Extraction of Au(III) by Microbially Reduced Metal-Organic Frameworks

An Adsorbent for Efficient and Rapid Gold Recovery from Solution: Adsorption Properties and Mechanisms

Adsorption is an efficient and highly selective method for gold recovery. Introducing rich N/S organic groups to combine with metal-organic frameworks (MOFs) as adsorbents is regarded as a practical and efficient approach to enhance gold recovery. Herein, a MOF (zirconium isothiocyanatobenzenedicarboxylate MOF, UiO-66-NCS) was designed to combine with amidinothiourea (AT) to form UiO-66-AT (zirconium amidothiourea-benzenedicarboxylate MOF) for efficient and rapid adsorption. The prepared UiO-66-AT delivers an improved adsorption capacity (about 903.02 mg/g at 1000 mg·L-1 of the initial Au3+) and an impressive adsorption rate within minutes (about 10 min for 200 mg·L-1 Au3+). Meanwhile, it exhibits sustainable stability after 5 cycles with a retention rate of 99.52% and excellent adsorption selectivity of 98.76% in actual wastewater. According to advanced characterizations and Density Functional Theory (DFT) simulation, the mechanism might be elaborated as electrostatic adsorption, chelating coordination, and chemical reduction. The modified active groups of the MOF provide the adsorption sites for Au(III) and the rapid reduction of Au(0). UiO-66-AT maintains a large adsorption capacity and high surface reduction activity while realizing stable application in multiple cycles, which is of good practical application value.

Shewanella oneidensis: Biotechnological Application of Metal-Reducing Bacteria

What is an unconventional organism in biotechnology? The γ-proteobacterium Shewanella oneidensis might fall into this category as it was initially established as a laboratory model organism for a process that was not seen as potentially interesting for biotechnology. The reduction of solid-state extracellular electron acceptors such as iron and manganese oxides is highly relevant for many biogeochemical cycles, although it turned out in recent years to be quite relevant for many potential biotechnological applications as well. Applications started with the production of nanoparticles and dramatically increased after understanding that electrodes in bioelectrochemical systems can also be used by these organisms. From the potential production of current and hydrogen in these systems and the development of biosensors, the field expanded to anode-assisted fermentations enabling fermentation reactions that were - so far - dependent on oxygen as an electron acceptor. Now the field expands further to cathode-dependent production routines. As a side product to all these application endeavors, S. oneidensis was understood more and more, and our understanding and genetic repertoire is at eye level to E. coli. Corresponding to this line of thought, this chapter will first summarize the available arsenal of tools in molecular biology that was established for working with the organism and thereafter describe so far established directions of application. Last but not least, we will highlight potential future directions of work with the unconventional model organism S. oneidensis.

Construction of MoS2@Activated Alumina Beads as Catalysts for Rapid Gold Recovery from Au(S2O3)23- Solution

Gold recovery from thiosulfate leaching solution Au(S₂O₃)₂^3- is regarded as a tough task because of the low efficiency and complex procedure in current technology, which hindered the industrial application of this eco-friendly technique. In this work, a MoS₂@activated alumina bead composite (MoS₂@AA) was constructed through a simple hydrothermal anchoring method and served as a catalyst to recover gold from Au(S₂O₃)₂^3- solution for the first time. The microstructure and chemical component of MoS₂@AA were systematically analyzed. In addition, batch experiments were carried out to explore the recovery behavior of Au(S₂O₃)₂^3- (concentration: 10 to 200 ppm). Ascribing to the extraordinary optical property of MoS₂@AA, Au(S₂O₃)₂^3- could be directly reduced to Au⁰ by photogenerated electrons and then form a two-phase interface of gold/MoS₂@AA. As a result, the recovery of Au(S₂O₃)₂^3- can reach up to 98% on MoS₂@AA, which was much higher than traditional methods. More importantly, the reduced Au⁰ could be desorbed from MoS₂@AA through a supersonic method, achieving one-step Au⁰ recovery from Au(S₂O₃)₂^3-. This novel strategy used in this research has great significance to the development of Au(S₂O₃)₂^3- recovery in the future.