Surface characterization of biochar from agricultural residues for environmental applications

Abstract

Bio-waste materials banana (Musa ealbisiana) leaves, cassava (Manihot esculenta) peels, mango (Mangifera indica) leaves, plantain (Plantago lanceolata) leaves and peels were pyrolyzed at different temperatures; 300, 400, 450, 500 and 600 ^oC using a muffle furnace. The biochar samples obtained were characterized and properties evaluated for their potential application in soil for agronomic and environmental benefits. The measured physico-chemical properties; pH, bulk density, percentage yield and electrical conductivity varied with temperature of pyrolysis and somewhat with the source of the bio-waste. Surface morphology and elemental composition were determined from Scanning Electron Microscopic (SEM) and Energy Dispersive X-ray (EDX) measurements and showed variations in texture, porosity and elemental composition with pyrolysis temperature. The produced biochar yields were in the range 16.1 to 84.6% and highest for banana leaves (BL) pyrolysed at 300 ^oC. The scanned images showed a remarkable surface morphology for all the biochar samples obtained at temperatures ≥ 450 ^oC. The pH obtained indicate the alkaline nature of the biochars with mean values > 7.5 except for cassava peels (CP) pyrolysed at 300 ^oC having a value of 5.5. From the elemental analysis, the high carbon content (> 60%) at higher temperatures (> 450 ^oC) of the biochars and the molar O/C ratios may suggest the suitability of the biochars in applications for long-term carbon sequestration and also promising candidates for soil amendment due to increase in macro porosity.