TM 5-814-8
silver sulfide and in these forms represents mini-
Flash plating.
--Principal plating.
mal risk of toxicity.
--Rinsing.
form (Cr+6) in some bleach solutions. However,
Drying.
hexavalent chromium is reduced to the trivalent
(b) The major waste sources are rinse water
form (Cr+3) by strong reducing agents present in
overflow; fume-scrubber water; batch-dumps of
photographic wastewaters.
spent acid, alkali, or plating bath solutions; and
(e) Cyanide is present in bleaching solu-
spills of the concentrated solutions. Important
parameters include pH, cyanides, emulsifying and
tions as potassium ferrocyanide. After chemical
wetting agents, and heavy metals. Cyanide is
action by other reducing agents and by oxidation
converted to highly toxic hydrogen cyanide gas at
of silver, complex insoluble cyanide compounds are
low pH; therefore, cyanide-plating solutions must
formed. These cyanide complexes are potentially
not be mixed with acid-cleaning or acid-plating
dangerous as their degradation releases toxic
.
cyanides.
solutions.
(f) Boron is present in photographic wastes
(8) Wastes from munitions manufacture.
Wastes generated from munitions manufacture
in small quantities and is usually precipitated as
originate from manufacturing areas as well as
calcium borate.
.
loading, assembling, and packing (LAP) areas.
(7) Metal plating wastes. Metals are plated
Wastewaters are generated from the manufacture
onto both metallic and nonmetallic surfaces for
decoration, corrosion inhibition, increased wear
and use of explosive chemicals such as
resistance, or improved hardness. Commonly
trinitrotoluene (TNT), nitroglycerine, cyclonite
plated metals are copper, cadmium, chromium,
(RDX), HMX, and tetryl. The amount and compo-
nickel, tin, and zinc. The surface to be plated
sition of munitions wastewaters varies with the
explosive being produced.
serves as a cathode. An electrode made of the
(a) TNT (CH3C 6H 2( N O2)3). In TNT manu-
metal being deposited in most instances acts as
the anode. With some metals, such as in chro-
facture, toluene is reacted with nitric acid in a
mium plating, an inert anode is used and the
three-step process, using fuming sulfuric acid as
plating bath supplies the metal deposited. Nonme-
a catalyst and drying agent. Excess acids are
tallic surfaces to be plated must be made conduc-
washed away from the crude TNT, forming in a
tive by application of a conductive material such
waste stream known as "yellow water". Un-
as graphite. Metal stripping, cleaning, pickling,
wanted beta- and gamma-TNT isomers are selec-
and phosphatizing are preparation steps for the
tively removed from the desired alpha-TNT in a
actual plating operation. Anodizing of aluminum
solution of sodium sulfite (sellite). This purifica-
in a chromate bath is considered a related opera-
tion step generates a dark red-colored waste
.
tion since it produces a waste similar in charac-
known as "red water". The purified TNT is then
teristics to plating waste.
recrystallized, dried and flaked. TNT contains up
(a) A wide range of processing steps is
to 0.4 percent dinitrotoluene (DNT) which also is
used in the plating operation. Selection of such
an explosive and considered hazardous. The
steps is based on the type of material receiving
washdown water from processing areas contains
the plated layer, the type of metal being plated,
suspended TNT and is known as "pink water".
individual plating technique preferences, and vari-
Originally, production was a batch-type operation,
ous final product requirements. A typical plating
however nearly all plants have been converted to
operation will include the following steps:
continuous-type systems, as shown in figure 3-2.
Cleaning by solvent decreasing and/or
The continuous operations normally employ chem-
alkaline cleaner.
ical recycle and result in a smaller quantity of
Rinsing.
more concentrated waste than the batch-type
Acid cleaning or pickling.
operations. Typical wastewater characteristics
Rinsing.
from both types of operations are presented in
Surface preparation such as phospha-
tizing.
table 3-11.
3-15
Previous Page
