CHEMISTRY IN TICINO 146

CHIMIA 49 (1995) Nr. 5 (Moi)

Chimia 49 (1995) 146-148 apply this new security mark, based on the © Neue Schweizerische Chemische Gesellschaft diffraction of light and used by govern- 1SSN0009-4293 ments to secure banknotes, passports, and identity cards, onto its precious metals. Beside fine precious metals Argor- Argor-Heraeus SA Heraeus produces jewellery alloys and semi-finished products for the watch in- dustry, thus connecting Canton Ticino with Alessandro Ruffoni* the most renowned manufacturers located at the opposite end of the country.

An Example out of the Everyday's Profile Argor-Heraeus figures in the Good Laboratory Practice: The Search for Delivery List for gold, silver, platinum, Excellence in the Analysis of Gold Argor SA was established at Chiasso in and palladium, and its smelter-as sayer 1951 and became active in the refining of mark is recognized and accepted interna- Cupellation (Fire Assay) gold and the production of gold, silver, tionally as a warranty of quality. Closest Gold is traded since the oldest times, platinum, and palladium bars. Union Bank attention is devoted to the technological and its high value made it soon necessary of Switzerland acquired an 80% holding in advance in the area of assaying techniques to determine its purity with the highest 1960 and effected the full takeover in and Argor-Heraeus' specialists are ac- possible accuracy. Cuneiform tablets in- 1973. In view to the future, a partnership tively involved in international normali- dicate that the Babylonians used the fire was agreed in 1986 with We. Heraeus zation carried out by the relevant ISO assay technique in the 14th century B.C. GmbH, Hanau, designed to secure the working group. when they suspected that gold sent by an enterprise renamed Argor-Heraeus SA an A new kind of fine gold bar, the kine- Egyptian pharaoh was impure. It is thus to edge over its competitors in regard to the bar™, was introduced in 1993. Develop- believe that this has to be considered the know-how for the processing of precious ed in cooperation with Landis & Gyr Com- first chemical analysis developed in the metals. We. Heraeus holds a 25% partic- munications, it bears a KINEGRAMTM, a history. ipation in the new firm. patented security feature providing added The fire assay, various features of which The unique link between Union Bank protection against counterfeiting; Argor- are also cited in the Old Testament, con- of Switzerland, a universal bank active in Heraeus holds in exclusivity the license to tinued to be used and to be improved all parts of the world, and We. Heraeus, one of the leading high-technology com- panies in the precious metal sector, can be regarded as trend-setting and future-ori- ented in nature. The combination of a bank and an in- dustrial firm offers the customers of the jointly-owned subsidiary Argor-Heraeus SA essential advantages, be it in connec- tion with the financing of materials or in the area of the constantly changing tech- nological environment, to name only the most important ones. The new refinery, opened at Mendrisio in 1988 and enlarged in 1994, employs 85 people and disposes of facilities for the electrolytic gold and silver refining, for the wet chemical parting of low grade, precious metal bearing materials and for the refining of platinum and palladium, of a modern foundry with induction furnaces and with a continuous casting facility al- lowing an output of more than 400 kg/h of fine gold, and of a department for the mechanical manufacturing of small bars, medals, and coins, and of semi-finished products; modern installations for the treat- ment of waste water and air care for an efficient environmental protection.

*Correspondence: A. Ruffoni Argor-Heraeus SA CP 279 CH-6850 Mendrisio Fig. 1. Cupellation is performed in a specially designed furnace at some 1100° CHEMISTRY IN TICINO 147

