High purity silver microcrystals recovered from silver wastes by eco-friendly process using hydrogen peroxide

- Simple, rapid, highly efficient, and environmentally friendly process for large scale silver recovery.
- The morphology of the recovered product can be easily controlled.
- The recovered silver microcrystals are in high purity (up to 99.99%).
- A direct usage of the recovered silver microcrystals as a raw material for wearable silver jewelry was explored.

A simple, rapid, and environmentally friendly process using hydrogen peroxide, was developed for recovering high purity silver directly from industry and laboratory wastes. Silver ammine complex, [Ag(NH3)2]+Cl−, derived from AgCl were generated and then directly reduced using H2O2 to reliably turn into high purity microcrystalline silver (99.99%) examined by EDS and XRD. Morphology of the recovered silver microcrystals could be selectively tuned by an addition of poly(vinyl pyrrolidone). The main parameters in the recovering process including pH, concentration of Ag+ and the mole ratio of H2O2:Ag+ were carefully optimized though the central composite design (CCD). The optimized condition was employed for a trial recovery of 50 L silver ammine complex prepared from a collection of silver-wastes during 3-year research on industrial nanoparticle production. The recovered silver microcrystals >700 g could be recovered with 91.27%. The remaining solution after filtering of the recovered silver microcrystals can be used repeatedly (at least 8 cycles) without losing recovery efficiency. Matrix interferences including Pb2+ and Cl− play a minimal role in our silver recovery process. Furthermore, the direct usage of the recovered silver microcrystals was demonstrated by using as a raw material of silver clay for creating a set of wearable silver jewelries.

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