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From 2013.igem.org

Contents 1 13-05 - 19-05-13 1.1 Gold Recovery from Electronic Waste 1.2 Precipitation of Gold from Electronic Waste 1.2.1 Protocol 1.2.2 Result

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.

Precipitation of Gold from Electronic Waste

Protocol

In order to evaluate optimial cultivation temperature of D. acidovorans, glycerol stock was streaked on ACM plates and incubated at RT, 30°C and 37°C ON. The next day, plates were covered with 200 µl 0.5% soft agar supplemented with 27 µl "dissolved electronic waste" solution.

Result

D. acidovorans showed intermediate, postponed purple-black coloring upon addition of "dissolved electronic waste" soft agar. Strongest coloring was observed on plates incubated at room temperature and 30°C. Delftibactin expression seems to be significantly decreased in D. acidovorans cultivated at 37°C. Reduced coloring further indicates lower gold ion concentration in the solution recovered compared to th ecommercially availible gold chloride solution [100 g/l]
We could therefore prove capability of D. acidovorans to specifically recover solid gold from dissolved electronic waste.

Fig.9.1 "Dissolved electronic waste" and D. acidovorans.

Fig.9.2 ACM plates prior to addition of gold chloride solution.

Fig.9.3 ACM plates covered with gold chloride solution T= 0:00 h.

Left plate: RT, upper plate: 30°C, lower right plate: 37°C

Fig.9.4 ACM plates covered with gold chloride solution T= 0:30 h.

Fig.9.5 ACM plates covered with gold chloride solution T= 1:00 h.

Fig.9.6 ACM plates covered with gold chloride solution T= 1:30 h.