Strong Base Anion Exchange Resin Research Articles

Rhenium sorption from simulated solution with AM-p-2 resin in dynamic mode

The article summarizes the research results on rhenium recovery with AM-p-2 strong-base macroporous styrene-divinyl benzene anion exchange resin with dimethylammonium functional groups from the simulated sulphuric medium and rhenium elution in dynamic mode attaining the recovery rate exceeding 90 % after approximately 1 500 bed volumes. Total dynamic exchange capacity 81.0 mg/g was measured, and column sorption parameters were evaluated using corresponding models. The authors denoted that the total dynamic exchange capacity values defined experimentally and calculated by Thomas fit were close. We studied rhenium elution with the solution containing ammonium nitrate 250 g/L and sulphuric acid 25 g/L yielding rhenium-rich solution that is ~63 times higher comparing to the initial solution. A clear peak in the elution profile allows getting rhenium-rich eluates. The research results will be necessary when defining mass-transfer parameters and designing equipment for processing industrial liquors and waste with rhenium recuperation.

Adsorption of Chromium (VI) from Aqueous Solution Using Nano TiO2 Doped Strong Base Anion Exchange Resin

Background: The evolution of environmentally-safe methods for treating hazardous chemicals in wastewater, particularly urban and industrial wastewater, has increased interest over recent years. The chromium-containing wastewater is produced by industries from steel, metallurgical, electroplating, chemical, refractory, leather tanning, dye manufacturing, mining, cementing, textiles, etc. Consequently, advanced techniques are essential for treating chromium-polluted water. Objective: The prime objective of this effort was to assess the adsorption performance of nanoTiO2 (nanoparticles of average crystallite size 19.15 nm) doped strong base anion exchange resin (TDTulsion) for Cr(VI)to that of the host Tulsion A-62 (MP). Methods: The tests were carried out in batches in the temperature-controlled water bath shaking unit, with 30 ml of the aqueous solution containing Cr(VI) and a certain amount of resin being stirred for 6 hours at 303 K. Using a standard diphenylcarbazide (DPC) procedure at 540 nm, the solution was spectrophotometrically analyzed for Cr(VI). Results: The majority of the Cr(VI) ions are adsorbed by the anion exchange resins Tulsion A- 62(MP), and TD-Tulsion is in the pH range of 4.0 to 5.0. The maximal sorption capacity of Cr (VI) was established to be 181.5 and 204.8 mg/g for Tulsion A-62(MP) and TD-Tulsion, respectively. Conclusion: The TD-Tulsion has a substantially better adsorption capacity than Tulsion A-62(MP) under similar conditions. The outcomes show that modifying anion-exchange resin with nano titanium dioxide improves adsorption performance in Cr(VI) removal from drinking water and contaminated water.

Important properties of anion exchange resins for efficient removal of PFOS and PFOA from groundwater

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) present in various water sources have raised a serious concern on their health risk worldwide. Anion exchange is known to be one of the effective treatment methods but the resin properties suitable for theses contaminants have not been fully understood. We examined four commercially available anion exchange resins with different properties (DIAION™ PA312, HPA25M, UBA120, and WA30) and one polymer-based adsorbent (HP20), for their PFOA and PFOS removal in the batch experiment. All or a part of the selected resins were further characterized for their functional group, surface morphology and pore size distribution. The 72 h batch experiment with the 100 mg/L PFOA or PFOS in the laboratory pure water matrix showed a superior capacity of the strong base anion exchange resins, the porous-type HPA25M and PA312, and the gel-type UBA120, for PFOA removal (92.6–97.9%). Among those resins, the high porous HPA25M was suggested most effective due to its remarkably high reaction rate and effectiveness to PFOS (99.9%). In the groundwater matrix, however, the performance of the those anion exchange resins was generally suppressed, causing up to 71% decrease in their removal rates. The least matrix impact was observed for PFOS removal by HPA25M, which indicated the resin's high selectivity to the contaminant. The physiochemical analysis indicated that the presence of relatively large pores (1 nm–10 nm) over HPA25M played an important role in the PFAS removal.

