764
K. Miwa et al.
Fig. 5 Sn smelting furnace (outlook)
Table 3 Typical composition of Sn–Pb metal
Au (g/t)
Ag (g/t)
Pb (%)
Sn (%)
Sb (%)
Bi (%)
20
4500
50
45
3.5
0.5
In the leaching process, tin dissolves with the following reaction.
Sn + 2NaOH + O 2 + 2H 2 O = Na 2 Sn(OH) 6
In the alkaline condition, tin is preferentially dissolved into aqueous liquid than
lead. However, if too much free NaOH remained after tin leaching, lead would be
also leached and would affect the electrowinning. So, to avoid lead leaching, NaOH
feed is calculated based on tin composition of each Sn–Pb ingot: target-free NaOH
content after tin leaching is under 25 g/L.
Purification
In the purification process, at first, metal tin shot (about 99%-Sn) is fed and remaining
lead is substituted by tin with the following reaction.
NaHPbO 2 + H 2 O +
1
2
Sn =
1
2
Na 2 Sn(OH) 6 + Pb
K. Miwa et al.
Fig. 5 Sn smelting furnace (outlook)
Table 3 Typical composition of Sn–Pb metal
Au (g/t)
Ag (g/t)
Pb (%)
Sn (%)
Sb (%)
Bi (%)
20
4500
50
45
3.5
0.5
In the leaching process, tin dissolves with the following reaction.
Sn + 2NaOH + O 2 + 2H 2 O = Na 2 Sn(OH) 6
In the alkaline condition, tin is preferentially dissolved into aqueous liquid than
lead. However, if too much free NaOH remained after tin leaching, lead would be
also leached and would affect the electrowinning. So, to avoid lead leaching, NaOH
feed is calculated based on tin composition of each Sn–Pb ingot: target-free NaOH
content after tin leaching is under 25 g/L.
Purification
In the purification process, at first, metal tin shot (about 99%-Sn) is fed and remaining
lead is substituted by tin with the following reaction.
NaHPbO 2 + H 2 O +
1
2
Sn =
1
2
Na 2 Sn(OH) 6 + Pb