Critical Minerals: Current Challenges and Future Strategies

of thirty-five CMs and produces than 50% of net Abstract The demand for Critical Minerals (CMs) is soaring because of their extensive use in renewable energy generation, energy storage, energy transmission, scientific instrumentation, and a wide range of communication, military, and transport technologies. However, the supply of CMs faces several critical challenges like For environmentally sustainable development of the CM industry, countries need to make significant investments in advanced competitive research, development of efficient environment-friendly mining, extraction, and processing technologies, creation of robust environmental policy frameworks, and workforce development solutions.


Introduction
A "critical mineral" is defined as a substance that serves an essential function in manufacturing product(s), whose supply chain is vulnerable to disruption, and the absence of which could lead to substantial consequences for the country's economy or national security [1,2]. The demands of CMs, including lithium, nickel, cobalt, graphite, and rare earth elements (REEs), are soaring because of their essential role in clean energy transmission and storage technologies. Clean-energy technologies generally require more CMs than conventional fossil fuel-based technologies. For instance, an electric vehicle uses five times the amount of minerals compared to a combustion-engine vehicle, and a windmill requires eight times the minerals needed by a gas-fired power plant with the same capacity [3]. The push for 'greener' energy generation (wind, solar and geothermal) and related storage solutions could result in a demand of 3 billion tons of minerals and metals and a 500% increase in the production of CMs such as graphite, lithium, and cobalt and a by 2050 [4].
One of the biggest challenges is that the production of different CMs is concentrated in a few countries. For instance, >80% of Pt is produced by South Africa and Zimbabwe, Australia and Chile produce > 75% of all Li, 75% of Co is produced by Dominion Republic of Congo (DRC) [5][6][7][8][9]. For a few other CMs, a single country controls more than 50% of global production (e.g., China for REEs, Australia for Li, DRC for Co, South Africa for Pt) [6]. The US currently has no domestic production for fourteen out of thirty-five CMs and produces less than 50% of net For environmentally sustainable development of the CM industry, countries need to make significant investments in advanced competitive research, development of efficient environment-friendly mining, extraction, and processing technologies, creation of robust environmental policy frameworks, and workforce development solutions. Keywords: Critical minerals; Rare earth elements; Geopolitics; Mining; Extraction; Processing; Recycling; Environmental impacts; Environmental remediation

International Journal of Environmental Sciences & Natural Resources
demand for seventeen other CMs [10]. Due to such low in-house production, the US is mainly dependent on imports from other countries to meet its demand (e.g., 80% REEs imported directly from China). The increasing demands of CMs could drive global geopolitics and result in trade wars in the near future. Therefore, individual countries need to develop and enhance their national CM resources and supplies in an environmentally responsible manner.

