Smelting Jarosite and Sulphur Residue in a Plasma Furnace
399
Fig. 8 Pilot ScanArc furnace at Hofors, Sweden. In the middle tapping of jarosite slag and on the
right water granulated slag after fuming. The slag volume is around 1/7 of the feed volume and
around 1/2 of the weight of the feed
higher lime or alumina content, and somewhat lower silica content. These parameters
are controlled by addition of lime/alumina, addition of LPG/coke and PG-power in
combination with feed rate.
The reactor gas is a mixture of CO/CO 2 , H 2 /H 2 O, elemental sulphur S
o (g), SO 2 (g),
vapour of lead, zinc, and other volatilized elements.
Post-combustion of reactor gas will ensure complete oxidation of sulphur and
other species. Cooling of oxidized process gas will solidify the fume into fine-grained
mixed metal oxides that follow the gas stream into the gas cleaning system where
the fume product is separated from the gas. The fully combusted gas then leaves the
process via a stack into the atmosphere.
Figure 8 shows the Pilot ScanArc furnace and water granulated fumed slag.
Table 1 shows typical analysis after smelting stage and fuming stage, and Table 2
shows the average distributions of elements into the fume and slag after smelting and
fuming.
The slag shows surprisingly low levels of Zn and Pb already after the smelting
stage. Slag analysis after step 1 was Zn 1–3% and Pb about 0.1–0.3% and after step
2: Zn < 1%, Pb < 0.03% target levels have been achieved consistently in several
tests. The chemical composition of elements can vary significantly based on the feed
mixture into the zinc processing and thus has effect into final slag and fume dust
compositions after smelting and fuming.
Recoveries of valuable metals from the combined waste and jarosite have been: Zn
> 90%, Pb > 99%, Ag 75–85%, In 60–70%, and Ge 80–90%. Many of the impurities
end up in the fume or gas phase: As > 98%, Hg 100%, Cd 98%, and Sb 97%. Most of
the F and Cl reports to the fume as well. CEN leaching tests were carried out of the
produced final fumed slag. Three samples á 5 kg were taken from the final tapping.
Table 3 shows the leaching test results together with acceptance criteria for inert
landfill. Highlighted in red is the element Sb that did not pass the acceptance criteria
399
Fig. 8 Pilot ScanArc furnace at Hofors, Sweden. In the middle tapping of jarosite slag and on the
right water granulated slag after fuming. The slag volume is around 1/7 of the feed volume and
around 1/2 of the weight of the feed
higher lime or alumina content, and somewhat lower silica content. These parameters
are controlled by addition of lime/alumina, addition of LPG/coke and PG-power in
combination with feed rate.
The reactor gas is a mixture of CO/CO 2 , H 2 /H 2 O, elemental sulphur S
o (g), SO 2 (g),
vapour of lead, zinc, and other volatilized elements.
Post-combustion of reactor gas will ensure complete oxidation of sulphur and
other species. Cooling of oxidized process gas will solidify the fume into fine-grained
mixed metal oxides that follow the gas stream into the gas cleaning system where
the fume product is separated from the gas. The fully combusted gas then leaves the
process via a stack into the atmosphere.
Figure 8 shows the Pilot ScanArc furnace and water granulated fumed slag.
Table 1 shows typical analysis after smelting stage and fuming stage, and Table 2
shows the average distributions of elements into the fume and slag after smelting and
fuming.
The slag shows surprisingly low levels of Zn and Pb already after the smelting
stage. Slag analysis after step 1 was Zn 1–3% and Pb about 0.1–0.3% and after step
2: Zn < 1%, Pb < 0.03% target levels have been achieved consistently in several
tests. The chemical composition of elements can vary significantly based on the feed
mixture into the zinc processing and thus has effect into final slag and fume dust
compositions after smelting and fuming.
Recoveries of valuable metals from the combined waste and jarosite have been: Zn
> 90%, Pb > 99%, Ag 75–85%, In 60–70%, and Ge 80–90%. Many of the impurities
end up in the fume or gas phase: As > 98%, Hg 100%, Cd 98%, and Sb 97%. Most of
the F and Cl reports to the fume as well. CEN leaching tests were carried out of the
produced final fumed slag. Three samples á 5 kg were taken from the final tapping.
Table 3 shows the leaching test results together with acceptance criteria for inert
landfill. Highlighted in red is the element Sb that did not pass the acceptance criteria