As the world continues to gradually lessen its dependence on fossil fuels by developing renewable energy technologies, a new problem is arising: many of these new technologies are manufactured using rare earth elements and other scarce minerals. These metals are already heavily used in the manufacturing processes of consumer electronics, aerospace, and medical devices.
In the cleantech arena, rare earth elements such as lanthanum, neodymium, europium and yttrium, are used in the manufacture of batteries, energy-efficient lighting, and magnets (needed for electric vehicles and wind turbines). Other scarce minerals, such as gallium, indium and high-purity silicon, are used in photovoltaic panels.What do we mean when we say rare?
While rare earth elements are actually found throughout the earth’s crust, they are not often found in high enough concentrations to be economically exploitable. Currently, China produces about 97% of the world’s rare earth elements as concentrations are high there and barriers to mining are practically non-existent. For many years, American manufacturers were happy to pay to import them from China because the price was right, and the obstacles to mining for them here were numerous.
However, China has recently reduced its quota of rare earth element exports, sending countries such as the U.S. and Japan into a panic. Due in part to its control over most of the world’s rare earth element supply, China’s own cleantech industry is booming. In order for other countries to stay in the game, rather than handing over almost all production of electronics and cleantech products over to China, they must find ways to loosen China’s stronghold over these materials.Drill, baby, drill or resource recovery?
One solution that many countries are pursuing is local mining. But while there are other sources of rare earth element ores, such as in the United States, Canada, and Australia, more test drilling and economic feasibility studies must be conducted before mining can begin. Even then, it may take years before any of these mines would be ready for production. The bureaucracy involved in obtaining the proper permits in the U.S. and the valid protection of endangered species that have also made utility-scale PV installations and transmission lines a not-so-simple endeavor are also obstacles to domestic mining of rare earth elements.
Another possible solution to this problem is to recover these elements from the waste created in the manufacturing process. As a leading exporter of the world’s electronics, and major consumer of rare earth elements, Japan has begun to develop various recovery methods, ranging from chemical to biotechnological processes. Teams from the University of Tokyo and Osaka Prefecture University, and from Hitachi in the private sector, have succeeded in metal separation and recovery. However, these processes are not more cost-effective than importing from China, even at higher import rates. The work and research taking place in Japan is important, but has not yet proven to be a viable replacement for Chinese imports. In order to reduce dependency on China, more efficient recovery methods must be developed.
One way to recover rare earth metals that is being developed in the U.S. is through the proven wastewater treatment method of flash vacuum distillation, which separates clean water from pollutants in a controlled atmosphere chamber. With this technology, industrial wastewater can be treated, while recovering valuable rare earth elements.
Rare earth and transition metal salts can be concentrated effectively using this wastewater treatment method because they have extremely high vaporization temperatures, typically in the thousands of degrees Fahrenheit. Flash vacuum distillation systems typically operate at temperatures of 120 degrees to 150 degrees Fahrenheit, therefore ensuring that rare earth elements are not damaged or vaporized. The applied vacuum depresses the boiling point of the liquid to be treated, and under these negative pressure conditions, water boils at 120 degrees Fahrenheit, thereby leaving behind the metals in the distillation bottoms. Wastewater containing rare earth metals can therefore be concentrated by a factor of 50 to 100. In most cases, the highly concentrated solution can then be recycled back into the refining process. The distillated water collected from the distillation process is of high purity and can also be recycled back into the process.Increased efficiency, lower costs
Wastewater treatment solutions can also be used to make existing chemically based metal recovery systems more efficient and less costly. In a case study conducted on an Oregon-based rare earth recovery facility, it was found that flash vacuum distillation was able to optimize the metal recovery process, as the chemical solution used in the recovery process was recaptured and used again, thus limiting the facility’s waste and increasing the lifespan of necessary materials. The new wastewater treatment system used much less water and energy than the company’s previous method of treatment, successfully recycling the chemical solvent back into the rare earth element recovery process.
***David Delasanta is a senior vice president at ThermoEnergy.