Effects of Pyrolysis Temperature and Chemical Modification on the Adsorption of Cd and As(V) by Biochar Derived from Pteris vittata

Abstract

Phytoremediation can be applied successfully to solve the serious worldwide issue of arsenic (As) and cadmium (Cd) pollution. However, the treatment of biomass containing toxic elements after remediation is a challenge. In this study, we investigated the effective use of biomass resources by converting the As hyperaccumulator P. vittata into biochar to adsorb toxic elements. Plant biomass containing As was calcined at 600, 800, and 1200 °C, and its surface structure and adsorption performances for As(V) and Cd were evaluated. Pyrolysis at 1200 °C increased the specific surface area of the biochar, but it did not significantly affect its adsorption capacity for toxic elements. The calcined biochar had very high adsorption capacities of 90% and 95% for As(V) and Cd, respectively, adsorbing 6000 mmol/g-biochar for As(V) and 4000 mmol/g-biochar for Cd. The As(V) adsorption rate was improved by FeCl₃ treatment. However, the adsorption capacity for Cd was not significantly affected by the NaOH treatment. In conclusion, it was found that after phytoremediation using P. vittata biomass, it can be effectively used as an environmental purification material by conversion to biochar. Furthermore, chemical modification with FeCl₃ improves the biochar's adsorption performance.

Keywords: arsenic; biochar; cadmium; phytoremediation.

Figure 1

The surface structure of P. vittata biochar by SEM observation. Left column: Magnification 250×; Right column: Magnification 1000×; (a) Pyrolysis temperature: 600 °C; (b) Pyrolysis temperature: 800 °C; (c) Pyrolysis temperature: 1200 °C.

Figure 2

The surface structure of FeCl₃-modified P. vittata biochar by SEM observation. Left column: Magnification 250×; Right column: Magnification 1000×; (a) Pyrolysis temperature: 600 °C; (b) Pyrolysis temperature: 800 °C; (c): Pyrolysis temperature: 1200 °C.

Figure 3

The surface structure of NaOH-modified P. vittata biochar by SEM observation. Left column: Magnification 250×; Right column: Magnification 1000×; (a) Pyrolysis temperature: 600 °C; (b) Pyrolysis temperature: 800 °C; (c) Pyrolysis temperature: 1200 °C.

Figure 4

As(V) and Cd adsorption isotherms for biochars at various pyrolysis temperatures. (a) Pyrolysis temperature: 600 °C; (b) Pyrolysis temperature: 800 °C; (c) Pyrolysis temperature: 1200 °C.

Figure 5

As(V) adsorption isotherms for FeCl₃-modified and unmodified biochars at various pyrolysis temperatures. (a) Pyrolysis temperature: 600 °C; (b) Pyrolysis temperature: 800 °C; (c) Pyrolysis temperature: 1200 °C.

Figure 6

Cd adsorption isotherms for NaOH-modified and unmodified biochars at various pyrolysis temperatures. (a) Pyrolysis temperature: 600 °C; (b) Pyrolysis temperature: 800 °C; (c) Pyrolysis temperature 1200 °C.

Figure 7

Adsorption rates of As(V) and Cd on biochars with and without chemical modification at each initial concentration. (a) As(V) adsorption of unmodified biochar; (b) Cd adsorption of unmodified biochar; (c) As(V) adsorption of FeCl₃-modified biochar; (d) Cd adsorption of NaOH-modified biochar.