B21B-0427
Effect of Freeze-Thaw Cycles on Grain Size of Biochar

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Zuolin Liu, Brandon Dugan, Caroline A Masiello, Helge Martin Gonnermann and Jeffrey A Nittrouer, Rice University, Houston, TX, United States
Abstract:
Biochar may improve soil performance by altering soil physical properties such as porosity, density, hydraulic conductivity, and water holding capacity. Because these physical properties of soil-biochar mixtures are associated with the grain size of the soil and the biochar, they may change if biochar particles are physically broken down in the environment. In cold regions, biochar may be fragmented into smaller particles when water in biochar’s internal pores expands during freezing. This expansion may mechanically break particles. In this study we investigate if freeze-thaw cycles affect grain size of biochars produced at two temperatures (350°C and 500°C) from four types of feedstock (mesquite, pine, sewage waste, and miscanthus). Prior to freeze-thaw cycles, biochar’s internal porosity increases with pyrolysis temperature and also varies with feedstock type. In our study, the highest internal porosity is 0.82±0.11 for 500 °C miscanthus biochar and the lowest internal porosity is 0.27±0.01 for 350 °C sewage waste biochar. Our biochars also have different median grain diameter (D50) and aspect ratio (AR). The largest D50 is 4836±132 μm for 350 °C miscanthus biochar and the smallest D50 is 2238±13 μm for 350°C sewage waste biochar. The highest AR is 0.85±0.01 for 500 °C sewage waste biochar and the lowest AR is 0.31±0.01 for 350 °C miscanthus biochar. After characterizing the initial properties of biochars, we saturated our biochar using synthetic rain water and subjected them to 10 freeze-thaw cycles (freeze at -19±3°C for 8 hours and thaw at 20±0°C for 16 hours). We expect that D50 will be reduced and AR will be changed by freeze-thaw cycles and the effect will vary with biochar porosity. Ultimately this work will help constrain how biochar particle size changes due to freezing, which can be extrapolated to understand transients in soil performance associated with biochar particle size.