Straw is an important fiber material for virgin pulp production in some Asian countries.However,the cooking black liquor from straw is relatively difficult to recover using conventional Tomlinson process due to the presence of silica.Gasification with direct causticization has been thought a promising way to recover wood kraft black liquor thus drawn a lot of attentions.Whether the concept is suitable for straw black liquor is not clear yet due to the possible interaction between silica and direct causticization agents.This paper took TiO2 and recycled Na2O?3TiO2 as direct causticization agents,and found that it is different of silica transfer mechanism between these two agents.