Anaconda Mining has successfully completed an extensive array of circuit upgrades and regularly scheduled maintenance with minimal downtime at its Pine Cove mill in Newfoundland. Anaconda planned to make modifications to various areas of the mill, precipitated by the replacement of its two rotary drum filters. As a result, during the latter part of September and early October, the Pine Cove team installed new drum filters, relined the primary ball mill, converted a pregnant solution tank to be a fourth leach tank, added a new pregnant solution tank, modified all leach tanks and performed other routine maintenance items.The scheduled upgrades and maintenance work included various items in both the front end (grinding/flotation) and back end (leaching/filtration) of the mill. As such, the modification program was divided into stages to minimise shutting down the entire mill and enable certain portions of the circuit to operate while work was done in other areas.
On September 19, 2011, grinding and flotation were suspended to allow ball mill relining and flotation circuit maintenance. The profile of the replacement lifters is expected to sustain target production rates during times when crushed feed is coarser and/or harder. In addition, other routine maintenance items were addressed such as repairs to the feed chute, wear and tear inspections, preventative maintenance associated with electrical equipment and installation of a new impeller and stator in the SFR flotation cell. This stage of the plant upgrades was completed on September 24 allowing the resumption of grinding and flotation to fill the leach tanks.
During the same period, the leach and filtration circuits continued to process circuit inventory from the leach tanks. As each leach tank was drained, it was converted to an “up-comer” configuration with larger baffles to assist in maximizing leach recovery. The previous configuration was susceptible to losses during times of high flotation production and required much greater operator attention. In addition, a new collection sump for leach product was fabricated and installed to allow leached product to be pumped to the new drum filters which are 3 m higher than the original units. Also, the sump offers more operating flexibility in case there is a change in retention time or maintenance is required.
Beginning on September 25, the filtration circuit was decommissioned to allow for the installation of new drum filters. The new Rotary Vacuum Drum Filters (RVDF) installation was completed on October 3, followed by cloth installation, re-pulper and new pump discharge installation. The units were fully commissioned and fully operational on October 7. The actual installation was completed on schedule, although some modifications to the platforms were necessary for safety and operational improvements.
The new drum filters have considerable flexibility to allow the two units to be operated in series, parallel or taken off-line individually for maintenance, thus minimising downtime. The new feed pump system is expected to provide operators more precise control in feed rate to allow maximum throughput during fluctuations in concentrate production.
Additional plant upgrades during the period included a new pregnant solution tank with a 40,000-litre capacity. With a new tank, the original pregnant solution tank was reconfigured to a leach tank, providing an additional 40 hours of retention time and greater capacity to the leach circuit.
Since the RVDF filters became fully operational, the Pine Cove team has been working to optimise the modifications made in the circuit, balancing the flow of material and regaining a steady state. The company expects to return to normal operating parameters throughout the entire circuit by the end of October, at which time, it can measure the impact of the modifications on the mill’s results.
President and CEO, Dustin Angelo, stated, “The many circuit improvements undertaken recently are expected to complement the mill upgrades made last summer and help us consistently operate at target levels. Although Pine Cove just started full production, the mill has already exhibited positive signs that the recent modifications will prove to have a long-term benefit. Most importantly, the company recognises and appreciates the cooperation and effort by both its employees and the various contracted forces while these modifications were performed. All work was performed without a single safety incident adding to the Company’s continued safety achievements.”
