Production and Characterization of Biochars from Slow Pyrolysis of Different Biomass Materials to Evaluate Properties as Soil Amendments

Abstract

Biochar, a carbon (C)-rich solid material produced by the thermo-chemical conversion of biomass in an oxygen-limited environment, has been attracting interest due to its potential as a soil amendment. In this study, biomass materials derived from rice (Oryza sativa) straw (RS), rice hull (RH), water hyacinth (Eichhornia crassipes) (WH), and mahogany flower receptacles (Swietenia macrophylla) (MFR) were slowly pyrolyzed under temperatures ranging from 300–650°C using a biochar producing stove. The morphological characteristics and physicochemical properties of biochars were studied using the Brunauer-Emmett-Teller (BET) automated nitrogen multilayer physisorption system, field emission–transmission electron microscopy (FE-TEM), and X-ray energy dispersive spectrometry (EDS). Biochars originating from light materials (RS and WH) showed higher concentrations of essential plant nutrients such as nitrogen (N), phosphorus (P), and potassium (K). The biochar originating from woody MFR had low concentrations of essential plant nutrients. The surface area of the materials was in the 0.473–78.208 m2/g range. The RS and RH biochars demonstrated high surface area with 45.511 and 78.208 m2/g, respectively. The WH biochar showed a low surface area of 9.845 m2/g while the surface area of the MFR biochar was particularly very low at 0.473 m2/g. The high angle annular bright-field (HAABF) images, spectra, and elemental X-ray maps of all the four biochars revealed areas high in carbon, potassium, chlorine, calcium, magnesium, silicon, and aluminum. These biochar properties and mineral agglomerates suggest that biochars can be used as a soil amendment to improve soil fertility.