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ConRoast (South Africa)

 
 

Jubilee’s unique access to the ConRoast process enables Jubilee to unlock the inherent PGE (platinum group element) values in the traditional chrome ores via the extraction of PGEs and chrome from near- or at-surface platinum containing chrome reefs.

These ores were traditionally only mined for its in-situ chrome with the PGEs either lost as part of the run-of-mine ore sale or trapped within the tailings from the chrome beneficiation process and deposited on surface. The ability of the ConRoast process to recover the PGEs from this chrome dominant ore structure affords Jubilee an unique opportunity to unlock the inherent PGE values.

Jubilee’s medium-term plans envisage constructing PGE concentrator plants capable of producing up to 15 000oz of PGEs in concentrate annually and targeting growth to reach an annual production of 50 000oz of PGEs in concentrate within five years through access to near or at-surface platinum containing chromite reefs.

Conventional ‘six-in-line’ platinum smelting technology, though well understood, is at least 30 years old and is highly polluting, particularly from emissions of fugitive sulphur dioxide gas.

   
 

However, the principal drawback of conventional technology is that it is largely unsuited to the processing of chrome-rich UG2 reef, nickel-rich Platreef ores and chrome rich LG and MG reefs, without mixing concentrates from these resources with those from the Merensky reef. The UG2’s higher concentration of chromite affects conventional smelting process by gradually choking furnaces with insoluble chrome spinels with collateral damage to furnace linings.

While the current platinum smelter operators are largely locked into their conventional plants, emerging producers have until now been constrained to having their UG2 concentrates smelted by these operators, who have to blend these concentrates with their UG2Merensky concentrates. This has significant limitations on the new producers’ capacity. Various other experimental smelting technologies have been tried over the years, but with limited success.

The ConRoast process developed, tested, proved and patented by Mintek, South Africa’s state-owned minerals technology laboratory - represents a major advance. It opens up the possibility of mining the vast tonnages of UG2 reef that form part of the platinum-rich Bushveld Complex, that otherwise may remain unexploited as the relatively easy access Merensky reef is depleted and no longer available for blending with UG2.

Fundamentally, the ConRoast process involves removing sulphur from metal sulphide concentrate prior to smelting in a DC arc furnace, which under reducing conditions produces molten iron droplets to capture PGEs, nickel, copper and cobalt . These droplets settle out into an iron alloy prior to refining the alloy recovery and separation of the individual base metals from the PGMs.

Sulphur dioxide is removed from the concentrate and captured in the roasting plant for conversion into sulphuric acid, a process that has obvious environmental advantages. ConRoast is therefore not limited by the sulphide content of metal ores and so can treat a wide range of ores. Also importantly, the DC-arc furnace using ConRoast process is not adversely affected by the chromite impurity in concentrate that characterises platinum concentrates from m UG2, LG and MG reefs, unlike the AC-arc furnaces used in conventional ‘six-in-line’ process.

Chromite in PGM concentrate is difficult to smelt in conventional lower-temperature AC-arc furnaces, as it forms high-density high melting point chrome spinels (a chrome compound of magnesia and silicate) that solidify on furnace walls and in the slag. This reduces furnace volumes and efficiencies. As a result, conventional furnaces can only accept feeds containing 1.5% to 2.5% chromite. In contrast, ConRoast process enables furnaces to accept any proportion of chromite.

Jubilee has completed a design and engineering study for its first 5 MW DC Arc ConRoast smelter.

 
 

 

 
   
 

ConRoast Photo Gallery

 
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