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Chrome Bearing Wastewater Treatment
System
Process Description
Wastewater from chrome plating and brightening
operations contains soluble chrome.
In the case of chrome plating, They use a
highly soluble form of chrome known as Hexavalent Chrome or CR+6.
In order to remove this form of chrome from water it must first be
reduced to trivalent chrome or CR+3. After chrome reduction, the
chrome is precipitated, coagulated, flocculated and removed from the
waste steam by clarification.
The typical method to reduce and remove CR6+
from wastewater is as follows:
Stage 1 Chrome Reduction:
pH is lowered to pH 2.5 while adding a reducing agent such as sodium
metabisulfite or ferric sulfate converting CR+6 to CR+3.
Stage 2 Precipitation:
pH is adjusted upward to a pH of 8-9.5 to the optimum chrome
hydroxide precipitation point. Often, a coagulant such as ferric
sulfate is added to enhance metal co-precipitation and the formation
of “pin floc”.
Stage 3 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 4 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 accumulate in the sludge chamber. The
clarified water then exits the clarifier and flows downstream to
sewer or further treatment if necessary.
Clarifier Sludge Handling:
The accumulated sludge is periodically removed from the clarifier
and sent to a sludge holding tank where it further thickens for
disposal or dewatering.
Sludge Dewatering:
Sludge dewatering is typically handled by a Filter Press. After
processing a batch of "sludge" the filter press is emptied of
“chrome cake” which is a semi solid of approximately 20-35 %
solids. Chrome cake is high in chrome and sulfite and should be
disposed of according to environmental regulations.
APPLICATIONS:
Plating shops are found in typically two
categories, captive and independent shops. Some industries operate
their own captive, in house plating operation while others outsource
to an independent plating operation.
Typical industries include:
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Automotive suppliers
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Plumbing fixtures such as faucets, shower
heads, hose assemblies
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Aerospace
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Automotive, trucks, motorcycles - chrome
body parts
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Appliance makers
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Metal forming such as conduit, nails,
nuts, bolts and screws, electrical parts.
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Jewelry makers
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Plating shops, captive or independent
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