Lighting-like pulses turn toxic red mud into building materials | 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.

From the article: 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.”