Influence of Pyrolysis Temperature on Biochar Property and Function as a Heavy Metal Sorbent in Soil

Abstract

While a large-scale soil amendment of biochars continues to receive interest for enhancing crop yields and to remediate contaminated sites, systematic study is lacking in how biochar properties translate into purported functions such as heavy metal sequestration. In this study, cottonseed hulls were pyrolyzed at five temperatures (200, 350, 500, 650, and 800 °C) and characterized for the yield, moisture, ash, volatile matter, and fixed carbon contents, elemental composition (CHNSO), BET surface area, pH, pHpzc, and by ATR-FTIR. The characterization results were compared with the literature values for additional source materials: grass, wood, pine needle, and broiler litter-derived biochars with and without post-treatments. At respective pyrolysis temperatures, cottonseed hull chars had ash content in between grass and wood chars, and significantly lower BET surface area in comparison to other plant source materials considered. The N:C ratio reached a maximum between 300 and 400 °C for all biomass sources considered, while the following trend in N:C ratio was maintained at each pyrolysis temperature: wood≪cottonseed hull≈grass≈pine needle≪broiler litter. To examine how biochar properties translate into its function as a heavy metal (NiII, CuII, PbII, and CdII) sorbent, a soil amendment study was conducted for acidic sandy loam Norfolk soil previously shown to have low heavy metal retention capacity. The results suggest that the properties attributable to the surface functional groups of biochars (volatile matter and oxygen contents and pHpzc) control the heavy metal sequestration ability in Norfolk soil, and biochar selection for soil amendment must be made case-by-case based on the biochar characteristics, soil property, and the target function.

Effect of Temperature on the Structural and Physicochemical Properties of Biochar with Apple Tree Branches as Feedstock Material

“…Pyridine (pyridine ring vibration and C-H deformation) [53] This result is likely due to the degradation and depolymerization of cellulose, hemicelluloses and lignin [29]. Instead, intensities of O-H (1325 cm −1 ) stretching [29] and aromatic C=C and C=O stretching of conjugated ketones and quinones (1600 cm −1 ) [52] decreased with temperature which may suggest that phenolic and carboxylic compounds in lignin had been degraded [54]. There was also pyridine in biochars (781 cm −1 ) [53], which was one of the heterocyclic nitrogen compounds commonly observed during pyrolysis [55].…”

Soil Health, Crop Productivity, Microbial Transport, and Mine Spoil Response to Biochars

“…Biochars can also have metal sorption properties when used as a soil amendment [11,73,74]. Their ability to bind metals arises from their porosity, surface area, and surface functional groups [75,76].…”

Comparison of Biochar Formation from Various Agricultural By-Products Using FTIR Spectroscopy

“…Feedstock property and pyrolysis condition were described in detail in previous reports (Uchimiya et al, 2011(Uchimiya et al, , 2013aKlasson et al, 2014). Briefly, lignin (L25) was obtained from a cellulosic ethanol plant (Örnsköldsvik, Sweden) as wet powder and was air dried (Klasson et al, 2014).…”