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RE: chromium recovery/ water recycling


Most of the sludge generated would be from the caustic step.  More than 90
percent of the sludge generated can often be traced to the use of hard
water.  Segregation of the caustic and chromium wastestreams should be
looked at as a way of rendering the sludge nonhazardous.

I would look into converting tanks 4 and 5 to closed loop operation.  A
resin bed system can be used to remove chromium and to clean up the water
for reuse.  Be sure to use demineralized water in these tanks.  The cost
will not be that high once converted to closed loop. Hot demin water is
often specified for the tank 4 rinse (many shops use a still rinse for
sealing the coating).  The important parameter to monitor is silica. This
type of operation is very common in the aerospace industry.


-----Original Message-----
From: Donatus.Wielkens@dep.state.fl.us
Sent: Monday, March 27, 2000 9:32 AM
To: p2tech@great-lakes.net
Subject: chromium recovery/ water recycling

Dear P2tech members,

I am looking for options for a facility to recover chromium and recycle
water from their conversion coating process.  Conversion coating is also
as chrome phosphate etch.  A process that treats the metal surface, here
aluminum extrusions, providing protection and good adhesion for the final 
paint coating. Aluminum is extruded to profiles of up to 40 ft length. 
Workpieces are pretreated, painted, and shipped to customers for final
manufacturing. Production is 18 million pounds/year.

Extrusions are taken through a five-diptank chromium conversion process
to an electrostatic applied paint finish. Stage 1) caustic wash, 2) water
rinse, 3) chrome phosphate dip, 4) water rinse, 5) water rinse.  Tanks 1, 3
5 are heated. Flow of effluent is constant from tanks 2, 4 and 5 to a water
treatment system.  Chromium concentration effluent tanks 4 and 5 is less
1.0 (one) mg/liter!  Occasionally, contents of tanks 1 and 3 are partly
discharged into the treatment system. Hexavalent and trivalent chromium in
water is treated using the standard chromium reduction/chemical
process.  This process generates 136,000 pounds of partly dewatered  sludge
(filter press) for disposal  and 2.6 million gallons of water for discharge
sewer.  This is "industry practice", we have been told. Non-chrome
are not an option (customer specs).  Also, I think tanks 1 and 2 contain
quantities of dissolved aluminum which could be considered for recovery by
commercial processes. 

I have searched the archives and the Internet; no success so far. 

Are there feasible, cost-effective options?  Would appreciate your input.

Thanks, Don Wielkens, Donatus.Wielkens@dep.state.fl.us FDEP, P2Program