The proposed process plant for the Woodlawn Project is designed for co-treatment of fresh underground feed and reclaimed tailings using conventional and fine grinding followed by differential flotation to produce copper, lead and zinc concentrates.
Report context
This technical report, dated 29 May 2015 and prepared for Heron Resources Limited, describes the proposed processing route for the Woodlawn Project. The process recovery method is based on co-treatment of the underground resource and retreatment of process tailings from the existing tailings storage dams. A Front End Engineering Design (FEED) study was completed on the Woodlawn Tailings Retreatment Project in 2012 (Sara, 2012), and the metallurgical testing regime conducted as part of the FEED laid the basis for the co-treatment flowsheet design. The proposed flowsheet allows for operation commencing with plant feed of 100% tailings reclamation as the underground mining operation ramps up to full production.
Processing route
Introduction
The selected process recovery method has been based on co-treatment of the underground resource and the retreatment of process tailings from the existing tailings storage dams (TDs). The process plant will consist of both conventional and fine grinding circuits, then utilise differential flotation for the extraction of copper, lead and zinc concentrates. The concentrates will be filtered on-site for export via either Port Kembla or Port Botany.
Process Design Basis
The plant has been designed on the basis of a 50% blend of fresh underground feed being co-treated with 50% reclaimed tailings from the three existing tailings dams located adjacent to the process plant location. Initial operation will treat 100% tailings reclamation feed, whilst the mining operations develop the decline to mine the fresh underground material.
Overview of Plant Feed
Feed to the new treatment plant will consist of both fresh sulphide underground material and reclaimed tailings on a nominal 1:1 blend ratio. Following completion of the PEA, the blend ratio may be refined during future studies.
Fresh underground mineralisation will be mined and delivered to a Run of Mine (ROM) pad for processing through a two stage crushing circuit designed to provide a crusher product size suitable as feed to a ball mill. Crushed feed will be stored in a fine ore bin prior to reclaim via a conveyor system to the primary ball mill. The primary ball mill will run in a closed circuit with hydrocyclones to produce a flotation feed P80 classification size of 75µm.
The tailings will be reclaimed from the three existing tailings storage dams (Tailings Dam South, Tailings Dam West and Tailings Dam North) via a hydraulic mining method, with the material then being screened and pumped to the process plant. The reclaimed tailings will be thickened and ground to a P80 of 30µm prior to the co-treatment flotation circuit.
Co-treatment Flotation Circuit
The co-treatment flotation circuit will utilise a talc, copper, lead and zinc differential flotation sequence. Talc cleaner concentrate recovered from the talc flotation cleaner cell will be discarded to final tails to remove some of the talcose gangue ahead of the differential flotation circuit. A differential flotation circuit for copper, lead and zinc will be utilised with concentrate regrind stages in the copper, lead and zinc circuits to produce sales grade concentrates. The copper circuit will also utilise a rougher and scavenger tailings regrind circuit prior to the lead flotation stage. Tailings from the flotation plant will be thickened for recovery of process water and to provide underground paste fill material, with slime tailings deposited into a new tailings dam, Tailings Storage Facility No 4 (TSF4).
Crushing – Underground Plant Feed
A two stage crushing circuit has been selected based on similar applications and on the historical data from Woodlawn operations. Fresh underground material will be reclaimed by a front end loader to a ROM bin. Feed will be reclaimed by a vibratory grizzly pan feeder which will screen out undersize material and feed to the primary jaw crusher. Underground feed will be reduced in size to a P80 of 105mm at the primary crushing stage, based on a close side setting of 100mm on the jaw crusher.
Primary crushed feed will be conveyed to a product screen with oversize directed to a secondary cone crusher. The secondary crusher will provide for the additional size reduction with a close side setting of 22mm. The secondary crushing stage will be closed circuited with the product screen. The final product size will be controlled by the product screen bottom deck to generate a ball mill feed sized material with a P80 of 10.5mm. Product sized material will be conveyed to a fine ore bin for subsequent reclaim to the primary ball mill.
