Encyclopedia of Environmental Science and Engineering, Volume I and II

108 AIR POLLUTION SOURCES

Part 2. Major Air Pollution Sources (continued)

Metals industry Nature of activity Type of air pollution problems

METALLURGICAL COKE

MANUFACTURE

Coking is the process of heating coal in an

atmosphere of low oxygen content, i.e.,

destructive distillation. During the process

organic compounds in the coal break down to

yield gases and a relatively non-volatile

residue.

Visible smoke, hydrocarbons, carbon monoxide, sulfur

dioxide, nitrogen oxide and ammonia originate from

by-product coking operations.

COPPER SMELTERS Copper is produced primarily from low-grade

sulfide ores, which are concentrated by

gravity and subjected to melting and

purifying procedures.

The raw waste gases from the process contain significant

amounts of dust and sulfur oxides.

FERRO ALLOY PRODUCTION Ferro alloys is the generic term for alloys

consisting of iron and one or more other

metals. The major method used to produce

ferro alloy for steel making is the electric

furnace process. In this process suitable

oxides are reduced to the appropriate metals.

Most of the emissions of carbon monoxide and

particulates (dust) are a direct result of the electric

furnace, which uses carbon as the reducing agent.

BRASS AND BRONZE INGOTS

(COPPER ALLOYS)

Obsolete domestic and industrial copper-bearing

scrap is the basic raw material of the brass

and bronze ingot industry. The ingots are

produced from a number of different furnaces

through a combination of melting, smelting,

refining, and alloying of the process scrap

materials.

The exit gas from the furnaces may contain fly ash, soot

and smoke and some zinc oxides. Other particulate

emissions include the preparation of raw materials and

the pouring of ingots.

GRAY IRON FOUNDRY The major type of furnace used to produce gray

iron castings is the cupola, which uses an

extremely hot bed of coke to melt the iron.

Emissions from cupola furnaces include CO dust and

fumes, smoke, and all vapors.

SECONDARY LEAD

SMELTING

Furnaces similar to the ones mentioned above

are used to melt impure leaded scraps into

desirable products (hard-lead, semi-soft lead,

and pure lead).

The primary emissions from lead smelting are

particulates, lead oxides, and carbon monoxides.

SECONDARY MAGNESIUM

SMELTING

Magnesium smelting is carried out in crucible or

pot type furnaces charged with magnesium

scraps, melted and poured into perspective

molds.

Emissions from magnesium smelting include particulate

magnesium (MgO), oxides of nitrogen, sulfur dioxide

and chloride gases.

IRON AND STEEL MILLS To make steel, iron ore is reduced to pig iron,

and some of its impurities are removed in a

blast furnace. The pig iron is further purified

in other processes (open hearth, Bessemer

converters, basic oxygen furnaces, or electric

furnaces).

Particulates and carbon monoxide are the major pollutant

emissions resulting from the various furnace reactions.

LEAD SMELTERS The ore from primary lead produced contains

both lead and zinc. After melting, the metals

are concentrated.

Effluent gases from the various concentrating processes

include considerable particulate matter and sulfur

dioxide.

ZINC SMELTERS Most domestic zinc comes from zinc and lead

ores. Another important source of raw

material for zinc metal has been zinc oxide

from fuming furnaces, the roasted are

electrolytically purified.

Dust, fumes, and sulfur dioxide are evolved from zinc

concentrate roasting.

SECONDARY ALUMINUM

OPERATIONS

Secondary aluminum operations involve making

lightweight metal alloys for industrial castings

and ingots. Copper, magnesium, and silicon

are the most common alloying constituents.

Emissions from secondary aluminum operations include

fine particulate matter and small quantities of gaseous

chlorides and fluorides.

STEEL FOUNDRIES Steel foundries produce steel castings by melting

steel metal and pouring it into molds. The

basic melting process operations are furnace

charging, melting, tapping the furnace into a

ladle and pouring the steel into molds.

Particulate emissions from steel foundry operations

include iron oxide fumes, sand fires, graphite and metal

dust. Gaseous emissions from foundry operations

include oxide of nitrogen, oxides of sulfur, and

hydrocarbons.

SECONDARY ZINC

PROCESSING

Zinc processing includes zinc reclaiming

(separation of zinc from the scrap), zinc oxide

manufacturing (distilling metallic zinc into

dry air stream), and zinc galvanizing (flux

cover over zinc).

A potential for particulate emissions, mainly zinc oxide,

occur, if the temperature of the furnaces is very high

(100°F). Small quantities of ammonia chloride,

nitrogen oxides, and carbon monoxides are also emitted

into the atmosphere.

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