Chromatographic Separation of Rare Earth Elements as MGDA Complexes on Anion Exchange Resins

Chromatographic separation of rare earth elements (REE) as anionic complexes with chelating aminopolycarboxylate ligand methylglycine N,N-diacetate (MGDA) was studied experimentally. A synthetic mixture of La, Nd, and Eu were used to model a REE mixture obtained from processed secondary sources such as phosphogypsum (PG). In the REE extraction from PG, the REEs can be recovered with MGDA to obtain the REE–MGDA mixture. Three strong base anion exchange resins (Dowex 1X8, IRA-402, and IRA-410) were used as the separation materials. Successful separation of the REEs by elution with dilute HNO3 and HCl was attributed to differences in the stabilities of the REE–MGDA complexes. The pKa values of the complexes were determined by titration to be 3.81, 3.25, and 2.96 for La, Nd, and Eu, respectively. Fractionation of the ternary La-Nd-Eu mixture (with a 1:1:1 mole ratio) were studied. La was recovered at approximately 80% purity and 80% yield, but strong trade-offs between the yield and the purity of Nd and Eu must be made. Chromatographic separation was found to be an efficient process option, considering its simplicity and the recovery of several product fractions. The initial process design offers a promising starting point for investigating more advanced process configurations for the efficient recovery of pure REE from phosphogypsum.

Iodine Removal from Carbonate-Containing Alkaline Liquids Using Strong Base Resins, Hybrid Resins, and Silver Precipitation

The ability of several material types to remove aqueous iodine from a mildly alkaline, carbonate-rich nuclear waste stream was evaluated: strong base anion exchange resins (SBARs), hybrid resins, Ag-containing materials, and Bi-containing hybrid resins. A combination of batch testing and flow-through column testing was used in the evaluation. In batch testing, hybrid resins CHM-20, SIR-110-CE, and RTBI were shown to have high efficiency for the removal of both iodide and iodate simultaneously, while Ag-containing materials and SBAR demonstrated high capacity for iodide removal. One example of each material type (CHM-20, A532E, and Ionex 400) was further evaluated for their sorption isotherms and column performance. The Langmuir isotherm, or a Langmuir–Freundlich hybrid isotherm, best described the sorption of iodide to the CHM-20 hybrid resin and Purolite A532E. The Freundlich isotherm best described the uptake of iodate to CHM-20 and A532E and for both iodide and iodate to Ag-containing Ionex 400. In column testing, Purolite A532E had exceptional performance for overall iodide removal. However, with the capacity demonstrated, the A532E resin would exceed class C waste classification before breakthrough initiated, and column change-outs in processing would be dictated by eventual waste classification, not breakthrough. Ionex 400, a Ag-zeolite, was observed to degrade over time under mild alkaline column conditions, whereas the hybrid CHM-20 was limited in the single pass through design and would be best suited for applications where iodide and iodate are present and recirculation of the column effluent is feasible. This work highlights the feasibility of commercially available materials to separate radioiodine from liquid environments.

Elimination of free fatty acid from palm oil by adsorption process using a strong base anion exchange resin

Deacidification is one of the important processes to obtain a suitable raw feedstock for the production of bio-transformer oil. This work proposed an alternative process for reducing the acidity of refined palm oil by adsorption of the free fatty acids (FFAs) using anion exchange resins (AER). The effect of the types of functional groups (tertiary amine and quaternary ammonium group) and the resin structure (gel and macroporous structure) of the commercially available resins were characterized and investigated for their adsorption ability. The adsorption kinetic and experimental conditions such as adsorption time, the moisture content in resin, and resin amount were studied. The gel-type strong-base anion exchange resins exhibited the best performance for the FFAs removal. This result suggests that the quaternary ammonium functional groups in the resin have a high dissociation capacity for anion exchange and the gel-type resins easily access by the FFAs molecules. The effect of types of functional groups is stronger than that of the resin structure. The adsorption mechanism mainly occurred via an ion exchange equilibrium rather than the hydrogen bond complex. The FFAs adsorption on the resins conformed to the pseudo-second-order kinetic model. Under optimum conditions (room temperature, atmospheric pressure, resin dosage of 0.4 wt%, and 8 h adsorption time), the Pall Tec PTA304 resin reduced the acidity in palm oil from 0.5 to 0.02 mg KOH/g with the adsorption capacity at the equilibrium of 589.5 mg/g, achieving approximately 95 % FFAs removal. The negative values of ΔGads0 and ΔHads0 demonstrated that the FFAs adsorption on the Pall Tec PTA304 resin was a spontaneous and exothermic process. This study provides an insight into the interactions between FFAs and anion exchange resins that is useful for further development of palm based bio-transformer oil.

