Bio-electrochemical systems for the remediation of metal-ion effluents

PhD ThesisThe roots of this study stem from the applied sciences of microbiology and electrochemistry to form the exciting new field of bio-electrochemistry. Our aim here being the application of bioelectrochemical processes for social and environmental value in toxic metal ion remediation and recovery from the discharge of aqueous mine and industrial effluents. This within a broader vision of reducing the present burden caused by industrial and mining anthropogenic activity on the planet we inhabit. These processes we have explored within a green chemistry philosophy with the application of chemical engineering principles. Our aims being (i) to further the scientific state of art and (ii) conceptualize the feasible engineering of novel metal remediation strategies, with the lucrative application of bacterial cells as green “nanofactories” and recovery of metallic biogenic nanoparticles with application in the ever growing field of nanotechnology. The proof of principle has been evaluated with a systematic study of Au3+, Co2+ and Fe3+ metallic cationic species (Co < 500 ppm) dissolved in acidic (pH < 3) aqueous electrolytes and their removal by microbiological (chapter 3) and bioelectrochemical (chapter 4) processes. Electrochemical remediation as described by electronation charge transfer at an electrified interface for various potentials causes the electrodeposition of metal ions upon electrode surfaces and hence separation by phase transformation. Of note, base cations such Co2+ and Fe3+ co-deposited with the evolution of hydrogen gas could be applied as electron donors for chemolithotrophic bacteria as part of dissimilatory respiration. Microbial biosorption of metal ions by means of ionized groups located on the outer membrane of the outer lipopolysaccharide leaf of gram negative bacteria, with some evidence of bio-reduction via dissimilatory and redox resistance mechanisms, with biogenic nanoparticles produced as a consequence. Bio-electrochemistry formed by the collaboration of these two processes where electroactive bacteria such as that of the Shewanella genus are known to respire by the application of cathodic currents directly via bio-nanowires or indirectly using in-situ electron mediators or in-situ hydrogen production. The effects of bacteria on electronation thermodynamics were investigated in chapter 4 with observed positive shifts in reversible potentials (Er) for AuCl3- electrodeposition

Membrane electrolysis for separation of cobalt from terephthalic acid in industrial wastewater

Recovery of valuable metals from wastewaters containing both metals and organics is challenging with current technologies, in part due to their interactions. Typical approaches are chemical intensive. Here, we developed a membrane electrolysis system coupled to an acidic and alkaline crystallizer to enable separate precipitation of the organics and metals without additional chemicals. The target industrial wastewater contained mainly purified terephthalic acid (PTA), benzoic acid (BA), p-Toluic acid (PA), cobalt (Co), and manganese (Mn). We examined the removal and recovery efficiency of PTA and cobalt from two types of synthetic stream and the real process stream using several configurations. The acidic crystallizer reached a removal efficiency of PTA of 98.7 +/- 0.2% (Coulombic efficiency 99.71 +/- 0.2%, pH 3.03 +/- 0.18) in batch tests of the simple synthetic stream. The alkaline crystallizer achieved a cobalt recovery efficiency of 94.51 +/- 0.21% (Coulombic efficiency 87.67 +/- 0.31%, pH 11.37 +/- 0.21) in batch tests of the simple synthetic stream (TPA and Co). Then, the system was operated continuously with complex synthetic stream (TPA, BA, PA, Co and Mn). The alkaline crystallizer achieved a cobalt recovery efficiency of 97.78 +/- 0.02% (Coulombic efficiency 90.45 +/- 0.17%)at pH 11.68 +/- 0.02. The acidic crystallizer obtained a PTA removal efficiency of 61.2 +/- 0.1% (Coulombic efficiency 62.3 +/- 0.2%) over 144 h (pH 3.71 +/- 0.03). A real stream was tested over 5 h runs in batch showing 31.1 +/- 1.0% PTA (Coulombic efficiency 26.5 +/- 0.2%) and 82.92 +/- 0.22% cobalt removal (Coulombic efficiency 75.27 +/- 0.31%) at pH 2.71 +/- 0.12 and 8.07 +/- 0.02, respectively. However, micron-scale precipitates were generated from real stream tests. To conclude, the membrane electrolysis cell coupled with acidic and alkaline crystallizers enabled simultaneous separation of PTA and cobalt as solid precipitates from a complex stream with no chemical addition. The efficiencies were lower with the real stream than the synthetic streams, showing the impact of matrix effects and the need to optimize the performance of the crystallizers

Selective metal extraction by biologically produced siderophores during bioleaching from low-grade primary and secondary mineral resources

