New challenges and applications of supported liquid membrane systems based on facilitated transport in liquid phase separations of metallic species

The linear economic model based on "take-make-dispose" has become unsustainable, revealing the necessity of shifting towards a circular economy (CE) approach, in which secondary raw materials play a key role in closing material cycles. In this context, industrial effluents with metallic content, are considered a potential secondary source for these elements, the lack of the availability of the appropriate technology being the main barrier when implementing circular economy principles at industrial scale. In this regard, supported liquid membrane (SLM) systems based on facilitated transport may be decisive. Thus, the objective of this research paper is to show the potential of facilitated transport systems to foster the transition to a more sustainable management of industrial metallic effluents. To accomplish that, three different applications of supported liquid membrane systems in acidic industrial effluents will be presented: a) Zn/Fe separation, b) Ni/Cd separations and c) Removal of hexavalent Cr. Additionally, the recovery and separation of two different critical raw materials, i.e. Li and rare earth elements will be discussed. Although facilitated transport systems have been successfully applied to both, Zn/Fe and Ni/Cd separation, as well as to hexavalent Cr removal, further work should be done for the successful recovery and separation of Li and rare earths with supported liquid membrane systems, especially in terms of selectivity improvement and validation with real industrial effluents.Financial support from the Spanish Ministry of Science, Innovation and Universities under the projects PID2020-115409RB-I00 and RTI2018-093310-B-I00 are gratefully acknowledged

Extraction of Bio-based Organic Acids using Supported Liquid Membranes with Novel Solvents

A thesis submitted to The University of Manchester for the degree of Doctor of Philosophy in the Faculty of Science and Engineering.Novel green solvents and supported liquid membranes were studied for the recovery of bio-based organic acids from model fermentation broths. As fundamental building blocks for the chemical industry, the production of organic acids from renewable feedstock have been broadly developed. Among them, succinic acid, levulinic acid, and fumaric acid have been highlighted as leading representatives. Nevertheless, their downstream separation and purification still require further research to build a suitable green production route. This turns the development of environmentally-friendly extractants as well as efficient separation methods into priority key research areas for bio-separations. The growing number of available green solvents, such as ionic liquids, eutectic solvents, and bio-based solvents, makes unbearable the experimental screening process to find the most appropriate extractant. In this work, the molecular interactions driving the overall extraction performance for the organic acids were systematically analysed. Experimental measurements of the liquid-liquid extraction and solid-liquid equilibria, as well as thermodynamic modelling using the quantum chemistry-based COSMO-RS method, were carried out. Organic acids extraction yields and solubilities, systems excess energies, activity coefficients, and energies of solutions are reported. The combination of structurally different acids and extraction solvents arise complex interactions; however, hydrogen bonding showed to determine the overall behaviour. As a result, a straightforward selection guide was developed based on the organic acids partition coefficients in the extractant/water system, ln(K), system's water affinity, ln(y), and separation process spontaneity, G. Furthermore, the dissolution process of the organic acids in green solvents displayed an endothermic and spontaneous process with an enthalpy-entropy compensation effect. The separation is driven by the new and stronger interactions formed, increasing the order of the systems. The state-of-the-art on sustainable applications of liquid membrane technology was thoroughly reviewed. Despite its high potential to replace conventional liquid-liquid extraction processes, some operational issues must be overcome and better predictive models developed. The feasibility of green-supported liquid membranes for succinic acid recovery was explored. As suggested by previous results, the solvent-phase affinities became key in the extraction performance. Experimental extractions were carried out to assess the effect of the green solvents and receiving phase. Commercial polyvinylidene fluoride (PVDF) porous membranes were impregnated with four different green solvents: the eutectic solvents DL-menthol:OctA and N4444Cl:OctA, the bio-based solvents eucalyptol, and the ionic liquid [C4pyrr][Tf2N]. The acid recovery for all liquid membranes was 50%, 51% and 59% with pure water and alkaline aqueous solutions of 0.1M and 0.5M NaOH in the stripping phase, respectively. It was found that extraction yield indeed depends on the pH of the stripping phase and that the solute permeation rate depends on the extraction solvent. For the first time, a permeability model based on experimental data and activity coefficients computed using the COSMO-RS method was developed. Moreover, the novel Permeability Activity-Based Linear Operation (PABLO) method was developed and proposed to determine the theoretical stages number and mass transfer area in a countercurrent cascade extraction system. Overall, this thesis comprehensively covers two research needs for the bioseparations of key building blocks. The contributions will certainly enhance the development and design of green production routes, boosting the next generation of sustainable chemicals and biorefinery industries.This work was funded by the CONICYT PFCHA/ DOCTORADO BECAS CHILE/2017−72180306.Peer reviewe

