Leaching process

An increasing problem with the pulping chemical recovery system, is the presence of chloride and potassium in the recovery boiler. Chloride and potassium increase inter alia the stickiness of carryover deposits and dust particles to the recovery boiler tubes, which accelerate fouling, corrosion and plugging of the recovery boiler. As the environmental legislation becomes more stringent, the degree of system closure increases. The present invention relates to a process by which the collected precipitator dust (1) is leached (2), at a temperature exceeding 50 DEG C, for a residence time sufficient to get a chloride and potassium enriched leach solution (4) and to remove at least a part of the content of metal ions in a solid phase (3). Said leach solution is electrochemically treated (5), preferably in an electrodialysis cell, in order to remove at least a part of the chloride and potassium therein. By the present process, the problem of sticky deposits in the recovery boiler can be substantially reduced. This means an improved energy efficiency as well as a higher degree of recovery of the pulping and bleaching chemicals.