Extracting and purifying metals

 

Issues

Activated carbons are used in the adsorption of certain metallic compounds, notably gold, which uses different extraction processes. In use for nearly twenty years and implemented by PICA, these processes allow for the use of low-grade ores and full extraction of the metal.

The price of the precious metal and the performance of these techniques continue to make gold extraction from iron ore a profitable operation, even if sometimes only a gramme of gold per ton of iron ore is extracted from deep underground!

Activated carbons constitute a key element in the viability and profitability of these mining operations.

Targeted compounds

  • gold
  • copper
  • zinc
  • magnesium

Ore cast iron

Ore cast iron

Solutions

The ore is ground to a granulometry of 75 microns. It is then added to a sodium cyanide mixture that is designed to dissolve the gold in the form of gold cyanide. Lime is added in order to maintain the pH within the range of 9 and avoid the release of hydrogen cyanide; a lethal gas.

This mixture is then placed in contact with activated carbons at a rate of 5 to15 g of carbon per litre of mixture via a reverse flow system. The gold cyanide is adsorbed by the carbon and the loaded carbon is removed - what remains is gold cyanide in a concentrated solution called gold rich liquor. This liquor is then electrolyzed and the gold is placed on iron electrodes. The resulting gold has a high level of purity. The regenerated activated carbon is then re-used in a new cycle; small process losses are compensated by adding a small percentage of new carbon.

PICA supplies coconut-based activated carbon to several mining industries located in Asia, North and South American, Australia, and Africa.

Its range of products and services is set apart from that of its competitors. PICA has great expertise in the entire extraction process: assisting clients in the adjustment of parameters of extraction lines; in the analysis of yields and the optimum use of carbons. The laboratory at its Vierzon plant plays an essential role in this respect by carrying out performance measures on carbons at different stages of their life cycle.

The activated carbons offered by PICA for these applications are extremely hard, protecting against losses through abrasion (and consequently in adsorbed gold) found among the lower grade carbons on the market.

The PICA approach

Focus on non-significant site testing:

It is commonplace to carry out adsorption tests on gold production sites. However, caution is necessary as adsorption kinetics are highly influenced by pH and the presence of cations (ionic solution force) In the same way, gold adsorption capacity must be realized through very short contact times (a few hours) that are more representative of the process. This is the reason for PICA developing an original method of measurement to avoid such parameters and incorrect results. This skill is offered to gold producers in order to help them optimize the in situ reactivation of activated carbons. This is also beneficial to the client.

In addition, PICA's activation procedure allows activation at the centre, to ensure the activated carbons retain optimum adsorption capacity despite abrasion.

The dedicated line of PICA products and services:

PICAGOLD