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Safety and Pollution Aspects

Many electrolytes are based on cyanide. This is particularly true for gold. Cyanide is very
poisonous and must be handled with great care.
A golden rule is never to allow drinking and eating in an electroplating facility and to have
very strict control and procedures in the plating shop. Protective overalls and visors
should be worn and changed regularly. Cleanliness is vital. For safety, cyanide
electrolytes and plating salts should be kept in locked cupboards. Keep cyanides and
acids apart from each other. Acid will react with cyanide to liberate deadly hydrogen
cyanide gas!
Old electrolytes, as well as cleaners and rinse waters must be disposed of safely and
NOT thrown away down the sink or drain. The consequences of doing so are too awful to
contemplate!
Acid based, non-cyanide electrolytes must also be handled with care.
All reputable salt or electrolyte manufacturers will provide Materials Safety Data
Sheets on their products and give good advice on health and safety procedures

Gold Electroplating Systems

There are many electroplating systems on the market for putting pure gold and gold alloy
deposits on to gold jewellery and on to base metals for decorative applications. There are
also many others for technical applications such as electrical contacts and connectors,
where the coating properties must have a certain technical performance.
The electrolytes can be classified into cyanide and non-cyanide based and may contain
small alloying additions to control colour and other properties. All cyanide-based
electrolytes are based on the use of gold potassium cyanide salt, KAu(CN)2, which
contains about 68% gold. However, most electrolytes do not contain anything like this
concentration of gold. Some electrolytes are acid, others neutral and others are alkaline,
as shown in the classification in Table 1.
Electrolyte pH Gold Alloying Metals
Type complex
Alkaline 8 – 13 KAu(CN)2 Cu, Cd, Ag, Zn
Neutral 6 – 8 KAu(CN)2 Cu, Cd, Ag
Weakly acid 3 – 6 KAu(CN)2 Co, Ni, In, Fe
Acid 0.5 – KAu(CN)4 Co, Ni, In, Sn
2.5
Cyanide-free, 8 – 10 Na3Au(SO3)2 Co, Ni, In, Sn
alkaline
Table 1 – Electrolytes for gold alloy electroplating
The range of colours possible and bath and deposit characteristics of electroplating
systems from one well-known manufacturer are shown in Figures 3 – 5. Note the optimum
bath temperature is often above ambient. The gold concentration is quite low – about 0.1
– 7.0 g/l and the speed of plating ranges typically from about 10 – 75 mg/amp/min. The
time to plate 1 micron thickness ranges from 3 – 15 mins.
Bath type: 1 2 3 4
Gold content, g/l 8 – 108 12 – 16 1 – 2 –
Bath temperature 60 – 70°C 50°C 70 – 75°C 50°C