Anion Exchange Resin and Inorganic Anion Parameter Determination for Model Validation and Evaluation of Unintended Consequences during PFAS Treatment.

When implementing anion exchange (AEX) for per- and polyfluoroalkyl substances treatment, temporal drinking water quality changes from concurrent inorganic anion (IA) removal can create unintended consequences (e.g., corrosion control impacts). To understand potential effects, four drinking water-relevant IAs (bicarbonate, chloride, sulfate, and nitrate) and three gel-type, strong-base AEX resins were evaluated. Batch binary isotherm experiments provided estimates of IA selectivity with respect to chloride ( ) for IA/resin combinations where bicarbonate < sulfate ≤ nitrate at studied conditions. A multi-IA batch experiment demonstrated that binary isotherm-determined values predicted competitive behavior. Subsequent column experiments with and without natural organic matter (NOM) allowed for the validation of a new ion exchange column model (IEX-CM; https://github.com/USEPA/Water_Treatment_Models). IA breakthrough was well-simulated using binary isotherm-determined values and was minimally impacted by NOM. Initial AEX effluent water quality changes with corrosion implications included increased chloride and decreased sulfate and bicarbonate concentrations, resulting in elevated chloride-to-sulfate mass ratios (CSMRs) and Larson ratios (LRs) and depressed pH until the complete breakthrough of the relevant IA(s). IEX-CM utility was further illustrated by simulating the treatment of low-IA source water and a change in the source water to understand the resulting duration of changes in IAs and water quality parameters.

Adsorption of Chromium(VI) from Aqueous Solution using Iron Oxide Loaded Strong Base Anion Exchange Resin

A hybrid adsorbent (FO-Tulsion) was prepared by altering Tulsion A-62(MP), a commercial strongly basic anion-exchanging resin, with hydrated ferric oxide (HFO) particles of average crystallite size 49.6 nm and the removal of Cr6+ from water on Tulsion A-62(MP) and HFO-Tulsion was observed under optimized parameters. This study examines the effectiveness of chromium(VI) removal from water utilizing Tulsion A-62(MP) and Fe-loaded Tulsion A-62(MP) as selective sorbent materials. As the resin and HFO-ion-exchange Tulsion’s mechanism was rather easy and after 210 min of Cr6+ solution interaction, the optimum equilibrium was reached. Almost all the chromium ions was removed by the sorption process when the pH was between 4.0 and 5.0. The Freundlich and Langmuir adsorption isotherms were used to compare the equilibrium data for Cr6+ adsorption and it was found that both are highly suitable for Cr6+ adsorption. Under the same conditions, evaluation of the adsorption attainment of the prepared HFO-Tulsion and the anion resin indicated that the HFO-Tulsion had an elevated adsorption capability with a value of 207.18 mg/g than the anion resin (181.55 mg/g). The resulting hybrid resin was studied using spectroscopic and solid-state methods. Adsorption is governed by first-order reversible kinetics. It is possible that modifying anion resin with hydrated ferric oxide can greatly pick up the adsorption performance in the elimination of Cr6+ from drinking water and polluted water.

