The Status and Potential of Metals Recovery from Coal Fly Ash by High-Temperature Chlorination

Coal fly ash is a potential commercial source of aluminum, iron, and titanium. A high-temperature chlorination process (HiChlor) is under development at the Ames Laboratory to remove these metals and purify the products. A reduction-chlorination reaction is used to convert the metal oxides in the fly ash to volatile metal chlorides. Bench scale tests have been conducted by flowing chlorine gas through a horizontal fixed-bed composed of a fly ash-graphite mixture. The amounts of iron, aluminum, titanium, and silicon removed have been determined as a function of reaction time (0.5 to 2 hours) and temperature (750 degrees C to 900 degrees C). On-stream product gas analyses of CO, CO2, and Cl2 using a gas chromatograph have permitted calculation of chlorine balances and reaction rates in terms of the O2 evolution rate. Reaction controls, surface area and particle size distributions as a function of fly ash conversion, and final conversion limitations also have been investigated