Effects of wet and dry ball milling on the physicochemical properties of sawdust derived-biochar

Abstract

Ball milling has been used as a green method for the modification of biochars in recent years. Therefore, the effects of physicochemical properties of biochars derived from sawdust via dry and wet mechanical ball milling and hand lapping were integrally compared in this study. Elemental analyses show the significant reduction of the C content and increase in the ash content for the resulting 12 h-wet-ball-milled biochar. The specific surface areas of the dry- and wet-ball-milled biochars were significantly larger than those of the pristine and hand-lapping biochars. Scanning electron microscopy (SEM) images of the biochars show that 12 h of wet ball milling produced smaller and better-distributed particles. Good thermal stability of the resulting biochars (less than 5% of mass losses) was confirmed by thermogravimetric (TG) analysis. Fourier transform infrared (FT-IR) spectra show that long-term wet ball milling (12 h) increased the functional groups of the resulting biochars. The various ball milling processes have no obvious impact on the phase in the biochars characterized by the x-ray diffraction (XRD) pattern. Overall, long-term wet ball milling (12 h) is a simple method for the preparation of smaller and better-distributed biochar composites.