Using plants to remediate metals

Context

Significant areas of land are contaminated with metals from anthropomorphic activities but also from naturally occurring geological deposits with, for example, 5 % of polluted sites in the EU containing > 100 mg/kg nickel. Some of these metals are rare elements; there are substantial amounts of platinum group metals present in mine tailings, a mining process waste product.

These metals are used in an increasing number of biotechnological applications, with suitable substitutes lacking, global reserves depleting and existing reserves vulnerable to geopolitically-controlled supply restrictions. Yet, despite these factors, and the high environmental impacts of extraction, after use metals are often dispersed back into the environment.

One way to capture these metals, while re-vegetating, detoxifying and stabilising contaminated areas is through phytomining: the use of plants to take up, and concentrate metals. 

Using plants to extract metals from the environment is not a new idea, but the costs of growing, harvesting and transporting metal-rich plant biomass, in addition to the cost of smelting to the base metal, have been prohibitive to the development of metal phytoextraction.

The research

Our research is using biology to understand the mechanisms behind metal uptake and storage and apply this knowledge to improve metal uptake specificity, develop value-added products from metal-rich biomass, and recover metals for reuse.

We have shown that plants can take-up and deposit palladium and gold as nanoparticles with in vivo catalytic activity. Our research in collaboration with colleagues at the Green Chemistry Centre of Excellence, is now discovering how nickel-rich, pyrolysed plant biomass can be used to catalyse the conversion of the surrounding plant biomass into platform molecules for biofuels, and to breakdown some plastics into their monomer components for recycling.