Suspension stability and mobility of Trap-Ox Fe-zeolites for in-situ nanoremediation

Fe-zeolites for the adsorption and oxidative degradation of nitroaromatic compounds in water

Nitroaromatic compounds (NACs) are prominent explosives. In this context, these toxic substances were released into the environment and cause long-lasting groundwater contamination. In preparation of a possible in-situ remediation, colloidal Fe-zeolites were investigated for their capabilities as adsorbents and oxidation catalysts. It was shown that the Fe-zeolites FeBEA35 and FeFAU55 are potent inorganic adsorbents for NACs and simultaneously capable of activating H2O2 as Fenton-like oxidation catalysts. Adsorption isotherms of 15 NACs on both zeolites were measured to evaluate the option of coupling adsorptive contaminant enrichment with oxidative degradation. The faujasite-type zeolite FeFAU55 showed a distinct S-type adsorption behaviour and reached significantly higher NAC loadings of > 20 wt%. For FeBEA35, L-type adsorption isotherms and maximum loadings qmax of about 4 wt% were obtained. Degradation of all NACs, monitored by nitrate formation, was observed. Apparent rate constants of the NACs with hydroxyl radicals in a homogeneous, stoichiometric Fenton reaction were related to the heterogeneous system to examine the role of adsorption on the oxidative degradation. Beneficial influence of the adsorption on the oxidation rates was identified. The results of this work open up promising prospects for future application of Fe-zeolites for the in-situ remediation of NAC-contaminated groundwater.

Sustainable Management of Salt Slag

The management of salt slag, a waste from the secondary aluminum industry, is associated with huge environmental concerns due to the risk of atmospheric pollution (emission of toxic gases), groundwater contamination (high salt content that can percolate and cause an increase in salinity) and soil unavailability (large extensions required for disposal). Therefore, the development of a sustainable process for its treatment and recovery is of the utmost importance. In this work, a two-step process for the valorization of salt slag was developed that rendered zeolite as the main added-value product and NaCl and NH3 as byproducts. First, salt slag was hydrolyzed at 90 °C and at a solid/water ratio of 1/3. More than 90% of salt and ~90% of ammonia were recovered. In a second step, the hydrolyzed slag was completely transformed into a NaP zeolite under mild hydrothermal conditions. The zeolite exhibited specific surface area (17 m2 g−1), cation exchange capacity (2.12 meq g−1) and zeta potential (−52 mV) values that represent good characteristics for use in the removal of metal ions from aqueous effluents. The transformation of salt slag into zeolite can be considered a sustainable process with a high contribution to the circular economy.

Highly efficient removal of aluminum, iron, and manganese ions using Linde type-A zeolite obtained from hazardous waste

Coal acid mine drainage (AMD) contaminates natural water to form mine-impacted water (MIW), which is characterized by high levels of acidity, sulfate, and metallic ions. This study investigates the use of a Linde Type-A (LTA) zeolite obtained from a hazardous industrial waste for Al³⁺, Fe²⁺, and Mn²⁺ removal from synthetic aqueous solutions. The aim of this study is to stablish a basis for the subsequent treatment of MIW in order to obtain reuse water. In a central composite rotatable design (CCRD) study, 8.25 g L^-1 zeolite and 147 rpm were the optimal conditions for treating the multicomponent solution, yielding 99.9, 99.9 and 99.3% removal for Al³⁺, Fe²⁺, and Mn²⁺, respectively. Isothermal studies showed that the affinity of the ions by the zeolite were ranked as Al³⁺>Mn²⁺>Fe²⁺. The best fitting isothermal models for monocomponent solutions were Tóth, Freundlich, and Sips for Al³⁺, Fe²⁺, and Mn²⁺, respectively. In the multicomponent solution, Sips and Freundlich were the better fitting models for Al³⁺ and Mn²⁺, respectively, indicating a weakness of the sorbate-sorbent interactions. Kinetic studies revealed that the quantitative removal of Al³⁺ was achieved in 5 min. The multicomponent solution was transformed into water that was suitable for non-potable use after an optimal time of 60 min. The results demonstrate that LTA zeolite synthetized from hazardous waste has a high potential for remediating contaminated water by metallic ions at low dosages and short times. Using LTA zeolite for remediating contaminated water could make a positive contribution to the circular economy and environmental sustainability.

Iron-Montmorillonite-Cyclodextrin Composites as Recyclable Sorbent Catalysts for the Adsorption and Surface Oxidation of Organic Pollutants

Iron-clay-cyclodextrin composites were designed as sorbent catalysts to adsorb and oxidize pollutants from water. The clay-iron backbone served as a mechanical support and as a heterogeneous Fenton catalyst, and the cyclodextrin monomers or polymers cross-linked with polyfluorinated aromatic molecules were used to accommodate adsorption of the pollutants. The composite based on iron-clay-cyclodextrin-polymers (Fe-MMT-βCD-DFB) exhibited superior adsorption and degradation of the model pollutants, bisphenol A (BPA), carbamazepine (CBZ), and perfluorooctanoic acid (PFOA), compared to the monomer-based composite and the native iron clay. The variety of adsorption sites, such as the polyfluorinated aromatic cross-linker, cyclodextrin toroid, and iron-clay surface, resulted in high adsorption affinity toward all pollutants; BPA was primarily adsorbed to the cyclodextrin functional groups, CBZ showed high affinity toward the Fe-MMT surface and the Fe-MMT-βCD-DFB composite, whereas PFOA was adsorbed mainly to the βCD-DFB polymer. Degradation, using H₂O₂, was highly efficient, reaching over 90% degradation in 1 h for BPA and CBZ and ∼80% for PFOA. The composite also showed excellent degradation efficiency in a multicomponent system with all three model pollutants. Furthermore, the composite's activity remained steady for five consecutive cycles of adsorption and degradation. The ability to remediate a broad range of pollutants, and the high overall removal exhibited by this novel material, demonstrates the potential for future application in water remediation technologies.

