Behavior and Distribution of Heavy Metals Including Rare Earth Elements, Thorium, and Uranium in Sludge from Industry Water Treatment Plant and Recovery Method of Metals by Biosurfactants Application

Table 1

Sequential extraction procedure for fractional determination of metallic elements.

Step	Fraction	Extraction reagents	Ratio of sludge : reagent	Extraction condition
1	F1	Extrapure water	7 : 70	Shake 6 h, 30°C
2	F2	0.05 mol·dm^−3 Ca(NO3)2	7 : 70	Shake 24 h, 30°C
3	F3	2.5% CH3COOH	7 : 70	Shake 24 h, 30°C
4	F4	6% H2O2	7 : 120	Water bath, 95°C (Evaporate)
		2.5% CH3COOH	7 : 70	Shake 24 h, 30°C
5	F5	0.1 mol·dm^−3 (COOH)2 + 0.175 mol·dm^−3 (COONH4)2 + Ascorbic acid	7 : 210	Water bath, 6 h, 95°C; Occasional shaking
6	F6	HNO3 + HF		Microwave digestion