Leaching of Turkish Oxidized Pb–Zn Flotation Tailings …
457
dissolution was obtained at 0.5 M CA concentration, 80 °C leaching temperature,
and 1/10 S/L ratio under tested conditions with Oreks flotation tails. More than 90%
Zn dissolution was achieved with 17.4% Fe, 14.2% As, and 7% Pb co-dissolutions.
Up to 80 °C leaching time and 120 min leaching time, there was an increase in Zn
dissolution; but at 180 min leaching time, Zn dissolution almost reaches a plateau.
With increasing temperature, Fe > As > Pb co-dissolutions increase. Up to 60 °C
leaching temperature, As is the second most co-dissolved metal. At 80 °C and 60 min
leaching time, Fe co-dissolution exceeds As co-dissolution. At 80 °C leaching time,
Pb co-dissolution remains almost constant at 7% for 3 h leaching period. Maximum
90.1% Zn dissolution with 14.2% As, 17.4% Fe, and 6.8% Pb co-dissolutions was
obtained using 0.5 M citric acid concentration at 80 °C leaching temperature and
180 min leaching time. Metal dissolution selectivity difference between Zn and As
was 75.9%, between Zn and Fe 72.7%, and Zn and Pb 83.3%.
As the leaching time and temperature increase, Zn dissolution increases significantly, and As, Fe, and Pb dissolutions slightly increased. Most of the organic acids
solubility increases with increasing temperature. Increase in Zn dissolution was highest in the first 30 min, and after that, there was a slight increase in the Zn dissolution.
pH values of the solution increase in the first 30 min indicating the consumption of
H
+ ions. After 30 min, pH values reach a plateau suggesting very slight contribution
of H
+ ions in the dissolution reactions. After 30 min leaching, anions in the solution
interact with solid surface for dissolution.
Table 4 compares the effect of % solid on metal extractions at the 0.5 M CA concentration and 80 °C leaching temperature for different leaching times. Under these
test conditions, as the leaching time increases Zn dissolution increases significantly.
With increasing S/L ratio, Zn dissolution slightly decreases at 2/10 and significantly
decreases at 3/10 S/L ratio. As % solid increases, As, Fe, and Pb co-dissolutions also
decrease. Ag dissolution was zero with CA for all conditions. At S/L ratio of 1/10,
75%; at 2/10, 53%, and 3/10 41% Zn dissolution was obtained for 30 min leaching
time. At S/L ratio of 1/10, 90%; at 2/10, 88%; and at 3/10, 34% Zn dissolution was
obtained for 180 min leaching time. At S/L ratio of 3/10, Zn dissolution drastically
decreased along with very low Pb, As, and Fe co-dissolutions. Table 4 also shows
the PLS analyses results after 180 min leaching time. Metal dissolution rates for 1/10
S/L ratio is much closer to 180 min leaching results than 2/10 S/L ratio. The decrease
in metal dissolutions with increasing solid % is due to less lixiviant in the medium.
The best condition was 0.5 M CA concentration, at 80 °C leaching temperature, and
1/10 S/L ratio. 1/10 S/L ratio requires about 40 g/L CA usage.
Since higher quantities of Zn are leached at higher S/L ratios, the ionic strength
(concentration of total ions in the solution) of the resultant solution increases. Solubility is affected by the ionic strength of the solution in that, as the solution’s ionic
strength increases, the solubility will be decreased (if the ions are like ions). Thus, in
the case of higher S/L ratios, the solubility decreases as the ions are leached from the
solids. Since there are more ions to be leached (due to the presence of more solids), a
lower percentage of the ions can be leached, because the ionic strength and viscosity
of the solution will increase as more ions are leached [8]. Herrero et al. (9) found
that decreasing the S/L ratio increased the percentage of metal leached, due to the
457
dissolution was obtained at 0.5 M CA concentration, 80 °C leaching temperature,
and 1/10 S/L ratio under tested conditions with Oreks flotation tails. More than 90%
Zn dissolution was achieved with 17.4% Fe, 14.2% As, and 7% Pb co-dissolutions.
Up to 80 °C leaching time and 120 min leaching time, there was an increase in Zn
dissolution; but at 180 min leaching time, Zn dissolution almost reaches a plateau.
With increasing temperature, Fe > As > Pb co-dissolutions increase. Up to 60 °C
leaching temperature, As is the second most co-dissolved metal. At 80 °C and 60 min
leaching time, Fe co-dissolution exceeds As co-dissolution. At 80 °C leaching time,
Pb co-dissolution remains almost constant at 7% for 3 h leaching period. Maximum
90.1% Zn dissolution with 14.2% As, 17.4% Fe, and 6.8% Pb co-dissolutions was
obtained using 0.5 M citric acid concentration at 80 °C leaching temperature and
180 min leaching time. Metal dissolution selectivity difference between Zn and As
was 75.9%, between Zn and Fe 72.7%, and Zn and Pb 83.3%.
As the leaching time and temperature increase, Zn dissolution increases significantly, and As, Fe, and Pb dissolutions slightly increased. Most of the organic acids
solubility increases with increasing temperature. Increase in Zn dissolution was highest in the first 30 min, and after that, there was a slight increase in the Zn dissolution.
pH values of the solution increase in the first 30 min indicating the consumption of
H
+ ions. After 30 min, pH values reach a plateau suggesting very slight contribution
of H
+ ions in the dissolution reactions. After 30 min leaching, anions in the solution
interact with solid surface for dissolution.
Table 4 compares the effect of % solid on metal extractions at the 0.5 M CA concentration and 80 °C leaching temperature for different leaching times. Under these
test conditions, as the leaching time increases Zn dissolution increases significantly.
With increasing S/L ratio, Zn dissolution slightly decreases at 2/10 and significantly
decreases at 3/10 S/L ratio. As % solid increases, As, Fe, and Pb co-dissolutions also
decrease. Ag dissolution was zero with CA for all conditions. At S/L ratio of 1/10,
75%; at 2/10, 53%, and 3/10 41% Zn dissolution was obtained for 30 min leaching
time. At S/L ratio of 1/10, 90%; at 2/10, 88%; and at 3/10, 34% Zn dissolution was
obtained for 180 min leaching time. At S/L ratio of 3/10, Zn dissolution drastically
decreased along with very low Pb, As, and Fe co-dissolutions. Table 4 also shows
the PLS analyses results after 180 min leaching time. Metal dissolution rates for 1/10
S/L ratio is much closer to 180 min leaching results than 2/10 S/L ratio. The decrease
in metal dissolutions with increasing solid % is due to less lixiviant in the medium.
The best condition was 0.5 M CA concentration, at 80 °C leaching temperature, and
1/10 S/L ratio. 1/10 S/L ratio requires about 40 g/L CA usage.
Since higher quantities of Zn are leached at higher S/L ratios, the ionic strength
(concentration of total ions in the solution) of the resultant solution increases. Solubility is affected by the ionic strength of the solution in that, as the solution’s ionic
strength increases, the solubility will be decreased (if the ions are like ions). Thus, in
the case of higher S/L ratios, the solubility decreases as the ions are leached from the
solids. Since there are more ions to be leached (due to the presence of more solids), a
lower percentage of the ions can be leached, because the ionic strength and viscosity
of the solution will increase as more ions are leached [8]. Herrero et al. (9) found
that decreasing the S/L ratio increased the percentage of metal leached, due to the