Stripping baths are employed in electroplating plants in order to remove metal deposited on the electroplating racks. Stripping involves submerging the racks in a weak acid solution containing amines, and passing DC current through them in order to free the metals. Triethanolamine, monoethanolamine, diethylamine, triethylamine and ethylenediamine are among the amines employed, generally in the form of their nitrates, chlorides or acetates. Some of these amines are secondary amines with the ability to form N- nitrosamines directly; other amines, such as triethanolamine, may become contaminated by secondary amines, or may react further to form nitrosamines as a result of cleavage reactions.
Creation of a standard analysis method for nitrosamines in stripping baths; in cooperation with the institution for statutory accident insurance and prevention in the mechanical engineering and metalworking industry testing of material and air samples for amines, nitrosamines and metals were carried out including drafting of recommendations for stripping chemicals.
A large number of stripping baths were tested for N- nitrosamines. The results demonstrated clearly that nitrosamines may be formed when secondary amines are employed. The highest concentration detected was 26 mg/kg, in a diethylamine-based bath. This concentration exceeds the permissible limit value by a factor of 26. The TRK (technical exposure limit) value for nitrosamines at the workplace was almost reached. N-nitrosodiethanolamine concentrations of up to 21 mg/kg (four times the limit value) were detected in diethanolamine-based baths. Stripping baths based upon monoethanolamine, ammonia and diethylenetriamine were free of nitrosamines.
metal workingType of hazard:
Chemische Arbeitsstoffe, Krebserregende StoffeDescription, key words:
stripping baths, nitrosamines, analysis procedures