How temperature affects biochar properties for application in coal mine spoils? A meta-analysis

Abstract

Biochar application in agricultural and metal mines has been studied widely; however, very few studies have been conducted on its application as an amendment for the restoration of coal mine degraded land. Thus, for the application of biochar for coal mine spoil restoration, the best pyrolysis temperature profile needs to be established. Biochar produced at different pyrolysis temperatures has distinct physio-chemical and nutritive properties, which impact its performance when applied as an amendment. The objective of the current study is to conduct a meta-analysis on the pyrolysis temperature and summarize the results using forest plots. The current study quantifies the effect of pyrolysis temperature on biochar production and its optimum nutritional properties. Based on pyrolysis temperature, biochar has to be categorized into low (< 450 °C), moderate (450–550 °C) and high-temperature biochar (> 550 °C). The pH range of biochar was 6.6–12.3 for high pyrolysis temperature and 5.8–11.1 for medium pyrolysis temperature. However, cation exchange capacity was in the range of 3.18–187 m mol kg− 1 for high pyrolysis temperature. For medium and low, the range was 4.63-210 m mol kg− 1 and 23.6–228 m mol kg− 1, respectively. Similarly, at low pyrolysis temperature, the organic content was 14.3–88%, while it was 4.7–60% and 11.2–86.2% for high and medium. Also, the nutrient contents such as Ca, Fe, Mg, and K were high at moderate temperature conditions. The study concluded that low to moderate pyrolysis temperature was best suited for coal mine spoil restoration.Graphical