Efficient removal of hexavalent chromium ions from simulated wastewater by functionalized anion exchange resin: Process optimization, isotherm and kinetic studies

In the present study, hazardous heavy metal ion hexavalent chromium (Cr(VI)) was removed from aqueous solution by using Indion GS-300 (IGS-300), strong base anion exchange resin. The process parameters for the removal of Cr(VI) were optimized using response surface methodology (RSM) approach. Procured resin was analyzed by various techniques like FTIR, and FESEM associated with elemental analysis which provided functional groups and surface structure of the adsorbents. Various batch adsorption experiments were conducted by varying parameters such as Cr(VI) concentrations from 5 mg/L to 45 mg/L, 2 to 10 pH, IGS-300 resin dosage between 0.38 and 1.88 g/L, and temperature of 20–40 °C with 90 min fixed contact time. Fixed time was determined from preliminary study of the present work. The maximum adsorption capacity of IGS-300 resin was found 294.11 mg/g and 98.20% of removal achieved with optimum conditions of 4 pH, 1.50 g/L adsorbent dosage, 15 mg/L Cr(VI) concentration and 35 °C temperature. The experimental data was found with best fitted Freundlich Isotherm and pseudo second order kinetic model. Regeneration study was also done on the adsorbed resins using different solution includes water, 0.1 M HCl, and 0.1 M NaOH. Up to 3 cycles of 0.1 M NaOH treatment, resin showed >50% Cr(VI) removal in aqueous solution whereas water and HCl were found less effective on third cycle. Therefore, this study found that IGS-300 resin is more efficient adsorbent for the removal of Cr(VI) from aqueous solutions and possessing highly significant regeneration capacity.

Novel chromatographic purification of succinic acid from whey fermentation broth by anionic exchange resins.

Replacement of the petroleum-based refineries with the biorefinery is regarded as an essential step towards a "zero" waste (circular) economy. Biobased succinic acid (SA) is listed by the United States Department of Energy among the top ten chemicals with the potential to replace chemicals from petroleum synthesis with renewable sources. Purification of bio-based succinic acid from fermentation by-products such as alcohols, formic acid, acetic acid and lactic is a major drawback of fermentative SA production. This study addresses this issue through a novel chromatographic separation using three distinct anionic resins: Amberlite IRA958 Cl (strong base anion exchange resin), Amberlite HPR 900 OH (strong base anion exchange resin) and Amberlyst A21 (week base anion exchange resin). The influence of process variables such as flow rate (0.18 BV/h, 0.42 BV/h and 0.84 BV/h), eluent concentration (1%, 5% and 10% HCl) and temperature (20, 30 and 40°C) were investigated. The results indicated SA separation efficiency of 76.1%, 69.3% and 81.2% for Amberlyst A21, Amberlite HPR 900 OH and Amberlite IRA958 Cl, respectively. As the regenerant HCl concentration increased from 1 to 10%, calculated succinic acid separation efficiencies decreased from 80.3 to 70.7%. Notably, as the regenerant strength increased from 1 to 10%, the total amount of organic acids desorbed from the resin sharply increased. At operation temperatures of 20, 30 and 40°C, SA separation efficacies were 81.2%, 73.9% and 76.4%, respectively. The insights from this study will be of great value in design of chromatographic separation systems for organic acids.

Comprehensive oxidative process for the removal of antimony from the surfaces of nuclear reactor coolant systems

An oxidative process using hydrogen peroxide for the dissolution of metallic antimony, stripping of the dissolved antimony ions, and the compatibility of the oxidative process with the structural materials present in the coolant systems of nuclear reactors have been investigated. This process has direct application for the removal of antimony activity and thereby reducing the radiation exposure hazard to the operating personnel. The rate of dissolution of metallic antimony increased in the presence of hydrogen peroxide. The re-deposition of dissolved antimony on the oxide coated carbon steel coupons was ≤0.02 mg/cm2. Three substrates investigated, namely, strong base anion exchange resin and two chitosan-TiO2 based substrates, for the removal of dissolved antimony were equally efficient. The process could dissolve antimony without any significant re-deposition on the oxide coated carbon steel surface and could dissolve antimony incorporated in the oxide film of zircaloy. Corrosion compatibility of relevant alloys, namely, carbon steel, incoloy-800, Zr2·5Nb and monel-400, at pH 10.2 and 9.0, showed that only monel-400 underwent pitting type of attack at pH 10.2.

