Environmental Engineering Reference
In-Depth Information
4.5.1 Leather Tanning Industry
The leather tanning industry, in a sense, has an unique position in the food and nonfood
agroprocessing industries in that it has to rely on the availability of an animal source for
its raw material. The different kinds of leathers produced from raw hides and skins are
functions not only on the production process, but also of the source material, i.e., the ani-
mal species. The variety of source material include (a) cattle, sheep, pigs, and horses for
hides and (b) reptile, crocodile, snake, etc., for the more exotic leathers. The size of the total
industry, together with the range in sizes of the industries and variety of raw materials
(animal species) devoted to production of hides and leathers, requires one to pay attention
to the impacts on the geoenvironment in the processing of the raw material into product
form (see Figure 4.8). The estimates are that about 2 billion m 2 of leather are produced
a year with a market value of about $40 billion. When some of the leather material is
processed into consumer goods, for example, leather footwear, where it is estimated that
about 65% of the 2 billion m 2 is utilized, the market value of the produced footwear is in
the order of about $150 billion. There is an interesting counter argument that states that
production of leather is in effect an environmental conservation effort since it removes the
burden of disposal of the hides and skins of slaughtered animals.
There is intensive use of water mixed with various additives during the beamhouse pro-
cess shown in the upper portion of Figure 4.8, and also in the many other processes accom-
panying tanning and fat liquor and inishing. The additives and aids used in the diverse
Beamhouse
Muscle, fat, excess tissue
Hair
removal
Salts
Cured
skins
treated
with salt
Lime and
sodium
sulfate
Fleshing
Soaking
washing
Leaves, bark, oak, hemlock, etc.
Vegetable
tanning
Bating
Cr 2 (SO 4 ) 3
Enzymes with sulfate
or chloride
Chrome
tanning
Pickling
pH ≤ 3
Fat
liquor
= Liquid and/or
solids discharge
Leather
finishing
Solvents, lacquer, pigments, wax, etc.
Oils and greases
FIGURE 4.8
Major processes in leather tanning. The process used to remove hair and the outer protein layer from hides is
called bating (middle right-hand process shown in the diagram). Note: Additives and aids used in the various
processes and also the many discharge points denoted by the broader arrows.
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