Results

Executive resume of the ENVNANOMINPREC (WP1- 2022)

Looking for new, environmentally friendly, and easily accessible sorbents for wastewater treatments, the idea of considering nano minerals precursors as new potential products for water depollution has arisen and made the aim of this project. In order to achieve the project scope, a set of objectives (WP), with corresponding research activities (A) are set as detailed below.

The first stage (WP1) consisted of the synthesis and characterization of nano minerals in nano minerals and the absence of organic compounds. As many minerals form via an amorphous phase we considered nano precursors of iron oxyhydroxides and carbonates as two main materials to be investigated in this scope.

Nano minerals synthesis was carried out using economically affordable chemical inorganic compounds as well as nontoxic organic compounds such as etilen di-amino tetra acetic acid (EDTA) and etilen di- amino di-succinic acid (EDDS), via well-controlled simple hydrolysis coprecipitation methods.

Nano minerals characterization was carried out by using microscopic, crystallographic, spectroscopic techniques as well as and surface properties characterization methods for morphology, particle size, crystallography and mineralogy, the presence of organic content, and surface area and pore volumes, respectively.

 The results showed that the addition of organic chelating agents EDTA and EDDS led to changes to the amorphous calcium carbonate transformation to end products with various morphologies and crystallinities, thus playing an important role as scaffolding matrices for amorphous nano precursors nucleation and ultimately affecting significantly surface properties such as surface area and pore volumes of the final micro mineral polymorphs. Moreover, the increasing addition of organic compounds has led to an inhibition of nano minerals formation (an observation that will be investigated in detail in the next stage of the project). For the amorphous iron oxyhydroxides mineral called ferrihydrite, the addition of EDTA and EDDS has led to minor changes in nano minerals morphologies conducting to a slight increase in crystallinity (more obvious for the FHY-EDTA system) and a substantial decrease in surface properties such as surface area and pore volumes. The spectroscopic results showed that the organic content is present in the structure of nano/micro mineral products and together with the microscopy results suggested that the organics played an important role as a scaffolding for the final structures of nano minerals polymorphs.

Besides the above main proposed activities, additional studies on magnetic organic containing iron oxyhydroxides have been tested as potential adsorbents for dye removal from wastewater.

As deliverables of the first stage of the project activities, the following can be considered: Research and scientific achievements: (i) elaboration of well-characterized nano minerals; (ii) selection of the ones with better surface properties relevant to adsorption processes that will be tested for pollutants removal in further stages of the project. Results dissemination: (i) participation in national and international conferences, (ii) attendance to international workshops/courses for training team members. A manuscript is in progress to be submitted by the end of the year. Personal and professional achievements: teamwork by interchanging valuable research and admin expertise among team members, extending individual experience within the project field.

  Thank you to the great team (dr. Maria Ignat, dr. Cristina Georgiana Coromelci si dr. Elena Andreea Maftei) that has put all their efforts to achieve the outcomes of the first stage of the project! We acknowledge dr. Mihai Ciolan at RAMTEC and dr. Gabriel Ababei at INFT Iasi for their help with SEM and TEM analysis, respectively.                               

Dr. ing. Loredana Brinza (Tepes)

Executive resume of the ENVNANOMINPREC (WP 2 and WP 3 - 2023)

The second stage of the project aimed at: use of synchrotron techniques and/or setting up a lab-based methodology for on line monitoring of nanoparticles transformation in solution, in situ and in real time. This was done by developing new method and protocols using a spectrophotometer device equipped with a special kit for in situ injection of initial solutions and which will be allowed signals while the nanoparticles start to nucleate, form and grow, to be recorded, processed and modelled. In addition, it aimed at investigating the iron oxyhydroxides and calcium carbonates nano and micro minerals as potential adsorbents for persistent dyes (i.e., RY) and toxic metals (i.e., Cr) removal from aqueous solutions. Pollutants removal studies (using manly adsorption but also photodegradation and coprecipitation processes) at varying process conditions were carried out to derive their optimal uptake parameters and optimum operational conditions to be used and reused in multiple cycles for wastewater treatment/depollution.

