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New environment-friendly smelting technology aims to enter platinum industry

9th August 2013

By: Sashnee Moodley

Senior Deputy Editor Polity and Multimedia

  

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T o satisfy the need for more environment-friendly smel- ting technology in the platinum industry, minerals and metallurgical specialist Mintek developed and piloted, among others, the ConRoast process, which it hopes to commercialise in the next few years.

The process, which is licen-sed to mine-to-metal specialist Jubilee Platinum, treats nickel/copper and platinum-group metal (PGM) sulphide concentrates.

It is based on the removal of sulphur by roasting prior to smelting, followed by the smelting of the dead-roasted concentrate in a direct current (dc) arc furnace using an iron-based alloy as a collector for nickel, copper, cobalt and PGMs.

The technology comprises a roaster, dc furnace and an atomiser. The alloy product from the smelting step is water-atomised to allow for the rapid leaching of the fine particles.

Mintek’s pyrometallurgy division acting manager Isabel Geldenhuys says furnaces in the platinum industry traditionally use matte smelting, which is the treatment of sulphide ores or concentrates with enough heat to melt the sulphide minerals in the ore or concentrates to reach a molten metal sulphide phase.

The ConRoast process aims to deal with environmental concerns such as the release of excessive sulphur emissions.

The patented process uses reductive smelting in an open-arc dc smelting process to produce an iron alloy, in which the valuable metals are collected. Owing to the properties of dc smelting, process temperature control is not an issue.These furnaces operate with a relatively independent power supply and, as such, power control is not strongly reliant on the slag composition in the furnace.

“Materials are roasted prior to being fed into the dc furnace to remove sulphur content in a controlled environment. The materials, which now contain low levels of sulphur, are fed hot into the furnace. This reduces the energy requirement for the smelting step, as well as dra- matically reducing sulphur emissions. The dc arc furnace is well known for its ability to handle fine-feed materials and is operated under strong reducing conditions at high temperatures,” Geldenhuys explains.

She adds that the high temperatures assist in avoiding the commonly experienced problem of magnetite or chromite spinel build-up in a furnace. Following this process, alloy smelting, instead of matte smelting, is employed.

This smelting process is ideally suited to the upper group two (UG2) ores rather than Merensky ore. UG2, which contains higher amounts of chromium and chromium oxide, is a challenge for matte smelting furnaces to process on its own, as it can result in spinel build-up in furnaces.

Further, with regard to add-ressing energy concerns, dc furnaces are well sealed and the technology can indirectly deal with energy concerns as reductive smelting creates carbon monoxide, which can be used for cogeneration purposes, Geldenhuys points out.

Mintek has been trialling dc smelting technology at its facility in Johannesburg for global mining giant Anglo American for the last year as part of a two-year pilot contract.

“We hope to assist junior miners through new technology to gain access to smelting technology and, therefore, add value to their resource, as many juniors currently sell their concentrate to bigger companies for processing. We hope the new technology will create jobs and local wealth,” Geldenhuys says.

She says Mintek also aims to develop recycling technologies using dc furnaces to access the urban mining concept, which entails encouraging local communities to collect electronic scrap to be recycled.

In line with this, the company plans to develop recycling technology in the form of a small mobile furnace to pot- entially provide small-scale processing options.

Recycling of electronic waste in South Africa could, therefore, become community-based projects, enabling all citizens to collect and recycle through accessible community centres where sorting and separation could create jobs and business opportunities.

Edited by Tracy Hancock
Creamer Media Contributing Editor

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