Treatment of ammoniacal copper etchants

Ammoniacal ammonium chloride etchants are widely used to etch copper during the manufacture of printed circuit board (PCBs). Etching efficiency declines above 110 to 130 g/L copper and this concentration must be restored once the concentration reaches 150 to 170 g/L copper. The annual European arising of spent etchant (about half the U.S.A. arising) is estimated to contain 2250 Mg copper. Disposal of spent etchant involves a loss of resources and is usually environmentally unacceptable. This paper reviews methods for the regeneration of spent etchants with co-recovery of a saleable copper product. Whilst large volume flows of spent etchant are regenerated commercially, there is a need for methods appropriate to on-site treatment by the smaller PCB producer. Experimental developments designed to meet this need, using either supported liquid membranes impregnated with a diketone extractant or an electrochemical cell divided by solid ion exchange membrane, are described. The performance of the ion exchange membranes tested in the membrane cell was found to be inadequate for this application. It is concluded that a supported liquid membrane process, after further development, in combination with copper electrowinning from an acidic solution may fulfil the need for on-site treatment by the smaller PCB producer.