patent abstract: "method for leaching recovery boiler ash". The present invention relates to a novel method to be used in conjunction with a single-stage or multi-stage process for leaching ash from the recovery boiler of a pulp mill, particularly when the ash contains a significant amount of carbonate. In the method, calcium compounds, more preferably calcium oxide (cao) and / or calcium hydroxide (ca (oh) 2), are employed as additives in one or more leaching stages. The liquid fraction formed in the leaching process is used outside the main chemical recovery cycle, preferably as a substitute for sodium hydroxide purchased from the pulp mill bleaching line. The solids fraction may be mixed with a stream of black liquor from the plant or subjected to further processing to separate the calcium compounds for recycling.
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