The Influence of Dosing Modes of Coagulate on Arsenic Removal

Table 1

Processes of the sequential extraction.

Step	As (V) speciation	Extraction reagent	Extraction method
I	Soluble	50 mL of distilled water (pH 6.5)	Shaken for 2 h at 25°C
II	Nonspecifically sorbed	50 mL of 0.05 mol/L (NH4)2SO4	Shaken for 4 h at 20°C
III	Specifically sorbed	50 mL of 0.05 mol/L NH4H2PO4	Shaken for 16 h at 20°C
IV	Poorly crystalline hydrous oxides of Fe	50 mL of 0.2 mol/L NH4^+-oxalate buffer (pH 3.25)	Shaken for 4 h in dark at 20°C
V	Well-crystallized hydrous oxides of Fe	50 mL of 0.2 M NH4^+-oxalate buffer + 0.1 M ascorbic acid (pH 3.25)	Shaken for 0.5 h at 96°C