Visualizing Environmental Science

Economic Geology: Useful Minerals 305

Ore

Air shaft Main shaft

Overburde

n Overburden

Ore

c. Subsurface mining In a shaft mine, a hole is dug straight

through the overburden to the ore, which is removed up through

the shaft in buckets.

d. Subsurface mining In a slope mine, an entry to the ore is dug

at an angle so that the ore can be hauled out in carts.

or collapsing walls, and prolonged breath ing of dust in

subsurface mines can result in lung disease.

Subsurface mining may be done with under ground

shaft mines or slope mines. A shaft mine, often used for

mining coal, is a direct vertical shaft to the vein of ore

(Figure 12.6c). The ore is broken up underground and

then hoisted through the shaft to the surface in buckets.

A slope mine has a slanting passage that makes it possible

to haul the broken ore out of the mine in cars rather

than to hoist it up in buckets (Figure 12.6d). Sump

pumps keep a subsur face mine dry, and a second shaft is

usually installed for ventilation.

Processing Minerals Processing minerals often in-

volves smelting. Purified copper, tin, lead, iron, manga-

nese, cobalt, or nickel smelting is done in a blast furnace.

Figure 12.7 shows a blast furnace

used to smelt iron. Iron ore, lime-

stone rock, and coke (modified

coal used as an industrial fuel)

are added at the top of the fur-

nace, while heated air or oxygen

is added at the bottom. Chemical

reactions take place throughout the furnace as the ore

moves downward: The iron ore reacts with coke to form

molten iron and carbon dioxide, whereas the limestone

reacts with impurities in the ore to form a molten mix-

ture called slag. Both molten iron and slag collect at the

bottom, but slag floats on molten iron because it is less

dense than iron. The slag is cooled and then disposed of.

Note the vent near the top of the iron smelter for exhaust

gases. If air pollution control devices are not installed,

many dangerous gases are emitted dur ing smelting.

smelting The pro-

cess in which ore is

melted at high tem-

peratures to separate

impurities from the

molten metal.

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Towerlike furnaces separate metal from impurities in the ore. The

energy for smelting comes from a blast of heated air.

1. How does mineral consumption differ between
   highly developed and developing countries?


2. What are the steps involved in surface mining?
   in subsurface mining?


3. Why and how are minerals smelted?

Iron ore,

coke, and

limestone

Exhaust

gases

Hot gases

used to

preheat air

Molten iron

Preheated air

or oxygen

Molten slag

230 °C

525 °C

945 °C

1510 °C

Adapted from Joesten, M.D., and J.L. Wood.

World of Chemistry

, second editon.

Philadelphia: Saunders College Publishing (1996).