Lead Metal Production at Paroo Station Mine Using …
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washed and treated with sodium carbonate to convert the lead sulphate to lead carbonate in the DeS leach step (desulphurization). High conversion rates of sulphate
to carbonate were achieved in the test work. A large proportion of the anglesite was
initially occluded within cerussite grains in the flotation concentrate, so the first MSA
leach step was found to be critical to ensuring that the anglesite was exposed to the
conversion reaction.
The DeS leach residue was simply floated in a step analogous to the flowsheet used
in the flotation concentrator to recover a flotation concentrate comprising the lead
carbonate produced in the DeS leach step thus eliminating a difficult solids/liquid
separation step. The flotation tailings from this step would be discharged to the main
tailings stream in the flotation plant.
The flotation concentrate was then thickened and filtered with the primary flotation
concentrate and thus recycled to the MSA leach eliminating a second MSA leach
step and subsequent solid/liquid separation step.
It is worth noting at this point that while the ore mineralogy indicates the presence
of only minor/trace sulphides, the flotation concentrate contains 2–3% of the lead as
lead sulphide, mainly as a result of the sulphidisation step in the flotation concentrator.
In a reaction analogous to copper sulphide leaching with the ferrous/ferric sulphate
couple, lead sulphide can be leached with the ferrous/ferric methanesulphonate couple. Ferrous methanesulphonate is converted to ferric methanesulphonate in the MSA
leach by addition of an oxidant such as air or oxygen. The galena is thus effectively
leached in the MSA leach circuit using iron taken into solution from gangue leaching
reactions.
The liquor from the MSA leach thickener overflow thus contains all of the lead
leached and may pass to an optional impurity removal step ahead of liquor filtration and electrowinning. The solution can be purified by lime addition to form iron
and aluminum hydroxide precipitates. In the demonstration plant, this step was not
required due to the high quality of concentrate recovered via column flotation.
The electrolyte is filtered and passes to a tank house where the lead is electrowon
onto lead started sheets. The tank house and subsequent material handling steps are
fully automated to minimize the potential for operator contact with lead solutions. All
of the cells are equipped with anode brushes to scrub acid mist from the cell off-gas.
Cathodes are recovered at a rate of about 200 kg unit every minute. The lead is melted
in an induction furnace and the molten lead is cast into 25 kg ingots and a proportion
of the molten lead is cast into starter sheets for recycle to the electrowinning facility.
The target is to produce lead ingot of +99.99% lead purity as demonstrated in test
work to date. The majority of the impurity is due to minor metals in the commercial
lead sheet used for starter sheets in the pilot plant so reaching the target lead grade
is not considered to be an issue.
Refinery residues will be discharged to the existing tailings storage facility and will
contain substantially lower residual lead values than the existing flotation tailings.
The flowsheets for the grinding, flotation, and hydrometallurgical plant designs
are shown in Figs. 3, 4 and 5.
143
washed and treated with sodium carbonate to convert the lead sulphate to lead carbonate in the DeS leach step (desulphurization). High conversion rates of sulphate
to carbonate were achieved in the test work. A large proportion of the anglesite was
initially occluded within cerussite grains in the flotation concentrate, so the first MSA
leach step was found to be critical to ensuring that the anglesite was exposed to the
conversion reaction.
The DeS leach residue was simply floated in a step analogous to the flowsheet used
in the flotation concentrator to recover a flotation concentrate comprising the lead
carbonate produced in the DeS leach step thus eliminating a difficult solids/liquid
separation step. The flotation tailings from this step would be discharged to the main
tailings stream in the flotation plant.
The flotation concentrate was then thickened and filtered with the primary flotation
concentrate and thus recycled to the MSA leach eliminating a second MSA leach
step and subsequent solid/liquid separation step.
It is worth noting at this point that while the ore mineralogy indicates the presence
of only minor/trace sulphides, the flotation concentrate contains 2–3% of the lead as
lead sulphide, mainly as a result of the sulphidisation step in the flotation concentrator.
In a reaction analogous to copper sulphide leaching with the ferrous/ferric sulphate
couple, lead sulphide can be leached with the ferrous/ferric methanesulphonate couple. Ferrous methanesulphonate is converted to ferric methanesulphonate in the MSA
leach by addition of an oxidant such as air or oxygen. The galena is thus effectively
leached in the MSA leach circuit using iron taken into solution from gangue leaching
reactions.
The liquor from the MSA leach thickener overflow thus contains all of the lead
leached and may pass to an optional impurity removal step ahead of liquor filtration and electrowinning. The solution can be purified by lime addition to form iron
and aluminum hydroxide precipitates. In the demonstration plant, this step was not
required due to the high quality of concentrate recovered via column flotation.
The electrolyte is filtered and passes to a tank house where the lead is electrowon
onto lead started sheets. The tank house and subsequent material handling steps are
fully automated to minimize the potential for operator contact with lead solutions. All
of the cells are equipped with anode brushes to scrub acid mist from the cell off-gas.
Cathodes are recovered at a rate of about 200 kg unit every minute. The lead is melted
in an induction furnace and the molten lead is cast into 25 kg ingots and a proportion
of the molten lead is cast into starter sheets for recycle to the electrowinning facility.
The target is to produce lead ingot of +99.99% lead purity as demonstrated in test
work to date. The majority of the impurity is due to minor metals in the commercial
lead sheet used for starter sheets in the pilot plant so reaching the target lead grade
is not considered to be an issue.
Refinery residues will be discharged to the existing tailings storage facility and will
contain substantially lower residual lead values than the existing flotation tailings.
The flowsheets for the grinding, flotation, and hydrometallurgical plant designs
are shown in Figs. 3, 4 and 5.