Dual Role of Biochars as Adsorbents for Aluminum: The Effects of Oxygen-Containing Organic Components and the Scattering of Silicate Particles

Abstract

The adsorption of aluminum by biochars produced at different temperatures from rice straw (RS) and cattle manure (CM) was studied to determine the dual roles of biochar for aluminum adsorption. The compositional structures and surface charges of the biochars and ashes with and without Al loading were analyzed by Fourier-transform infrared spectroscopy, ζ-potential, scanning electron microscopy, and X-ray diffraction. The Al adsorption isotherms were fit well by the Langmuir model. The adsorption of Al to the biochars produced at 400 and 700 °C was much greater than the adsorption to the precursory materials and ashes. We found that the organic components and silicate particles within the biochars served as dual adsorptive sites for Al. The complexation of Al with organic hydroxyl and carboxyl groups and the surface adsorption and coprecipitation of Al with silicate particles (as KAlSi3O8) both contributed to the Al adsorption of the biochars. After the biochars were loaded with Al, the ζ-potentials of the biochars and ashes increased as a function of pH. The positive charge was maximized at pH 4.5, which is similar to the pH at which the maximum positive charge occurs for silica. The charge reversal was caused by the Stern-layer adsorption of hydrolyzed aluminum species (i.e., Al(OH)(2+) and Al(OH)2(+)) on the silicate surfaces via hydrogen bonds.

Effect of biochar aging on surface characteristics and adsorption behavior of dialkyl phthalates

“…As listed in Table 2, XPS-measured O contents were higher in oxidized biochars than their precursors, elucidating greater relative oxidation of BOX700 surface to BOX300. These oxygen containing functional moieties on biochars can regulate the bioavailability and mobility of toxic metals and oxidation treatment with HNO 3 :H 2 SO 4 (to induce aging) may promote this process (Qian and Chen, 2013).…”

“…It is likely that alteration of the surface properties in aged biochar may decrease their adsorption to hydrophobic organic contaminants. Nevertheless, oxygen enrichment in aged biochar has augmented their sorption capacity for heavy metal ions (Qian and Chen, 2013;Uchimiya et al, 2011;Cao et al, 2009). Immobilization of heavy metal (especially Pb and Cu) can be directly correlated with biochar oxygen rich functional moieties (carbonyl, hydroxyl, and phenolic) (Uchimiya et al, 2011).…”

Sorption of Cu2+ on humic acids sequentially extracted from a sediment

“…According to the FTIR spectra (Fig. S2), the oxygen-containing functional groups of HA fractions included hydroxyl groups (i.e., H-bonded AOH at 3405 cm À1 and phenolic/aliphatic AOH at 1235 cm À1 ), carboxyl groups (i.e., ACOOH at 1632 cm À1 ) and carbonyl groups (i.e., AC@O at 1714 cm À1 ) (Qian and Chen, 2013). According to the results of NMR analysis (Table S1), the oxygenated alkyl C and carbonyl C contents of HAA, HAB and HAC were almost unvaried, and the sum of oxygenated alkyl C and carbonyl C contents for the four HA fractions were also almost the same.…”

Tar Conversion and Vapor Upgrading via in Situ Catalysis Using Silica-Based Nickel Nanoparticles Embedded in Rice Husk Char for Biomass Pyrolysis/Gasification

“…FTIR spectra also displayed the silicon-containing group vibration absorptions at ∼1098, 797, and ∼467 cm −1 that are assigned to the Si−O−Si group, which became less intense implying the formation of silicon crystal at high temperature. 58,61 Subsequently, the IR absorption peaks of these organic functional groups in the RHC and RHC supported catalysts were weakened or disappeared after copyrolysis with RH ( Figure 7B). It is possible that the tar molecules could be initially adsorbed in the pore frameworks of RHC, and they were released and decomposed via further catalytic pyrolysis.…”