Comparative investigation of PFAS adsorption onto activated carbon and anion exchange resins during long-term operation of a pilot treatment plant

Widespread contamination of groundwater with per- and polyfluoroalkyl substances (PFAS) has required drinking water producers to quickly adopt practical and efficacious treatments to limit human exposure and deleterious health outcomes. This pilot-scale study comparatively investigated PFAS adsorption behaviors in granular activated carbon (GAC) and two strong-base gel anion exchange resin (AER) columns operated in parallel over a 441-day period to treat contaminated groundwater dominated by short-chain perfluorocarboxylic acids (PFCA). Highly-resolved breakthrough profiles of homologous series of 2–8 CF2 PFCA and perfluorosulfonic acids (PFSA), including ultrashort-chain compounds and branched isomers, were measured to elucidate adsorption trends. Sample ports at intermediate bed depths could predict 50% breakthrough of compounds on an accelerated basis, but lower empty bed contact times led to conservative estimates of initial breakthrough. Homologous PFAS series displayed linear (GAC) and log-linear (AER) relationships between chain-length and breakthrough, independent of initial concentration. AERs generally outperformed GAC on a normalized bed volume basis, and this advantage widened with increasing PFAS chain-length. As designed, all treatments would have short full-scale service times (≤142 days for GAC; ≤61 days for AERs) before initial breakthrough of short-chain (2–4 CF2) PFCA. However, AER displayed far longer breakthrough times for PFSA compared to GAC (>3× treatment time), and breakthrough was not observed for PFSA with >4 CF2 in AERs. GAC had a finite molar adsorption capacity for total PFAS, leading to a stoichiometric replacement of short-chain PFCA by PFSA and longer-chain PFCA over time. AERs quickly reached a finite adsorption capacity for PFCA, but they showed substantially greater selectivity for PFSA whose capacity was not reached within the duration of the pilot. Breakthrough characteristics of keto- and unsaturated-PFSA, identified in the groundwater by suspect screening, were also evaluated in absence of reference standards. Modified PFAS structures (branched, keto-, unsaturated-) broke through faster than linear and unmodified perfluorinated structures with equal degrees of fluorination, and the effects were more pronounced in GAC compared to AERs. The results highlight that the design of robust PFAS treatment systems should consider facets beyond current PFAS targets including operational complexities and impacts of unregulated and unmonitored co-contaminants.

Bioregeneration of sulfate-laden anion exchange resin

Ion exchange technology removes ionic compounds from waters effectively but treatment of the spent regenerant is expensive. The bioregeneration of sulfate-laden strong base anion exchange resin was successfully tested using both pure and mixed sulfate-reducing bacterial cultures. The resin was first used for removal of sulfate from neutral (pH 6.7 ± 0.5) synthetic sodium sulfate solutions, after which the spent resin was regenerated by incubating with a viable sulfate-reducing bacterial culture in batch and column modes. In the batch bioregeneration tests, the achieved bioregeneration was 36–95% of the original capacity of the fresh resin (112 mg SO42−/g) and it increased with regeneration time (1–14 days). The capacity achieved in the column tests during 24 hours of bioregeneration was 107 mg SO42−/g after the first regeneration cycle. During the bioregeneration, sulfate was mainly reduced by the sulfate-reducing bacteria (approx. 60%), but part of it was only detached from the resins (approx. 30%). The resin-attached sulfate was most likely replaced with ions present in the liquid sulfate-reducing bacterial culture (e.g., HCO3−, HS−, and Cl−). During the subsequent exhaustion cycles with the bioregenerated resin, the pH of the treated sodium sulfate solution increased from the original 6.7 ± 0.5 to around 9. The study showed that biological sulfate reduction could be used for sulfate removal in combination with ion exchange, and that the exhausted ion exchange resins could be regenerated using a liquid sulfate-reducing bacterial culture without producing any brine.

Bromate Removal from Water Using Ion Exchange Resin: Batch and Fixed Bed Column Performance

ABSTRACT In this study, the removal of bromate, a regulated ozone by-product, was evaluated using a strong-base anion (SBA) exchange resin in batch and column experiments. The kinetics studies in batch mode showed that film diffusion-controlled bromate exchange in SBA and the isotherm studies showed that the Langmuir model fitted the experimental results with a maximum exchange capacity of 296.66 mg BrO3 −/g (~1.3 meq/mL resin). In the fixed-bed column studies, breakthrough curves were obtained under different operating conditions to examine the effects of feed flow rate, inlet bromate concentration, and bed height on column performance. A modified n-order Bohart and Adams model (n-BAM-c), which considered the asymmetry of the breakthrough curve and flow channeling, was applied for the first time to describe the experimental data obtained from the column and to predict the breakthrough curves. It was found that n-BAM-c fitted the experimental data well (R2 > 0.99) and the effects of the key operating conditions on the model parameters were determined. Overall, the results show that SBA exchange is suitable for bromate removal from water and n-BAM-c could be a powerful tool for the design and upscaling of bromate ion exchange columns.

