Gunnar Nordberg
Occurrence and Uses
Palladium (Pd) occurs in nature with platinum or gold, as the selenide. It is found in nickel sulphide ores and in the minerals stibiopalladinite, braggite and porpezite. The concentration of palladium in the Earth’s crust is 0.01 ppm.
Palladium has been used in gold, silver and copper alloys in dentistry. Alloys are also used for bearings, springs and balance wheels in watches. Palladium is used as a catalyst in the manufacture of sulphuric acid. In powder form it serves as a catalyst in hydrogenation. The sponge form is used for separation of hydrogen from a mixture of gases. Silver alloys are used for electrical contacts. Palladium (II) complexes have been studied as antineoplastic drugs.
Palladium chloride (PdCl2·2H2O), or palladous chloride, is used in photography toning solutions and for the manufacture of indelible ink. It is an agent used for transferring pictures to porcelain, for electroplating watch parts, and for finding leaks in buried gas pipes. Palladium chloride is associated with copper chloride in catalyzing the production of acetaldehyde from ethylene.
Palladium oxide (PdO), or palladous oxide, is used as a reduction catalyst in the synthesis of organic compounds. Palladium nitrate (Pd(NO3)2) is used in the separation of halides. Palladium trifluoride (PdF3) is an active oxidizing agent.
Hazards
Studies indicate cases of allergy and contact dermatitis caused by palladium in dental alloys and fine jewellery. In one study palladium-based alloys were associated with several cases of stomatitis and oral lichenoid reactions. In this same study palladium allergy occurred mainly in patients with a sensitivity to nickel. Palladium chloride produces dermatitis and allergic skin sensitization in workers exposed daily. In addition, it should be regarded as an eye irritant. Palladium hydroxide was used in the past to treat obesity by injection; this form of treatment gave rise to localized necrosis and was discontinued.
Safety and Health Measures
Correct exhaust ventilation is necessary when working with palladium and its compounds. Good personal hygiene, proper protective clothing and medical surveillance are important measures in preventing the risks associated with sensitization. Adequate sanitary facilities must be provided.