An Alternative Solution to the Silica Problem in Wheat Straw Pulping

Abstract

As a preliminary study, wheat straw pulps were prepared by soda-oxygenanthraquinone (SOAQ) pulping to investigate the silica content in pulp and black liquor. The results showed that 88.4% of the silica remained with the pulp in this process. In this study the oxide-added SOAQ pulping process was used to further enhance silica precipitation on pulp by adding 1 to 3% oxide such as Al{2}O{3}, CaO and MgO. The results indicated that the optimum oxide-added soda-oxygenanthraquinone pulping conditions for wheat straw were: alkali charge on o.d. raw material, 16%; anthraquinone (AQ) charge on o.d. raw material, 0.1%; Al{2}O{3} charge on o.d. raw material, 3%; temperature, 140 C; time at maximum temperature, 40 min; oxygen pressure, 8 kg/cm2 ( 0.79MPa); and liquor-to-straw ratio, 5:1. It was found that the oxide-added SOAQ process increased silica precipitation on pulps by about 9% compare to the SOAQ pulping process. It was concluded that the oxide-added SOAQ process gives the best precipitation of silica onto pulp and also gives good pulp physical and optical properties. The method offers a practical and radical solution to the silica problem.