Impact of low-temperature pyrolysis on ash and physicochemical properties of straw biochar: Multivariate analysis and implications for agricultural and environmental use
Limei Chen, Naïf Abdullah Al-Dhabi, Wenke Ai, Songlin Sun, Yutao Peng, Chong Gao, Yuchen Zhuo, Wangwang Tang, Yaoyu Zhou, Chaoran Sun
Abstract
This study aimed to systematically investigate the effects of low-temperature pyrolysis on the physicochemical properties and their internal connection. This work evaluated the influences of low-temperature pyrolysis on proximate analysis, element composition, stability, and structural features of prepared straw biochar from two feedstocks pyrolyzed at 225 °C to 600 °C. The different indicators, including yield, pH, fixed carbon (FC), volatile matter (VM), ash, C, H, O, N, P, K, Mg, Zn, and stability indexes, all followed exponential function with temperature ( R 2 > 0.82). As the pyrolysis temperature increased from 225 °C to 400 °C, most physicochemical properties of straw biochar demonstrated a rapid change. Additionally, 400°C was a crucial turning point, all biochar physicochemical indicators showed a slowly changing trend at temperatures above 400 °C. Factor and hierarchical clustering analyses yielded identical results. The physicochemical properties can be classified into two groups of intrinsically connected properties: (1) yield, O, H, VM, VM/FC, H/C, and O/C, and (2) N, Zn, Mg, P, K, FC, pH, ash, and C. The quantitative relationships between ash and other properties of the tobacco and rice straw biochar revealed that ash was positively and exponentially associated with pH, FC, C, P, K, Mg, and Zn ( R 2 = 0.73–0.96). Conversely, negative exponential relationships were found with yield, VM, H, O, VM/FC, H/C, and O/C ( R 2 = 0.83–0.96). This work supplies data support for a better understanding of the intrinsic characteristics of straw biochar, especially in scientific preparation and utilization. • Vital relationships between low temperature and biochar properties were shown. • A significant change in straw physicochemical properties at 225–400°C. • There are two groups of intrinsically connected properties. • There was an exponential relationship between ash and most indicators.