Oyster Shell Modified Tobacco Straw Biochar : Improving the Adsorption Performance of Ca-Loaded Biochar Under Acidic Conditions

In order to improve the phosphate adsorption capacity of Ca-loaded biochar under acidic conditions, Ca was loaded as Ca(OH) 2 on the biochar pyrolyzed at 500°C by high-temperature calcination-ultrasonic treatment-stirring impregnation method using tobacco straw and oyster shell as the raw materials (Ca-BC). The results showed that oyster shells became CaO after high temperature calcination, which was converted into Ca(OH) 2 and had an activation and pore expansion effect on biochar during the stirring impregnation process. The Ca(OH) 2 on the surface of biochar was preferentially neutralized with H + in the solution when the solution was in acidic condition, which led to chemical precipitation of Ca-BC with phosphate under alkaline conditions, and the adsorption capacity was increased by 3-15 times compared to the other Ca-loaded biochar. The maximum adsorption capacity obtained from the Langmuir adsorption isotherm was 88.64 mg P/g, and the adsorption process followed pseudo-second-order kinetics. Ca-BC showed excellent phosphate removal performance while treating four actual wastewaters with removal rates reaching above 90%. This study provides an experimental basis for efficient phosphorus removal by Ca-modified biochar under acidic conditions and for the application in real wastewater