Effects of silica on chemical recovery in the direct causticization of wheat straw black liquor
Hongyou Yuan, Shubin Wu, Xiuli Yin, Daliang Guo, Guijin Wang, Zhaoqiu Zhou, and Chuangzhi Wu
TAPPI JOURNAL,15(8)
Straw black liquor is relatively difficult to recover using the Tomlinson process because of the presence of silica in inorganic components. Gasification with direct causticization might serve as a promising alternative; however, the interaction between silica and direct causticization agents needs to be evaluated. In this work, desilication was achieved using a laboratory-scale membrane electrolysis cell adopted from the chlor-alkali industry. Then raw and desilicated straw black liquors were carried out through direct causticization with titanium dioxide (TiO2) and recycled sodium tri-titanate (Na2O·3TiO2) at 850°C using a tube furnace. The results show that these two agents exhibit different silica transfer mechanisms. When using TiO2, approximately 80% of the silica is retained in the solid residue after hydrolysis because of chemical interactions. Almost all of the silica transfers to the hydrolysis-derived white liquor when using Na2O·3TiO2. This means that the process of treating straw black liquor by direct causticization
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