Remediation of Soils Contaminated by Fluoride Using a Fermentation Product of Seaweed (Eucheuma cottonii)

Table 1

Extraction processes of various fluoride fractions in the soil.

Fluoride species	Extraction process
Water-soluble fluoride (Ws-F)	Distilled water
	Shake for 30 min at 60°C
Exchangeable-fluoride (Ex-F)	1 mol/L MgCl2
	Shake for 1 h at 25°C
Fe/Mn bound fluoride (Fe/Mn-F)	0.04 mol/L NH4.HCl
	Shake for 1 h at 60°C
Organic matter-bound fluoride (Or-F)	Step 1: 3 ml of 0.02 mol/l HNO3 + 10 ml 30% H2O2
	Step 2: 12 ml of 3.2 mol/L NH4 acetate
	Shake for 30 min at 25°C
Residual fluoride (Res-F)	Tot-F minus the above for species of fluoride