Hydrometallurgical Processes

Of the many processes that have been proposed for the hydrometallurgical pro­duction of copper, the majority have been developed only as far as bench scale.

The driving force behind hydrometallurgical processes is environmental protec­tion, when no SO₂ is produced from sulphide concentrates, but sulphides are ox­idised to water soluble sulphates or preferably to elemental sulphur, which is in­ert and can be stored safely .

Most sulphidic concentrates also contain iron. The problems of iron disposal can be illustrated by the zinc industry, where jarosite, goethite and haematite proc­esses have been used for a long time. The key requirements for a hydrometallur­gical sulphide concentrate process are not dictated by the quality of copper, which is easy to achieve with SX-EW, but rather the fates of the major by-products, sul­phur and iron. These problems have not yet been solved well enough.

The leaching processes developed far enough that they can be presumed to be emerging techniques, are the Intec process and Cominco's CESL process. The development of the bioleaching of chalcopyritic copper concentrates is also pro­ceeding fast, as Billiton is developing a “Biocop”-process.

Conclusions and Recommendations

About 90 % of the world’s copper production from ores is now manufactured from sulphidic ores by pyrometallurgical techniques. Hydrometallurgical copper pro­duction has, however, become more important during the last decade. In the year 2000 more than 20 % of copper is expected to be produced by the leaching of cop­per ores or concentrates.

Only the pyrometallurgical copper process is used in Finland to recover cop­per from copper concentrates. Selenium, tellurium, silver, gold, platinum and pal­ladium are recovered in the process as by-products.

The pyrometallurgical treatment of copper sulphide concentrates common­ly includes two types of operations, smelting and converting. In the smelting phase, part of the sulphur and iron in the concentrate feed is oxidised with oxygen-en­riched air at about 1,200°C and a molten sulphide phase (matte) rich in copper is produced. Copper converting consists of air oxidation of the molten matte from smelting. Converting removes the iron and sulphur from the matte and produces crude molten metallic blister copper. The slag formed is discarded after a purifica­tion step. Blister copper is fire-refined and cast into anodes. The anodes are elec­trorefined to pure copper cathodes. The remaining anode slime is further treated to recover the remaining metals.

The main solid waste from the process is the remaining slag which has to be stored in a tailings area. Liquid effluents from pyrometallurgical processes are of minor importance because these processes are essentially dry. Liquid effluents result from the:

1. cooling water system;

2. from the sulphuric acid plant attached to the smelter ;

3. from wet gas cleaning systems.

Wet gas cleaning systems produce a weak acid. They also collect arsenic, mercury, selenium and fine dust particles containing other impurities. The major environmental problem results from the release of SO₂ and particulate emissions.

The best available technique to produce copper from sulphidic concentrates consists of the following unit processes:

• The concentrates are stored indoors and dried in multicoil steam dryers.

• A loss-in-weight feeding system is used to feed the concentrate.

• The flash smelting flash converting process is used.

• The slag is cleaned.

• Blister copper is refined in the anode furnace and cast into anodes.

• Copper anodes are electrorefined to cathodes using permanent cathodes.

• The cleaned gas stream from the furnaces is routed to a modern double con­tact acid plant.

The plant is equipped with a good environmental control system.