458
M. Kaya et al.
Table 4 Effect of S/L ratio on metal dissolution at 0.5 M CA concentration and 80 °C leaching
temperature
Citric acid (CA)
Zn (%)
As (%)
Fe (%)
Pb (%)
S/L ratio: 1/10, time
80 °C
0.5 M
1/10 S/L
400 rpm
30 min
74.5
12.8
11.5
6.6
60 min
81.5
13.7
13.9
6.8
120 min
89.9
14.4
16.3
7.0
180 min
90.1
14.2
17.4
6.8
Metal
Dissolution
Order
Zn > As > Pb > Fe
S/L ratio: 2/10, time
80 °C
0.5 M
2/10 S/L
400 rpm
30 min
53.3
10.2
10.6
4.3
60 min
63.0
10.8
12.5
4.4
120 min
74.8
11.7
14.8
4.6
180 min
88.0
12.4
17.2
4.8
PLS
70.9
10.3
14.5
4.8
Metal
Dissolution
Order
Zn > Fe > As > Pb
S/L ratio: 3/10, time
80 °C
0.5 M
3/10 S/L
400 rpm
60 min
41.3
7.3
10.1
3.0
120 min
49.5
7.3
11.6
1.5
180 min
46.9
7.3
11.1
0.9
240 min
34.0
6.5
11.1
0.6
PLS
30.4
6.5
11.8
0.6
Metal
Dissolution
Order
Zn > Fe > As > Pb
presence of a greater amount of lixiviant per unit of solids and, therefore, a greater
chance of solid-liquid contact [9]. In addition, at higher S/L ratios, because of the
high Zn quantities leached for the amount of solution available, the solution became
saturated with Zn, preventing more Zn from being leached and limiting the overall
Zn recovery. Studies involving the leaching of electric arc furnace dust (EAFD) have
shown that increasing the solution density decreases the percentage of the Zn that
is dissolved [10]. Decreasing S/L ratio, not only decreases the suspension density,
but also reduces the viscosity of the whole system and therefore decreases the mass
transfer resistance at the solid-liquid interface [11]. Metal dissolution decreases with
increasing S/L ratio due to the faster saturation of the liquid. Ru¸ sen et al. [12], on the
other hand, found that decreasing slurry density had little effect on Zn extraction,
resulting in only about 3% increase in Zn extraction, when the density was lowered
by 100 g/l [12].
Increasing CA concentration from 0.5 to 1.0 M at 1/10 S/L ratio at 60 °C and
80 °C significantly increased Zn dissolution (Table 5). 1.0 M CA dissolved maximum
84.4% Zn as opposed to 74.7% with 0.5 M CA dosage at 120 min leaching time and
60 °C leaching temperature. At 80 °C leaching temperature, maximum Zn dissolution
M. Kaya et al.
Table 4 Effect of S/L ratio on metal dissolution at 0.5 M CA concentration and 80 °C leaching
temperature
Citric acid (CA)
Zn (%)
As (%)
Fe (%)
Pb (%)
S/L ratio: 1/10, time
80 °C
0.5 M
1/10 S/L
400 rpm
30 min
74.5
12.8
11.5
6.6
60 min
81.5
13.7
13.9
6.8
120 min
89.9
14.4
16.3
7.0
180 min
90.1
14.2
17.4
6.8
Metal
Dissolution
Order
Zn > As > Pb > Fe
S/L ratio: 2/10, time
80 °C
0.5 M
2/10 S/L
400 rpm
30 min
53.3
10.2
10.6
4.3
60 min
63.0
10.8
12.5
4.4
120 min
74.8
11.7
14.8
4.6
180 min
88.0
12.4
17.2
4.8
PLS
70.9
10.3
14.5
4.8
Metal
Dissolution
Order
Zn > Fe > As > Pb
S/L ratio: 3/10, time
80 °C
0.5 M
3/10 S/L
400 rpm
60 min
41.3
7.3
10.1
3.0
120 min
49.5
7.3
11.6
1.5
180 min
46.9
7.3
11.1
0.9
240 min
34.0
6.5
11.1
0.6
PLS
30.4
6.5
11.8
0.6
Metal
Dissolution
Order
Zn > Fe > As > Pb
presence of a greater amount of lixiviant per unit of solids and, therefore, a greater
chance of solid-liquid contact [9]. In addition, at higher S/L ratios, because of the
high Zn quantities leached for the amount of solution available, the solution became
saturated with Zn, preventing more Zn from being leached and limiting the overall
Zn recovery. Studies involving the leaching of electric arc furnace dust (EAFD) have
shown that increasing the solution density decreases the percentage of the Zn that
is dissolved [10]. Decreasing S/L ratio, not only decreases the suspension density,
but also reduces the viscosity of the whole system and therefore decreases the mass
transfer resistance at the solid-liquid interface [11]. Metal dissolution decreases with
increasing S/L ratio due to the faster saturation of the liquid. Ru¸ sen et al. [12], on the
other hand, found that decreasing slurry density had little effect on Zn extraction,
resulting in only about 3% increase in Zn extraction, when the density was lowered
by 100 g/l [12].
Increasing CA concentration from 0.5 to 1.0 M at 1/10 S/L ratio at 60 °C and
80 °C significantly increased Zn dissolution (Table 5). 1.0 M CA dissolved maximum
84.4% Zn as opposed to 74.7% with 0.5 M CA dosage at 120 min leaching time and
60 °C leaching temperature. At 80 °C leaching temperature, maximum Zn dissolution