Adsorption of acetic acid on ion exchange resin in aqueous and non-aqueous conditions: batch equilibrium study and thermodynamic analysis

ABSTRACT Adsorptive removal of acetic acid from aqueous and non-aqueous solutions was carried out using strong base anion exchange resin at 303, 313, and 323 K. The effect of concentration of acetic acid, nature of solvent, and temperature on adsorption of acetic acid and swelling of the resin were investigated. Adsorption of acetic acid and swelling of the resin were favoured in non-polar solvents for a given temperature. Adsorption of acetic acid was favoured at 303 K and decreased with an increase in temperature. Langmuir isotherm model was fitted to equilibrium adsorption data to determine the Langmuir adsorption constant and saturation capacity of the resin. Further, thermodynamic parameters viz. ΔGO, ΔHO, and ΔSO were estimated. The negative values of ΔGO and ΔHO showed that the adsorption of acetic acid on the resin was spontaneous and exothermic in nature.

Regeneration and modelling of a phosphorous removal and recovery hybrid ion exchange resin after long term operation with municipal wastewater

Adsorption represents one of the most promising process for phosphorous (P) removal and recovery from municipal wastewater, but questions about its long-term stability remain. The goals of this work were (i) to assess changes in morphology and adsorption performances of hybrid anion exchanger (HAIX) LayneRT after 2.5 years of operation in a 10 m3 d−1 demonstration plant fed with secondary-treated municipal wastewater, (ii) to optimize the LayneRT regeneration procedure, and (iii) to evaluate the suitability of the ion exchange model to describe P adsorption on LayneRT. LayneRT is composed of hydrated ferric nanoparticles dispersed in a strong base anion exchange resin. Batch and continuous flow adsorption/desorption tests were conducted with the resin used for 2.5 years, regenerated with two alternative solutions: NaOH, reactivating mainly the iron nanoparticles active sites, and NaOH + NaCl, also regenerating the active sites of the ion exchange media. The physicochemical characterization by Scanning Electron Microscope indicated that regeneration by NaOH significantly reduced the deterioration of the resin surface, even after 59 adsorption/desorption cycles. Lab-scale continuous flow tests showed that the resin regenerated with either solution featured P adsorption performances very close to that of the virgin resin. The isotherm tests showed that P adsorption by LayneRT was effectively simulated with the ion exchange model. This study confirms that LayneRT is a durable, resistant and promising media for P recovery from wastewater.

Boron Removal from Aqueous Solutions by Strong Base Anion-exchange Resin Batch and Column Experiments

Borate ion exchange capacity of Purolite NRW600 strong base anion resin in hydroxide form and mixed bed NRW600+NRW100 ion exchange was investigated with static experiments. Anion exchange resin was saturated with 0.1–45 g/dm3 concentration boric acid solution in a static mixer at 20, 30, 40 and 50 °C at 150 rpm for 24 hours. Remaining borate content of saturation solutions was deter-mined with ion chromatography and ICP-OES. The amount of fixed borate as borate anions increased with the saturation borate concentration as well as in case of simple anion exchange as in case of mixed bed.Column sorption-elution study was carried out by using strong base anion exchange resins (Purolite NRW600 and Amberlite IRN78). Resins in hydroxide and in chloride forms were saturated in column with 5–40 g/dm3 boric acid solution in excess. The resin was then eluted with 200 cm3 salt free water with 5 cm3/min at 25 °C and then eluted by 1 mol/dm3 sodium-sulfate solution with 5 cm3/min. The effluent was collected and analyzed for borate content by titrimetric method. In chloride form the resin adsorbed and released much less borate. Effective borate and polyborate sorption needs hydroxide ions in resin phase.

