Removal of silicon from green liquor with low-temperature precausticizing, TAPPI JOURNAL January 2017

ABSTRACT: Nonwood materials contain a high percentage of silicon, which causes numerous problems in the chemical recovery section. Researchers previously proposed the method of silicon removal by two-stage causticiz-ing at temperatures of 90ºC to 95ºC, finding that the desilication rate was about 72.9% and the causticizing efficiency was 22.7% when 30% of the causticizing quicklime (calcium oxide; CaO) was added. The present paper deals with the desilication of green liquor recovered from wheat straw black liquor by a low-temperature precausticization method. The results showed that about 89.3% silicon removal and 10.3% causticizing efficiency were achieved under the following precausticizing conditions: added lime amount of 20%, temperature of 20ºC, and reaction time of 60 min. While precausticizing at 90ºC with the same lime amount, only about 63.5% silicon removal and 13.0% causticizing efficiency were gained. Therefore, precausticizing with low temperature was beneficial for silicon removal and retention of carbonate (CO₃^2-).

Application: Removal of silicon from green liquor with precausticizing at low temperature can effectively increase the desilication rate, which could mitigate the issues caused by “silicon influence” and improve the  recycling of lime mud.

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