The paper discusses sorbent chemistry and process chemistry of the ADVAnced siliCATE(ADVACATE) process, a simple, low-cost add-on technology for SO2 control, easily retrofitted on existing utility boilers with minimal disruption. It is considered to be capable of removing 90% of SO2 at a Ca/S stoichiometry of 1.0 and at less than half the cost of a typical wet scrubber. The sorbent is produced by atmospheric (normally 90 C) slurrying of Ca(OH)2 and fly ash, as a source of silica. Alternate sources of silica (e.g., diatomaceous earth, bentonic or montmorillonic clay, sand, and waste glass) were also found to promote the formation of high surface area, highly reactive materials. Recycle and slurry mixing have been incorporated into the process to achieve simultaneous flue gas humidification and enhanced SO2 absorption. The unit operation of mixing slurry with recycle solids has shown the feasibility of mixer operation with production of solids containing up to 50% moisture. Waste glass-based silicates have particular application to control of acid-gas emissions from waste incinerators. Potential improvements over conventional acid-gas controls are discussed.