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New copper process floats off arsenic

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Australia ranks fourth in the world as a copper producer, with six per cent of world production, after Chile (35%), the US (10%) and Indonesia (eight per cent).

Arsenic occurs at varying levels in some copper orebodies and is a significant environmental hazard in the copper smelting process when emissions are released into the atmosphere.

The arsenic in the ore is contained in copper-arsenic sulphide minerals such as enargite and tennantite.

In Australia, miners delivering copper concentrates to smelters that contain high levels of arsenic are subject to substantial penalties, making some copper ore deposits uneconomical.

However, researchers from CSIRO Minerals have discovered that variations to the chemical flotation process widely used at mine sites to produce copper concentrates enable a much easier separation of arsenic from the copper ore. Early removal of arsenic avoids dispersing such toxic elements through downstream processing of concentrate.

The breakthrough involves using electrochemical processes during flotation. By studying individual copper minerals’ flotation behaviour, including the copper-arsenic minerals, the CSIRO team has identified several electrochemical windows that make it possible to selectively float copper-arsenic minerals from other copper minerals.

This produces a much purer form of copper concentrate with low arsenic content that can be supplied to smelters.

The process involves some changes to existing chemicals used in the separation process as well as possible changes to the flotation gas, such as the use of nitrogen instead of oxygen.

CSIRO Minerals experimental scientist Leanne Smith says depending on the concentrate grades of the ore, it may mean the difference between selling the concentrate or not, or getting the best price.

“[I]n the long term, it’s also better for the environment because you’re not sending that arsenic to the smelter,” Smith says.

“If you’re running a flotation process, then this wouldn’t be that difficult to implement,” she says.

This story first appeared in the February issue of the CSIROs Process magazine.

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