|
Phosphatizing Wastewater Treatment
System
Process Description
Phosphatizing wastewater is from metal surface
preparation operations where the metal is either sprayed or dipped
in a hot phosphatizing solution. The phosphatized metal surface is
then ready for painting, bonding with plastic or rubber, cold
extrusion or alone as a metal preservative.
Phosphatizing wastewater typically from
rinsing and batch dumps is at a low pH of ~2.5, is hot (~110F), and
contains a soluble form of phosphate. In order to remove this
soluble form of phosphate it must first be made insoluble. The
insoluble phosphate is then coagulated, flocculated and clarified by
sedimentation.
The typical method to reduce and remove
phosphate from wastewater is as follows:
Stage 1 Precipitation and Coagulation:
pH is raised from ~2.5 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 phosphate is insoluble.
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:
Phosphatizing 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
operation.
Typical industries include:
-
Plating shops, captive or independent
-
Automotive, trucks, motorcycles – Metal to
rubber suspension and body parts
-
Automotive suppliers
-
Can making plants – phosphatizing for
corrosion resistance
-
Steel coil coating – large steel coils are
phosphatized for corrosion resistance and painting preparation.
-
Metal forming such as conduit, nails,
nuts, bolts and screws, electrical parts.
-
Aerospace – corrosion resistance surface
prep
-
Appliance makers – phosphatizing is done
to internal parts for corrosion resistance prior to painting
-
Computer component makers – phosphatizing
is used as a dielectric surface prep
|
