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Electroplating Wastewater Treatment
System
Process Description
Electroplating wastewater comes from surface
plating operations where the metal is dipped in an electroplating
solution of various types of metals and then rinsed.
Typical plating includes brass, nickel,
cadmium, zinc, silver, copper, and gold. Electroplating wastewater
is typically from washing, rinsing and batch dumps and is at a low
pH of ~3-5 and contains soluble forms of the various metals. In
order to remove soluble metals from the wastewater it must first be
made insoluble. The insoluble metal is then coagulated, flocculated
and clarified by sedimentation.
The typical method to reduce and remove
soluble electroplating metals from wastewater is as follows:
Stage 1– Precipitation and Coagulation:
pH is raised from ~3 to 8.5 with the pH controller using caustic
while adding a coagulant such as ferric chloride. Testing of the
wastewater may confirm that a coagulant is not needed. A “pin floc”
is developed indicating the metal is insoluble. Some applications
have plating enhancing chemicals present, emulsifiers and such that
may require more sophisticated high performance coagulants to break
the bonds and allow the metal to precipitate.
Stage 2 - Flash Mix:
The wastewater with it’s precipitated pin floc is introduced to the
flash mix zone where a polymer flocculent is added. This stage
maximizes flocculent dispersion throughout the coagulated
wastewater.
Stage 3 - Flocculation:
The wastewater is now introduced to the slow mix zone to agglomerate
the pin floc into larger rapid settling particles.
Clarifier, Inclined Plate:
The flocculated wastewater is introduced into the clarifier where
the settling particles land on the inclined plates and are directed
downward and into the sludge chamber. The clarified treated water
then exits the top of the clarifier and flows downstream to sewer or
further treatment if necessary.
Clarifier Sludge Handling:
The resulting clarifier waste sludge is periodically removed from
the clarifier at a slow rate and sent to the sludge holding tank
where it further thickens and accumulates a batch for disposal or
processing in a filter press.
Sludge Dewatering:
The thickened clarifier sludge is allowed to accumulate sufficiently
to provide a full batch for the Filter Press. The filter press is
pumped full of the sludge until it is full. The filter press is
then emptied of the “cake” which is a semi solid of approximately
20-35 % solids. Sludge cake is high in phosphate and should be
disposed of according to environmental regulations.
APPLICATIONS:
Electroplating shops are found in typically
two categories, captive and independent shops. Some industries
operate their own captive, in house electroplating operation while
others outsource to an independent operation.
Typical industries include:
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Electroplating shops, captive or
independent
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Automotive suppliers, trucks, motorcycles
etc – Metal to rubber suspension and body parts
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Jewelry mfg
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Machine tool mfg.
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Metal forming such as stamped metal parts
that require plating of various types.
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Building materials, cadmium plated nuts,
bolts etc. .
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Aerospace
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Wire forming - nails, screws etc
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Appliance makers
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Electronics – gold and silver plating of
electrical connectors etc.
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