Siderophores are a class of biogenic macromolecules that have high affinities for metals in the environment, thus could be exploited for alternate sustainable metal recovery technologies. Here, we assess the role of siderophores in the extraction and complexation of metals from an iron oxide-rich metallurgical processing residue and a low-grade primary Ni ore. Evaluation of the biological siderophore production by three pseudomonads, P. fluorescens, P. azotoformans and P. putida identified that P. putida could generate the highest siderophore yield, which was characterized as a hydroxamate and catecholate mixed-type pyoverdine PyoPpC-3B. Key physicochemical parameters involved in raw siderophore mediated metal extraction were identified using a fractional factorial design of experiments (DOE) and subsequently employed in purified PyoPpC-3B leaching experiments. Further targeted experiments with hydroxamate and catecholate functional analogues of PyoPpC-3B confirmed their marked ability to competitively or selectively leach and chelate hard metal ions, including Al(OH)(4)(-), Mn2+ and Zn2+. Interestingly, complexation of Mn and Zn ions exceeded the natural affinity of pyoverdine for Fe3+, thus despite the low metal recoveries from the materials tested in this study, this work provides important new insights in siderophore-metal interactions

Near-zero-waste processing of low-grade, complex primary ores and secondary raw materials in Europe: technology development trends

With an increasing number of low-grade primary ores starting to be cog-effectively mined, we are at the verge of mining a myriad of low-grade primary and secondary mineral materials. At the same time, mining practices and mineral waste recycling are both evolving towards sustainable near-zero-waste processing of low-grade resources within a circular economy that requires a shift in business models, policies and improvements in process technologies. This review discusses the evolution towards low-grade primary ore and secondary raw material mining that will allow for sufficient supply of critical raw materials as well as base metals. Seven low-grade ores, including primary (Greek and Polish laterites) and secondary (fayalitic slags, jarosite and goethite sludges, zincrich waste treatment sludge and chromium-rich neutralisation sludge) raw materials are discussed as typical examples for Europe. In order to treat diverse and complex low-grade ores efficiently, the use of a new metallurgical systems toolbox is proposed, which is populated with existing and innovative unit operations: (i) mineral processing, (ii) metal extraction, (iii) metal recovery and (iv) matrix valorisation. Several promising novel techniques are under development for these four unit-operations. From an economical and environmental point of view, such processes must be fitted into new (circular) business models, whereby impacts and costs are divided over the entire value chain. Currently, low-grade secondary raw material processing is only economic and environmentally beneficial when the mineral residues can be valorised and landfill costs are avoided and/or incentives for waste processing can be taken into account

Sustainable metal recovery from secondary resources : screening and kinetic studies using analogue heterotrophic metabolites

This study presents a sustainable approach for metal extraction from a range of secondary resources. Organic acids analogue to those commonly produced by heterotrophic microbes are applied via a two-step heterotrophic bioleaching approach. New insights into leaching mechanisms are developed and the potential use of the leaching residues as cementitious component is evaluated. Tested materials include a jarosite sludge from Zn refining, four ferrous metallurgy residue sludges and two dry automotive recycling shredder residues. Screening experiments tested three organic acids (i.e. citric, gluconic, oxalic acid) and their combinations. Four physicochemical factors were varied, i.e. the solid/liquid ratio between 5 and 15%, total organic acid concentration between 20 and 200 mM, leaching times of 2 to 4 h and horizontal stirring reactor mixing rate. The highest extraction capacity was achieved for a Cr/Ni rich sludges from steel treatment with up to 96% Ni and 91% Cr extraction at a 5% S/L and a mixture of 100 mM citric and 100 mM oxalic acid. Further scale-up kinetic studies on this Cr/Ni sludge validated the optimal leaching conditions. Modelling of kinetic leaching data indicated pore diffusion rate as a bottleneck of the overall leaching process. Screening tests of the leached residue indicated potential use as sulfate-rich addition to cement, or as part of low-performance binders for large scale civil works

Process analysis of AuCl 4 - sorption leading to gold nanoparticle synthesis by Shewanella putrefaciens

International audienceA process evaluation of AuCl4 - ( < 300 mg/L, < pH 3, H2 e-donor) sorption kinetics and mass transfer analysis by initially viable Shewanella putrefaciens is presented here. Following on from previous reports of a thermodynamically spontaneous reaction, high sorption capacity of 1346 mg/g and significant evidence of zero valent gold nanoparticles (AuNPs) deposited within the bacterial cell wall. Linear and non-linearized kinetic modelling of the data shows a good fit to a pseudo second-order model and theoretical analysis of diffusional limiting steps suggest diffusion on the surface or through the cell wall to be the process rate limiting step. Process analysis of microbial gold synthesis, provides a foundation for the design of smart reactor systems for process intensification

