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Apr 11 -- Phytomining entails the accumulation of specific metals in plants by root absorption and storage in plant cells, followed by the harvesting and processing of these plants (for example, burning) to produce bioore from which metals can be recovered. Tailored agricultural engineering could augment natural metal hyperaccumulation in plants, allowing metals to be extracted from terrestrial environments without the requirement for blasting, comminution, or a flotation stage, as in traditional ore mining. In the present state of the art for phytomining, traditional agronomy practices are used to boost rates of metal accumulation into biomass, and burning and smelting are used for post-harvest processing, which is currently done in the laboratory and in hectare-scale demonstrations. Phytomining could potentially become a carbon-negative supply of critical minerals for the clean energy transition if optimized plants could be coupled with advancements in post-harvest processing, such as extraction without burning the biomass.

Phytomining could fill a key technology gap in the field of alternative metal sources. Phytomining 1) does not require the blasting, crushing, and other processes that microbe-based biomining requires; 2) has the potential to unlock terrestrial resources that are 10-200 times larger and 5 to 6 orders of magnitude more concentrated than those found in the U.S. exclusive economic zone ocean waters; and 3) takes advantage of the fact that plants naturally and efficiently break down rock, accumulating soluble metals that can be upgraded to cathode materials and other high-value chemicals at a lower cost. If phytomining is successful, it has the potential to unlock a significant reservoir of critical minerals in the top surface of the continental crust, potentially realizing a carbon-negative source of critical minerals in the United States.

The purpose of this RFI is to solicit input for a potential future ARPA-E research program focused on technologies related to harvesting high value metals essential for the clean energy transition from terrestrial environments using metal hyperaccumulators (HAs). The goal is to establish economic, sustainable, and low carbon-footprint domestic supply chains of high value metals to promote an accelerated clean energy transition without supply chain constraints. ARPA-E is seeking information at this time regarding transformative and implementable technologies that could:

(a) Identify or develop hyperaccumulators suitable for economically viable phytomining in the United States. Examples include agronomic techniques to domesticate hyperaccumulating species, yield higher biomass, and to control the seed dispersal; systems biology approaches to gain desired phenotypes such as high rates of growth, fast metal uptake, and accumulation of optimal metal compounds in parts of the plant that are optimal for extraction with low carbon-footprint approaches. ARPA-E's interest includes perennial species with high biomass and high metal uptake, including tree species, and any hyperaccumulators that could be grown on high-metal, nonarable lands in the US such as ultramafic serpentine soil and mine tailings.

(b) Increase total metal uptake in hyperaccumulators that can be grown at large commercial scales in the United States. Examples include microbiome engineering to dissolve metals and engineering hyperaccumulators to grow deeper roots to expand the pool of metals available without strip mining. System-level approaches are encouraged to address the questions in this RFI. For example, employing integrated rhizosphere engineering, metal transport, and accumulation to desired locations in the plants such as saps, accumulation of metals in desired chemical forms, and monitoring/analysis tools.

(c) Extract metal from hyperaccumulators using processes that produce the lowest possible carbon emissions, ideally even carbon-negative. Examples include pre-treatment of biomass before or after drying to increase the yield, new metallurgical routes to extract metals with high yields and low impurities, and novel approaches to extract metals in desired chemical forms. ARPA-E is seeking information regarding extraction strategies without emitting carbon accumulated in the biomass back into the atmosphere. System-level approaches are encouraged to address the questions in this RFI. For example, employing integrated treatment of biomass to utilize accumulated carbon while extracting metals, co-processing of more than one type of biomass, integration with existing biomass processing routes, and recycling and recovery towards circular processes and economy.

(d) Produce high-value, high-purity chemical forms of metals directly from phytomining, which can enter the value chain of battery manufacturing and other clean-energy technologies without further processing. ARPA-E is seeking information for shortening the routes to clean energy-relevant mineral forms that can be used with minimal additional cost (CAPEX, energy, processing).

Note that some approaches may fit several of the technology categories described above. For instance, systems biology optimization of hyperaccumulators could be used to develop hyperaccumulators that are suitable for the climate and soil in the United States, while also increasing biomass, increasing metal uptake, and yielding the desired physical or chemical form of the metals of interest. Using nickel as an example target metal, ARPA-E is seeking information for new approaches that could reach at least 500 kg Ni/ha per year and >90% net greenhouse gas reduction compared to the state-of-the-art HPAL (high pressure acid leaching) process based on a lifecycle analysis.

RFI notice: https://arpa-e-foa.energy.gov/Default.aspx#FoaId3baf58ef-101e-49c9-8475-5ba97f459312
RFI document: https://arpa-e-foa.energy.gov/FileContent.aspx?FileID=7cd05922-8a1d-4638-96d2-1e6310afd946

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