Balances worth their weight in gold

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Source: Mettler - Toledo Int. Inc

Balances play a central role in refining precious metals. They are used to ensure that the gold and silver content is measured with the highest possible accuracy. Argor-Heraeus relies on balances to meet the stringent regulations issued by the London Gold Bullion Association and the Jewelry and Watch industries.

The Argor-Heraeus gold refinery processes precious metals and produces semi-finished components for distribution to the watch and jewelry industry. METTLER TOLEDO balances are used to ensure that the gold and silver content is checked and controlled with the highest possible accuracy throughout the entire refinery process.

Accuracy is as precious as gold
“We already use third generation METTLER TOLEDO balances in our gold and silver refinery where the highest weighing accuracy and reliable results are essential,” replied Lorenzo Medici, manager of SC Engineering at Argor-Heraeus, when asked about his experience with METTLER TOLEDO balances.

The importance of weighing becomes immediately evident during the factory tour at Argor-Heraeus located in Mendrisio in the southern part of Switzerland. Precision weighing plays a crucial role in the most important process steps, such as incoming inspection, within the foundry and for refining and finishing steps. The weight is checked before and after each process step in order to closely monitor any weight differences.

Gold under full control
All data is recorded and fed into the IT system in order to closely monitor the flow of gold material. The balance’s diverse connectivity options optimize the easy integration into the current ERP system and the printed reports, together with the data integration, ensure permanently traceable results for the accountability of every gold sample.

From fire assay to final product
One of the most impressive and yet age-old processes in gold refining is the so-called ‘fire assay’; a gravimetrical method used to determine the purity of gold. This assay plays an important role throughout the entire refining process from accepting raw materials through to the finished product.

Gold samples are accurately weighed on Excellence XP6 Micro Balances for the fire assay process then mixed with a defined amount of silver and wrapped in a lead foil. Each sample is then placed into a cupel and heated in a furnace at 1200 °C. The cupel, made of compressed magnesium oxide powder, absorbs the melted and oxidized base metals leaving a precious metal drop in the cupel. After solidification, the resulting bead is flattened to a thin plate and treated in a nitric acid bath to remove any silver. The resulting pure gold plate is subsequently re-weighed on the Micro Balance to determine the sample’s fine gold content. Argor-Heraeus is highly satisfied with METTLER TOLEDO’s Excellence XP6 Micro Balance as it generates fast yet accurate results-an important element for employees weighing so many samples per day.

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