Impacts of carbonization temperature on the Pb(II) adsorption by wheat straw-derived biochar and related mechanism

摘要

To determine the quantitative correlations between physicochemical characteristics and Pb(ll) adsorption amounts of biochar fractions, we prepared wheat straw-derived biochar under various carbonization temperatures (300-900 degrees C). The different fractions of the wheat straw-derived biochar, water-soluble material (WM), acid-soluble material (AM), and organic material (OM), were acquired. The ash content, ultimate analysis, pH, ion strength (IS),cation exchange capacity(CEC),and acidic functional groups(AFG) were characterized. The Pb(II) adsorption amounts of different biochars and their fractions were determined. The results revealed that the proportions of biochar fractions (WM, AM, and OM) varied with various carbonization temperatures. The maximum Pb(II) adsorption amount of wheat straw-derived biochar (q(Total)) was 157.95 +/- 0.13 mg/g obtained at 800 degrees C, and the quantitative correlations between Pb(II) adsorption amount (q) and carbonization temperature (T) can be elaborated by q(Total) = 170.72-336.62exp(-0.0035T) (R-2 = 0.97), q(WM) 106.18-390.10exp (-0.0046T) (R-2 = 0.98), q(AM) = 496.16-477.74exp(-0.0001T) (R-2 = 0.79), and q(OM) = 1.80 + 34.69exp (-0.0038T) (R-2 = 0.85). For rate of contribution (RC) for Pb(II) adsorption, when T < 400 degrees C, the order was AM (60.72 +/- 733%) > OM (23.41 +/- 7.33%) > WM (15.87 +/- 0.30%); however, when T >= 400 degrees C, the order was WM (52.31 +/- 0.85% - 67.65 +/- 2.99%) > AM (29.65 +/- 0.46% - 35.77 +/- 0.12%) > OM (2.30 +/- 0.47% - 12.02 +/- 2.43%). Moreover, q(WM) and q(AM) exhibited significant positive linear correlations with ash (q(WM) = 9.92Ash - 123.65, and q(AM) = 2.13Ash - 0.49), q(Total) was predominantly affected by ash content (q(Total) = 10.97 Ash - 95.49). The EDX, XRD, and FTIR analysis results further clarified that ion exchange and precipitation were the main adsorption mechanisms for Pb(II) adsorption by wheat straw-derived biochar. (C) 2019 Elsevier B.V. All rights reserved.