The US Department of Energy (DOE) Advanced Research Projects Agency - Energy (ARPA-E) announced up to $5 million in funding (DE-FOA-0002784, Topic E) to evaluate the feasibility of extracting rare earth and other high-value trace critical minerals from macroalgae.

Seaweeds accumulate trace metals in such an efficient way that this process is sometimes used to clean up polluted harbors. It would be transformative if we could harness that capability to harvest the critical rare earths we need for a net-zero economy in a low-impact way using this natural ability.

—ARPA-E Director Evelyn N. Wang

ARPA-E is interested in receiving full applications investigating the feasibility of extracting critical minerals, specifically Rare Earth Elements (REEs) critical for the production of electric motors and generators, and high-value Platinum Group Metals (PGMs), from macroalgae cultivated and/or harvested within the US Exclusive Economic Zone (EEZ).

The targeted outcomes of this topic are:

1. An understanding of what environmental, temporal and ecological factors influence the PGM/REE metal content of ocean-grown macroalgae. Factors including but not limited to cultivation region, cultivation mechanism, the effects of water quality and proximity of natural mineral sources, and harvest strategy are of interest.

2. Identification of the mechanism of biological metal absorption and hyperaccumulation by ocean macroalgal biomass, including the maximum capacity and absorption rate thereof, variability and location of mineral concentration within the macroalgal holobiont, variation among species, impact of harvesting strategies, and underlying cellular and molecular mechanisms.

3. Development of methods to extract critical minerals from the macroalgae at high output purities that can dovetail with existing and nascent macroalgal valorization streams developed for the other components of macroalgae such as carbon compounds, macroand micro-nutrients, utilizing existing waste streams from seaweed biorefineries. Within scope is continuous mineral extraction from growing macroalgae without destruction of the plant. Note that the research thrust described is only concerned with adding value to existing or nascent macroalgal processing streams that already valorize aspects of the biomass other than the PGM/REE metals of interest.

4. A techno-economic analysis of these methods, considering the sensitivity to the inputs investigated in items (1), (2) or (3).

Background. REEs and PGMs are critical in the manufacture of modern energy and national security technologies, including high-performance magnets required for wind turbines, electric vehicles, high-energy-density battery electric storage, high efficiency lighting, solar panels, and other technologies either core or ancillary to the renewable energy industry.

While demand continues to increase, economically and environmentally viable deposits are difficult to realize and extraction from existing terrestrial deposits remains costly in terms of energy inputs and emissions outputs.

Furthermore, many of these deposits are located outside the United States, creating supply chain vulnerabilities for the energy goals and national security of the country. ARPA-E noted that some of the critical minerals most important to decarbonization are also the most vulnerable to disruptions in trade, including three minerals critical to the production of the permanent magnets used in wind turbine generators and electric vehicles: Neodymium, Dysprosium, and Praseodymium.

Economic vulnerability vs. disruption potential for critical minerals in 2016. The REEs of concern to this funding opportunity include Neodymium, Dysprosium, Praseodymium, and Terbium (not depicted). PGMs including Platinum and Palladium are of secondary importance in terms of disruption potential, but offer opportunities toward economic feasibility due to their high value. Figure from USGS 2019 Critical Minerals Review.

Research has shown that macroalgae may be an effective bioaccumulator of critical minerals and that macroalgae may be particularly well suited to absorbing neodymium and dysprosium. Much of this past research has primarily focused on macroalgae exposed to contaminated seawater featuring anthropogenically enhanced concentrations of specific types of critical minerals associated with industrial pollution. These studies have also indicated that different species may absorb different metals at varying rates, and that the positive indicators of absorption strength vary by species or desired mineral.

ARPA-E wishes to reduce this uncertainty and refine the scientific understanding of bioaccumulation in macroalgae in an effort to consider the mechanisms, technical, and the economic feasibility of adding a critical minerals extraction processing chain to existing cultivated macroalgae processing streams.

Technical areas of interest. ARPA-E seeks to fund projects in two Technical Areas: Macroalgae Composition (i.e., the critical mineral composition of marine macroalgae) and Element Extraction from Macroalgae.