Dissimilatory reduction of sulfate, mediated by various species of sulfate-reducing bacteria (SRB) and a few characterized species of archaea, can be used to remediate acid mine drainage (AMD). Hydrogen sulfide (H 2 S/HS À ) generated by SRB removes toxic metals from AMD as sulfide biominerals. For this, SRB are usually housed in separate reactor vessels to those where metal sulfides are generated; H 2 S is delivered to AMD-containing vessels in solution or as a gas, allowing controlled separation of metal precipitation and facilitating enhanced process control. Industries such as optoelectronics use quantum dots (QDs) in various applications, e.g. as light emitting diodes and in solar photovoltaics. QDs are nanocrystals with semiconductor bands that allow them to absorb light and re-emit it at specific wavelength couples, shifting electrons to a higher energy and then emitting light during the relaxation phase. Traditional QD production is costly and/or complex. We report the use of waste H 2 S gas from an AMD remediation process to synthesize zinc sulfide QDs which are indistinguishable from chemically prepared counterparts with respect to their physical and optical properties, and highlight the potential for a empirical process to convert a gaseous "waste" into a high value product.

Dissimilatory reduction of sulfate, mediated by various species of sulfate-reducing bacteria (SRB), can be used to remediate acid mine drainage (AMD). Hydrogen sulfide (H2S/HS-) generated by SRB can be used to remove toxic metals from AMD as sulfide biominerals. For this, SRB are usually housed in separate reactor vessels to those where metal sulfides are generated; H2S is delivered to AMD-containing vessels in solution or as a gas. This allows more controlled separation of metal precipitation and facilitates enhanced process control. Industries such as optoelectronics use quantum dots (QDs) in, for example, light emitting diodes and solar photovoltaics. QDs are nanocrystals with semiconductor bands that allow them to absorb light and re-emit it intensely at specific wavelength couples. Small nanoparticles have the possibility to get electrons shifted to a higher energy and then emit light during the relaxation phase. The QD elemental composition and the presence of doping agent determines its electronic band gaps and can be used to tune the QD to desired emission wavelengths. Traditional QD production at scale is costly and/or complex. Waste H2S gas from growth of SRB has been used to make zinc sulfide QDs which are indistinguishable from ’classically’ prepared counterparts with respect to their physical and optical properties. Clean recycling of minewater bioremediation process waste gas into high value QD product is described.