Critical Materials Recovery from Solutions and Wastes: Retrospective and Outlook

One of the greatest challenges facing society in the 21st century is providing better living standards to all people while reducing and minimizing the impact of human activities on Earth’s global environment and climate. During the past decade, sustainability has emerged as a unifying framework for addressing the global environmental, economic, and societal challenges facing the world. The Brundtland Commission of the United Nations defined “sustainable development” as “that which meets the needs of the present without compromising the ability of future generations to meet their own needs” (available online at http://www.un-documents.net/ocf-02.htm). Materials are the building blocks and pillars of a sustainable society and global economy. There is a growing realization that the implementation of clean-energy technologies of the 21st century will require large amounts of critical metals including rare-earth elements (REEs), platinum group metals, copper, lithium, gallium, and precious metals (e.g., silver and gold). Significant amounts of phosphorus (P) will also be needed as the world faces the daunting challenge of doubling the amount of food it currently produces in order to feed around 9 billion people by 2050. As a society, we utilize and consume large amounts of minerals, metals, P, and other materials produced by mining with little or no recycling. Thus, our current management and stewardship of Earth’s mineral and metal resources are not sustainable. Increasingly, impaired water (e.g., seawater, brines, and municipal/industrial wastewater) and solid wastes (e.g., discarded consumer products and sludge) are being viewed as alternative sources of critical metals and valuable elements to address global materials availability and supply challenges. Thus, in the next decades, environmental scientists/engineers, business leaders, and policy/ decision makers will be confronted with a new set of exciting opportunities and challenges to advance the viability of critical materials recovery from impaired water and solid wastes. In this special issue of Environmental Science & Technology (ES&T), we highlight recent advances on the recovery of critical/valuable metals and P from “wastes”. Two key goals of this special issue are to (1) provide a retrospective and outlook of the state-of-the-field; and (2) bring into focus crosscutting scientific, technological, and environmental challenges along with corresponding societal and regulatory issues