The Angas Zinc Mine, located in South Australia, is owned and operated by Terramin Australia Ltd. The mine exceeded all production start-up expectations by using the latest technology in Outotec Larox CC filters, which is drying higher than expected grades of zinc and lead concentrate. Following commissioning in July 2008, the site was brought into full production six months early, in January 2009.
In its first year of life, the low-cost mine, with a resource of 2.4 million tonnes and situated only 60 km from Adelaide, has produced nearly 23,000 tonnes of high-grade lead and zinc concentrate by the end of its second quarter.
The mine's start-up performance far exceeded expectations, due in part to an advanced filtering and drying system. Angas' installation of two Outotec Larox CC filters for its zinc and lead concentrators is fed by two Larox Flowsys peristaltic pumps.
Hose compressions reduced by 50%
The feed pumps employ a single, bearing-mounted eccentric roller design which compresses each hose once during a 360 degree operating cycle. This feature reduces the hose compressions required by 50%, when compared to traditional peristaltic pumps that use two sliding shoes.
Filters in action
The two Outotec Larox CC filters in-situ use capillary action within ceramic discs to dewater the lead and zinc concentrates. The extracted filtrates are very high in clarity while the dried filter cakes meet required transport moisture limits (TMLs) for their ore grades.
After slurry thickening, the pumps feed the relatively coarse lead (P80, 50 μm) and zinc (P80, 71 μm) concentrates into their respective filtering system. Here, concentrates coat the ceramic disc segments during immersion in slurry baths, dewatering starts immediately via capillary action. Extracted filtrate passes through the microporous structure in each disc before being transferred away by a small 2.2 kW vacuum pump. The dried filter cake which remains is continuously scraped off as the discs rotate.
When lead grades rose higher than expected soon after installation, the filters were quickly upgraded, providing Angas with a 30% increase in filtration capacity, allowing the handling of higher lead concentrates when the ore grade is high. As a result of this upgrade, the lead filter can capably handle higher lead head grade ore and increase production while still producing filter cake under the required TML. The Outotec Larox CC filter, with new ultrasonic positioning between the discs, is currently being used by Angas at rates of 75% to 90% over a 24-hour period, depending on the ore grade being received.
The many benefits of using the Outotec Larox CC filters and Larox Flowsys Peristaltic include a plug-and-play design, no downtime is required for maintaining filter discs, only once-a-month maintenance checks are needed for filter ultrasonics and seals, and routine filter backwashing is automatic and takes only half an hour per shift. Feed pump hose leaks can be easily detected, revolution counters can record pump hose life (thereby reducing unscheduled stoppages) and processing noise levels can be kept to a minimum.
Angas's general manager John Burgess reports he is “pleasantly surprised” at the ongoing performance of his dewatering system. “It's a good mine that is professionally set out and producing on its investment because things are done right.” So much so in fact, that the Algerian government is interested in what Terramin are doing at the Angas mine for Terramin's development of its large Tala Hamza zinc deposit in Algeria.
How do Outotec Larox CC filters work?
Outotec Larox CC filters are formed with sintered alumina sectors that have a membrane with uniform micropores that create suction through capillary action. This microporous filter medium allows only liquid to flow though. The filtrate is drawn through the ceramic discs as they are immersed into the slurry bath and a cake forms on the surface of the discs. Despite an almost absolute vacuum on the filtrate side, no air penetrates the filter media. Consequently, the filters only require a small vacuum (2.2 kW) pump to transfer the filtrate from the discs to the filtrate receiver. This is in stark contrast to conventional vacuum filters that have a high leakage of air through the filter cake and therefore require a large vacuum pump.
The main stages of operation
There are five principal stages in the continuous operation of Outotec Larox CC filters. The first stage is cake forming, followed by cake drying and optional cake washing, then cake discharge, backflow washing, with the final stage being disc regeneration.
Outotec Larox CC filters are best suited to filter feed slurries with consistent, high solids concentration. The filters are used widely for dewatering base metals concentrates and a high capacity variant has also been developed specifically for fine iron ore, chromite and ferrochrome. There are thousands of Outotec Larox CC filters installed globally on applications including copper, gold, chromite, cobalt, molybdenum, iron, nickel, zinc, lead and pyrite.
Outotec Larox CC filters are highly energy efficient filters. Due to the capillary action of the filters, energy consumption for dewatering is exceptionally low. The ceramic media's micropores also ensure an extremely clear filtrate. Another advantageous design feature is that ancillary equipment is integrated into the filters, making them simple to install and operate. This simple construction requires only occasional maintenance stops and the filters run continuously without the need of operator intervention. The disc is constructed for long life, with few wearing parts – so maintenance is kept to a minimum.