Microwave Assisted Recovery Of Platinum

Abstract:

Platinum metals are used in various areas of the industry preferred as catalyst. Traditional the quote of recycling is very high and the primary production is in the same scale than the as secondary production. With view of the constantly rising platinum return flows the cost structure of the secondary production becomes more relevant.The platinum containing ores are separated by grinding and flotation from the pace, even if the production of other metals is the preliminary goal. The platinum metals remain with the electrolytic refining of the by products, mostly in the anode sludge or in chemical procedures they build an insoluble residue. For the production of the individual platinum metals in general concentrates of 70-90 % are used.The concentrates are subjected to a dissolving process and the individual metals are separated first roughly and refined afterwards on the commercial purity. The platinum metal is transferred by special oxidation and reduction steps into soluble salt, that crystallizes and can be filtered off.After the first precipitation the platinum salt is not yet purely enough and special cleaning steps are always submitted. In the case of platinum sal ammoniac the salt is calcined at 800°C developing a platinum sponge. The platinum sponge is solved again. This time consuming cycle is passed through, until the platinum has the necessary purity.The main goal of the process development done by InVerTec was to reduce the process time during the calcining step and during solving the platinum by implementing microwaves with 2.45 GHz as energy source.In the paper a comparison of the conventional and micowave process is discussed. A main topic is the influence of the MW-power control (power level, pulse length, local plasma ignition) on the platinum sponge morphology.In the second part of the paper the re-dissolving process of the platinum sponge in a chorine saturated hydrochloric acid is discussed.To achieve high solving rates the temperature of the platinum has to be as high as possibly. On the other hand the solubility the chorine in the hydrochoric acid has to be as high as possible to increase the platinum conversion. But with increasing temperature of the hydrochoric acid the solubility of the chorine strongly decreases.This conflictive behavior can be overcome by microwave heating the suspension.Especially if high power MW-pulses are used the MW-heated solving process is much more effective than the conventional heated process.

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