Cementation

The precipitation of a metal from its solution by the addition of another less noble metal is known as cementation. The fundamental equation for copper recovery from copper-bearing pregnant liquors on iron is:

In practice, the copper bearing solution is passed over scrap iron, such as detinned and shredded cans. Subsequent separation, washing, reduction, and pulverizing produces a copper powder that contains considerable amounts of iron and acid insolubles, such as alumina and silica. Contamination with gangue varies and depends on the nature of the pregnant liquor.

Significant reduction in iron and alumina levels is possible through the use of V-trough or inverted precipitators that allow faster precipitation rates and more efficient iron utilization. Table 7 shows chemical analyses of cement copper from different sources. Copper and iron are present, partly as oxides.

Table 7 Chemical analyses of cement copper from various location (dry basis)

Component

Composition, wt%, for location

A

B

C

D

Total copper

75

83.0

87.4

85.0

Iron

6

2.4

0.7

10.0

Sulfur

1

0.5

1.1

Nitric acid insolubles

2

0.7

1.9

Hydrogen loss

16

Calcium oxide

0.08

Aluminum oxide (alumina)

1.2

0.5

Silicon dioxide

0.4

Lead

0.2

Oxygen

9.5

0 0

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