536
N. Okajima et al.
Fig. 6 Flowsheet for Pb, Sb, Bi, and Sn, recovery from Pb sulfate in the HMC
This removal reduces the Cu grade in Pb sulfate to <1%. Some residues that
contain Zn hydroxide or Pb sulfate are raw materials for HMC and may be sold to
other companies.
Pb Recovery in the HMC
The flowsheet for Pb, Sb, Bi, and Sn recovery from Pb sulfate in the HMC is shown
in Fig. 6. The process comprises carbonation, an electric furnace, a Harris furnace,
electrorefining, and Pb anode slime treatment [5]. One of the main feeds to the HMC
is Pb sulfate from the copper smelter. Examples of the chemical compositions of
other raw materials, tankhouse residue, and slime treatment residue, are shown in
Table 3. Lead is contained as lead sulfate in it, and it is converted to lead carbonate
by carbonation, and sulfur is removed from the raw material as shown in Eq. (2).
3PbSO 4 + 3Na 2 CO 3 + H 2 O → 2PbCO 3 · Pb(OH) 2 + CO 2 + 3Na 2 SO 4
(2)
Table 3 Raw material composition for the HMC (%)
Pb
Zn
Bi
Sb
Sn
Tank house residue
<0.1
<0.1
17
23
0.3
Slime treatment residue
12
<0.1
<0.1
38
–