Aluminum production creates a toxic byproduct known as red mud. In an effort to cut down on this waste, researchers have figured out a way to send electric pulses through the mud to purify it and allow it to be reused instead of discarded.
The aluminum-creation process begins with bauxite ore, a raw material that contains desirable aluminum-rich minerals but also a host of impurities including silica and iron and titanium oxides. To get to the aluminum, crushed bauxite is mixed with a hot and concentrated sodium hydroxide solution. This allows the aluminum minerals to dissolve while other impurities remain solid.
After the solution settles or is filtered, the aluminum minerals are harvested, forming a material known as alumina, and the rest of the materials form a solid waste known as red mud. This waste product is highly toxic because of its high alkalinity and heavy metal concentration. It is estimated that for every ton of alumina produced, one to two tons of red mud is created.
Seeking a way to reuse this waste stream, researchers from Rice University turned to a process known as flash Joule heating, in which they zapped red mud with a short high-powered electrical pulse, akin to a flash of lightning. This vaporized the harmful metals in the red mud, and left behind a purified compound rich in aluminum. They found that adding a small amount of chlorine gas to the chamber containing the red mud improved the process.
“The speed and simplicity of this method set it apart,” said Qiming Liu, co-first author of the study. “In just 60 seconds, we extracted 96% of the iron and nearly all the toxic species, while retaining almost all the aluminum.”
The researchers then turned the purified red mud into super-strong ceramics, which, they say, can be used as building materials. They also say that the cleaned mud could also be used over again to create more aluminum.
“Our research presents a potential game-changing solution for the red mud crisis,” said James Tour, the study’s corresponding author. “This advance is massive from an industrial perspective, turning what was once a toxic liability into a valuable asset in under one minute.”
Purifying the red mud offers multiple environmental benefits, says the research team, including a reduced need for bauxite mining, lower greenhouse gas emissions, and a cleaning up of toxic waste piles that cause environmental disasters.
The new method is now being scaled up by Flash Metals USA, a spinoff from Rice. The team says it can potentially be used in other industries such as steel manufacturing. It joins another method reported last year in which red mud was processed via plasma into green steel as an additional way to deal with the toxic substance, which is produced at a rate of nearly 200 million tons per year.
“This is not just about red mud; it’s about changing our perspective on waste,” concluded Tour. “If we can apply this method to other industrial residues, it could represent the beginning of a new era in sustainable materials recovery.”
The research has been reported in the journal Applied Materials and Interfaces.
Source: Rice University
