System and Process for Reducing Chemical Losses in Treating Ash Produced in a Recovery Boiler of a Wood Pulping Process

A method of treating ash produced in a wood pulping process, comprising:

• a. recovering ash from a recovery boiler in a wood pulping process;
• b. directing the ash to an ash leaching tank;
• c. mixing water or an aqueous solution with the ash in the ash leaching tank and leaching chloride from the ash which yields a slurry comprising sodium sulfate and burkeite crystals and a solution containing sodium, potassium, chloride, sulfate and carbonate;
• d. subjecting the slurry comprising the sodium sulfate and burkeite crystals and the solution containing chloride, sulfate and carbonate to a solid-liquid separator and producing a centrate containing sodium, potassium, sulfate and chloride and a concentrate comprising a slurry or wetcake;
• e. recycling the slurry or wetcake to the wood pulping process;
• f. recovering sodium, potassium, carbonate and sulfate from the centrate rich in chloride by subjecting the centrate to a nanofiltration process or an ion exchange process which produces a purge stream rich in chloride and a recycle stream depleted in chloride but including sodium, carbonate and sulfate;
• and
• g. recycling the recycle stream depleted in chloride but including sodium, potassium, carbonate and sulfate to the ash leaching tank where the recycle stream is mixed with the ash and the water or aqueous solution.