Leaching of Chloride and Potassium from Electrostatic Precipitator Catch, 1998 International Chemical Recovery Conference Proceedings

Chloride and potassium are two non process elements (NPE’s) in the pulp mill recovery system, whose ions are very soluble in alkaline solutions. They can therefore accumulate to high levels in a tightly closed mill, and cause problems, e.g., on recovery boiler operation. A number of methods available for the removal of chloride and potassium from the recovery system have been briefly reviewed. In particular, the feasibility of removing these chemicals from the electrostatic precipitator catch in a leaching- evaporation process was studied in detail in this work. A series of experiments on a bench-scale was conducted to establish the optimum operating conditions of such a process.

The experiments have shown that the removal of chloride and potassium from the chemical recovery system can be achieved by leaching the precipitator dust with water, without losing more than a small fraction of the Na2 SO4 present in the precipitator dust. Subsequent treatment of the leachate stream leaving the leaching step by evaporation may be used to further decrease the loss of sulfate, without affecting the removal of chloride and potassium.