The Earth is crawling with microorganisms. Some types of microbes even help break down rocks into soils. Companies have used this property to mine gold and copper in a process called biomining or bioleaching. Microbial mining is an attractive alternative to traditional mining, which operates at high temperatures and uses harsh chemicals.
Rock that contains the desired mineral, called “ore,” must be treated to extract the mineral. For example, conventional gold mining uses harmful chemicals like cyanide to get the gold out of the rock. Traditional mining needs to take great care to not let cyanide get into the environment, but using microbes eliminates the need for harsh chemicals. In copper mining, the ore is heated up to 1500 degrees Fahrenheit. Microbes can work at room temperature.
Biomining isn’t limited to only copper and gold. Scientists are also looking to use biomining for valuable rare earth elements (REEs). REEs are in the first row of the bottom section under the periodic table, plus scandium and yttrium.
The elements highlighted in orange are the rare earth elements. Image credit: Sciworthy
REEs are everywhere in modern life, such as in the screen you are looking at right now! They’re also in the phone in your pocket, the wind turbine making energy for that phone, and most other electronics. REEs have become so important, our demand is outpacing our supply, making them “critical elements.” So where are we going to get these vital elements if the Earth is running out? One answer is space.
A 2019 experiment on the International Space Station tested how effective microbes are at getting REEs out of a rock called basalt. Basalt is a common rock on Earth, as well as the Moon and Mars. Changes in gravity affect microbial growth, so scientists tested whether they could still extract REEs in low gravity.
The scientists set up chambers with basalt and a medium for the microbes to grow in. They then sent these chambers to the International Space Station, where they could control the strength of the gravity. Astronauts tested the REE extraction abilities of the microbes in three simulated gravities. These were: Earth gravity, a lower Martian gravity, and microgravity. Microgravity is near zero and simulates gravity on asteroids or The Moon. The experiment was also run on Earth as a “true Earth gravity” control.
The experiment showed that the bacteria Sphingomonas desiccabilis could leach up to four times as many REEs as controls without microbes. This bacterium extracted more rare earth elements from the basalt under Martian and Earth gravities compared to microgravity. The scientists also tested two other bacterial species, but neither performed as well as S. desiccabilis.
The microbes did not store the REEs, but instead released them into the liquid they were grown in. It is easier to extract the elements from the liquid solution than out of the bacterial cells.
They also were able to leach cerium, which tends to be harder to leach than other REEs. Cerium is used in burn medicines, specialty glass, catalytic converters, and more. Traditional leaching techniques leave behind this important element, while microbes do not.
As metals have started to become more scarce on Earth, people are looking to The Cosmos for resources. This study shows that microbes can extract rare earth elements in gravity weaker than Earth’s. This opens the possibility of going to other planets to mine these critical REEs. Not only did they show this is possible, but even identified a specific species that could be used in future endeavors. The future of REE mining may be in space, and Sphingomonas desiccabilis may be able to help.