Preconcentration of heavy metals by Donnan dialysis

The aim of this study was to investigate the applicability of Donnan dialysis for the preconcentration of iron from synthetic wastewaters. Moreover, the competition between magnesium and calcium on the preconcentration of iron as well as the effect of adding a complexing agent (EDTA) on the enrichment factor of iron were also studied. Heavy metals are of great concern because of their extreme toxicity, even at low traces. Even with the sensitivity and selectivity of existing analytical techniques, direct determination of heavy metals is not always possible due to the low concentration of the ions. For this reason there is a great necessity for the preconcentration of heavy metals prior to their determination. Donnan dialysis experiments were performed in a laboratory scale with a dialysis cell, according to an experimental design created with the MODDE 8.0 software also used for modelling the process. Experiments were conducted with a full factorial design, which consisted in 11 experiments, three (3) of were central points. Donnan dialysis was proved to be a feasible technique to preconcentrate iron from synthetic wastewater samples. However, the metal competition decreased the enrichment factors of the main metal to be preconcentrated and the presence of the complexing agent in the receiver side did not affect the preconcentration process. Microscope images were taken to study the membrane structure. Membrane fouling caused by the absortion of iron explained the low enrichment factors and poor reproducibility of the process. Moreover, it was observed that the regeneration process was not good enough to regenerate properly the membrane. Different studies were done with another membrane and with another metal such as copper; nonetheless similar results were achieved.Outgoin

Membranes for Water and Wastewater Treatment

Water is a vital element for life and the environment. Water pollution has been documented as a contributor to a wide range of health problems. In recent years, the water quality levels have suffered great deterioration because of rapid social and economic development and because it is used to “dump” a wide range of pollutants.This book entitled “Membranes for Water and Wastewater Treatment” contains featured research papers dealing with recent developments and advances in all aspects related to membranes for water and wastewater treatment: membrane processes, combined processes (including one membrane step), modified membranes, new materials, and the possibility to reduce fouling and to improve the efficiency of enhanced processes. The papers compiled in this Special Issue can be read as a response to the current needs and challenges in membrane development for water and wastewater treatment.Half of the research articles correspond to concrete and practical applications of the use of membrane processes in different fields of the industry, with the aim of treating and conditioning water and wastewater. The studies reveal the treatment of industrial streams, mining, recycled paper industry, olive mill, urban wastewater, etc. Another important percentage of studies are related to membrane modification processes, with the aim of obtaining new materials with better performance in the separation processes, thus describing the use of membranes modified with chitosan, nanoparticles, and other organic compounds. This field also includes studies related to fouling and its modeling

Transport mechanism in ionic liquid membranes and the study of thiomersal biodegradation

The initial goal of this work was the development of a supported liquid membrane (SLM) bioreactor for the remediation of vaccine production effluents contaminated with a highly toxic organomercurial – thiomersal. Therefore, two main aspects were focused on: 1) the development of a stable supported liquid membrane – using room temperature ionic liquids (RTILs) – for the selective transport of thiomersal from the wastewater to a biological compartment, 2) study of the biodegradation kinetics of thiomersal to metallic mercury by a Pseudomonas putida strain. The first part of the work focused on the evaluation of the physicochemical properties of ionic liquids and on the SLMs’ operational stability. The results obtained showed that, although it is possible to obtain a SLM with a high stability, water possesses nonnegligible solubility in the RTILs studied. The formation of water clusters inside the hydrophobic ionic liquid was identified and found to regulate the transport of water and small ions. In practical terms, this meant that, although it was possible to transport thiomersal from the vaccine effluent to the biological compartment, complete isolation of the microbial culture could not be guaranteed and the membrane might ultimately be permeable to other species present in the aqueous vaccine wastewater. It was therefore decided not to operate the initially targeted integrated system but, instead, the biological system by itself. Additionally, attention was given to the development of a thorough understanding of the transport mechanisms involved in the solubilisation and transport of water through supported liquid membranes with RTILs as well as to the evaluation of the effect of water uptake by the SLM in the transport mechanisms of water-soluble solutes and its effect on SLM performance. The results obtained highlighted the determinant role played by water – solubilised inside the ionic liquids – on the transport mechanism. It became clear that the transport mechanism of water and water-soluble solutes through SLMs with [CnMIM][PF6] RTILs was regulated by the dynamics of water clusters inside the RTIL, rather than by molecular diffusion through the bulk of the ionic liquid. Although the stability tests vi performed showed that there were no significant losses of organic phase from the membrane pores, the formation of water clusters inside the ionic liquid, which constitute new, non-selective environments for solute transport, leads to a clear deterioration of SLM performance and selectivity. Nevertheless, electrical impedance spectroscopy characterisation of the SLMs showed that the formation of water clusters did not seem to have a detrimental effect on the SLMs’ electrical characteristics and highlighted the potential of using this type of membranes in electrochemical applications with low resistance requirements. The second part of the work studied the kinetics of thiomersal degradation by a pure culture of P. putida spi3 strain, in batch culture and using a synthe tic wastewater. A continuous ly stirred tank reactor fed with the synthetic wastewater was also operated and the bioreactor’s performance and robustness, when exposed to thiomersal shock loads, were evaluated. Finally, a bioreactor for the biological treatment of a real va ccine production effluent was set up and operated at different dilution rates. Thus it was possible to treat a real thiomersal-contaminated effluent, lowering the outlet mercury concentration to values below the European limit for mercury effluent discharges