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Re: chromium recovery/ water recycling
Add additional rinse tanks and flow very low rate from the last back to the
first in each part of the cycle. Replace each original rinse with three
tanks, flow at very very low rates. Use RO water for the rinses. Put the
first (most contaminated) rinse into the treatment tank as make up water.
Do not put the chromating tank into the treatment system -- your goal is to
recycle the contents of this tank or send it out for treatment. Only the
hydroxide tank should go to treatment and it should only require
neutralization for pH control. But test to be sure.
You can eliminate the chromium content from effluents by eliminating rinse
water and chromating treatment from going to the effluent at all.
I did this with a major plating operation -- we took it to zero discharge by
this process, with a rare change out of the process tanks. Also improved
quality and productivity.
Ralph E. Cooper, Ph.D., J.D.
San Antonio, TX 78231
----- Original Message -----
Sent: Monday, March 27, 2000 11:31 AM
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,
> 5 are heated. Flow of effluent is constant from tanks 2, 4 and 5 to a
> 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
> (filter press) for disposal and 2.6 million gallons of water for
> 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