Turning Waste into Energy: Q&A with Dr. Wen Song

April 29, 2020

Earlier this year, UT PGE assistant professor Wen Song received a $320,000 grant from the UT Energy Institute to co-lead a multidisciplinary project on “Enabling the Sustainable Energy Transition: Economic Recovery of Rare Earth Elements”.

The goal is to develop new, scalable technologies to extract rare earth elements from coal ash and other waste streams to provide a domestic source of critical materials, while reducing environmental impact and costs. In the following Q&A, Song discusses the versatility of rare earth elements in technology, renewable energy and security, and how this research will impact the overall energy landscape.

1/ What is your team aiming to achieve in your rare earth elements research?
Rare earth elements (REEs), and critical materials in general, are of fundamental importance to the sustainability of our society’s energy, environmental, technology and national security needs. The challenge with rare earth elements is not that they are particularly rare, but rather that they rarely occur as concentrated, mineable ores. It is for this reason that the economic production of REEs is limited in the U.S.

Our group aims to identify and extract these mineral resources from alternative materials that are available ubiquitously and domestically in an economic and environmentally benign manner. For example, we estimate that the total REEs found in annual U.S. coal fly ash production, if extractable, has the potential to supply the world’s current demand. Another benefit of extracting REEs from coal fly ash is that these types of waste products are associated with a negative health impact on the communities close to coal-fired power plants, specifically particulates in the air and acid-mine drainage of the waterways. So if we can extract these materials and produce something economic out of it, then that is a win-win.

2/ Why is it important to have access to rare earth elements for a sustainable energy future?
REEs, and critical minerals in general, are necessary to enable the functionality of solar panels, magnets for wind power, vehicle electrification, and grid-scale energy storage. For example, motors in hybrid vehicles require about 10 kg of lanthanum per vehicle. Beyond that, REEs also enable technologies with improved energy efficiency and energy security. So, we need these materials on a day-to-day basis.

A second issue is that the accessibility to REEs have become a question of national security in recent years. Currently, the REE’s market is dominated largely by China, where about 90 percent of REEs are sourced, extracted, and separated. That makes the U.S. prone to volatility in terms of pricing and geopolitics. The sourcing, extraction, and separation of REEs is an interdisciplinary problem spanning geoengineering, reactive transport, plasma physics, and economic/environmental analyses. Excitingly, our project draws expertise from teams of researchers in petroleum and geosystems engineering, aerospace engineering and engineering mechanics, geosciences, and public affairs.


Dr. Wen Song and Ph.D. student Sheila Gerardo 

3/ What, specifically, are you tackling in this project?
In this project, we are working on a couple of things. My Ph.D. student, Sheila Gerardo, is characterizing fly ash materials for REE’s content, and developing novel methods of separating the REEs from the bulk ash material. So far, we have collected three samples of fly ash across the U.S., and her analyses show significant levels of REEs that are potentially viable for economic recovery.

The big question is: “how do we actually extract the REEs out of these materials?” Here, a major challenge lies in the nature of how the REEs are situated within the fly ash particles. Typically, the REE-bearing minerals are absorbed onto clay particles within the coal. As a result of coal combustion where temperatures are high enough that the clay particles melt, the fly ash that forms are glass spheres on the order of about 50 micrometers. That is smaller than the width of your hair. Importantly, the REE-bearing minerals tend to be encapsulated within the glass spheres. So, extracting a difficult-to-access material out of something so small is incredibly challenging. Our team aims to develop new techniques to leverage these existing coal fly ash resources in hopes of recovering REEs economically.

4/ How did you come up with the idea for this research?
I have always been interested in energy as a whole. Oil and gas play an important role in our energy mixture, but I have been curious about the broader energy landscape, and the resources that we require to ensure a sustainable, reliable energy future. An important bottleneck that is limiting the scale and pace of our energy transformation is due to the lack of affordable material resources, namely REEs and critical minerals. In the project, we hope to demonstrate the viability of our proposed technology for REE extraction and separation. Current technologies leverage leaching and surface reactions, achieves only about 15 percent of the available resource. From a cost and environmental perspective, this is incredibly prohibitive. Our team is targeting 99 percent recovery of the REEs in an environmentally-benign and economic manner.

5/ Do you need active coal plants to obtain the coal fire ash?
The REEs contained within the current annual U.S. production of fly ash alone, if extracted, has potential to supply the current world demand. So, there is a potential opportunity here. As our society weans off of coal-fired electricity generation in favor of more environmentally-benign resources, there is a considerable existing stockpile of fly ash. Specifically, the U.S. and the world in general have been burning coal for a long time and at a great scale and, until now, fly ash has been regarded as a waste material and has not been converted to a useable product at scale. So, there is a lot to work with.

6/ What are the consequences for ignoring this type of research?
Our ability to transform the energy landscape, environmental implications, resource security, and price volatility are some of the most important consequences for ignoring this research. On the flip side, the importance and potential of this work is equally demonstrated.

7/ What do you hope this research achieves?
I think that as an engineer, we want to make a positive impact on society and this is one way of doing it. In the near-term, the goal is to prove that our concept is technologically feasible. With this interdisciplinary team, I am hoping to create a center for strength and research excellence around rare earth and critical minerals recovery.