Figures (8)  Tables (3)

    • Figure 1. 

      SEM-EDS of amendments. (a) Biochar; (b) ferrihydrite, (c) ferrihydrite modified biochar; (d) sulfur-ferrihydrite modified biochar.

    • Figure 2. 

      Initial solution pH-dependent experiments of (a) Cd(II), and (b) As(III) adsorption on amendments. (BC: Biochar; FH: Ferrihydrite, FB: Ferrihydrite modified biochar; SFB: sulfur-ferrihydrite modified biochar).

    • Figure 3. 

      Kinetic of (a) Cd(II), and (b) As(III) adsorption on amendments. (BC: Biochar; FH: Ferrihydrite, FB: Ferrihydrite modified biochar; SFB: sulfur-ferrihydrite modified biochar).

    • Figure 4. 

      Isotherms of (a) Cd(II), and (b) As(III) adsorption on amendments. (BC: Biochar; FH: Ferrihydrite, FB: Ferrihydrite modified biochar; SFB: sulfur-ferrihydrite modified biochar).

    • Figure 5. 

      (a) FTIR, and (b) SEM-mapping spectra of amendments before and after Cd(II) and As(III) sorption. (BC: Biochar; FH: Ferrihydrite, FB: Ferrihydrite modified biochar; SFB: sulfur-ferrihydrite modified biochar).

    • Figure 6. 

      XPS spectra of C 1s, O 1s, Fe 2p, S 2p for amendments (a)–(d) before, and (e)–(h) after Cd(II) and As(III) adsorption; and (i) As 2p, and (j) Cd 3d for amendments after Cd(II) and As(III) adsorption. (BC: Biochar; FH: Ferrihydrite, FB: Ferrihydrite modified biochar; SFB: sulfur-ferrihydrite modified biochar).

    • Figure 7. 

      The potential mechanisms of Cd (II) and As(III) by SFB.

    • Figure 8. 

      The available and fraction of (a), (c) Cd(II), and (b), (d) As(III) in soil after amended by SFB. F1: the acid soluble fraction; F2: the reducible fraction; F3: the oxidizable fraction; F4: the residual fraction. Data points and error bars represent mean ± S.D. (n = 3). Different letters indicate a significant difference (p < 0.05). (BC: Biochar; FH: Ferrihydrite, FB: Ferrihydrite modified biochar; SFB: sulfur-ferrihydrite modified biochar).

    • Parameter BC FH FB SFB
      Yield (% dry wt.) 50.12 N.D. N.D. N.D.
      Ash (% dry wt.) 36.61 N.D. N.D. N.D.
      pH 11.48 4.36 10.86 10.58
      C (%) 10.58 0.00 61.43 36.72
      O (%) 39.05 34.27 15.37 32.23
      S (%) 0.00 0.00 0.00 3.36
      Fe (%) 4.41 65.73 12.96 7.98
      Surface area (m2 g−1) 64.20 294.91 175.35 185.16
      Pore volume (cm3 g−1) 0.0696 0.1804 0.1263 0.1305
      Pore diameter (nm) 4.84 2.46 3.05 2.89
      N. D.: Not detected.

      Table 1. 

      Characterization of amendments

    • Toxic metal(loid)s Amendments Pseudo first-order model Pseudo second-order model
      R2 K1 Qe (mg g−1) R2 K2 Qe (mg g−1)
      Cd BC 0.955 0.002 12.68 0.991 0.002 13.65
      FH 0.986 0.001 13.81 0.995 0.001 15.32
      FB 0.730 0.003 17.60 0.860 0.003 18.73
      SFB 0.896 0.001 23.93 0.941 0.01 26.42
      As BC 0.845 0.021 1.72 ± 0.04 0.979 0.022 1.81 ± 0.02
      FH 0.974 0.035 3.32 ± 0.04 0.961 0.030 3.42 ± 0.02
      FB 0890 0.034 3.62 ± 0.03 0.956 0.028 3.71 ± 0.02
      SFB 0.926 0.056 3.95 ± 0.08 0.931 0.022 4.08 ± 0.04

      Table 2. 

      Kinetic parameters for Cd(II) and As(III) adsorption onto amendments

    • Toxic metal(loid)s Amendments Langmuir parameters Freundlich parameters
      R2 b Qm (mg g−1) R2 Kf 1/n
      Cd BC 0.936 0.021 41.36 0.899 0.637 1.68
      FH 0.905 0.027 45.28 0.835 0.591 2.48
      FB 0.960 0.022 64.44 0.917 0.628 2.75
      SFB 0.959 0.022 76.69 0.914 0630 3.24
      As BC 0.939 0.841 4.06 0.976 0.333 1.84
      FH 0.798 1.552 4.98 0.886 0.256 2.86
      FB 0.846 0.846 6.72 0.961 0.361 2.84
      SFB 0.902 0.522 8.28 0.979 0.409 2.94

      Table 3. 

      Isotherms parameters for Cd(II) and As(III) adsorption onto amendments