Effects of pH and Suspended Matter on the Physico- Chemical Properties of Black Liquor from Alkali-Oxygen Pulping of Rice Straw

Black liquor (BL) can be regarded as the energy and alkali resource of the pulping mill. In this work, the effects of the characteristics of black liquor derived from the alkali-oxygen pulping of rice straw were studied. Through analyses of the chemical and physical properties, especially the thermodynamics properties, which depend on suspended matter and alkalinity, it was shown that the removal of the suspended matter from the black liquor could effectively improve its thermodynamic properties, particularly in making its solids content reach up to more than 56% at the turning point of its viscosity. Moreover, sodium salt played an important role in the presence of macromolecules and silica in the BL. When the BL was adjusted to pH = 11 with NaOH, the filtered BL had the lowest silica content, the highest volumetric isothermal expansivity (VIE), was more susceptibility to thermal cracking, and was more suitable for processing for alkali recovery.