Avoiding pitfalls when modeling removal of per- and polyfluoroalkyl substances by anion exchange.

Per- and polyfluoroalkyl substances (PFAS) are receiving a great deal of attention from regulators, water utilities, and the general public. Anion-exchange resins have shown high capacities for removal of these substances from water, but there is currently a paucity of ion-exchange treatment models available to evaluate performance. In this work, important theoretical and practical considerations are discussed for modeling PFAS removal from drinking water using gel-type, strong-base anion-exchange resin in batch and column processes. Several important limitations found in the literature preclude movement toward model development, including the use of inappropriate isotherms, inappropriate kinetic assumptions, and experimental conditions that are not relevant to drinking water conditions. Theoretical considerations based on ion-exchange fundamentals are presented that will be of assistance to future researchers in developing models, designing batch and column experiments, and interpreting results of batch and column experiments.

Using layered double hydroxides and anion exchange resin to improve the mechanical properties and chloride binding capacity of cement mortars

Chloride-induced corrosion results in the deterioration of concrete structures. To resolve this issue, two types of synthetic layered double hydroxides (LDHs) 2D nanoflakes based on CaFe-NO3 and CaFeAl-NO3 and a strongly basic anion exchange resin (SBAER) were developed for removing chloride ions from simulated sea sand (SSS) mortars. We investigated the combined effect of SSS mortars blended with chloride adsorbents using the response surface methodology (RSM). A Box-Behnken Design (BBD) was used to discuss the independent variables (CaFe-NO3 LDHs, CaFeAl-NO3 LDHs, and SBAER) and evaluate the response of compressive strength and free chloride content concerning admixture content. Experimental results showed that the free chloride content of the samples decreased upon the addition of LDHs and SBAER due to a synergistic effect, which resulted in the formation of LDHs-Cl, [N+(CH3)3Cl−], Friedel’s salt (FS), and Kuzel’s salt (KS). The optimal range of the admixture content was determined to be 0.3–0.6 wt% CaFe-NO3 LDHs, 0.2–0.5 wt% CaFeAl-NO3 LDHs, and 0.2–0.5 wt% SBAER. In conclusion, LDHs and SBAER exhibited excellent chloride binding capacity, which makes them promising candidates for use as high-efficiency and stable chloride composite adsorbents in marine concrete.

Evaluation of a drop-in waste volume reduction method for liquid investigation derived waste containing per- and polyfluoroalkyl substances

Development of on-site treatment strategies for PFAS-containing investigation derived waste (IDW) will decrease the potential for secondary release following off-site disposal, lower disposal costs, and promote more effective long-term management of PFAS-laden waste. Herein, we report the application of a simple, drop-in treatment that utilizes one of two PFAS sorbents: bituminous granular activated carbon (GAC) or strong base anion exchange resin (IX) and a small circulation pump to adsorb and concentrate PFAS impacted mass from liquid IDW collected from two sites with disparate water chemistries and synthetic IDW amended with PFAS-containing aqueous film forming foam (AFFF). Bench scale intermittent circulation experiments revealed that bituminous granular activated carbon (GAC, 0.5 mg/mL) removed up to 97.0 ± 1.4% and 96.4 ± 0.5% of PFOS and PFOA, respectively, in both site-derived IDW sources. Improved performance was observed in experimental treatments containing a strong base anion exchange resin (IX, 0.5 mg/mL), where up to 99.4 ± 0.1% and 96.7 ± 0.2% of PFOS and PFOA were removed, respectively. High chloride concentrations (20 g/L) reduced removal of short chain perfluorocarboxylates (PFBA and PFHxA) using GAC or IX, but high salt concentrations had negligible effects on the removal of PFOA, PFBS, PFHxS, or PFOS. Excellent scalability was observed in mesoscale experiments, where the majority of amended PFAS mass was removed from synthetic IDW within five days of vessel circulation using two different PFAS-capture configurations. Combined PFOS and PFOA concentrations were reduced to levels below 0.07 μg/L using either GAC or IX for both configurations. Results generated in this study support the application of this approach as an economical strategy for potential waste volume reduction in IDW destined for off-site disposal.