A preliminary economic assessment evaluated two processing options for the Huakan J&L milling plant, both incorporating heavy media separation, grinding, flotation, pressure oxidation, and cyanidation.
Report context
This preliminary economic assessment (PEA) for the Huakan J&L milling plant was completed by Micon in 2006. The report presents two flowsheet options: Option A, producing a single saleable lead concentrate, and Option B, producing both saleable lead and zinc concentrates. The conceptual plant design for the single saleable concentrate is based on testwork carried out by PRA on ore types making up a composite sample with a head grade of 8.1 g/t Au, 72.4 g/t Ag, 3.2% Pb, and 4.8% Zn. Micon estimated life-of-mine average feed grades of 6.42 g/t Au, 69.8 g/t Ag, 2.2% Pb, and 3.6% Zn. The main source of assay data for this report is a study dated November 2, 2006, prepared for BacTech by PRA. Additional process parameters were identified from an October 1998 report prepared by H.A. Simons, which was based on testwork conducted by PRA under the direction of Beattie Consulting Ltd.
Processing route
Crushing
Ore is delivered by mine trucks to the plant and fed through a grizzly with 400 mm openings to the ROM feed hopper. Ore is extracted by an apron feeder and fed to a jaw crusher. Secondary crusher product is 80% passing 18.3 mm. The crusher is designed for a nominal rate of 62.5 t/h operating 16 h/d at 80% availability, with a design rate of 117.2 t/h. Primary crusher closed-side setting is 64 mm, secondary crusher closed-side setting is 16 mm.
Heavy media separation
HMS may be used to selectively remove non-sulphide gangue materials by applying a specific gravity of 2.95 to 3.00. The separators are filled with a bath of ferrosilicon slurry at a specific gravity of 2.9. Low specific gravity waste floats, while high specific gravity ore sinks. Approximately 40% of the mill feed is removed as float with less than 2% of contained metals lost. Float is removed by paddles and laundered to drainage screens for medium recovery. Sink is removed by bucket elevators and fed to single deck screens, then transferred to a live bin ahead of the rod mill.
Grinding
The HMS concentrate reporting to the grinding circuit comprises 60% of the feed to the HMS circuit, or 900 t/d of coarse sink. The primary grinding rod mill discharge product typically has a size passing of 800 µm. The secondary grinding ball mill operates in closed circuit with a cyclone, with target cyclone overflow 80% passing 65 µm. Total feed tonnage to grinding is 900 t/d nominal, 1,000 t/d design.
Lead flotation
Ball mill ore slurry discharge at 40% solids is fed to a conditioning tank, which overflows to lead rougher flotation cells. The lead flotation circuit is a conventional lead-zinc differential flotation circuit. Aero242, xanthate, and cyanide are added to the roughers, cleaners, and regrind circuit. MIBC is used as a frother, and lime as a pH modifier. Concentrate from rougher cells is fed to cleaner cells, with five stages of cleaning. Final concentrate is sent to a pressure filter for dewatering.
Zinc flotation (Option B only)
Lead rougher tailing, lead-scavenger tails, and zinc spill returns are conditioned with copper sulphate and lime. The overflow is treated with lime to raise pH, mixed with xanthate, Dowfroth 250, and MIBC, and pumped to zinc roughers. Zinc rougher tailing is discarded from the circuit as final flotation tails. Final concentrate is pumped to the dewatering circuit.
Dewatering
Lead concentrate is thickened to 80% solids in a 10.6-m diameter thickener. Zinc concentrate (Option B) is thickened to 70% solids using an 11.6-m diameter thickener. Concentrates are filtered using pressure filters with an area of 31 m² for lead concentrate, and 35 m² for zinc concentrate.
Bulk sulphide flotation
For Option A, tails from lead flotation are run through bulk sulphide flotation to recover all remaining sulphides, including gold and silver bearing minerals, sphalerite, arsenopyrite, and pyrite. For Option B, the same process is carried out on the zinc flotation tails. The flotation concentrate is thickened, filtered, and sent to pressure oxidation.
Pressure oxidation
Total pressure oxidation of the bulk sulphide concentrate is carried out in an autoclave using oxygen produced in a dedicated plant on site. Autoclave discharge slurry is neutralized using limestone. The PO residue is filtered to produce a solids feed to cyanidation. For Option A, zinc recovery from the neutralization filtrate is realized either by lime neutralization, sulphide precipitation, or zinc solvent extraction. This PEA assumes precipitation of zinc hydroxide using lime. For Option B, no zinc recovery circuit is needed.
