Sustainable synthesis of uniform silica microspheres from green liquor of wheat straw pulping and application in natural rubber

Abstract

In order to recycle alkali chemicals from wheat straw alkaline pulping waste liquor effectively, an environmentally friendly route was developed to remove silicate containing in the green liquor of wheat straw pulping. In this route, silica (SiO2) microspheres were synthesized from wheat straw green liquor (WSGL) using carbon dioxide (CO2) as the precipitating reagent and anhydrous ethanol as the dispersant at different stirring rates. The resulting SiO2 microspheres with narrow size distribution had an amorphous structure with a diameter of about 190 nm under the optimal synthesis conditions with a pH value of 8.6, a stirring rate of 100 r min−1, and an ethanol addition amount of 60 ml. In this optimized route, the SiO2 removal rate (SRT) of WSGL was more than 99%. Except CO2, all the chemical reagents used in the designed process had been validly used. The SiO2 microspheres obtained from WSGL could be used as reinforcing agents to strengthen the mechanical properties of natural rubber.