In the first step, the feedstock is ground into small particles to maximize the surface area for acid leaching. In the next step, particles are acid-leached at high temperature using hydrochloric acid. All the metals (except titanium, but including rare earth elements) dissolve as chlorides. Specifically, alumina and iron dissolve to form aluminum chloride (AlCl3) and ferric chloride (FeCl3). Silica and titanium remain insoluble and are removed by filtering.
The leachate is processed by first precipitating the aluminum chloride and removing it as aluminum chloride hexahydrate (ACH), the precursor of alumina. The ACH then goes through calcination and is transformed into alumina. The ferric chloride, which is still in the leachate, is hydrolyzed, using a low-temperature process, producing a pure ferric oxide precipitate while regenerating hydrochloric acid. The ferric oxide (hematite) is very pure and can be sold commercially as a specialty by-product.