Tuesday, 15 October 2013

A fascinating visit to Minera Valle Central

Today I took part in a visit to Minera Valle Central, an optional day in the Procemin '13 programme. It was perhaps the most interesting mine visit that I have ever made, so it was surprising that of the 300+ delegates registered for the conference, only about a dozen signed up for this.

Valle Central started operating in 1992 with the purpose of recovering copper and molybdenum from the concentrator tailings of Codelco's El Teniente Division, the world's largest underground copper mine, fed to the plant by gravity flow in a 40km long launder. In the first stage, the operation was focused on the treatment of the fine fraction of the tailings, operating a 100,000 tons per day flotation plant, in a novel cascade arrangement, resulting in a low grade concentrate, which could then be upgraded in a conventional flotation plant.

After 1992, Valle Central developed an expansion program to increase its production, by incorporating the recovery of the copper contained in the coarse fraction of the tailings. This coarse fraction represents approximately 45% of the copper in the tailings, which could not be recovered by the cascade plant designed only for the treatment of the fine fraction of the El Teniente tailings.

By the end of 1996, Valle Central began the operation of a new 30,000 tons per day plant, incorporating grinding and classification of the coarse fraction of tailings, feeding a conventional flotation circuit.

The current process consists of classification of all tailings, assaying around 0.12% Cu, that are received daily from El Teniente, as well as tailings assaying around 0.3% Cu recovered by high pressure monitoring from the old tailings dump, grinding the coarse fraction in closed circuit, followed by conventional flotation, recovering a concentrate from the fine fraction, and producing final saleable copper and molybdenum concentrates. In 2012 the plant produced 23,000 tones of copper and 970,000 lbs of molybdenum.

What was particularly fascinating was the process of 'cascade flotation', unique to this operation. I will not attempt to describe it now- I am preparing a YouTube video of the process which I hope to have ready next week.

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