Grinding – Underground Plant Feed
Crushed underground feed will be milled in a ball mill circuit closed by hydrocyclones. The primary ball mill will be an overflow ball mill (4.42m diameter by 5.0m equivalent grinding length equipped with a 1,600kW mill motor). The circuit will be closed with hydrocyclones to provide for a flotation feed size P80 of 75µm and will be designed to operate at a recirculating load of up to 300%. A fixed speed mill has been selected for the sulphide mineralisation and will operate at 75% critical speed with a 35% ball charge. A primary cluster of 250mm cyclones will be used to obtain the required flotation feed classification size. Lime will be added when required in the primary mill stage to ensure a pH prior to flotation of 5.5 to 6.0.
Grinding – TSF Reclaim
Reclaimed tailings will be thickened in an 18m diameter high rate feed preparation thickener to achieve an underflow density of between 60% and 70% solids (w/w). Thickener underflow will be pumped to the IsaMill feed surge tank. The grinding mill selected is an IsaMill M10000 unit that will have a volume of 10m³ and will be equipped with a 3.0MW drive. Mill feed slurry will be ground from an average feed size F80 of 106µm to a product size P80 of 30µm using ceramic grinding media. The grinding mill will be configured in open circuit. Lime is added to the mill feed to maintain a pH of 5.5 to 6.0.
Talc Flotation Circuit
Product discharged from both the underground grinding stage and tailings reclaim grinding stage will be transferred to the talc flotation circuit consisting of a conditioning stage, roughing stage and one stage of cleaning. The final talc concentrate will be pumped to the flotation tailings sump for disposal. Talc flotation rougher tails will feed the copper flotation circuit.
Reagent additions in the talc flotation circuit include sodium meta-bisulphite (SMBS) and lime added to the talc conditioning tank, and frother added to the feed box of the talc rougher flotation stage. The talc flotation circuit will comprise five 10m³ talc rougher tank cells and one 10m³ talc cleaner tank cell.
Copper Flotation Circuit
The talc rougher tailings will be pumped to the copper conditioning tank. The copper flotation circuit will comprise a conditioning stage, roughing and scavenger stages followed by a regrind and two stages of cleaning on the concentrate and a regrind stage on the circuit tail stream. The final copper concentrate will be pumped to the copper concentrate dewatering circuit and the copper flotation tailings will be pumped to a tail regrind circuit ahead of lead flotation.
The copper flotation circuit will comprise one 10m³ copper tank cell, two 10m³ copper rougher tank cells, four 10m³ copper scavenger tank cells, one SMD Detritor 355kW copper regrind mill, five 1.5m³ conventional copper cleaner cells, three 1.5m³ conventional copper recleaner cells, and one IsaMill M5000 copper tail regrind mill fitted with a 1,500kW motor. The copper rougher concentrate will be pumped to a regrind mill circuit closed with hydrocyclones for concentrate size reduction to a P80 of 20µm.
Lead Flotation Circuit
Classified and reground tails from the copper scavenger and copper cleaner will be pumped to the lead conditioning tank. The lead flotation circuit will comprise a conditioning stage, roughing/scavenger stage followed by lead regrind and two stages of cleaning. The final lead concentrate will be pumped to the lead concentrate dewatering circuit and the lead rougher/scavenger flotation tailings and lead cleaner tailings will be pumped to the zinc flotation circuit.
The lead flotation circuit will comprise two 20m³ lead rougher tank cells, five 20m³ lead scavenger tank cells, one SMD Detritor lead regrind mill (355kW model fitted with a 500kW motor), one 5m³ lead cleaner agitated conditioning tank, six 4.25m³ conventional lead cleaner cells, and five 1.5m³ conventional lead recleaner cells.
Zinc Flotation Circuit
The lead rougher/scavenger tailings and lead cleaner tailings from the lead flotation circuit will be pumped to the zinc flotation circuit. The zinc flotation circuit will consist of a zinc roughing and scavenger circuit, a cleaner circuit and a cleaner scavenger circuit. The zinc concentrate will be pumped to the zinc concentrate thickener and the final tailings will be pumped to the tailings thickener circuit.
