ProAu, a bio-protein, is produced by a special microbe that can absorb valuable metals from industrial wastewater. It is a unique thermal stable protein from hot springs, with high selectivity and fast adsorption rates for gold recovery. ProAu can recover gold ions from waste streams of printed circuit board (PCB) factories or other sources. This means that this technology literally turns wastes into gold, and not just ordinary gold, but nano-gold worth $1/g.

ProAu uses functional proteins secreted from a novel thermophilic bacterium as an absorbent. Its functional proteins are not only natural but also pass human allergy, cytotoxicity, and environmental bacteria toxicity tests. These proteins have strong metal binding amino acids that allow them to bind strongly with gold. Using a proprietary immobilization process, the ProAu technology allows proteins to graft onto aldehyde modified biomass easily, at a density as high as 60 mg/g, and thus recovers gold at low concentrations.

Figure I: Functional proteins immobilized on an aldehyde modified substrate to absorb gold from industrial wastewater at low cost

Unlike other chemical precipitation or ion-exchange methods used in metal recovery and wastewater treatment plants, ProAu causes much less secondary environmental pollution due to its biodegradability. It is especially suited for gold recovery because of its strong preference for absorbing gold at a low concentration that other methods are unable to achieve. It has a much higher magnitude of adsorption efficiency (over 90%) than many other metal ions in extremely dilute solutions, under the same conditions (even to <1 mg/L). Moreover, its gold adsorption capacity is two orders of magnitude higher than that of other proteins and commonly used resins.

In addition to recovering gold from industrial wastewater, ProAu can also be applied to cosmetic or artistic products by introducing brilliant colors, while also acting as an anti-bacteria agent in these products. The nano-gold sample prepared from ProAu has the same anti-bacteria character as its counterpart prepared from traditional liquid chemical methods. These gold nano-particles can also find applications in high-tech industries as catalysts, electron conductors, sensors, bio-inhibitors, and probes. This technology can also be used for recovering gold from geothermal fluid. Since this mining operation has a potential to integrate with the geothermal power generation, it may generate extra revenue on top of geothermal energy itself. ProAu technology systems also have a small footprint, enabling them to be integrated flexibly in existing factory layouts.

Figure II: By combining geothermal and gold mining, there will be more economical resources available in the world

In a world of growing populations and things, resources need to be recoverable to achieve sustainability in all aspects of industrial development. ITRI’s ProAu provides a bio-adsorbent that effectively recovers gold in the form of nano-particles from industrial wastewater and geothermal streams at sub-ppm levels, bringing us new gold mines while contributing to a sustainable world we can all thrive in.