Refurbished Larox® pressure filter solves dewatering constraints at Xstrata Nickel Australasia`s Cosmos site in WA

Despite low nickel prices during the 2008-2009 global financial crisis and unexpected sea freight delays, Metso and Cosmos worked closely together during the filter project to overcome these obstacles. The end result was the commissioning of a large, modern pressure filter at Cosmos with 28% more capacity than the old one and within a 9-month timeframe that coincided with Cosmos’s mill optimization.

With its dewatering constraints solved by a freshly painted, refurbished, and modernized Larox pressure filter, Cosmos is ready to produce new benchmark dewatering rates. These improved rates will meet Xstrata Nickel Australasia’s (XNA’s) production target of 13k nickel tonnes per annum (Ni t pa) for 2010, a significant increase from 7.5k Ni t pa in 2009. 

Cosmos is a remote nickel-sulphide operation situated about 900 km northwest of Perth in Western Australia. The mine produces high-grade nickel concentrate containing 18-22% nickel that is trucked south to Esperance Port and shipped to Xstrata Nickel’s Sudbury smelter in Canada.

Throughout 2009, Cosmos systematically upgraded and optimized its processing plant in preparation for XNA’s doubled 2010 production target. The plant’s debottlenecking process included a review of a 17-year-old Larox pressure filter, inherited from the Cosmos site when XNA bought out Jubilee Mines in February 2008.

The Cosmos filter review identified that the Larox^® pressure filter model Larox^® PF 25/32 (25 m²) was working to full capacity for its configuration and that its small size would become a constraining factor in meeting XNA’s higher production rate. Service technicians from the Metso Perth office were sought for a filter audit, as well as a quote for upgrading and modernizing the existing equipment to a 32/32 capacity. 

Metso's filter assessment found that the structural components were badly corroded after extensive outdoor weathering. Metso deemed the filter’s life to be very limited and that an upgrade and modernization of its mechanical parts were not in Cosmos’s best interest long term. 

Concurrently planned with debottlenecking the dewatering constraints, Cosmos’s mill optimization was scheduled for completion within nine months. This timing, however, didn’t allow for a longer delivery time that was required for a brand-new filter replacement. In response, Metso searched worldwide for an available, suitable, second-hand pressure filter.

Providentially, a hydraulic Larox^® pressure filter model Larox^® PF 32/38 (32 m 2 ) was sitting unused in England, leftover from a previous starch and chemical operation. It was perfect for Cosmos’s needs. Further expandable to a maximum capacity of 24 plates (38 m 2 ) (i.e. a Larox^® PF 38/38 size), the available second-hand filter could also be easily converted to an abrasive minerals slurry application.

During the filter’s shipping to Finland, its refurbishment and modernization, then it's further shipping to Perth, Metso kept Cosmos continually up-to-date with the filter’s progress. As a result, when unexpected logistics delays occurred during the filter’s shipping travels, Cosmos was able to readily accommodate these reports into the filter’s installation schedule.

The refurbishment and modernization of this second-hand filter also produced an ecological benefit by reducing the unnecessary carbon footprint of new filter manufacture through the use of an existing one.

When the filter sailed into Perth, Metso agents quickly contacted Australian custom agents and within just a few days, the filter was released and ready for delivery to site. The filter was carefully trucked to Cosmos in an upright position with an accompanying traffic escort, arriving at its final destination by the end of July 2009.

An Metso team arrived at Cosmos a day after the filter and promptly assisted site supervisors Ross Saxby and Glenn Kearns and their teams to undertake the required installation preparations.

The old filter was removed using a mobile 180t crane and over the subsequent 11 days, the teams prepared a reinforced steel platform for bearing the weight of the new filter’s larger structure and attached load cells. The filter platform also needed additional reinforcement for bearing the weight of a fully-loaded pressure filter sized as a Larox^® PF 38/38.

The second-hand filter was successfully installed and began operating the first week of August 2009. Despite its sea freight delays, the newly commissioned filter met Cosmos’s increased production schedule, on time for Cosmos’s planned mill optimization.

Stewart Keenan, Cosmos’s maintenance superintendent, remembers Metso’s involvement at the filter changeover: “I was more than happy with the services Metso provided, particularly in the way they followed up. They were here night and day as soon as we shut the old filter off. They gave back-up support and the servicing technical guys were first-rate.”

Site General Manager, Andrew Millar, also gives credit to his Cosmos teams: “They got everything done in the timeframe and safely as well, considering the team worked in congested environments and with an 180t crane. Cosmos achieved 1 year LTR-free and 1 million man-hours LTR-free during the mill optimization period. If we had to do this project over again, we’d consider buying a second-hand filter from Metso again for sure.”

Cosmos’s refurbished and modernized pressure filter operates automatically and requires minimal attention. A 12-month warranty added to an Metso service agreement gives Cosmos’s workforce time to learn the filter’s fine-tuning needs. They are assisted by an Metso technician who is located in the vicinity for optimal customer support.

In the reconfiguring and re-piping of the processing plant, float circuitry and dewatering system, Cosmos also upgraded the SAG mill’s capacity, upsized the compressed air tank, added extra flotation capacity and installed a small ISA mill for regrinding concentrate.

The ten-year-old, second-hand filter’s new life expectancy has been extended by an additional 15 years and already producing high volumes with energy-saving benefits for Cosmos. One example is the filter’s newly affixed load cells, which are enabling optimization of the feed cycles through accurate logging of the production tonnage at regularly set intervals.

Keenan reports: “There weren’t really any hidden costs with our filter project. A couple of optimization changes were made along the way that required a separate costing. In particular, load cells were added for ensuring that cake thickness is consistent 100% of the time, saving unproductive time when using old time-based slurry feed termination parameters. We also added guards around the pinch valves to prevent any safety risk.

Metso Australia Service’s structure of four regional areas ensures Metso Service can provide extensive professional installation and maintenance capability and be close to its customer sites.

As a global filter solution provider of equipment, service and spare parts, Metso’s primary intention is to maintain ongoing cooperation with its customers. As a happy Metso customer, Keenan sums up the Cosmos filter project by saying: “All went very well. It was a really good project. There was lots of communication between Metso and Cosmos after the filter decision was made so there were no surprises. So all in all, our second-hand Larox^® filter is a success story – it came on budget, on time for production and with no injuries”.

*This case study has been written prior to the merger of Metso and Outotec.