Kinetic Study of The Photoelectrochemical Gold Recovery from Diluted Chloride Solutions

Abstract

Au(III) was recovered from an acidic aqueous solution via a photoreduction technique under UV light irradiation. Titanium dioxide nanopowder was applied as a photocatalyst. Gold was deposited onto TiO 2 surface in the form of nanoparticles with average dimensions between 20 and 30 nm. The influence of the Au(III), TiO 2 and methanol initial concentrations on the reaction rate was determined. It was shown, that the rate of the gold photoreduction strongly depends on the concentration of TiO 2 and methanol. The recovery of gold from the diluted acidic solutions containing as much as 1.97 and 0.197 mg/dm 3 of Au(III) was also carried out. Obtained results suggest, that it is possible to recover about 45% of gold. Besides the losses during the filtration process due to the application of very fine TiO 2 particles, oxygen dissolved in the solution as well as the hydrogen ions may take part in parasitic reactions and thus decrease the Au yield.Keywords: Gold, recovery, photoreduction, TiO 2 , aqueous solutions Przeprowadzono odzysk jonów Au(III) z kwaśnych, chlorkowych roztworów wodnych metodą fotoredukcji pod wpływem światła UV. Jako fotokatalizator wykorzystano proszek dwutlenku tytanu o rozmiarach nanometrycznych. W wyniku redukcji kompleksu chlorkowego Au(III), na powierzchni TiO 2 otrzymano fazę metaliczną w formie nanocząstek o rozmiarach w zakresie od 20 do 30 nm. Zbadano wpływ stężeń początkowych Au(III), TiO 2 i metanolu. Badania wykazały, że szybkość fotoredukcji Au(III) silnie zależy od stężenia dwutlenku tytanu i metanolu. Przeprowadzono również badania nad odzyskiem złota z rozcieńczonych roztworów zawierających 1.97 i 0.197 mg/dm 3 Au(III). Otrzymane wyniki wskazują, że przyjęta metoda pozwala odzyskać około 45% złota z roztworu. Niska wydajność procesu może być spowodowana stratami w procesie filtracji związanymi z zastosowaniem nanokrystalicznego TiO 2 , tlenem rozpuszczonym w roztworze oraz jonami H + , które mogą ulegać redukcji w konkurencyjnych, równoległych reakcjach.

Design of Metal@Titanium Oxide Nano-heterodimers by Laser-Driven Photodeposition: Growth Mechanism and Modeling

“…A set of coupled reactions needs indeed to be solved in order to describe the global scheme “M n + + ne – → ... → M 0 ”, preventing a rigorous definition of a simple reaction rate. This is particularly true for the reduction of Au 3+ which involves three stages, photoreduction of Au 3+ to Au 2+ , disproportionation of two Au 2+ in Au 3+ and Au + , and finally photoreduction of Au + to Au 0 ; note that this mechanism is still the subject of important research, in particular when characterizing nucleation and growth of gold NPs in solutions. − Nonetheless, investigations of the photoreduction of Au 3+ in the presence of TiO 2 anatase and P25 show that the photoreduction of Au 3+ to Au 0 can be assimilated to the pseudo-first-order net reaction when investigating its kinetics over time scales long compared to those involved in the photoreduction mechanism. This statement should therefore apply here when considering the time scale for the growth of gold NDs.…”

Lead molybdate – a promising material for optoelectronics and photocatalysis

“…Ce 4+ /Ce 3+ redox couple) in the electrolyte, a photoelectrochemical photocurrent switching effect may be induced. On the one hand, the adsorption of alizarin onto the PbMoO 4 surface leads to a very efficient generation of cathodic photocurrent which may be effectively utilized in photocatalytic applications, such as the photoreduction of metals from wastewater 50 or generation of the reactive oxygen species (ROS) for water purication purposes. The materials exhibit also a notable photocatalytic activity towards the mineralization of organic pollutants which strongly depends on the synthetic conditions.…”

“…The information on these parameters enables the utilization of semiconductor nanoparticles in solar fuel cells, photocatalytic systems, 48 information processing devices 49 and even hydrometallurgy. 50 The Photoelectrochemical Photocurrent Switching Effect (the PEPS effect), which may be dened as the ability of a semiconductor to generate either anodic or cathodic photocurrents depending on the stimulus (the wavelength of the incident light or the electrode potential), is interesting from the information processing viewpoint. On the other hand, a suitable value of the conduction band edge potential gives the opportunity to use this material for the generation of the reactive oxygen species (ROS).…”

Enhanced photocatalytic reduction of concentrated bromate in the presence of alcohols

“…While chemically-doped photocatalysts have been extensively studied, another strategy for improving photocatalysis via decreasing recombination of electron-hole by adding alcohols to bromate solutions has not been investigated. As alcohols (i.e., methanol (MeOH) and ethanol (EtOH)) have been proven as sacrificial reagents to scavenge holes from the valence band of semiconductors, aqueous photocatalysis in the presence of alcohols has been demonstrated as a promising approach for chemical reduction reactions [23][24][25][26][27].…”