The Bureau of Mines has been investigating the use of solid mineral wastes for removing sulfur oxides from flue gases. A literature survey identified more than 20 materials that are available in large quantity, have thermodynamic potential of reacting with so2, and can be supplied to the north central United States for less than $20 per ton. Reactivity of these materials toward so2 was determined experimentally over a temperature range of 130 deg to 700 deg c. In most cases, so2 was absorbed, but capacity and rate of absorption were low. However, two waste products, red mud and lead-zinc ore tailings, absorbed substantial quantities of so2. Lead-zinc ore tailings consist primarily of dolomitic carbonates. Their use was evaluated in differential kinetic experiments and by injection into a small pulverized coal-fired furnace. Results showed that injection of the tailings is probably less attractive than injection of limestone. Red mud, the byproduct of bauxite refining, was also studied in differential kinetic experiments and by injection into the furnace. Results showed that, when the injection method is used, the short residence time prevents efficient so2 removal. Experiments demonstrated, however, that if a reactor is employed to increase residence time a high degree of so2 removal can be obtained at 550 deg c. The red mud can be thermally regenerated at 650 deg c. A conceptual regenerable process has been suggested.
Proc. 3D Min. Waste Util. Symp., IIT Inst., Chicago, Illinois, March 14- 16, 1972, PP. 153-160