Shewanella putrefaciens for the remediation of Au3+, Co2+ and Fe3+ metal ions from aqueous systems

This study reports the investigation and application of gamma proteobacteria of the Shewanella genus, Shewanella putrefaciens CN32 bacterium, applied as a prototypical dissimilative bacterium for the remediation of Au3+, Co2+ and Fe3+ ions in aqueous systems. Green chemistry principles were applied to the remediation process, i.e. no chemicals are used to treat the metal ion solutions and process where carried out at ambient temperatures. Some emphasis upon the possibility of metal recovery as metallic nanoparticles (NPs) using bacterial cells was also given. Batch assays were carried out with de-oxygenated solutions containing metal ions of relatively low concentrations (<300mg/L) and low pH (<pH 3) in the presence of bacteria cells and H2. Biosorption of all metal ions was found to be a fast process, with a good fit to Freundlich adsorption isotherms. Transmission electron microscopy analysis of assays after 24h of incubation gave significant evidence of the precipitation of zero-valent metallic gold nanoparticles (AuNPs) in the extra-cellular medium and the outer cell wall, by initially active and deactivated bacterial cells

Membrane electrolysis for separation of cobalt from terephthalic acid in industrial wastewater

Recovery of valuable metals from wastewaters containing both metals and organics is challenging with current technologies, in part due to their interactions. Typical approaches are chemical intensive. Here, we developed a membrane electrolysis system coupled to an acidic and alkaline crystallizer to enable separate precipitation of the organics and metals without additional chemicals. The target industrial wastewater contained mainly purified terephthalic acid (PTA), benzoic acid (BA), p-Toluic acid (PA), cobalt (Co), and manganese (Mn). We examined the removal and recovery efficiency of PTA and cobalt from two types of synthetic stream and the real process stream using several configurations. The acidic crystallizer reached a removal efficiency of PTA of 98.7 +/- 0.2% (Coulombic efficiency 99.71 +/- 0.2%, pH 3.03 +/- 0.18) in batch tests of the simple synthetic stream. The alkaline crystallizer achieved a cobalt recovery efficiency of 94.51 +/- 0.21% (Coulombic efficiency 87.67 +/- 0.31%, pH 11.37 +/- 0.21) in batch tests of the simple synthetic stream (TPA and Co). Then, the system was operated continuously with complex synthetic stream (TPA, BA, PA, Co and Mn). The alkaline crystallizer achieved a cobalt recovery efficiency of 97.78 +/- 0.02% (Coulombic efficiency 90.45 +/- 0.17%)at pH 11.68 +/- 0.02. The acidic crystallizer obtained a PTA removal efficiency of 61.2 +/- 0.1% (Coulombic efficiency 62.3 +/- 0.2%) over 144 h (pH 3.71 +/- 0.03). A real stream was tested over 5 h runs in batch showing 31.1 +/- 1.0% PTA (Coulombic efficiency 26.5 +/- 0.2%) and 82.92 +/- 0.22% cobalt removal (Coulombic efficiency 75.27 +/- 0.31%) at pH 2.71 +/- 0.12 and 8.07 +/- 0.02, respectively. However, micron-scale precipitates were generated from real stream tests. To conclude, the membrane electrolysis cell coupled with acidic and alkaline crystallizers enabled simultaneous separation of PTA and cobalt as solid precipitates from a complex stream with no chemical addition. The efficiencies were lower with the real stream than the synthetic streams, showing the impact of matrix effects and the need to optimize the performance of the crystallizers

Metal recovery by microbial electro-metallurgy

Raw metals are fundamental to the global economy as they are essential to maintain the quality of our life as well as industrial performance. A number of metal-bearing aqueous matrices are appealing as alternative supplies to conventional mining, like solid industrial and urban waste leachates, wastewaters and even some natural extreme environments (e.g. deep marine sediments, geothermal brines). Some of these sources are already managed for recovery, while others are not suitable either because they are too low in content of recoverable metals or they contain too many impurities that would interfere with classical recovery processes or would be cost-prohibitive. Microbial electro-metallurgy, which results from the interactions between microorganisms, metals and electrodes, in which the electron transfer chain associated with microbial respiration plays a key role, can contribute to overcome these challenges. This review provides the state of the art on this subject, and summarizes the general routes through which microbes can catalyse or support metal recovery, leading to nano- and macro-scale materials. Competing sorption and electrochemical technologies are briefly revisited. The relevant sources of metals are highlighted as well as the challenges and opportunities to turn microbial electro-metallurgy into a sustainable industrial technology in the near future. Finally, an outlook to pursue functional materials through microbial electrometallurgy is provided