The work included a research program that brought together forefront knowledge on surface chemistry, mineral-water interaction, physical processes, environmental waste management, and waste/drinking water contamination. The activities carried out over the course of the project were directed along the three main objectives/work packages:
WP1. Study the retention potential of redox sensitive contaminants by (nano)magnetite, by performing a stepwise reduction of the ions of interest in order to develop a reactive barrier as a novel remediation technique. This work package was divided into two experimental parts:
a) We performed batch sorption experiments targeting toxic, acidic, and phosphate rich waste leachates. We focused on the effect of magnetite on U reduction, and As and Sb oxyanion removal, also, addressing the problems of high acidity, and high phosphate concentration, which are the major inhibitors of the treatments proposed so far. As such, we set the basis for an industrial process to decontaminate the aforementioned effluent waters by (i) first, using ZVI to increase the pH of the water while producing Fe2+, (ii) the precipitating phosphate ions as vivianite, and (iii) finally, using magnetite derived from steel industry wastes to immobilize toxic pollutants under different pH conditions and high phosphate concentrations. This three-step process provides new insights into a new ‘green’ route for the decontamination of drinking and waste waters.
b) We performed a series of flow-through controlled experiments through cylindrical aggregates in a microfluidic set up involving cylindrical structured PEGDA/nanomagnetite aggregates to obtain Break Through Curves (BTC) of the contaminants of interest. Antimony solution made with KSb(OH)6 at various pH values is used as the input solution. We showed the efficiency of the system and a significant retention of Sb depending on the initial concentration and the material of the aggregates.
WP2. Shed light into the driving processes during the microfluidics experiments and to investigate the contaminants’ uptake efficiency and mechanisms. We fully characterised the produced phases, following a multi-technique approach of synchrotron radiation based micro-probe techniques, such as X-ray absorption near-edge structure (XANES) and EXAFS (Extended X-Ray Absorption Fine Structure), combined with x-ray micro-fluorescence (µ-XRF) to map the diffusion of Sb within the PEGDA/nanomagnetite aggregates. We performed microfocus elemental and redox mapping of Sb on these aggregates, measuring its diffusion, and reduction particularly in their core to investigate the temporal distribution and the oxidation state of the reduced aqueous species of Sb produced by nanomagnetite reduction. We showed that Sb(V) reduction to Sb(III) is more efficient at low Sb initial concentrations, but the overall Sb removal from solution is increasing with the respective initial concentration.
WP3. Adaptation of a numerical (3D) reactive transport model to describe the μXAS and BTC measurements, in order to validate and compliment the experimental study. This model allows us to define the areas dominated by either diffusing or advective solute transport, identify the reaction zones and estimate the effect of kinetic parameters. The model will then be applied to the interpretation of natural system observations and to set up new water treatments based on such macroscopic devices.
During the course of the project, we extended our research network by collaborating with different European research groups in a national and international level. The results of the project were disseminated in various seminars organised by the host institution, in two workshops, and in four international conferences. One article is already accepted as a result of the work done for this project and enough material is produced for two more articles, already under preparation.
