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From 2013.igem.org

13-05 - 19-05-13

Gold Recovery from Electronic Waste

As test experiment, pins from an old CPU processor chip were dissolved.

Fig.0 Old motherboard from which we will recycle gold.

Step 1: Pins were mechanically removed and collected in a flask.

Fig.1.1 CPU from which pins will be removed.

Fig.1.2 Removed pins.

Step 2: Flask was put onto heating plate and covered in concentrated HCl.

Fig.2 Pins covered in HCl.

Step 3: HNO₃ was carefully added to the pins and heated.

Fig.3 Evolution NO2 gas.

Step 4: After several minutes of moderate heating, pins dissolved completely. The solution turned green.

Fig.4 Green solution of dissolved pins.

Step 5: The solution was carefully neutralized to pH ~6 in a step-wise manner using first 5 M, later 0.5 M NaOH.
Step 6: This led to precipitation of copper salts, indicated by the milky green coloring.

Fig.6 Milky solution following neutralization.

Step 7: In order to remove the precipitates, the solution was filtered using a buechner funnel and sterile filtrated (0.2 µm).

Fig.7.1 Filtering solution to remove precipitates.

Fig.7.2 Sterile filtering.

Fig.7.3 Filters used for sterile filteration.

Step 8: The final yellow-green gold containing solution was collected in a volumetric flask.

Fig.8Final gold containing solution.