Copper and zinc removal



Some galvanizing processes are performed on metal subsurfaces containing Zinc and/or Copper.
Nickel plating bath is acidic and, of course, performs an aggressive action either on pieces being treated, or on pieces eventually dropped on the bottom of the tank.
Either Copper or, in a more important way Zinc, disturbs Nickel deposition, creating dark deposition and penetration difficulties in low current density areas.
When high Zinc concentration is in the bath, plated Nickel is dark and the pieces’ colour after Crome plating is not optimal. .

CONVENTIONAL REMEDIES

The classical purification method for a polluted Nickel Plating bath is the usage of bended plates called “Selective Plates”.
They act using polluting metals feature of selectively depositing in low current density areas better than Nickel.
By inserting, during standstill, Selective Plates instead of pieces it is possible to obtain a bath purification.
This process is slow and expensive because, with the pollutants, great quantities of Nickel are deposited.
Companies specialized in producing Galvanic chemicals, created special “complex builders” that, in optimal conditions, chelate Copper and Zinc avoiding them to depose.
Nevertheless these processes do not represent the best solution of the problem.

THE SOLUTION

Idropan created a unit which, using a special Ion Exchange resin, can remove from the Nichel plating bath Copper, Zinc and Lead reducing them to very low values, thus restoring the normal operation of the process.
The resin, thanks to its particular exchange groups, does not operate on organic substances like Primary and Secondary Brighteners,Tensides, Levelers.
It is possible to obtain concentrations of Copper and Zinc of few parts per million so optimizing the deposition.

HOW DOES IT WORK?

The Unit is principally composed of:

Circulation Pump
Safety Prefilter (50uM)
Ion Exchange Column
Regeneration System

During working hours the system continuously recycles Nickel plating bath.
In this way it removes Copper, Zinc and Lead.
At regular intervals, determined during the first period of operation on an analyse base, (for example after 2-4 working weeks) becomes necessary the regeneration which, using hydrochloric acid in small quantities, removes held metals from the column bringing it to its initial conditions.

THE RESULTS

Connecting the system to a Nickel Plating line it is possible to keep Copper, Zinc and Lead under 5 ppm (mean value about 3 ppm )
In this conditions chemical performances of the bath are optimal.