Reclamation of nitric acid from solder strip. 1995.

TURI Technical Report No. 26. The manufacture of printed circuit boards is a complex, multi-step process. As part ofthe process, a tin/lead solder coating is applied to copper circuitry in order to protect the pattern from the subsequent ammoniacal etching process. After the unwanted copper is etched from the surface ofthe printed circuit board, the solder coating is stripped from the remaining circuitry with a proprietary aqueous solution ofnitric acid, iron salts, and various inhibitors and adjuncts. When the speed at which stripping occurs drops below the PCC specified limit, the solder strip solution is considered "spent" and the entire solution is replaced. However, if the metals can be separated from the stripping solution, it is possible that the solution could be reused continuously, with adds made only to replace dragout. In order to reduce the nitric acid by-product generation PCC has implemented a diffusion dialysis acid recycling process developed by Pure Cycle Environmental Technologies, Inc. This proprietary design features an extended membrane area configuration that efficiently promotes the removal and concentration of the acid up to 95% ofits original strength with very little power consumption. The purified acid is directed back to the process tank, while the contaminant-laden spent acid stream goes to metal recovery or waste treatment for further processing.

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