696
J. Dahlstrom et al.
Pb(II), As(III), As(IV), Sb(III), Sb(IV), Se(IV), Se(VI), and Cd(II)
During discharge, the battery forms lead sulfate (PbSO 4 ) according to the
following mechanism:
Pb + PbO 2 + 2HSO 4
−
+ 3H
+
2PbSO 4 + 2H 2 O
( 1 )
Over a battery’s life, the charging process will become less efficient, leading to
an increase in the concentration of lead sulfate that no longer participates in the
electrochemical reaction. Eventually, this sulfate accumulation renders the battery
unable to fulfill the application demand, and it is sent off for recycling. Some recyclers
opt to desulfurize the battery’s active materials in order to reduce the total SO 2
emissions that would result from the downstream smelting operations. The lead
sulfate and sulfuric acid are typically converted in the desulfurization process using
either sodium carbonate or sodium hydroxide:
PbSO 4 + Na 2 CO 3 → PbCO 3 + Na 2 SO 4
(2)
PbSO 4 + 2NaOH → PbOH + Na 2 SO 4
(3)
H 2 SO 4 + Na 2 CO 3 → Na 2 SO 4 + H 2 O + CO 2
(4)
H 2 SO 4 + 2NaOH → Na 2 SO 4 + 2H 2 O
( 5 )
This results in an insoluble lead byproduct (PbCO 3 or PbOH) and soluble sodium
sulfate (Na 2 SO 4 ). The products are filtered to capture the lead bearing materials,
with the sulfates sent downstream to the water treatment process.
Industrial Treatment Technologies
Most secondary lead operations rely on chemical precipitation techniques to remove
heavy metals from solution. Chemical precipitation occurs by converting soluble metals to insoluble products via the addition of chemical reagents. In practice, recyclers
employ one of three technologies:
(1) Iron co-precipitation
(2) Metal-sulfide precipitation
(3) Hydroxide precipitation via lime slaking.
J. Dahlstrom et al.
Pb(II), As(III), As(IV), Sb(III), Sb(IV), Se(IV), Se(VI), and Cd(II)
During discharge, the battery forms lead sulfate (PbSO 4 ) according to the
following mechanism:
Pb + PbO 2 + 2HSO 4
−
+ 3H
+
2PbSO 4 + 2H 2 O
( 1 )
Over a battery’s life, the charging process will become less efficient, leading to
an increase in the concentration of lead sulfate that no longer participates in the
electrochemical reaction. Eventually, this sulfate accumulation renders the battery
unable to fulfill the application demand, and it is sent off for recycling. Some recyclers
opt to desulfurize the battery’s active materials in order to reduce the total SO 2
emissions that would result from the downstream smelting operations. The lead
sulfate and sulfuric acid are typically converted in the desulfurization process using
either sodium carbonate or sodium hydroxide:
PbSO 4 + Na 2 CO 3 → PbCO 3 + Na 2 SO 4
(2)
PbSO 4 + 2NaOH → PbOH + Na 2 SO 4
(3)
H 2 SO 4 + Na 2 CO 3 → Na 2 SO 4 + H 2 O + CO 2
(4)
H 2 SO 4 + 2NaOH → Na 2 SO 4 + 2H 2 O
( 5 )
This results in an insoluble lead byproduct (PbCO 3 or PbOH) and soluble sodium
sulfate (Na 2 SO 4 ). The products are filtered to capture the lead bearing materials,
with the sulfates sent downstream to the water treatment process.
Industrial Treatment Technologies
Most secondary lead operations rely on chemical precipitation techniques to remove
heavy metals from solution. Chemical precipitation occurs by converting soluble metals to insoluble products via the addition of chemical reagents. In practice, recyclers
employ one of three technologies:
(1) Iron co-precipitation
(2) Metal-sulfide precipitation
(3) Hydroxide precipitation via lime slaking.