Nickel West, Australia, is among various mines that can use microwaves for CO2 storage in waste.
BHP
Mining produces billions of tons of waste rock annually. By reacting these unused rock piles with carbon dioxide, we can potentially eliminate considerable amounts of greenhouse gases from the atmosphere. The current technique, however, involves burning fossil fuels to heat rocks to high temperatures. Our findings suggest that activating carbon removal could allow these rocks to require less energy when reacting with CO2.
“It’s akin to microwave popcorn,” says Shawn Laurie, a technology developer at Arca, Canada. Instead of heating the entire rock, microwaves target specific molecules. This mechanism differs from how kitchen microwaves pop corn by heating water within the kernel.
Rocks serve to absorb CO2 from the atmosphere, mitigating emissions from fossil fuel combustion. Some projects enhance rock weathering by spreading crushed volcanic rocks on farms, which mineralize CO2 as they dissolve. Others inject CO2 into similar underground rocks. Numerous companies, including ARCA, are focused on utilizing mine tailings from extracting metals like nickel and chromium.
These metals frequently arise from ores rich in magnesium-bearing serpentine, which reacts with CO2. According to an analysis by ARCA, approximately 28 billion tons of such tailings exist globally, with 3 billion tons produced each year. They estimate that current tailings can store up to 8.7 billion tons of CO2, roughly equivalent to two years’ worth of U.S. emissions.
However, serpentine does not react quickly under normal surface pressures and temperatures. Heating rocks to elevated temperatures significantly enhances their reactivity and accelerates CO2 mineralization. Yet, this process usually necessitates the burning of fossil fuels to generate heat.
Utilizing microwaves to heat the rocks brings various advantages, asserts Peter Schuman from Arca. Instead of burning fuel for heat, this method relies on clean electricity, using less energy than conventional heating. Additionally, the treatment time for rocks is significantly shorter. This potentially enables mining companies to incorporate microwave processes into tailing treatments or even utilize them as standalone systems, he notes.
An application for a patent from the company reveals that Schuman and his Arca colleagues have successfully treated serpentine with microwaves for several minutes, enhancing their reactivity to CO2, inducing chemical changes, and consuming less energy than traditional heat treatment.
“By energizing the rock, you break the bonds within that structure and release magnesium,” states Scheuermann, which then reacts with CO2. Treated serpentine has been shown to react with significantly higher amounts of CO2 than untreated rocks, mineralizing the gas at an accelerated rate.
“The improvements they demonstrate are quite remarkable,” comments Raphael Santos, who reviewed the patent application at the University of Guelph, Canada. However, he notes that it’s challenging to ascertain from the documentation alone the exact quantity of serpentine treated by microwaves and how these results might translate to practical scenarios.
Scheuermann has not specified the exact amounts expected from microwave treatment in terms of CO2 capture in serpentine but mentions, “It’s a tremendous increase—by several orders of magnitude in both reaction rate and capacity.”
Currently, the company is only testing its approach in the lab and has yet to sell any of its 700 tons of CO2 removal. However, Scheuermann indicates that the scaled-up process would include supplying rocks through a chute or conveyor belt. Additionally, they have developed an autonomous rover designed to mix the tailings for optimal air exposure. Once the reaction concludes, a fresh layer of tailings is applied.
“This preprocessing using microwaves significantly enhances the likelihood of CO2 storage,” states Quin Miller from the Pacific Northwest Research Institute in Washington. “It’s promising,” he adds, noting that the treatment process also aids in extracting nickel, an essential metal for battery production, from the rocks.
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Source: www.newscientist.com