The zinc rougher scavenger circuit will comprise three 20m³ zinc rougher tank cells, five 20m³ zinc scavenger tank cells, five 10m³ zinc scavenger (2) tank cells, and an 1100kW SMD zinc regrind mill. The zinc cleaner and cleaner scavenger circuit will comprise one 5.0m³ zinc cleaner agitated conditioner tank, seven 4.25m³ zinc 1st cleaner conventional cells, six 4.25m³ zinc 2nd cleaner conventional cells, and nine 1.5m³ zinc 1st cleaner scavenger conventional cells.
Concentrate Production
Final copper, lead and zinc concentrates from the flotation circuits will be pumped to 6, 7 and 10m diameter high rate concentrate thickeners respectively. Flocculant will be added to increase the settling rate and underflow density to 60% solids.
The filtration section will be similar for copper, lead and zinc concentrates and will comprise concentrate storage tanks, filter feed pumps and three pressure filters. The copper concentrate storage tank will provide an operational surge time of 15 hours while the lead will provide 17.5 hours and the zinc 13 hours capacity prior to the filtration stage. The pressure filter will dewater the slurry to produce a filter cake containing nominally 9 to 10% (w/w) moisture.
Copper and zinc filter cakes will be stored on separate stockpiles inside the concentrate storage shed. The lead concentrate will be stored in a lead storage bin. Both copper and zinc concentrate will be loaded into half height containers for road transport to the bulk freight terminal at Port Kembla. Lead concentrate will be bagged into one tonne bulka-bags for transfer to a sea container, dispatched either through Port Botany or Port Kembla.
Paste Backfill Plant
Final flotation tailings from the zinc circuit will be pumped to a cluster of de-sliming cyclones. Cyclone underflow will gravitate to a paste filter feed tank. The underflow from the de-sliming cyclones will be transferred to a 500m³ capacity paste filter feed tank. A variable speed paste filter feed pump will transfer the material to a single horizontal belt vacuum filter at a feed density of 60% solids. Filter cake will be discharged into the feed chute of the dual shaft continuous paste mixer along with binder dosed at a proportion of the measured dry weight of the feed.
Tailings Thickening
The final tailings, consisting of the talc cleaner concentrate and the de-sliming cyclone overflow, will be transferred to an 18m diameter high rate final tailings thickener. Flocculant will be added to increase the settling rate and underflow density to between 45 and 55% solids (w/w). Underflow will then be pumped to TSF4.
Key reported parameters
| Parameter | Units | Design Value | Basis |
|---|---|---|---|
| Annual throughput (50/50 basis) | tpa | 1,500,000 | Design |
| Feed copper grade | % | 1.21 | Design |
| Feed lead grade | % | 2.34 | Design |
| Feed zinc grade | % | 5.50 | Design |
| Feed silver grade | g/t | 49 | Design |
| Feed gold grade | g/t | 0.56 | Design |
| Copper concentrate grade | % | 22 | Design |
| Copper recovery | % | 68 | Design |
| Lead concentrate grade | % | 45 | Design |
| Lead recovery | % | 65 | Design |
| Zinc concentrate grade | % | 45 | Design |
| Zinc recovery | % | 70 | Design |
| Underground feed primary grind size (P80) | µm | 75 | Design |
| TSF reclaim material primary grind size (P80) | µm | 30 | Design |
| Concentrate regrind grind size (P80) | µm | 20 | Design |
Project website: https://www.develop.com.au/woodlawn-project/
Technical qualifications
This technical report presents a Preliminary Economic Assessment (PEA) level study. The process design is based on co-treatment of the underground resource and retreatment of process tailings from existing tailings storage dams, with the FEED study completed in 2012 (Sara, 2012) and metallurgical testing outlined in Section 13.0 of the report. The blend ratio of 50% fresh underground feed with 50% reclaimed tailings may be refined during future studies. The process plant description and design criteria are based on proposed design and testwork results, not on actual operating data from a currently operating plant. Historical data from Woodlawn operations was used only for the selection of the two stage crushing circuit based on similar applications.
*Source: Woodlawn Project PEA – 29 May 2015, Sections 17.1, 17.2, 17.3*
