The invention relates to a method and apparatus for processing the black liquor of a pulp mill to recover the chemicals and energy therein. In the invention, the black liquor is pyrolyzed in a pyrolysis reactor (6), formed gaseous components are lead for utilization, sand is returned to a fluidized-bed boiler, and solid matter is mixed with water, whereby a soda-water solution is returned to the pulping process and solid carbon to the fluidized-bed boiler (1).