1. Sulfide minerals - most commonly present in the earths crust

a. Copper-Iron Sulfide

chalcopyrite (CuFeS2), bornite (CusFeS4)

b. Copper Sulfide

chalcocite (Cu2S)

2. Oxidized minerals- present to a lesser extent

(Carbonates, oxides, hydroxy-silicates)

Primary: ores

Secondary: scrap copper & copper alloys

Extraction of Copper:

Pyrometallurgical

Copper-Iron-Sulfides are not easily dissolved by aqueous solutions.

**Cu/Cu-alloy scrap---recovered by simple melting of high-purity scrap and smelting/refining of impure scrap**

Hydrometallurgical

Oxidized minerals, Copper Sulfide (Chalcocite)

Hydrometallurgical

Extraction of Copper

Leaching (heap), preceded by: crushing, agglomeration & acid curing, heaping

Solvent extraction Electrowinning

Ore Preparation:

Crushing, Agglomeration, Heaping

The crushed ore is agglomerated with sulfuric acid in revolving long

drums. This

(i) agglomerates the fines created during crushing and

(ii) acid cures the ore. The agglomerated material is then placed on

the leach heaps.

1. Leaching

2. Solvent

extraction

Electrolyte, 40 kg Cu/m3 Stripped cathod plates

3. Electrowinning

almost all of hydrometallurgically produced coppers are

produced by heap leaching

-sprinkling/trickling dilute H2S04-H20 solution through large

'heaps' of ore under normal atmospheric conditions

1. Heap leaching

(length of leach cycle:

days-months)

Impermeable base

Leach heaps are always built on an impermeable base (clay and/or synthetic material, see figure) . This permits complete collection of the leached Cu++ and prevents solution penetration into the underlying environment.

Ore placement

Leach heaps are laid on their impermeable base by (i) dumping ore from trucks or by (ii) stacking the ore with a mobile conveyor.

Aeration

A leach heap is a pile of ore pieces with the pieces surrounded by air. Lixiviant trickles through the heap down the ore surfaces and through cracks in the ore pieces.

Oxidized minerals are rapidly dissolved by sulfuric acid by reactions like:

CUO + H2S04 ---> Cu++ + SO4-- + H2O

Sulfide minerals, on the other hand, require oxidation, schematically

Cu2S + (5/2)O2 + H2SO4 --> 2Cu++ + 2SO4-- + H2O

in air

Pregnant solution collection

The solution then flows by pipeline from the collection trench to a pond or tank and sent from there by gravity or pumping to solvent extraction/ electrowinning for copper metal production.

__________________

Other Leaching Processes

Minor Cu leaching processes are in situ , tailings and agitation leaching of oxide concentrates and roaster calcines.

bacteria enzyme catalyst

(Thiobacillus

ferrooxidans)

2. Solvent extraction

The pregnant leach solutions produced by most leaching operations are:

(a) too dilute in Cu (1-6 kg Cu/m3)

(b) too impure (1 - 10 kg Fe/m3)

Solvent extraction provides the means for producing pure, high Cu++ electrolytes from dilute, impure pregnant leach solutions.

The process consists of:

(a) extracting Cu from aqueous pregnant leach solution into an organic extractant (oximes-aldoximes and ketoximes)

(b) separating the aqueous and organic phases by gravity

(c) stripping Cu from the organic extractant into high- H2S04 electrowinning electrolyte.

Extraction and stripping are carried out in large mixer-settlers.

3. Electrowinning

In this final step, the rich electrolyte is pumped through a series of tanks or "cells" in the Electrowinning tank house. Hanging in the tanks are insoluble lead plates, alternating with sheets of thin copper or stainless steel. Each lead plate serves as the anode pole of an electric circuit. The thin copper sheets, called starter sheets, or the stainless steel sheets, called blanks, serve as the cathode pole. A direct current passes from the anode through the electrolyte to the starter sheet or blank, causing the copper ions in the electrolyte solution to plate (attach) onto the starter sheet or blank. After six to seven days in the tank house, 100- to 300-pound copper cathodes that are 99.999 percent pure and ready for market are harvested. The electrolyte that has passed through the tank house, now depleted of its copper, is returned as "lean electrolyte" to the stripping step of the process to begin that cycle again.

Davenport, W.G., King, M., Schlesinger, M., Biswas, A.K. (2002). Extractive Metallurgy of Copper. Oxford, UK: ELSEVIER SCIENCE Ltd

U.S. EPA. (1994). EXTRACTION AND BENEFICIATION OF ORES AND MINERALS COPPER. Retrived on September 20, 2015 from http://www.epa.gov/wastes/nonhaz/industrial/special/mining/techdocs/copper/copper1a.pdf