A new demonstration plant is upcycling gypsum (calcium sulfate) — a material that is typically challenging to dispose of — at a metal-refining site using a process that combines salt-splitting electrolysis, caustic direct-air capture (DAC) and mineralization. Travertine Technologies, Inc. (Boulder, Colo.; www.travertinetech.com) will be deploying its namesake process technology at a facility owned by Sabin Metal Corp. (East Hampton, N.Y.; www.sabinmetal.com), located near Rochester, N.Y. “The Travertine Process will be processing a legacy stack of mined gypsum at the site and carbon dioxide captured directly from the air into sulfuric acid, green hydrogen and calcium carbonate. The gypsum is from a historical gypsum mine that operated at the site prior to Sabin acquiring the land. Sabin will be using the sulfuric acid we produce for recycling and refining precious metals,” explains Owen Cadwalader, chief operating officer at Travertine. Besides sulfuric acid, the process also produces a stream of “green” hydrogen in the electrolysis step, which will be evaluated as potential fuel for the site. Finally, adds Cadwalader, the carbonate product acts as a permanent carbon sink that will be tested for use as a supplementary cementitious material.
At the heart of the process is the electrolyzer unit, which splits sulfate salt into sulfuric acid and caustic (NaOH), and can be configured to also produce green hydrogen. “In the DAC unit, the caustic reacts with the CO2 in air to produce sodium carbonate and CO2-depleted air. The carbonate solution flows into our mineralization unit operation and reacts with the waste gypsum, forming the sulfate salt, which is recycled to the electrolyzer, as well as precipitated calcium carbonate, which permanently sequesters CO2,” says Cadwalader, also noting that the plant is designed for zero-liquid discharge.
All equipment is similar to equipment that has been used at the industrial scale for decades: the electrolyzer unit operation is inspired by membrane chlor-alkali; the DAC unit resembles a cross-flow cooling tower; and the mineralization unit consists of hydrometallurgical equipment. The project with Sabin Metals will be the largest demonstration of the Travertine Process to date, with a nameplate capacity of 125 ton/d of sulfuric acid.