Converting Minerals to Metals - Mining and the Environment: From Ore to Metal - page 257

FIGURE 6.6
Single Stage Leaching

Solids/
Ore

Fresh Solvent

Removal of materials by dissolving
them away from solids is called leach-
ing. An example is removing salt from
salty sand by extraction with water.

Contacting

Separating

Raffinate/
Spent Ore

Extract/
Pregnant Leach Solution

FIGURE 6.7
Leaching Process Versus Copper Ore
Grade and Comminution Size

Agitated
Leach

Vat
Leaching

Heap
Leaching

Dump Leaching

6

5

Source: US Congress 1988

4

3

2

1

0

1 8 25 150

Comminution size (mm)

In hydrometallurgical processing, two routes are common for removing metals from
ores. The first route is removing metals directly from ore. As discussed in Chapter Five
this is the case when selecting heap, dump, and underground (or in situ ) leaching. The
selection of the leaching methods very much depends on the ore type, ore grade, and com-
minution size ( Figure 6.7 ). Characteristics of these leaching operations applied to copper
processing are presented in Table 6.2 . The leach cycle depends on the ore type, and applied
leaching conditions.
Oxidized copper minerals such as azurite, malachite, tenorite, and chrysocolla, are com-
pletely soluble in sulphuric acid at room temperature. Extracting copper from these oxide
ores typically involves spraying the crushed ore with a sulphuric acid solution to dissolve
the copper. In heap leaching, large piles of oxide ore are placed on impermeable pads and
are sprayed with leach solution by a sprinkler system. The leach solution percolates down
through the heap over time, picking up copper as it travels along. A central drainage sys-
tem collects the copper bearing runoff at the bottom of the heap.

Oxidized copper minerals are
completely soluble in sulphuric
acid at room temperature.