Cyanidation
A six-stage carbon-in-leach (CIL) circuit is designed based on a retention time of 6 hours and a new carbon concentration of 20 g/L. Solids from filtration of the PO residue are slurried and fed to the train of six CIL tanks in series. Loaded carbon from the first CIL tank is collected on a screen and sent to the carbon stripping circuit. Slurry leaving the last CIL tank is passed over a safety screen before being sent to cyanide destruction.
Carbon stripping, carbon reactivation, and gold room
Loaded carbon is acid-washed and fed to a pressurized Zadra circuit to strip gold and silver. Pregnant solution is sent to two electrowinning cells to recover gold and silver. Carbon from the stripping circuit is fed to a diesel-fired rotary kiln for reactivation. Stainless steel wool containing gold from electrowinning is fed to an induction furnace to produce gold doré bars.
Cyanide destruction
CIL discharge slurry is pumped to two agitator tanks in series, and SO₂ and air are added to destroy cyanide before the slurry is pumped to the tailings disposal area.
Key reported parameters
| Parameter | Units | Option A One Saleable Concentrate | Option B Two Saleable Concentrates | Basis |
|---|---|---|---|---|
| Production | ||||
| Tonnes processed annually | t/y | 540,000 | 540,000 | Design |
| Saleable Pb concentrate production, average | t/y | 19,680 | 19,680 | Design |
| Saleable Zn concentrate production, average | t/y | – | 25,210 | Design |
| Gold production, LOM average | oz/y | 81,718 | 77,155 | Design |
| Silver production, LOM average | oz/y | 115,756 | 42,741 | Design |
| Key operating parameters | ||||
| Operating days per year | d/y | 360 | 360 | Design |
| Mill feed rate | t/d | 1,500 | 1,500 | Design |
| Chemical and metallurgical parameters | ||||
| Concentrate grade, Pb | % | 45 | 45 | Design |
| Concentrate grade, Zn | % | – | 53.5 | Design |
| Feed characteristics (LOM average) | ||||
| Average feed grade, Au | g/t | 6.42 | 6.42 | Micon estimate |
| Average feed grade, Ag | g/t | 69.78 | 69.78 | Micon estimate |
| Average feed grade, Pb | % | 2.20 | 2.20 | Micon estimate |
| Average feed grade, Zn | % | 3.60 | 3.60 | Micon estimate |
| Specific gravity | t/m³ | 3.36 | 3.36 | Design |
| Heavy media separation | ||||
| HMS float reject | % wt. of feed | 40 | 40 | Design |
| HMS media specific gravity | t/m³ | 2.9 | 2.9 | Design |
| Grinding | ||||
| Rod mill work index | kWh/t | 11 | 11 | Testwork |
| Ball mill work index | kWh/t | 11.5 | 11.5 | Testwork |
| Cyclone overflow P80 | micron | 65 | 65 | Design |
| Lead flotation | ||||
| Lead concentrate recovery | % Pb | 78.0 | 78.0 | Design |
| Zinc flotation | ||||
| Zinc concentrate recovery | % Zn | N/A | 72.1 | Design |
| Pressure oxidation | ||||
| Autoclave temperature | °C | 220 | 220 | Design |
| Total operating pressure | kPa | 2,800 | 2,800 | Design |
| Cyanidation | ||||
| Leach residence time | h | 6 | 6 | Design |
| Cyanide consumption | kg/t | 6 | 6 | Design |
| Lime consumption | kg/t | 10 | 10 | Design |
Project website: https://amebc.ca/exploration-in-british-columbia/
Technical qualifications
Only the summary of the referenced PRA report dated November 2, 2006 was available through Huakan. Additional process parameters were identified from the earlier October 1998 report prepared by H.A. Simons. The report notes that additional flowsheet development and pilot studies are required before design specifications can be finalized. Option B was not evaluated fully as Micon expressed doubt that the quantity of zinc flotation concentrate that would be produced at J&L would find a market, considering its arsenic content. The option of bioleach testwork was considered but noted that mountainous terrain at the J&L site limits level area available.
Source: Huakan J&L Milling Plant Preliminary Economic Assessment, 2006, Section 17.0 Recovery Methods.
