600
H. Nakano et al.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0
10
20
30
40
50
60
0
2 0
4 0
6 0
8 0
1 0 0
1 2 0
Flourine concentration in first stage
(mg/L)
Amount of aluminum sulfate (mL/L)
First-stage
neutralization
(left axis)
Second-stage
neutralization
(right axis)
Flourine concentration in second
stage (mg/L)
Fig. 6 Examination of two-stage neutralization treatment
Wastewater
containing fluorine at
high concentration
Alminium
sulfate
reactor
Thickener
Calcium hydroxide,
neutrization
reactor
Alminium
sulfate
reactor
Calcium hydroxide,
neutrization
reactor
Thickener
Slurry
tank
Filter press
Wastewarer
treatment plant
in lead smelter
Overflow
Spigot
Spigot
Overflow
Cakes
to
smelter
Fig. 7 Process flow for the high fluorine water
treatment). The spigots (sediment from under the thickener) of the primary and secondary thickeners are transferred to the primary neutralization tank to make use of the
unreacted calcium hydroxides and also condense the spigots further. The condensed
spigots are filtered by the filter press.
Results
By the two-stage of neutralization, fluorine concentration is decreased to less than
10 mg/L, and by the wastewater treatment in the smelter, the concentration is reduced
to 3–4 mg/L. Now, fluorine concentration of effluent water discharged from the plant
is very stable, 2–3 mg/L.