As deliverables of the second stage of the project activities, the following were considered and delivered:

Ø  Research and scientific achievements on:

- WP2: Kinetic studies of nanoparticles formation and transformation to derive information about transformation rates which determine the effect of organic/chelating agents on nanoparticles stability, formation and transformation and will have further implication on pollutants sequestration time frame. The use of synchrotron techniques and developing new lab-based methodology for in situ monitoring of minerals formation kinetic, were innovative aspects of WP2.

- WP3. Adsorption studies of persistent pollutants (i.e., Cr and RY dye) onto minerals (of iron oxyhydroxides for acidic to neutral aqueous solutions and of calcium carbonates for neutral to basic aqueous solutions) with and without organic chelating agents, aiming for materials with higher surface properties which could led to efficient removal of these pollutants. Products reusability in multiple adsorption cycles were considered.

Ø  Results dissemination: (i) participation to 3 national and international conferences, (ii) team members attendance to specific SAXS training and experiments run at synchrotron for kinetic monitoring of nanoparticles formation, growth and transformation. Two manuscripts were published in high impact factor journals (i.e., IF 8.6 and 5.82) from red and yellow zones (), one manuscript is submitted for review and another 3 manuscripts are in progress to be submitted next year.

Ø  Personal and professional achievements: teamwork by interchanging valuable research and administrative expertise among team members, extending individual experience within the project field.

Thank you to drd. Alecsandra Lupu, dr. Maria Ignat, dr. Cristina Georgiana Coromelci and dr. Elena Andreea Maftei for their efforts to achieve the outcomes of the second stage of the project! We acknowledge the help of dr. Mihai Ciolan at the RAMTEC, AICU, Iasi for help with SEM analysis and dr. Thomas Zinn and dr. Paul Wady at Diamond Light Source, UK for help with SAXS operation and data processing training. This work is supported by the Romanian Ministry of Research and Innovation, within, PN-III-P1-1.1-TE-2021-0207 (contract TE 24_2022).

Dr. ing. Loredana Brinza (Tepes)

ENVNANOMINPREC

Executive resume

Abstract

Many minerals form via an amorphous precursor. These precursors are thermostatically unstable, changing to more stable polymorphs function of environmental conditions. They are interesting due to their very high surface area, which makes them very efficient sorbents for various applications. During their transformation to crystalline minerals, the adsorbed elements are immobilized and sequestered within the transformation end products. In addition, the presence of inorganic co-ions and/or organic (macro) molecules, called additives, in a synthesis environment, could lead to partial or total stabilization and functioning of the amorphous phase. This can imply a longer time for pollutant uptake. Additives can also change the route for transformation and the type of transformation end products, working as a scaffolding for intermediate and/or end products. Changes in end members' morphology as a function of additives type, concentration and process conditions have a direct impact on particles' surface properties (surface area, charge and pore size), which again may impact on pollutants sorption efficiency. This phenomenon was observed occurring naturally, in bio mediated processes, but the mechanism of stabilization and kinetics are not yet known. Thus, this research focused on the synthesis, characterization and applications of iron oxyhydroxides and carbonate nano-precursors, their transformation kinetic, in situ, in the presence of organics and their applications for wastewater treatments.

I.                General objectives:

WP1. The synthesis and microscopic, crystallographic, spectroscopic and surface properties characterization of nano minerals in nano minerals and the absence of organic compounds (ie., ethylenediaminotetraacetic acid – EDTA and ethylenediamine-N,N'-disuccinic acid – EDDS). As many minerals form via an amorphous phase we considered nano iron oxyhydroxides and carbonates as the two main materials to be investigated in this scope.

WP2. Kinetic studies of nanoparticles formation and transformation to derive information about transformation rates which determine the effect of organic/chelating agents on nanoparticles stability, formation and transformation and will have further implications on pollutant sequestration time frame. The use of synchrotron techniques and the development of a new lab-based methodology for in situ monitoring of minerals formation kinetic were the innovative aspects of WP2.

 WP3. Adsorption studies of persistent pollutants (i.e., Cr and RY dye) onto minerals (of iron oxyhydroxides for acidic to neutral aqueous solutions and of calcium carbonates for neutral to basic aqueous solutions) with and without organic chelating agents, aiming for materials with higher surface properties which could lead to efficient removal of these pollutants. Product reusability in multiple adsorption cycles was considered.

