Kitsault Molybdenum Project — 2014 Technical Report

This article outlines the recovery methods for the Kitsault Molybdenum Project, a proposed open pit operation in British Columbia, Canada, with a nominal concentrator capacity of 40,000 t/d.

Article Body

This technical report details the recovery methods for the Kitsault Molybdenum Project, an open pit development in British Columbia, Canada. The process design is based on a concentrator with a nominal processing capacity of 40,000 t/d of ore, sized to the 75th percentile of ore characteristics, meaning the plant can deliver on, or better than, the target throughput for at least 75% of the ore. Metallurgical testwork used samples from two drilling campaigns, one in 2008 and the other in 2011, to establish the process design criteria for the proposed facilities.

The mineral processing plant is designed around conventional technology and proven equipment. The flowsheet incorporates a SABC (SAG mill, ball mill, pebble crusher) grinding circuit followed by bulk rougher–scavenger flotation. The bulk concentrate undergoes a multi-stage molybdenum cleaning circuit, including regrinding, to produce a final molybdenum concentrate. A separate circuit, using flotation cells, is designed for primary silver recovery and desulfurization, producing a saleable silver concentrate. The report also details process material requirements, water supply, and identifies risks related to grinding hardness, recovery confirmation, and silver variability.

Critical Data

Overview

The Kitsault Molybdenum Project is designed as an open pit operation with a concentrator throughput of 40,000 t/d, based on the 75th percentile ore characteristics. The process design criteria were developed from metallurgical testwork on samples from the 2008 and 2011 drilling campaigns. Where data was unavailable during flowsheet development, criteria were developed from reasonable assumptions, benchmarking, and modern modelling and simulation techniques. The plant is designed to process ore with a nominal feed grade of 0.11% Mo, with a target molybdenum recovery of 90% and a nominal silver concentrate grade of 2,000 g/t.

Key Process Stages

Ore from the open pit is crushed and stored in a coarse ore stockpile with a live storage capacity of 41,000 t. The grinding circuit is a SABC configuration. SAG mill discharge passes over a vibrating screen; the coarse fraction reports to a pebble crusher and is recycled to the SAG mill. Screen undersize is pumped to a cyclone pack, with the coarse material reporting to a 14 MW ball mill for grinding to near liberation size. Cyclone overflow feeds the rougher–scavenger bulk flotation circuit, which consists of six 300 m³ tank cells.

The bulk rougher–scavenger concentrate, containing molybdenite, some pyrite, and entrained non-sulphide gangue, is cleaned in a series of flotation stages. The 1st cleaner concentrate is reground, and the 1st cleaner tails report to the scavenger regrind thickener along with the scavenger concentrate. The reground 1st cleaner concentrate is upgraded in one mechanical and three column flotation steps, for a total of five cleaning stages, including a regrind of the 3rd cleaner concentrate, to produce the final molybdenum concentrate.

The molybdenum concentrate is thickened in the molybdenum thickener before being treated in a lead leaching circuit with hydrochloric acid. This step ensures the material meets customer specifications before shipment. The final silver concentrate from the silver circuit is thickened, filtered, and stored in a concentrate shed prior to shipping. Tailings from the cleaning circuits are processed through a de-pyritization flotation step. The resulting sulphide-depleted tailings report to the tailings cyclones, while the recovered sulphide material is either processed in the silver recovery circuit or sent directly to the final sulphide tailings disposal box. Final sulphide tailings are sent to the Tailings Management Facility (TMF) and disposed of sub-aqueously.

Additional Interesting Data and Summary

The process water system includes a tank sized for two hours’ requirement, with most water used in grinding and flotation. Fresh water is supplied from Clary Lake and pumped to a fresh/firewater tank at the mill site. Potable water is treated through a chlorination process and stored in a dedicated tank. Fresh water is used for clean water requirements, including spray water in flotation columns, cooling water for mill drives and lubrication systems, cooling water for plant air compressors, reagent mixing, and gland seal water. If the freshwater system is interrupted for a significant period, these needs can be met from the process water system.

All flotation and leaching reagents are commonly available bulk commodities, though the report notes that regrind media and regrind mill components may be single source, with alternative fine regrinding technologies to be examined in detailed engineering. Lime for pH control is delivered as pebble quicklime from Southern British Columbia, slaked and mixed on site. Fire prevention precautions are required in the concentrator due to reagent use.

Key Processes

• SABC grinding circuit (SAG mill, ball mill, pebble crusher)
• Rougher–scavenger bulk flotation (six 300 m³ tank cells)
• Molybdenum cleaner circuit with five flotation cleaning steps and regrinding
• Lead leaching of molybdenum concentrate with hydrochloric acid
• Silver recovery flotation circuit with regrinding and cleaning
• De-pyritization flotation for tailings desulfurization
• Sub-aqueous tailings disposal in the Tailings Management Facility

Source: Kitsault Molybdenum Project , 2014 Technical Report, 2014.

Project website: Kitsault Molybdenum Project, 2014 Technical Report