Analysis and characterization of metallic nodules on biochar from single‐stage downdraft gasification

Abstract

Biochar, which is a byproduct of gasification, is used in a wide range of fields such as water filtration, agriculture, and electronics, to name a few. The metals in the biomass were thought to end up either in the ash or distributed throughout the biochar. In this study, the goal was a more thorough characterization of biochar resulting from a single‐stage downdraft gasifier. One of the first observations was that some metals actually localize into small (~25 micron diameter) metallic nodules on the biochar surface. Further analysis included ultimate and proximate analysis, Brunauer–Emmert–Teller (BET) analysis, and scanning electron microscopy X‐ray spectroscopy (SEM‐EDS). Biomass fuel included corn grains, soybeans, and wood pellets, with wood biochar showing the highest fixed carbon content, at 91%, and the highest surface area, at 92.4 m2/g. The SEM analysis showed that certain minerals, including potassium, phosphorus, calcium, iron, nickel, silicon, and copper, formed nodules with over 50% metal mass next to pores in the carbon substrate. Aluminum, chlorine, magnesium, and silicon (in certain cases) were mostly uniformly distributed on the biochar carbon substrate. Corn biochar showed a high concentration in the nodules of 9%– 21% phosphorus and up to 67% potassium. Soybean biochar showed a similar trend with traces of iron and nickel of 2% and 4.1%, respectively, while wood biochar had a significant amount of potassium, up to 35%, along with 44% calcium, 3% iron, and up to 4.2% nickel concentrations. A morphology analysis was also carried out.