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To determine the quantitative correlations between physicochemical characteristics and Pb(II) adsorption amounts of biochar fractions, we prepared wheat straw-derived biochar under various carbonization temperatures (300–900 °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 °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) (R2 = 0.97), q WM = 106.18–390.10exp(−0.0046T) (R2 = 0.98), q AM = 496.16–477.74exp(−0.0001T) (R2 = 0.79), and q OM = 1.80 + 34.69exp(−0.0038T) (R2 = 0.85). For rate of contribution (RC) for Pb(II) adsorption, when T < 400 °C, the order was AM (60.72 ± 7.33%) > OM (23.41 ± 7.33%) > WM (15.87 ± 0.30%); however, when T ≥ 400 °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. Unlabelled Image • Impacts of carbonization temperature on proportions of fractions were different. • Rate of contribution (RC) was order as AM>WM > OM (T < 400 °C) and WM > AM>OM (T ≥ 400 °C). • Pb(II) adsorption amount (q) was correlated with ash and element composition. • The RC was highly correlated with ash, pH and ion strength (IS) (p < 0.01). • Linear correlations between q, RC and ash, IS, pH were established. [ABSTRACT FROM AUTHOR]

Magnetic carbonaceous adsorbents were synthesized by ball-milling biochar (BC) or activated carbon (AC) with Fe 3 O 4 nanoparticles, and their capacities to sorb methylene blue (MB) from water were evaluated and compared. Ball milling with magnetite not only improved the surface properties of the carbonaceous adsorbents, especially BC, but also introduced magnetic properties through mechanical extrusion. Furthermore, ball-mill extrusion increased the MB adsorption capacity of BC at all pH values by 14-fold, on average, but BC ball milled with magnetite had even greater MB adsorption capacity (27-fold, greater, on average). While ball milling of AC also improved its MB adsorption capacity (by almost 3-fold, on average), ball milling with magnetite did not further improve its MB adsorption capacity. All the magnetic adsorbents showed fast MB adsorption kinetics, reaching equilibrium within about 8 h. The Langmuir maximum MB adsorption capacity of the magnetic ball-milled BC (MBM-BC) was the highest (500.5 mg/g) among all the samples including the ones derived from AC. After five adsorption-desorption cycles, MBM-BC maintained about 80% MB removal capacity. The high MB adsorption capacity of MBM-BC was attributed to its increased surface area, opened pore structure, functional groups and aromatic CC bonds, which promoted π-π and electrostatic interactions. Findings from this study indicate that the magnetic ball-milled BC is a promising adsorbent due to its environmentally friendly synthesis, high efficiency, low cost, and convenience in operation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)