Abstract: A two-stage process for staged combustion of crushed retorted particles, especially sulfur and nitrogen-bearing shale, provides maximum heat from combustible materials in shale while emissions of carbon monoxide and oxides of sulfur and nitrogen are minimized. In the first stage, combustion is maintained under fluidizing conditions with a substoichiometric amount of oxygen. Off-gases from the first stage are burned in a second-stage combustion zone utilizing an oxygen-containing gas stream controlled to limit emission of carbon monoxide in the flue gas. To minimize production of sulfur oxides, combustion temperature is concurrently maintained below a peak value of 1700.degree. F. by introducing inert gas or recycled decarbonized fines to the first-stage combustion zone to reduce temperature therein.