Indispensable role of biochar-inherent mineral constituents in its environmental applications: A review

Abstract

Biochar typically consists of both carbon and mineral fractions, and the carbon fraction has been generally considered to determine its properties and applications. Recently, an increasing body of research has demonstrated that mineral components inherent in biochar, such as alkali or alkaline earth metals in the form of carbonates, phosphates, or oxides, could also influence the properties and thus the applications. The review articles published thus far have mainly focused on multiple environmental and agronomic applications of biochar, including carbon sequestration, soil improvement, environmental remediation, etc. This review aims to highlight the indispensable role of the mineral fraction of biochar in these different applications, especially in environmental applications. Specifically, it provides a critical review of current research findings related to the mineral composition of biochar and the effect of the mineral fraction on the physicochemical properties, contaminant sorption, carbon retention and stability, and nutrient bioavailability of biochar. Furthermore, the role of minerals in the emerging applications of biochar, as a precursor for fuel cells, supercapacitors, and photoactive components, is also summarized. Overall, inherent minerals should be fully considered while determining the most appropriate application for any given biochar. A thorough understanding of the role of biochar-bound minerals in different applications will also allow the design or selection of the most suitable biochar for specific applications based on the consideration of feedstock composition, production parameters, and post-treatment.

Use of Waste-Derived Biochar to Remove Copper from Aqueous Solution in a Continuous-Flow System

“…in which the mineral fraction predominates. 6,40 In the present study, the physicochemical properties that were most closely correlated with the parameters of the breakthrough curves (q e , t b , t e ) were %C, %N and %ash (Table S1). The highest positive correlation was found with the %ash, e.g.…”

“…In the present study, copper retention was highest in samples with an O/C molar ratio higher than 0.3 and high ash and phosphorus contents, above 40% and 3 g PO kg -1 , respectively (Table 1). As indicated by Xu et al 40 , the formation of metal carbonates and phosphate precipitates is favored in mineralrich biochars. Uchimiya et al 41 , also indicated that heavy metals retention by biochar is enhanced in low carbonized biochar materials.…”

Adsorption Behavior and Relative Distribution of Cd2+ Adsorption Mechanisms by the Magnetic and Nonmagnetic Biochars Derived from Chicken Manure

“…Both biochars were alkaline with high pH values (Table 1, 11.43 for CMB and 11.55 for M-CMB), suggesting that it would potentially remove heavy metals from acid mine drainage [24]. This was correlated to ash content, since the content of ash showed a positive correlation with the alkalinity of bicohar, as observed by many researchers [20,25,26]. High content of ash was also partly reflected by the SEM observations exhibiting many impurities on the surface of biochars ( Figure 1).…”

The Sewage Sludge Biochar at Low Pyrolysis Temperature Had Better Improvement in Urban Soil and Turf Grass

“…Agrafioti et al [24] obtained similar results and suggested biochar produced at low temperature could be more suitable to agricultural use rather than that derived from high temperature. Considering the more volatile loss and bioavailability reduction of mineral nutrients at high pyrolysis temperatures [37], it may be thus recommended that municipal sewage sludge be converted into biochar at low temperature, e.g., 200 • C, and then used as a nutrient supplement for urban soil. Moreover, a few studies have shown that the biochar derived from lignocellulosic materials has the ability to ameliorate soil physical parameters such as pore size, proportion of water-stable aggregates, bulk density, water retention, etc.…”