Differentiating Inorganics in Biochars Produced at Commercial Scale Using Principal Component Analysis

Abstract

Characterizing the inorganic phase of biochar, beyond determining element concentration, is needed for appropriate application of these materials because mineral forms also influence element availability and behavior. Inorganics in 13 biochars (produced from Poultry litter, switchgrass, and different types of wood) were characterized by proximate analysis, chemical analysis, powder X-ray diffraction (XRD), and scanning electron microscopy with energy-dispersive X-ray (SEM-EDX) spectroscopy. Principal component analysis (PCA) was used to compare biochars and characterize associations between elements. The biochars were produced using commercial-scale reactors and represent materials with properties relevant to field application. Bulk inorganic concentration and composition were responsible for differentiating biochars after PCA of chemical data. In comparison, differentiation based on PCA of diffractogram fingerprints was more nuanced. Here, contributions from cellulose and turbostratic crystalline C influenced separation between samples. It was also sensitive to mineral forms of Ca (whewellite and calcite). Differences in crystalline C and Ca minerals separated two biochars generated from the same willow feedstock using the same pyrolysis conditions at different temperatures. PCA of 606 SEM-EDX point scans revealed that inorganics belong to four main clusters containing Ca, Fe, [Al, Si], and [Cl, K, Mg, Na, P, S] consistent with XRD identification of calcite, magnetic Fe-oxide, silicates, and sylvite. It further suggested that amorphous P-containing minerals associated with Ca (not identified through XRD) were constituents of willow and poultry litter-derived biochars. However, unlike PCA of XRD, it was not able to differentiate the two biochars derived from willow. The three analysis methods provided different perspectives on the properties of the biochar inorganic phase. Combining information from multiple methods is needed to better understand the inorganic composition of biochars.

Effect of Banana-Waste Biochar and Compost Mixtures on Growth Responses and Physiological Traits of Seashore Paspalum Subjected to Six Different Water Conditions

“…Indeed, the ability of biochars to neutralize acidic soils may be influenced by the presence of various Ca-containing minerals. When compared to carbonate, oxalate may be less successful at neutralizing acidic soils [19]. The calcite formed, as a result, contributed to the alkalinity of the banana-waste biochar investigated, as seen by their high pH values of 9.30 [9].…”

Synthesis and Characterization of Hydrochar and Bio-oil from Hydrothermal Carbonization of Sargassum sp. using Choline Chloride (ChCl) Catalyst

“…was successfully carbonized to a carbon form (Khan et al, 2019). While the sharp peaks at 2θ = 25.98 o , 27.09 o , 28.3 o , 32.76 o , 34.32 o , 40.9 o , 42.98 o , 47.09 o , and 56.00 o in Figure 5 reflect inorganic components derived from seaweed ash content (Clemente et al, 2018). The peaks are per the results of the X-Ray Fluorescence (XRF) analysis of raw seaweed and hydrochar (Figure S1), which shows the content of several minerals such as Ca, Mg, Al, Fe, Si, K, Na, and Cl.…”

Modeling the biodiesel production using the wheat straw ash as a catalyst

“…This mineralogical composition is not unusual for biochars. Moreover, calcite, Mg, Ca-carbonate (CaxMg(1-x)CO3), and quartz were the most common crystalline phases identified in biochars [56,57]. In the literature, the presence of quartz in biochar is always associated with contamination of the raw materials from the soil (even after thorough washing) while the presence of the carbonate phases, in addition to the mentioned explanation, is related to the presence of carbonates in the original biomass, and even formation by the entrapment of CO2, evolving from the thermal decomposition of organic carbon, in the alkaline charred material [56].…”