Phytomining of rare and valuable metals

The exponential growth of low-grade mining ores and metal-polluted soils around the world during the last decades is expected to continue at a higher rate in the foreseeable future. Yet, the strategic and commercial importance of some elements found in those sub-economic ores and soils, their elevated market prices, and the corresponding environmental concerns have opened a window of opportunity for phytomining. This phytoextraction-based technology uses the ability of certain plants to uptake valuable metals, producing a bio-ore from the harvested biomass that allows metal recovery through smelting. Once applied at large scale, phytomining may either function as a standalone operation to retrieve the desired element or jointly with phytoremediation, financing the costs of the latter. This chapter reviews the advances of phytomining since its inception in the 1990s, focusing on the results obtained to date, with gold, nickel, thallium, and rhenium.