Encyclopedia of Environmental Science and Engineering, Volume I and II

110 AIR POLLUTION SOURCES

Part 2. Major Air Pollution Sources (continued)

Mineral products industry Nature of activity Type of air pollution problems

bituminous and authorite coal. The coal is

screened, classified, washed and dried at coal

preparation plants.

CONCRETE BATCHING Concrete batching involves the proportioning of

sand, gravel, cement, and water by means of

weight hoppers and conveyors into a mixing

receiver.

Particulate emissions consist primarily of cement dust,

but some sand and aggregate dust emissions do

occur during batching operations.

FIBERGLASS

MANUFACTURING

Fiberglass manufactured by melting various raw

materials to form glass, drawing the molten

glass into fibers, and coating the fibers with

an organic material.

The major emissions from fiberglass manufacturing

processes are particulates from the glass melting

furnace and the product coaling line.

FRIT MANUFACTURING Raw materials such as borax, feldspar, sodium

fluoride and soda ash are melted and then

quenched with water to produce shattered

small glass particles—called frit. The frit

particles are then ground into fine particles

used in enameling iron and steel or in glazing

porcelain or pottery.

The major emissions from frit-smelting operations are

dust and fumes (usually condensed metallic oxide

fumes) from the molten charge. A small quantity of

hydrogen fluoride also can be detected in the

emissions.

GLASS MANUFACTURE Nearly all glass produced commercially is

either soda-lime, lead, fused silica,

borasilicate, or 96% silicate. Soda lime glass,

being of the largest type, is produced on a

massive scale in large, direct fired,

continuous melting furnaces in which the

blended raw materials are melted at 2700 to

form glass.

Emissions from the glass melting operation consist

primarily of particulate (only a few microns in

diameter) and fluorides, if fluoride-containing fluxes

are used in the process.

GYPSUM Gypsum or hydrated calcium sulfate is a

naturally occurring mineral which hardens

when in contact with water to form a solid

crystalline hydrate. Gypsum is an important

building material, and if it loses its water of

hydration, becomes plaster of paris.

Gypsum rock dust and partially calcined gypsum dust

are emitted into the atmosphere from the grinding

and mixing of the gypsum material.

LIME MANUFACTURING Lime (CaO) is the high temperature product of

the calcination of limestone (CaCO 3 ). Lime is

manufactured in vertical or rotary kilns fired

by coal, oil, or natural gas.

Atmospheric emissions in the lime manufacturing industry

include the particulate emissions from the mining,

handling, crushing, screening, and calcining of the

limestone and the combustion products from the kiln.

MINERAL WOOL The product mineral wool is made by firing

charge material (slag wool and rock wool) in

a furnace with silica rock and coke, into long

fibrons tails for a “blanket” of wool.

Gases such as sulfur oxides and fluorides are major

emissions from cupolas or furnace stacks. Minor

particulate emissions are found in existing fumes.

PERLITE MANUFACTURE Perlite is a glassy, volcanic rock consisting of

oxides of silicon and aluminum combined as

a natural glass by water of hydration. By a

process called exfolication, the material is

slowly heated to release water of hydration

and thus expand the spherules into low-

density particles used primarily as aggregate

in plaster and concrete.

A fine dust is emitted from the outlet of the last product

collector in a perlite expansion plant. In order to

achieve complete control of these particulate

emissions a bag-house is needed.

PHOSPHATE ROCK

PROCESSING

Phosphate rock preparation involves the

benefication to remove impurities, drying to

remove moisture, and grinding to improve

reactivity.

Emissions in the form of fine rock dust may be

expected from drying and grinding operations.

SYNTHETIC FIBERS Synthetic fibers are classified into two major

categories—semi-synthetic, or “True

synthetic.” Semi-synthetics, such as viscose

rayon and acetate fibers, result when natural

polymeric materials such as cellulose are

brought into a dissolved or dispersed state and

then spun into fine filaments. True synthetic

polymers, such as nylon, orlon and dacron

result from addition and polymerization

reaction to form long chain molecules.

In the manufacture of viscose, rayon, carbon disulfide

are the major gaseous emissions. Some examples of

minor pollutants emitted from the drying of the

finished fiber are hydrocarbons and oil vapor (mist).

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