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chromium recovery/ water recycling




Dear P2tech members,

I am looking for options for a facility to recover chromium and recycle rinse
water from their conversion coating process.  Conversion coating is also known
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 prior
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
and
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 than
1.0 (one) mg/liter!  Occasionally, contents of tanks 1 and 3 are partly
discharged into the treatment system. Hexavalent and trivalent chromium in the
water is treated using the standard chromium reduction/chemical precipitation
process.  This process generates 136,000 pounds of partly dewatered  sludge
(filter press) for disposal  and 2.6 million gallons of water for discharge to
sewer.  This is "industry practice", we have been told. Non-chrome
alternatives
are not an option (customer specs).  Also, I think tanks 1 and 2 contain large
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