The effect of carbonate concentration in cyanide metal plating solutions

The purpose of this study was to determine the effect of carbonate concentration in copper, cadmium, silver, and gold cyanide plating solutions on the properties of the deposits and the plating range. A 267 milliliter Hull cell was used to investigate this problem. By using this apparatus the concentration of carbonate could be readily changed, and the effect which the change had on the current density range of the brightly plated region could be directly measured.

The investigation determined that for the Rochelle copper, sodium cyanide solution the magnitude of the bright range increased from 2.5 to 7.5 amperes per square foot with increasing sodium carbonate concentration up to six ounces per gallon, decreased to 2.0 amperes per square foot as the concentration increased from six to eight ounces per gallon, and exhibited no significant change with further increasing carbonate concentration up to twelve ounces per gallon. The optimum carbonate concentration ranged between four and seven ounces per gallon during which range the plating range fell between 0.5 and 8.5 ampere, per square foot.

For the cadmium cyanide (Cadalume) solution the investigation found that no conclusion can be made concerning the effect of increasing sodium carbonate concentration up to twelve ounces per gallon, above which concentration the bright range decreases with increasing concentration. The average plating range at carbonate concentrations below twelve ounces per gallon was between 35 and 100 amperes per square foot. The silver cyanide investigation led to the conclusions that the magnitude of the bright range increased from 4.0 to 4.3 amperes per square foot with increasing potassium carbonate concentration up to a concentration of four ounces per gallon, above which the bright range decreased rapidly with increasing carbonate concentration. Also concluded was that the optimum potassium carbonate concentration ranges between zero and four ounces per gallon, during which the plating range lies between 0.1 and 4.5 amperes per square foot.

For the gold cyanide solution the investigation found that the magnitude of the bright range increased from 0.4 to 3.5 amperes per square foot as the potassium carbonate concentration was increased from zero to two ounces per gallon, but decreased slowly with further increase in concentration. The optimum potassium carbonate concentration occurred at two ounces per gallon at which concentration the platina range was between 0.5 and 4.0 ounces per gallon.