The flowsheet shown is of a conventional type, for treatment of
200-300 tons per day of fluorspar ore containing lead, using
“Sub-A” Flotation.
If lead and zinc were present, the same flowsheet would apply to
remove a bulk sulphide concentrate which could be subsequently
refloated to produce the respective lead and zinc concentrates
suitable for marketing.
The best approach to effectively produce separate lead and zinc
concentrates should be established by test work. In some cases,
selective flotation is indicated initially. This may be
accomplished by removing a lead concentrate, then following this
process by conditioning and flotation of the lead tailing to
produce a zinc concentrate.
Crushing Circuit
Primary and secondary crushing are used for this plant tonnage.
Single stage crushing may be employed for tonnages up to 100 tons
per day.
Grinding Circuit
Two stage grinding, using the Rod Mill in open circuit, followed by
closed circuit ball mill grinding, is ideal because of the local
power requirement and the increased efficiency of grinding.
The Selective Mineral Jig may be utilized to recover galena in this
circuit. Presence of oxidized lead in the ore is overcome to a
great extent by removing it at a relatively coarse size, in the
jig.
Conditioning Tank
Conditioning of the classifier overflow is required if
sulphidization is employed to effect flotation of oxidized lead. A
second stage conditioning of the thickened lead tailing, after
repulping with fresh water, is required for flotation of the
fluorspar. Heating of the pulp at this point is often advantageous.
Fluorspar Flotation
The lead and fluorspar are recovered by Flotation of the
cell-to-cell type, permitting maximum recovery and grade of
concentrate. Wide acceptance of machines is well verified when
considering that over 95% of all acid grade fluorspar is processed
in the “Sub-A” Flotation Machine. Flexibility of these machines is
of prime importance where such high specifications must be met.
Multiple cleaning, always necessary in acid grade fluorspar plants,
can be performed without the help of pumps.
Lead tailing is thickened to remove the bulk of the reagents used
in the lead circuit. The clear overflow is re-circulated to the
grinding circuit.
Thickening and Filtering
Both concentrates are thickened and filtered. The thickened lead
concentrate is filtered on the Disc Filter. Thickened fluorspar
concentrate, at approximately 60% solids here, has a high filter
capacity of approximately 2000 pounds per sq. ft. per 24 hours. The
Fluorspar Filter with its stainless steel filter media, is
especially designed for this application.
Drying and Storage
The Standard Dryer effectively dries the filtered fluorspar
concentrate to less than 0.5% moisture, as required for marketing.
An elevated temperature in the dryer can also be used to burn off
small amounts of sulphur and lead.
A screw conveyor and bucket elevator as employed to transport the
dried fluorspar to the concentrate storage bins. Bins can be
conveniently discharged into rail road cars for shipment, while the
filtered lead concentrate may be marketed as produced, without
drying.