CHIMIA 49 (1995) Nr. 5 (Moi) through the centuries; the discovery of the acid, where the silver is dissolved com- sive devices, make it possible nowadays mineral acids in the Middle Age and the pletely, leaving a gold cornet deprived of to reach the same accuracy level of the fire development of precision balances with the other components initiall y present. This assay. ever improved accuracy contributed in a one is rinsed, dried and weighed again In comparison to the cupellation, XRF decisive manner to confer to this method accurately: the ratio between final and spectrometry has anyway some disadvan- the highest degree of analytical precision initial weight gives the gold fineness. tages: and of reliability. With some minor corrections allowed - the method fails to give a correctly As it is the case for most of the classical by the use of proof samples, this technique representative result if even limited analytical techniques for the determina- allows today a precision ranging around segregation occurs, because only a thin tion of the fineness of precious metals, the 0.1 parts per thousand by weight, abso- surface layer of the sample is analyzed fire assay, also called cupellation, is in fact lute, for high grade gold, and 1 part per - expensive calibration standards with a a refining procedure, just applied on a thousand for the most critical alloys, so chemical composition close to the one small scale. that the results are commonly given with ofthe sample (one series for each par- The gold samples, obtained by drill- four significant digits. ticular type of alloy) are required, be- ing, sawing or cutting, are weighed accu- Despite his venerable age this method cause of the strong matrix effects en- rately, inquarted with pure silver so that is still considered the most accurate avail- countered in XRF spectrometry the ratio between pure gold and the total able. It has recently been standardized by - large samples, with a diameter of sev- amount of precious metal becomes equal ISO for the analysis of jewellery alloys as eral centimetres, are required in order to 1:4, and compounded with lead; they ISO 11426, and it is the only analytical to obtain high precision results are then put into cupels made of magnesi- technique accepted by the London Gold - high investments are required for the um oxide or of some other porous, refrac- Exchange to evaluate the fineness of gold purchase of the device, and a payback tory material, and treated in the oxidizing bullion and karat gold. is thus possible only if high quantities atmosphere of a specially designed fur- of analysis have to be performed. 0 nace at a temperature of some 1100 • X-Ray Fluorescence Analysis Anyway, the fast response time, the There the base metals of the resulting melt An alternative analytical technique possibility to perform a full analysis of the are oxidized and absorbed by the cupel, being applied increasingly for production sample in a single run without the need of leaving a bright bead of precious metal. control in the industry is the X-ray fluores- prior separation of its different compo- This bead is then flattened down and rolled cence (XRF) analysis. The wavelength nents, and the possibility to introduce ex- into a cornet, which is subsequently sub- dispersive instruments, more sophisticat- tensive automatization make XRF analy- jected to a repeated treatment in nitric ed and expensive than the energy disper- sis a powerful instrument for the quality control and warranty in the industrial prac- tice.

ICP Analysis with Internal Standard Although not yet ready to replace fire assay or XRF analysis, this technique is meeting increasing interest, owing to the small sample size required, to the virtual absence of interferences between spectral lines of the usual alloy components and to the acceptable price of the analytical de- vices, atomic emission spectroscopy by inductively coupled plasma (ICP) is meet- ing increasing interest among precious metal analysts. Already published by ISO as Draft International Standard for the analysis of platinum and of palladium in jewellery alloys (ISO DIS 1] 494 and ISO DIS 11495), this particular analytical meth- od is presently undergoing extensive study within the Working Group Isorrc 174/ WG 1, looking for a further improvement of the achievable accuracy. This particular application of emission spectroscopy overcomes the relative de- ceiving reproducibility of lep (typically not much better than] % relative, a very poor one in the eyes of the gold analyst) by adding an internal standard, such as yt- trium, both in the calibration and in the sample solutions, and measuring simulta- neously the intensity ratio of the precious metal's and of the internal standard's emis- Fig. 2. Gold and silver are parted by repeated treatment in nitric acid sion line. In this wayan improvement of CHEMISTRY IN TICINO 148 CHIMIA 49 (1995) Nr. 5 (Mail

