Biochar production and characterization as a measure for effective rapeseed residue and rice straw management: an integrated spectroscopic examination

Abstract

Producing biochar from various agricultural and industrial biowastes through pyrolysis is recognized as an eco-friendly approach for solid waste management and remediation of contaminated soils. However, it remains debatable which type of feedstock and pyrolysis temperature could create biochar with better surface functionality and more suitable specific end use. Biochars prepared from rapeseed residue and rice straw at different pyrolysis temperatures (300 and 550 °C) were characterized using various chemical, physical, and spectroscopic techniques. Rapeseed residue and rice straw biochars produced at 550 °C had high pH (9.98 and 10.85, respectively), due to the decrease in total surface acidity with increasing temperature as demonstrated by Boehm titration data, and their high ash contents (18.70% and 24.21%, respectively). The negative charge on high-temperature biochar particles increased with pH, which was confirmed by the reduced zeta potential values (− 42.33 mV for rice straw biochar and − 31.86 mV for rapeseed residue biochar). The mineral phase of both biochars was dominated by sylvite and a small amount of dolomite and calcite, whereas quartz was only found in rice straw biochars. A pyrolysis temperature of 550 °C is suggested for producing biochars that can potentially immobilize toxic elements in the soil.