WP4. Environmental applications on real effluents of the most efficient adsorbents tested in WP3 and characterised in WP1. Quantitative targets here are 100% pollutant removal efficiency from real wastewater or pollutant concentration in effluents as low as or below the standard limits set by the environmental standards to be released to surface waters.

II.              Estimated results:

Minimum 4 articles submitted towards publication at the end of the project.
Participation to conferences
Project information and dissemination of its results via a designated web page. https://sites.google.com/view/envnanominprec/pagina-de-pornire/home

III.           Obtained results:

 Published article, submitted manuscripts and manuscripts in progress to be submitted:

1.      Andreea Elena Maftei, Imad Ahmed, Mariana Neamtu, Cristina Giorgiana Coromelci, Maria Ignat, Loredana Brinza, 2023. Nanocrystalline structured ethylene glycol doped maghemite for persistent pollutants removal, Environmental Science: Water Research and Technology, DOI: 10.1039/d2ew00986b.

2.      Cristina Giorgiana Coromelci, Andreea Elena Maftei, Mariana Neamtu, Gabriel Ababei, Loredana Brinza, Amorphous iron oxyhydroxides nano precursors used for dyes removal from aqueous solutions, 2023 online, Separation and Purification Technology vol 331, 1 march 2024, 125632. DOI:10.1016/j.seppur.2023.125632

3.     Cristina Giorgiana Coromelci, Andreea Elena Maftei, Maria Ignat, Loredana Brinza, 2023, Qualitative and quantitative investigations of Cr (VI) uptake by amorphous nanoparticulate ferrites doped with organic chelating agents, initially sent to evaluation towards Chemical Engineering Journal and Nano Research Journal. Manuscript sent to Ecotoxicology and Environmental Safety Journal.

4.      Iuliana Breaban, Imad Ahmed, Maria Ignat, Loredana Brinza, Synthesis, characterization and applications of magnetite nanoparticles for dye removal from aqueous solutions: adsorption, practical and theoretical approaches, manuscript in revision with Heliyon.

5.      Andreea Elena Maftei, Alecsandra Lupu, Juan Diego Rodriguez Blanco, Remi Rateau,8 Loredana Brinza et al., Cr removal via coprecipitation by carbonates and iron oxihydroxides, the effect of organic chelating agents, manuscript in revision with Environmental Research.

6.      Maria Ignat, Juan Diego Rodriguez Blanco, Loredana Brinza, Kinetic studies of ACC formation and transformation in the presence and the absence of organic chelating agents EDTA and EDDS: offline and in situ and real-time monitoring of the effect of organic compounds, in preparation to be submitted to Crystal Growth and Design.

7.    Alecsandra Lupu, Loredana Brinza, et al., Applications of amorphous iron oxyhydroxides in the presence and absence of organic chelating agents for Reactive Red removal: practical and theoretical approaches in preparation to be submitted after the project ends.

Results presented at 8 national and international conferences.

Web page: https://sites.google.com/view/envnanominprec/pagina-de-pornire/home

IV.            Selected activities and results in brief

-   Nanoparticulate ferrites and calcium carbonate minerals synthesized in the presence and the absence of organic chelating agents.  

-   Kinetic studies of nanominerals nucleation, growth and transformation to crystalline polymorphs. Development of new techniques at lab base for in situ and in real-time monitoring of nanominerals formation.

-   Applicative studies of dyes and toxic metals removal by ferrites (ferrihydrite, magnetite, maghemite) and calcium carbonates by adsorption but also photodegradation and coprecipitation

-   Adsorbent reuse studies, finding the best eluent for pollutant recovery, nanoparticle’s surface regeneration and functioning.

-   Geochemical modelling of pollutants (Cr(VI) and As(VI)) in solution to derive info about species available to bind at adsorbents surface, and geochemical modelling of adsorption processes respecting the experimental setup conditions

-   Experimental vs. modelling results comparison to see how well geochemical modelling can predict processes occurring in real systems/ environments.

-   Experimental studies of nano minerals' effect on polluted real effluents or surface waters

-   The entire research opened new perspectives for the professional development of the team members through knowledge and experience exchange.

Below, selected results are displayed followed by main results briefly summarized at the end of the report.

