Coal has gotten a bad rap these days because of its heavy contribution to rising greenhouse gas emissions, which cause global warming. It’s obviously a terrible means of generating electricity, but that doesn’t mean it’s game over for the material. It still has practical use by other means. For example, a new study shows people could use compressed blocks of pulverized coal to desalinate seawater.
The blocks function as the core component of a sunlight-powered off-grid water purification system. The inventors of the new method are currently processing the technology with commercial partners toward pilot-scale production of fresh drinking water.
Associate Professor Andrea Fratalocchi was struck with the idea for a new potential use for coal while reviewing the economic challenges of ending its use for power generation. Fratalocchi knew from long-standing research that the dark-colored material strongly soaks up sunlight, driving seawater desalination.
He recalled:
The two ideas clicked together: why don’t we use coal for a new economy in water desalination?
From that moment, he began leading a team of researchers at Saudi Arabia’s King Abdullah University of Science and Technology (KAUST) to investigate carbonized compressed powder (CCP). The material is made by grinding charcoal or coal into a powder, then compressing it back into a solid more porous than the original material. In addition, it can be molded to any shape desired.
However, instead of just compressing the powder as it was back into a solid, the team combined it with natural cotton fibers, then compressed it into 20 x 20-cm (7.8-in) blocks. Next, they placed the cotton-infused CCP blocks into a 34 x 34-cm (13.4-in) seawater-containing container, leaving the bottoms of the blocks exposed and touching the surface of the water.
The absorbent fibers drew water in and up through the block while sunlight heated the black surface. The liquid water turned to steam when it reached the hot surface, rising and condensing on the inside of a transparent pyramid cover. The condensation trickled down the sloped structure to a collection reservoir, where it could be harvested as fresh, drinkable water. The salt remained behind within the block. All they had to do was rinse the CCP in seawater to remove the salt. Like this, they could reuse the material many times.
The scientists say the desalination rate per unit of raw material is two to three times that of other solar desalination systems.
One of the team’s researchers, postdoctoral student Marcella Bonifazi, said:
CCP is abundant in nature and low-cost, as well as lightweight, versatile, and highly scalable from a fabrication point of view. The device produced fresh water for around one-third the cost of current state-of-the-art solar desalination technologies.
Valerio Mazzone, another researcher on the team who also developed the device as a postdoc, added:
The device could provide fresh water to the 1.6 billion people around the globe facing economic water shortages. According to the UN, access to water for agricultural production, even if only for supplemental watering of a vegetable garden or small crops, can make the difference between farming as a mere means of survival and a reliable source of livelihood.
The team calculated that a 16 square meter CCP desalination system could generate enough water to meet a typical family of four’s drinking, cooking, and agricultural needs.
The technology could soon be used for the first time in a pilot plant in Brazil via a partnership with Dutch startup PERA. It will serve the people in Brazil’s semiarid northeast region, desalinating brackish water to produce cooking and drinking water. Water scarcity is spreading rapidly, threatening the global population, so innovative and cheap solutions such as this are incredible.
Another researcher, Jeffrey Grossman, also found another use for coal. However, he highlights the material’s molecular complexity instead. His research shows that coal could serve as the basis for solar panels, electronic devices, or batteries when ground into a powder and processed.
Grossman collaborated with research scientist Nicola Ferralis and doctoral student Brent Keller to make a simple electrical heating device for defrosting airplane wings or car windows. As they developed the application, they also characterized the electrical, chemical, and optical properties of thin films of different kinds of coal – two bituminous types, anthracite and lignite. Their demonstration revealed that thin films made of this traditionally low-tech material possess many potential uses.
Grossman said:
When you look at coal as a material, and not just as something to burn, the chemistry is extremely rich. So, could we leverage the wealth of chemistry in things like coal to make devices that have useful functionality? The answer is a resounding yes.
Keller said that this study is the first to utilize coal for its electronic and optical properties for advanced devices.
These new uses for coal leave us with one fundamental question: Why set it on fire when it has so much potential in other applications?
