Weighing Performance in Gold and Silver Refineries

Precision weighing plays a crucial role in the most important process steps in gold and silver refineries. Be it for incoming inspection, within the foundry or for refining and finishing steps. The weight is checked before and after each process step in order to closely monitor any weight differences.

Weighing as a central role
Each incoming raw gold and silver bullion is check weighed in order to determine the exact delivery weight. Depending on the bullion’s weight, the goods can either be checked on an Excellence XP64001L Precision Balance’s large 64 kg capacity weighing platform or on a floor scale with a capacity of up to 1500 kg. Both balances can be connected to a single display mounted on an extra stand next to the balances. This guarantees better result visibility and easier user handling.

After incoming inspection, the material undergoes further analysis and refining steps in order to prepare semi-finished parts for the jewelry and watch industry and bullion with defined purity.

Finally, the bullion is carefully checked for nominal weight. If the weight falls below the accepted limit, the bullion goes back to the melting and processing stage, if it exceeds the upper limit, the weight is corrected to the nominal target tolerance. The Excellence XS603S Precision Balance, which has a readability of 1 mg and a removable front glass in the draft shield, is ideal for this final process step.

From fire assay to the 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 can be accurately weighed on Excellence XP6 Micro Balances 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 balances, allowing the determination of the sample’s fine gold content. METTLER TOLEDO’s Excellence XP6 Micro Balance is a perfect instrument for this task as it generates fast yet accurate results, an important element for employees weighing many samples per day.

Gold under full control
Often 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 ensuring the accountability of every gold sample.