Developing commercial phytoextraction technologies : practical considerations

Abstract

Several plant / metal combinations have been identified for the phytoextraction of heavy metals from soil. Commercial development of technologies for extracting metals from soil has been proposed; however, many obstacles must be overcome before successful implementation. This paper relates some of the practical problems and considerations we have encountered during our development of a commercial technology for phytomining of Ni from polluted and mineralized soils. Soil conditioning to maximize plant growth and metal uptake is first necessary, requiring extensive prior knowledge of the influence of soil pH and nutrient availability on growth and metal uptake. Seed planting methods also need to be determined, such as depth of sowing, potential mechanization and planting density. Growth during the year requires control of weeds, insects and diseases. Extensive prior work is necessary to ensure that the crop is free of these pests and regulatory approval may be required for nonlabel use of pesticides. Method of harvest is also a concern, as most past researchers have harvested material by hand. It is generally hoped that commercial forage harvest equipment will be adequate, but this may not be practical for some very low-growing hyperaccumulators. All these operations require extensive prior testing, often during multi-year evaluation, before commercial field operations can be started.