Synthesis of silica-composited biochars from alkali-fused fly ash and agricultural wastes for enhanced adsorption of methylene blue

• Published in: The Science of the total environment 2020-08, Vol.729, p.139055-139055, Article 139055
• Main Authors: Wang, Kaifeng, Peng, Na, Sun, Jianteng, Lu, Guining, Chen, Meiqin, Deng, Fucai, Dou, Rongni, Nie, Lijun, Zhong, Yongming
• Format: Article
• Language: English
• Subjects: Rice straw; Silica; Solid waste; Swine manure; Wastewater contaminant removal
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.139055

Two types of silica-composited biochars were prepared by mixing swine manure or rice straw with alkali-fused fly ash (AFFA) followed by pyrolysis. A 10% (w/w) AFFA modification improved the specific surface area, pore volume, and average pore size of the biochars. Certain surface oxygen-containing functional groups (i.e., –OH and CO) in the biochars were protected, and silicon–oxygen bonds (i.e., O–Si–O and OSi) were strengthened considerably by AFFA modifications during high-temperature pyrolysis. The adsorption capacity of biochar for methylene blue (MB) was enhanced after AFFA modification, and a modified biochar with the highest adsorption capacity was prepared at a pyrolysis temperature of 700 °C, pyrolysis holding time of 2 h, and an AFFA proportion of 10%. The MB adsorption capacity of the modified biochars significantly increased when the pH of the solution increased (from 3 to 13). The adsorption data were well described by a pseudo-second-order model and Langmuir isotherms. The maximum MB adsorption capacities of the modified swine manure and rice straw biochars were 143.76 mg/g and 131.58 mg/g, respectively. The adsorption capacities of the AFFA-modified biochars were 10.7–112.3% higher than those of the unmodified biochars. The enhanced MB adsorption capacities of the former appear to be attributed to their increased specific surface areas, increased porosities, strong oxygen-containing functional groups, and high contents of exchangeable sodium ions. These results indicate that industrial and agricultural wastes can be reused to produce novel silica-composited biochars with high MB removal capacity. Accordingly, these biochars could be effectively used to treat wastewater and thus to mitigate solid waste disposal-related problems. [Display omitted] •A new material synthesized from wastes can be used for wastewater treatment.•Silica-composited biochars are synthesized from fly ash and agricultural wastes.•Alkali-fused fly ash protects and increases oxygen-containing functional groups.•Silica-composited biochars have a high adsorption capacity for methylene blue.