Case Study: How to Estimate Gold Content in Gold-Plated Parts

Introduction:

Gold-plated parts are valuable for recycling due to the high value of gold, currently around $80 per gram. Estimating the gold content and its value, however, presents a significant challenge. In today’s case study, we examine what initially seemed like a straightforward task: estimating the gold content of parts with similar shapes and relatively simple surface areas. While this might appear easy, the conclusions demonstrate that only an actual refining process can provide truly accurate results.

Case Overview:

We analyzed two samples for this study:

• Part A – A “window” shaped component
• Part B – A “rod” shaped component

We applied three different methods to estimate the gold content:

1. Theoretical Calculation: This method involves measuring the thickness of the gold coating layer. Interestingly, we found that the coating thickness varied both between the two parts and even across the surface of each part. This variability could be due to differences in production lots and the geometry of the parts.

• Average thickness for Part A: 0.52 microns
• Average thickness for Part B: 0.60 microns

Other relevant data:

• Part A: Weight = 1.90 grams, Surface area = 3.6 cm²
• Part B: Weight = 1.42 grams, Surface area = 1.32 cm²

Using this data, we calculated the average gold content:

• Part A: ~1.83 g/kg
• Part B: ~1.08 g/kg

For ease of calculation, you can use our “gold plated parts calculator.”

2. Fire Assay: In this method, we used a traditional fire assay technique on a small sample of each part. The results were:

• Part A: 2.75 g/kg
• Part B: 1.2 g/kg

3. Actual Refining Process: The final method involved dissolving the gold and weighing the actual gold recovered. The results were:

• Part A: 2.79 g/kg
• Part B: 1.57 g/kg

Final Gold Content: After refining the entire lot, which consisted of several hundred kilograms, the actual gold content was:

• Part A: 2.22 g/kg
• Part B: 1.56 g/kg

Results Summary (Gold Content in g/kg):

Conclusions:

Despite the parts’ similarity and the simplicity of surface area calculation, estimating the actual gold content remains a complex task for several reasons:

1. The thickness of the gold coating is not uniform across the surface of the parts.
2. Parts produced in different production lots can have varying coating thicknesses.
3. Surface area calculations are not always entirely accurate.

The fire assay, while useful, relies on a small sample and may not represent the overall lot. In the case of gold-plated parts, preliminary tests are helpful for providing an estimate of the gold content. However, only a complete refining of all the parts in the lot can deliver precise results.

For assistance with recycling gold-plated parts, feel free to contact us at: Ami@agmetals.com