Preparation and reactivation of magnetic biochar by molten salt method: Relevant performance for chlorine-containing pesticides abatement

Figures & data

Table 1. Characteristic of FeCl₃, 2,4-DCP and atrazine.

	Ferric trichloride	2,4-DCP	atrazine
Molecular formula	FeCl3∙6H2O	C6H4Cl2O	C8H14ClN5
Molar mass, g/mol	162.204	163.00	215.68
Melting point, ºC	306°C	42–43ºC	173–175ºC
Boiling point, ºC	315°C	210ºC	200ºC
Solubility in water (20ºC)	soluble	4.5 g/L	0.07 g/L
Density, g/cm^3	2.90	1.38	1.187

Table 2. Salt composition, melting points, and eutectic temperatures (Yao, Li, and Zhao 2011).

Salt	Salt composition (mol %)	Melting points/eutectic temperatures (°C)
NaOH–Na2CO3	90%–10%	286

Figure 1. TG-DSC curves of the fir sawdust (a) and the fir sawdust mixed with FeCl₃∙6H₂O powder (b).

Figure 2. X-ray pattern of BC (a) and of MBC (b), and EDS spectrum of M-BC(c).

Table 3. Elemental analysis of MBC.

	C	H	O	N
Content	72.06%	3.76%	13.45%	1.05%

Figure 3. SEM images at different expansion ratios (a–d) and carbon, oxygen, and iron maps of MBC obtained by molten salt route (e–g). A color version is available online.

Figure 4. (a) Magnetic hysteresis loops of MBC. Digital image (inset) shows the magnetic separation by an ordinary magnet after 20 sec. (b) Raman spectrum of MBC. (c) N₂ adsorption/desorption isotherms. (d) Pore size distribution.

Figure 5. Adsorption kinetics for the 2,4-DCP (a) and atrazine (b) on MBC. Results of fitting experimental data to the first-order, the pseudo-second-order for the 2,4-DCP (c) and atrazine (d). Adsorption equilibrium isotherms for the 2,4-DCP (e) and atrazine (f). Initial concentration range, 20–200 mg L⁻¹; temperature range, 10–30ºC; adsorbents dosage, 0.05 g; working volume, 50 mL; contact time, 24 hr.

Table 4. The content of Cl⁻ and pesticides in the washing water and residues with molten NaOH–Na₂CO₃ method.

		NaOH/Na2CO3 + SMBC-1	NaOH/Na2CO3 + SMBC-2	SMBC-1	SMBC-2
DRE	Washing water	8.67%	9.70%	1.23%	2.98%
	Residues	56.83%	21.99%	ND	0.19%
DCP	Washing water	ND	—	43.82%	—
	Residues	ND	—	51.65%	—
Atrazine	Washing water	—	ND	—	56.38%
	Residues	—	3.78%	—	18.67%

Notes. SMBC, saturated magnetic biochar that exhausted with 2,4-DCP (SMBC-1) and atrazine (SMBC-2). ND, not detected. —, Not available.

Figure 6. The XRD pattern of salt residues after reaction.

Figure 7. The possible mechanism for the molten salt preparation and destruction.

Table 5. Fixed carbon content, pore volume, and relative sample yield for the samples derived in molten salt systems at 400ºC.

Biochar	Yield (%)	SBET (m^2/g)	Total pore volume (m^3/g)	Fixed carbon content (%)
MBC	98.2	405	0.36	61.0
Regenerated SMBC-1	68.7	398	0.31	58.2
Regenerated SMBC-2	71.2	402	0.32	60.8

Note. SMBC-1: MBC regenerated from the adsorption of DCP. SMBC-2: MBC regenerated from the adsorption of atrazine.

Table 6. Absorption capacity of regenerated MBC in several cycles.

Number of cycles	Absorption amount (mg/g)
	DCP	Atrazine
1	298.12	102.17
2	232.20	100.78
3	218.52	89.36
4	215.34	78.69

Yao, Z., J. Li, and X. Zhao. 2011. Molten salt oxidation: A versatile and promising technology for the destruction of organic-containing wastes. Chemosphere 84 (9):1167–1174. doi:10.1016/j.chemosphere.2011.05.061.

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