MIT engineers designed a nanofiltration process that could make aluminum production more efficient while reducing hazardous waste.
Used in everything from soda cans and foil wrap to circuit boards and rocket boosters, aluminum is the second-most-produced metal in the world after steel. By the end of this decade, demand is projected to drive up aluminum production by 40 percent worldwide. This steep rise will magnify aluminum’s environmental impacts, including any pollutants that are released with its manufacturing waste.
MIT engineers have developed a new nanofiltration process to curb the hazardous waste generated from aluminum production. Nanofiltration could potentially be used to process the waste from an aluminum plant and retrieve any aluminum ions that would otherwise have escaped in the effluent stream. The captured aluminum could then be upcycled and added to the bulk of the produced aluminum, increasing yield while simultaneously reducing waste.
The researchers demonstrated the membrane’s performance in lab-scale experiments using a novel membrane to filter various solutions that were similar in content to the waste streams produced by aluminum plants. They found that the membrane selectively captured more than 99 percent of aluminum ions in these solutions.
If scaled up and implemented in existing production facilities, the membrane technology could reduce the amount of wasted aluminum and improve the environmental quality of the waste that plants generate.
“This membrane technology not only cuts down on hazardous waste but also enables a circular economy for aluminum by reducing the need for new mining,” says John Lienhard, the Abdul Latif Jameel Professor of Water in the Department of Mechanical Engineering, and director of the Abdul Latif Jameel Water and Food Systems Lab (J-WAFS) at MIT. “This offers a promising solution to address environmental concerns while meeting the growing demand for aluminum.”
Lienhard and his colleagues report their results in a study appearing today in the journal ACS Sustainable Chemistry and Engineering. The study’s co-authors include MIT mechanical engineering undergraduates Trent Lee and Vinn Nguyen, and Zi Hao Foo SM ’21, PhD ’24, who is a postdoc at the University of California at Berkeley.
A recycling niche
Lienhard’s group at MIT develops membrane and filtration technologies for desalinating seawater and remediating various sources of wastewater. In looking for new areas to apply their work, the team found an unexplored opportunity in aluminum and, in particular, the wastewater generated from the metal’s production.
As part of aluminum’s production, metal-rich ore, called bauxite, is first mined from open pits, then put through a series of chemical reactions to separate the aluminum from the rest of the mined rock. These reactions ultimately produce aluminum oxide, in a powdery form called alumina. Much of this alumina is then shipped to refineries, where the powder is poured into electrolysis vats containing a molten mineral called cryolite. When a strong electric current is applied, cryolite breaks alumina’s chemical bonds, separating aluminum and oxygen atoms. The pure aluminum then settles in liquid form to the bottom of the vat, where it can be collected and cast into various forms.