Advanced Materials Research Vols. 20-21

Abstract: Mercury sorption on chitosan was investigated in batch and continuous systems. Chitosan sorption properties were determined through sorption isotherms. Langmuir and Freundlich equations were used for the modeling of isotherms at pH 5. In batch systems, maximum sorption capacities reached 550 mg Hg/g. Sorption kinetics have been studied as a function of sorbent particle size and stirring rate. Dynamic removal of mercury was tested in a fixed bed reactor investigating the following parameters: particle size, column size, flow velocity and metal ion concentration. Clark and Adams-Bohart models were evaluated for the simulation of breakthrough curves. This study shows that chitosan is an effective sorbent for the treatment and recovery of mercury from dilute effluents at near neutral pH.

Abstract: In recent years the use of microbial methods for decontamination or recovery of heavy metals from environment has increased. Microorganisms such as yeasts are potential bioremediators, removing metals via active or passive uptake. Pink-coloured and pigment-less yeast strains isolated from Agrio River, Patagonia Argentina, were tested for copper, nickel, cadmium and zinc tolerance. An agar-plate qualitative screening method using YNB-glucose agar at different metal concentrations was employed. The tolerance to the metals varied depending on the strain tested. A pigmented yeast strain (Agrio 16) was selected by its tolerance. The ability of this strain to copper uptake was investigated. The kinetics of bioaccumulation/biosorption with increasing copper concentrations up to 622.8 mg l-1 were carried out using viable and nonviable biomass. The values of constants k and n obtained for the Freundlich model are 0.0418 and 0.7430, respectively. The maximun sorption uptake capacity (q) for viable biomass was 81.6 mg of copper/g of biomass.

Abstract: The biosorption of arsenic species by dried lettuce leaves (L.sativa) was investigated. Arsenic sorption, that is not effective on in natura biomass, was enhanced when the biomass was previously loaded with Fe(III). Analysis of X-ray Absorption Near-Edge Spectroscopy (XANES) spectra showed that iron was incorporated as Fe(III) and arsenic as As(V), regardless the contact with the lowest or highest valence species of these elements. The features of Extended X-ray Absorption Fine-Structure Spectroscopy (EXAFS) spectra suggest that the nearest neighboring atoms of iron ions are the same in all the samples, even in the As-Fe loaded ones. These results indicate the arsenic oxyanions as the sorbed species on the iron-loaded biomass.

Abstract: Microbial reduction of Au(III) from HAuCl4 was demonstrated. Escherichia coli and Desulfovibrio desulfuricans reduced 1 mM Au(III) in 60 and 120 min at pH 6.9 and 2.3 respectively. TEM and elemental analysis showed the formation of Au(0) nanoparticles and their pH-dependent cellular localisation. The concept was applied to the recovery of gold from jewellery waste leachates using E. coli. Bio-Au(0) nanoparticles were tested for catalytic activity in the oxidation of glycerol, achieving 30% conversion to glyceric acid. A simple bioprocess for conversion of waste to new material is suggested.

Abstract: Since 1998 demand for the platinum group metals (PGM) has exceeded supply resulting in large price increases. Undersupply, combined with rising costs prompts environmentally friendly recycling technologies. Leachates containing PGM were produced from secondary waste sources using microwave leaching technology with the aim of recovering precious metals using bacterial biomass. Previous studies showed that metallised biomass exhibits catalytic activity; hence metal is not only recovered but can be converted into a valuable product. Cells of Escherichia coli MC4100 that had been pre-metallised with Pt were more effective at reducing PGM from the leachates. The solid recovered from the leachate onto the bacteria was characterised using X-ray Powder Diffraction (XRD) and Energy Dispersive X-ray Microanalysis (EDX). Metallised biomass was tested for catalytic activity (reduction of Cr(VI) to Cr(III)) to compare the ‘quality’ of polymetallic bacterial-based catalysts versus counterparts made from single and mixed metal model solutions.

Abstract: Nano-scale palladium was bio-manufactured via enzymatically-mediated deposition of Pd(II) from solution. The bio-accumulated metal palladium crystals were processed and applied onto carbon paper and tested as anodes in a proton exchange membrane (PEM) fuel cell for power production. Up to 85% and 31% of the maximum power generation was achieved by Bio-Pd catalysts made using two strains of bacteria, compared to commercial fuel cell grade Pt catalyst. Therefore, it is feasible to use bio-synthesized catalysts in fuel cells for electricity production.