V.             Selected essential scientific findings:

Nanoprecursors of carbonates and ferrite minerals were synthesized in the presence and the absence of complexation organic compounds, such as ethylene di-amino tetra acetic acid (EDTA), ethylene diamino di-succinic acid (EDDS) and ethylene glycol (EG). They were characterized by high-resolution microscopic techniques (SEM/TEM) to assess variations in size and morphology, by diffraction (XRD and SEAD) for crystallographic features and BET for surface properties. Spectroscopic characterization led to confirmation that organic compound was present in the nanoparticle structure, most probably complexing Fe and Ca during the synthesis. The results showed that the addition of EDTA and EDDS led to changes in the morphology of the final transformation polymorphs for carbonates, whereas for ferrite, such as ferrihydrite, it led to changes in nanoparticles amorphycity: the presence of high content of chelating agents (50% of Fe:org molar ratios) leading to a more ordered ferrihydrite (possibly new polymorphs with crystallographic features between 2 line ferrihydrite towards 6-line ferrihydrite).

Monitoring in situ and real-time the kinetic of carbonates formation in the presence and the absence of EDTA and EDDS, the results revealed different behaviours: EDTA did not affect significantly the process of Ca carbonate formation, timewise, whereas with increasing content of the EDDS (up to 25%) has led to 25% delays in calcium carbonates nanoparticles nucleation or growth of amorphous calcium carbonate transformation to final crystalline polymorphs. Although the two complexing agents are similar in composition, they are different in spatial structure (the EDDS is the cis isomer of the EDTA), and it seems that they have a different effect on minerals crystallization and growth. The delay in amorphous calcium carbonate transformation or amorphous phase stabilisation over a slightly longer term may have an important contribution to pollutant retention during coprecipitation of high surface area amorphous nanoparticulate minerals. As an example, the addition of EDDS – as an environmentally friendly (non-toxic) and easy biodegradable additive to wastewater treatment sites or carbonates-rich hydrothermal springs, may improve pollutants uptake (by being adsorbed on the high surface area of minerals amorphous precursors) and favour their sequestration (within crystalline and stable polymorphs during minerals transformation), hence, reduce their mobility in water bodies.

Laboratory-based environmental applications for persistent dyes removal, such as reactive yellow, by ferrites, such as ferrihydrite, magnetite and maghemite as well as calcium carbonates with 10% EDTA, showed very good removal, 100 % at dye concentrations of 10-20 mg/L, a concentration that is within the limits of effluents from textile industries1. The maximum uptake capacities by adsorption of these ferrites2,3 and calcium carbonate with 10% EDTA4 were determined to be between 30-40 mg reactive yellow/g adsorbent. The optimal conditions for efficient dye removal were mild acidic pH and dye concentrations up to 50 mg/L. All the results showed that usually dye removal takes place relatively fast, within 10-30 min, a fact that classifies the adsorption process over photodegradation processes for dye removal. However, at sites where dye concentration is elevated, our studies have shown that alternating adsorption with photodegradation conducted to an enhanced dye removal, these processes, having a great impact on Reactive Yellow removal when its concentration in solution is from 20 mg/L and higher – dye removal being 100%. Dye removal by photodegradation processes, using maghemite as catalysts that enhanced Fenton like photodegradation processes, although slower, may be a feasible alternative to be combined with adsorption at sites where wastewater contains elevated concentration and the treatment set up permits (i.e, open spaced landscape treatment plants exposed to natural day light UV).

It is important to mention that in some cases, in which polluted wastewaters were used, ferrite nanoparticles that were synthesized in the presence of chelating agents, EDTA/EDDS, have led to similar performance to ones without organics. These results may be related to the presence of background ions from wastewater that may form chemical bridges with large dye molecules, binding at the adsorbent surface.

Studies of ferric adsorbent reuse in multiple cycles have shown that ferrihydrite, magnetite and maghemite can be used in up to 8 cycles, remarkable being the ones with magnetic properties that can be easily recovered. As an efficient eluent, generally, a light basic solution has shown the best performance for dye recovery and adsorbent regeneration and functioning, as opposed to light acidic ones or chelating agents’ solutions.

 Adsorption studies carried out for inorganic pollutants removal, such as toxic Cr(VI) and As(V), by iron oxyhydroxides and calcium carbonates nanomaterials, have shown superior values, i.e., 100%, at mildly acidic pH values, for ferrites, in particular. Thus, total removal of hexavalent Cr(VI) was obtained for Cr in solution at concentrations of 10 mg/L, a concentration that is 100 times higher than the one stated in the environmental standard for effluent release in surface waters (0.1 mg/L)5.