the accuracy of the results by a factor of samples (arc and spark spectral sources, accuracy needed for this task requires spe- ten, at least, can be obtained. A further glow discharge lamp) and for solutions cial experience in the choice of the appro- improvement in the overall precision is (direct current plasma or inductively cou- priate analytical technique and in the ap- achieved by diluting by weight instead by pled plasma). plication of modifications of the proce- volume, and by the averaging of repeated Devices with fixed channels allowing dure needed in dependence of any partic- determinations, with strict conditions con- the simultaneous analysis of not less than ular case. Special care has further to be put cerning the acceptable relative standard twenty different metallic elements allow a in the sampling operations, so that the deviation. rapid analysis of the samples, with detec- analytical results are really representative tion limits ranging typically around I mg/ for the whole lot of material. Trace Analysis by Spectroscopical kg. The fineness of the samples is then The high responsibility related to the Techniques obtained subtracting the sum of the detect- precious metal analysis is thus attributed For the determination of the purity of ed impurities from 1000%0,achieving in by the Swiss law to sworn assayers, spe- fine gold (999.9%0) indirect determination this case a much better accuracy than the cially educated and subjected to the au- of the fineness is mainly used. one obtainable by fire assay. thority of the Swiss Federal Office for For the analysis of trace amounts of Precious Metal Control, as ultimate war- impurities atomic absorption spectrosco- The Ultimate Touch of the Sworn As- ranty for the accuracy and reliability of the py, which has been the working horse of sayer results. many laboratories during the last decades, has been replaced by atomic emission As one can see, there is no lack of good spectroscopy techniques. Different exci- analytical methods to determine the fine- tation sources are available both for solid ness of gold. Nevertheless, the ultimate

Chimia 49 (1995) 148-151 best price in the shortest time, through a © Neue Schweizerische Chemische Gesellschaft lSSN 0009-4293 high degree of specialisation and automa- tion, backed by large capacity. The level of automation enables PAMP PAMPSA SA to operate a competitive, efficient re- finery with a modest staff of 65 men and Production Artistiques Metaux women. This skilled team has long expe- rience in all aspects of refinining. They Precieux SA* combine to offer a wealth of knowledge in the treatment of precious metals.

Corrosion of Precious Metals Foreword

It is generally assumed that all pre- C. Marcolli and M. Gene] cious metals, i.e., those metals which have a high electropositive reading on the scale of the standard electrochemical potentials Company Profile opened its new gold refinery at Castel San of the elements, are characterised by total Pietro,just outside Chiasso, in 1984.Work chemical inertia and by inalterability in Production Artistiques Meraux Pre- is undertaken on a toll or on a full service relation to the air and corrosive surround- deux SA (PAMP SA) was established in basis. ings. Such assertions are certainly true, Chiasso, Switzerland, in 1977. Initially This high-technology refiner, which but cannot be intended as universal con- the company made its name by pioneering meets the strictest Swiss environmental cepts. a wide range of 999.9 small gold bars requirements, provides fuIl services in pre- The fact that e.g. silver turns brown, which all carried stylish designs on the cious metals, from pick-up of dore at the i.e., the tendency of the metal to be cov- reverse side. The most famous is the 'For- mine, through assaying, refining, edging, ered by nonconducting sulfurcompounds, tuna', depicting the Roman goddess For- and delivery of bars throughout the world. is one of the greatest problems in the tune emerging from a conch shell, which PAMP SA bars are accepted as good deliv- electric field and in jeweIlery, and has has won worldwide acclaim for PAMP ery by the Swiss National Bank, the Lon- been the subject of many studies. SA. don Bullion Market Association (LBMA), Gold, too, though characterised by a Building on this reputation as a serious the commodity exchange (COMEX) New standard positive electrochemical poten- producer of high quality bars, PAMP SA York, and the Tokyo Commodity Ex- tial with respect to silver, and therefore, by change (TOCOM). a greater degree of chemical inertia, is not PAMP SA prides itself on its agility inalterable (it dissolves in aqua regia) and and flexibility, as a fully accredited Swiss forms two very stabile oxides. refinery, able to provide unrivalled and The presence of spots of a persistent *Correspondence: PAM? SA comprehensive customer service. The phi- reddish-brown colour has been noted on CH-6874 Castel San Pietro losophy is to offer the best product at the the surface of fine gold bars of various