Structure and Chemical Composition of Low-silicon White Mud Based on Technology of Black Liquor Combustion Desilication

The sulfate process for bamboo pulp production encounters silicon interference during the pulping stage, necessitating desilication before the alkali recovery section. This study investigated the desilication of bamboo pulping black liquor (BPBL), demonstrating that silicon was removed effectively by adding Mg/Al compound desilication agent to the BPBL via burning at high temperature. The desilication extent can reach 84% when the desilication agent is added in the proportion of Mg/Al (magnesium sulfate and sodium metaluminate) in the ratio 1.25:0.75. Subsequently, less-silicon white mud (LSWM) can be prepared after black liquor (BL) combustion desilication. LSWM was compared with normal WM as a blank sample, and the morphology and physicochemical properties of two kinds of WM were characterized. X-ray diffractometry revealed that both types of WM are primarily composed of calcite crystalline CaCO3 and hydrated CaSiO3. Scanning electron microscopy, X-ray photoelectron spectroscopy, and particle size analysis demonstrated the reduced content of CaSiO3 generated in the LSWM. This result indicated that the Mg/Al compound desilication agent removed the silicon from the green liquor (GL), thereby reducing the residual silicon in WM. This reduction is beneficial to the calcination recovery and comprehensive utilization of WM.