We are happy to share that we have recovered our first Gold (Au) for this third update!
Remind as a team, has continued the recycling progress by using the output from the physical treatment (see the second update). The last physical treatment process was wet density separation, separating the heavy metallic fraction from the light non-metallic fraction. The heavy metallic fraction rich in precious metals (Gold, Silver) was then sent to the next recycling process by the hydrometallurgical route. Prior to the hydrometallurgical route, the heavy metallic fraction was heated to remove some impurities as a slag (melting slurry). We put the light non-metallic fraction in a sealed container. The hydrometallurgical process aims to recover the precious metals, in this case, Gold (Au), through selective dissolution by particular acid. The first step of the hydrometallurgical process was to put the heavy metallic fraction in a beaker glass and add some amount of Nitric Acid as a leaching reagent. Nitric acid is selective towards the base metals, thus dissolving all base metals (Copper, Nickel) and leaving the Gold as a precipitate. We did the leaching three times (each 30 to 60 minutes) to ensure the base metals were utterly dissolved in the solution. Then the filtration process was carried by a filter paper to remove the solid fraction. The liquid (pregnant solution), which is rich in base metals, was kept for another process to obtain other precious metals such as Copper, Palladium, and Silver. In the last step, We did the smelting to the solid fraction in a furnace with the help of an oxygen blower. Impurities will melt during the heating as a slag again, leaving pure solid Gold. Finally, 1.8 grams of Gold were produced from about 6 kg of IC Chips. We still have mixed boards and IC chips for our following recycling experiments. From the previous recycling, Remind has successfully recovered approximately 5 grams of Gold.
There were still many things to be improved, especially the recovery of each process. We lost almost half of the feed input during the grinding (see Update 2) and one-third during the hydrometallurgical process. Hopefully, we can improve the yield of recovered Gold for our subsequent recycling experiments.
In the end, the Gold was sent to the lab for analysis to measure the purity and composition. Because of the small amount of Gold that we obtained, we are still focusing on sending the Gold for analysis to evaluate the whole recycling process instead of selling it to local jewelry stores.