Chemists pinpoint green method to separate coal ash minerals, elements

Source: Elixsys Inc., Aiken, S.C. 

Chemical specialist Elixsys reports successful laboratory extraction of industrial-grade compounds from power generating stations’ coal combustion products (CCP). Through methods exhibiting “zero waste and environmental impact” and marketing agreements in place or progress, the company plans to bring finished materials to construction and industrial supply chains.

“We, along with our business partners, believe that Elixsys is the only company that has demonstrated an environmentally benign process for consuming all CCP,” says President Joe Preston. 

The company’s Module 2 method leaches fly ash by separating insoluble silica and solubilizing most of the remaining elements or compounds. The latter are then sequentially precipitated into calcium carbonate, aluminum hydroxide, iron oxide, and magnesium hydroxide, plus a concentrate bearing rare earth elements recoverable through more advanced processing. The silica, calcium carbonate and iron oxide have potential in cement and concrete production.

Module 2 has been demonstrated with repeatability and economic optimization, netting sufficient samples for market testing. Additional process options have been developed to further improve product purity. Elixsys will guide Module 2 along the path of a companion technology involving other coal-fired generating station byproducts. Module 1, the subject of recent pilot-scale testing, entails chemical conversion of synthetic gypsum—formed from limestone-based flue gas desulfurization—to calcium carbonate and ammonium sulfate. Some raw CCP feeds for Module 1 will produce those compounds, plus fly ash subject to the Module 2 cycle. 

“This technology will allow Elixsys to provide customers with a reliable, long-term domestic source of substantial volumes of chemicals and metals recycled from ash,” notes Director of Commercial Strategy Dan Curry. Beyond cement and concrete, he adds, recovered materials have application in fertilizers and herbicide additives and as specialty fillers for premium paper, plastics, rubber and coatings. —