In-situ treatment of herbicide-contaminated groundwater-Feasibility study for the cases atrazine and bromacil using two novel nanoremediation-type materials

Two injectable reactive and sorption-active particle types were evaluated for their applicability in permeable reaction zones for in-situ removal of herbicides ("nanoremediation"). As model substances, atrazine and bromacil were used, two herbicides frequently occurring in groundwater. In order to provide recommendations for best use, particle performance was assessed regarding herbicide degradation and detoxification. For chemical reduction, Carbo-Iron® was studied, a composite material consisting of zerovalent iron and colloidal activated carbon. Carbo-Iron reduced bromacil with increased activity compared to nanoscale zerovalent iron (nZVI). The sole reaction product, 3-sec-butyl-6-methyluracil, showed 500-fold increase in half-maximal-effect concentration (EC₅₀) towards the chlorophyte Scendesmus vacuolatus compared to the parent compound. The detoxification based on dehalogenation confirmed the dependency of the specific mode-of-action on the carbon-halide bond. For atrazine, neither nZVI nor Carbo-Iron showed significant degradation under the conditions applied. As novel subsurface treatment option, Trap-Ox® zeolite FeBEA35 was studied for generation of in-situ permeable oxidation barriers. Both adsorbed atrazine and bromacil underwent fast unselective oxidation. The transformation products of the Fenton-like reaction were identified, and oxidation pathways derived. For atrazine, a 300-fold increase in EC₅₀ for S. vacuolatus was found over the duration of the reaction, and a loss of phytotoxicity to non-detectable levels for bromacil.

Injection of Zerovalent Iron Gels for Aquifer Nanoremediation: Lab Experiments and Modeling

One of the main technical problems faced during field-scale injections of iron microparticles (mZVI) for groundwater nanoremediation is related to their poor colloidal stability and mobility in porous media. In this study, a shear-thinning gel, composed of a mixture of two environmentally friendly biopolymers, i.e., guar gum and xanthan gum, was employed to overcome these limitations. The slurry rheology and particle mobility were characterized by column transport tests. Then, a radial transport experiment was performed to mimic the particle delivery in more realistic conditions. The gel, even at a low polymeric content (1.75 g/L), proved effective in enhancing the mobility of high concentrated mZVI suspensions (20 g/L) in field-like conditions. The high radius of influence (73 cm) and homogeneous iron distribution were achieved by maintaining a low injection overpressure (<0.4 bar). Based only on the information derived from column tests, the MNMs 2018 software (Micro- and Nanoparticle transport, filtration, and clogging Model-Suite) was able to predict the particle distribution and pressure build-up measured in the radial domain. Experimental and simulated results showed good agreement, thus proving that a simplified experimental-modeling procedure based on 1D column tests could be used to effectively upscale the slurry behavior to more representative scales, e.g., radial domains.

The pH dependent surface charging and points of zero charge. VIII. Update

A critical review of the points of zero charge (PZC) obtained by potentiometric titration and of isoelectric points (IEP) obtained by electrokinetic measurements. The results from the recent literature are presented with experimental details (temperature, method, type of apparatus, etc.), and they are compared with the zero points of similar materials reported in older publications. Most studies of PZC and IEP reported in the recent papers were carried out for metal oxides and hydroxides, especially alumina, iron oxides, and titania, and the results are consistent with the PZC and IEP of similar materials reported in older literature, and summarized in previous reviews by the same author. Relatively few studies were carried out with less common materials, and IEP of (nominally) VO₂ and BN have been reported for the 1st time.

Biological effects of four iron-containing nanoremediation materials on the green alga Chlamydomonas sp

As nanoremediation strategies for in-situ groundwater treatment extend beyond nanoiron-based applications to adsorption and oxidation, ecotoxicological evaluations of newly developed materials are required. The biological effects of four new materials with different iron (Fe) speciations ([i] FerMEG12 - pristine flake-like milled Fe(0) nanoparticles (nZVI), [ii] Carbo-Iron^® - Fe(0)-nanoclusters containing activated carbon (AC) composite, [iii] Trap-Ox® Fe-BEA35 (Fe-zeolite) - Fe-doped zeolite, and [iv] Nano-Goethite - 'pure' FeOOH) were studied using the unicellular green alga Chlamydomonas sp. as a model test system. Algal growth rate, chlorophyll fluorescence, efficiency of photosystem II, membrane integrity and reactive oxygen species (ROS) generation were assessed following exposure to 10, 50 and 500 mg L^-1 of the particles for 2 h and 24 h. The particles had a concentration-, material- and time-dependent effect on Chlamydomonas sp., with increased algal growth rate after 24 h. Conversely, significant intracellular ROS levels were detected after 2 h, with much lower levels after 24 h. All Fe-nanomaterials displayed similar Z-average sizes and zeta-potentials at 2 h and 24 h. Effects on Chlamydomonas sp. decreased in the order FerMEG12 > Carbo-Iron® > Fe-zeolite > Nano-Goethite. Ecotoxicological studies were challenged due to some particle properties, i.e. dark colour, effect of constituents and a tendency to agglomerate, especially at high concentrations. All particles exhibited potential to induce significant toxicity at high concentrations (500 mg L^-1), though such concentrations would rapidly decrease to mg or µg L^-1 in aquatic environments, levels harmless to Chlamydomonas sp. The presented findings contribute to the practical usage of particle-based nanoremediation in environmental restoration.