Although Cr removal via adsorption has a significant performance: 100% of Cr was adsorbed up to 1 h at an initial concentration of 10 mg/L, adsorbent saturation being reached at Cr initial concentration over 100mg/L, with a maximum uptake capacity of 33 mg/g, at pH 5, very interesting are the results of adsorption vs coprecipitation that were carried out for comparative removal of Cr by both processes. They showed that Cr did not retain by coprecipitation with carbonates, its removal by ferrihydrite has shown much more effective (twice effective) via coprecipitation during ferrihydrite formation, than via adsorption (maximum uptake being ca. 70 mg/g). These results have an essential impact on applications of Cr removal by sequestration during coprecipitation and further, adsorption onto ferrihydrite, at contaminated sites where ferrihydrite forms naturally (i.e., acid mine drainage and at mining sites).

Similar to the dye organic pollutants removal from wastewaters studies, for the inorganic pollutants, such as hexavalent Cr, results showed that the presence of EDTA/EDDS within ferrihydrite structure, enhanced Cr uptake from the Blue Lake (Maramures County, Romania) contaminated with 10 mg/L hexavalent Cr, to approx. 100%.

Geochemical modelling of inorganic pollutants (i.e., Cr, As) in solution, showed ion species available to bind at the adsorbent surface and that no self-precipitation can occur, under the experimental conditions studied. Geochemical modelling of the adsorption process of Cr onto ferrihydrite, carried out under similar conditions to experimental ones, with two common adsorption models (HFO and FHY-DLM6-8) available in Visual Minteq, showed similar trends to the experimental results. However, quantitatively the results differ (ca 40-60%), and computational results overestimate Cr removal as compared to the experimental results. These differences can be explained by inconsistencies in compound species as well as their thermodynamic parameters in the database and also by the choice of the adsorption model used and its theoretical hypothesis. For example, the higher surface area for ferrihydrite (i.e., 600 m2/g) vs. experimentally determined (233 m2/g) of the ferrihydrite used in this study, could be a reason for this inconsistency. Comparing Cr results with previous results available in the literature, on this matter, it can be noticed that for Mo the modelling overlapped well with the experimental results, whereas for V geochemical modelling, under-estimate the experimental results obtained for these oxoanions removal by ferrihydrite9. Thus, careful attention needs to be addressed in the future to improving the geochemical modelling software and databases, to generate sensible outputs, as close as possible to real scenarios (polluted sites, polluted effluents, treatment sites, depollution stations).

VI.            Future perspectives: 

In perspective can be considered adsorption studies of other refractory organic dyes removal by ferrihydrite, magnetite and maghemite functionalised with different environmentally friendly organic molecules alternated or simultaneously carried out with photodegradation, process optimization and tests to pilot scales. Continuous investigation of dye adsorption on carbonates, with an enhancement of carbonate recovery by thermal treatment can be suggested. It is recommended to complete geochemical modelling databases and get in touch with the software modeller to suggest increasing flexibility of adsorption model parameters that are embodied by default. These might lead to better prediction of phenomena and processes that occur in real waters and would immensely help theoreticians in the simulation of various scenarios in natural complex environments.

VII.         Acknowledgements

Thank you to drd. Alecsandra Lupu, dr. Maria Ignat, dr. Cristina Georgiana Coromelci and dr. Elena Andreea Maftei for their efforts to achieve the outcomes of the project! We acknowledge the help of dr. Mihai Ciolan at the RAMTEC, Alexandru Ioan Cuza University of Iasi for help with SEM analysis and dr. Thomas Zinn and dr. Paul Wady at Diamond Light Source, UK for help with SAXS operation and data processing training. This work is supported by the Romanian Ministry of Research and Innovation, within, PN-III-P1-1.1-TE-2021-0207 (contract TE 24_2022).

Anexxe1. Snapshots of published articles, submitted manuscripts, graphical abstracts of manuscripts in progress, posters presented at selected conferences and abstracts of works sent to conferences.

Scientific Researched II, dr. ing. Loredana Brinza (Tepes)

On behalf of the ENVNANOMINPREC team