Strategies for Developing CM Industries
Countries with CM resources need to make serious investments in developing a sustainable supply chain for CMs and creating future growth capacity. The governmental agencies play a crucial role in evaluating the CM resources and funding the academia-industry consortia for applied and basic research related to CM and REEs. There is a need to improve understanding of the geological and geochemical controls on CM enrichment in particular basins, rocks, fluids, etc. For example, coal and coal byproducts (including run-of-mine coal, coal refuse, coal ash, acid mine drainage) are critical resources for CM and REEs. However, there are only a few studies on efficiently extracting CM and REE from these resources [11][12][13]. There is a vital need to develop geological models of ore occurrence, mineral processing, and extractive metallurgy [5]. Funding in geosciences, geochemistry, and chemical engineering should target the development of new tools for the exploration and efficient extraction of CMs. Further, new investments should be made in technologies that treat the leftover material from mining as a resource, develop urban mining techniques and find substitutes of CMs that are low in abundance [3].
Another useful strategy would be the recovery of CMs via effective recycling of industrial and electronic waste. It is estimated that each year ~50 million metric tons of e-waste are disposed in landfills worldwide, and only 12.5% of e-waste is currently being recycled for all metals [14]. Studies on life cycle assessments of CMs such as REEs have indicated that recycling electronic waste could be an encouraging supplement to conventional production processes [15]. An example of recycling iPhones can easily demonstrate the effectiveness of recycling in meeting the CM demands. Recycling of 10,000 iPhones has the potential to yield 190kg of aluminum, 77kg of cobalt, 71kg of copper, 9.3kg of tungsten, 4.2kg of tin, 1.1kg of REE, 0.75kg of silver, 0.18kg of tantalum, 0.097kg of gold and 0.01kg of palladium [16]. Boosting recycling technologies for lithium-ion batteries [9] could also contribute to CM and REE recovery from waste.
There is also a need to develop a skilled workforce to generate and maintain sustainable CM supply chains. Each CM ore or deposit is unique and requires different mining and processing technology. Therefore, even if we have sufficient resources, we need skilled scientists/workforce to resolve these complex issues. However, in countries like the US, there has been a steady decline in mining industry employment from 25,000 employees (3,750 with science degrees) in the 1980s to 1,500 with only 250 employees holding science degress [5]. Therefore, it is essential to create a workforce pipeline by engaging and training students at the college level in CM exploration, mining, and processing.
Finally, to promote the engagement of private companies in the CM industry, the governments should consider stockpiling, tax credits, and loan guarantees to reduce the risks associated with CM mining and processing. These targeted investments in CM research, mining, production, waste recovery, and recycling could potentially change the CM economics of countries and make them competitive with large producers like China.

Limiting Environmental Impacts of CM Industries
Although CMs support developing green energy technologies, their extraction, separation, and development can severely impact the environment and human health. The severity of these impacts can vary with mining operations, type of ore, processing of the mineral ore, local geology, and hydrogeology of the area. For example, lithium mining, processing, and manufacturing of lithium-ion batteries could have significant environmental impacts such as water depletion and pollution, increased toxicity on plants and animals, land subsidence, carbon emissions [17][18][19]. The process of REE extraction has also been reported to use harmful chemicals that generate high volumes of solid waste and wastewater [14]. Dumping of e-waste and improper treatment methods has been shown to leach large amounts of CMs and several other toxic elements in the soil and groundwater, especially in developing countries like Ghana, India, and China [20][21][22]. Cobalt mining in DRC has been criticized for using child labor and other irresponsible mining practices [9]. A biomonitoring study of cobalt mining in DRC reveals a substantial exposure of Co, especially in children, and the urinary concentrations of Co were found to be the highest ever reported for a general population [23]. These case studies indicate that high concentrations of CMs can be released in soil and water during CM mining and processing. However, there is still minimal understanding of the impact of the majority of the CMs on human health [14]. For instance, the maximum acceptable limits for CMs and REE in drinking water are still not available from environmental agencies and international health organizations. Therefore, is a critical need for regulatory agencies to develop and enforce permissible limits of CMs in water and soil. The impact of CM mining on sediment loads in regional watersheds and associated adverse effects on local flora and fauna also need to be assessed. Also, comprehensive remediation plans need to be implemented to effectively treat acid mine discharges and fully restore the mined areas. In addition, fine particulates, aerosols, volatiles and radioactive materials need to be monitored and regulated in CM and REE mining and processing facilities to limit human exposure and associated health hazards. Countries need to develop robust environmental policy frameworks to ensure that the development of CM industry creates no major threats to the environment and human health.

Concluding Remarks
The development of an environment-friendly sustainable supply of CMs faces several challenges. The governmental agencies, industries, academicians, and environmental advocacy groups need to work together to ensure appropriate policies and incentives are put in place to develop the CM industry. The government needs to invest in research, infrastructure, and workforce development to address the mining, processing, and maintaining supply chains of important CMs. The governmental agencies also need to ensure that adequate environmental policy and regulatory framework are developed and enforcement plans are put in place before expanding the CM industry. The industryacademia consortiums need to work together to explore innovative methods for improving the efficiency of mining, extraction, production, and recycling of CMs and ensuring these methods have minimal environmental impacts. This multi-stakeholder approach will resolve complex issues surrounding the economic development of CM industries and create comprehensive environmental checks and solutions.