Ion Exchange Regeneration Research Articles

Investigation of regenerable ion exchange system for 3-nitro-1,2,4-triazol-5-one (NTO) removal from wastewater

Effective treatment trains are needed to address insensitive munitions (IM) in wastewater. Ion exchange paired with oxidative munition degradation was evaluated for IM wastewater treatment. Herein, removal of 3-nitro-1,2,4-triazol-5-one (NTO) was the design basis due to its high concentration at ≥ 1,400 mg/L in IM wastewater. Removal of NTO from simulated IM wastewater by Purolite A532E IX columns was observed over 18 cycles. Overall, 89–99 % of NTO was removed from solutions containing only NTO, and 81–99 % NTO was removed from solutions also containing 2,4-dinitroanisole (DNAN), nitroguanidine (NQ), and hexahydro-1,3,5-trinitro-1.3.5-triazine (RDX). Only 2–34 % of NTO was removed when nitrate or perchlorate were present. Regenerant composed of 0.01 M HCl and 1 % MeOH removed NTO and allowed 12 cycles of repeated loading and unloading before resins needed to be replaced. Across a total of 18 cycles observed with differing influent and regenerant methods, NTO removal in a single column was 69±8 % and the regeneration efficiency 76±5 %. The NTO in spent regenerant solutions were completely degraded over 1.5 hr of ozone-nanobubble treatment and 7 hr of UV/H2O2 treatment. These results suggest that once optimized, ion exchange of NTO from munitions wastewater may be a viable technology to include in munitions wastewater treatment trains.

Integrating diffusion dialysis for sustainable acid recovery from ion exchange regeneration stages: Characterization of metal and non-metal ions migration

Seawater mining presents a potential option for recovering the European Union’s Critical Raw Materials (CRMs), but direct extraction from seawater is challenging due to their low concentrations, as most of them are Trace Elements (TEs) (at levels of mg/L or µg/L). Saltworks bitterns (ultraconcentrated brines resulting from the sea salt production process) offer an alternative solution, naturally concentrated up to 40 times more than seawater. These bitterns can be further processed with chelating Ion Exchange (IX) sorbents to selectively extract TEs. However, this process requires an acidic elution stage with strong acids, followed by neutralization, to recover TEs through precipitation, demanding extensive chemicals consumption. Diffusion Dialysis (DD) could be used to recover the excess acid without external reagents, using an acid-resistant Anion Exchange Membrane (AEM). This study evaluates DD through batch and once-through tests for acid recovery from simulated IX eluate generated in the elution stage of TEs (B, Ga, Ge, Co, Sr) recovery from saltworks bitterns.Batch tests achieved high recoveries for HCl (45–50 %) and H2SO4 (30–37 %), being the theoretical maximum attainable recovery equal to 50 %. B and Ge only partially permeated through the membrane (82 % rejection) by a diffusion mechanism in their neutral form (H3BO3(aq), H4GeO4(aq)). Ga, Co and Sr, in cationic form, were highly rejected (>96 %). Permeability followed the order Ga < Sr < Co ≪ Ge < B, due to the relevant charge and size. HCl permeability correlated linearly with concentration, while H2SO4 was inversely proportional. Once-through tests showed higher acid (74 % HCl, 62 % H2SO4) and oxoacid (66 % H3BO3(aq), 52 % H4GeO4(aq)) recovery at a low specific flow rate, or apparent flux, (0.38 L/(m2membrane·h)) due to increased residence time. Water to acid flow rate ratios did not affect species transport when an excess of water was guaranteed. Conversely, an influence was observed when the ratio was below 1, with a minimum at 0.18, where a very low passage of species was observed due to the reduced dilution volume of the dialysate solution (water). A 1D transport model, incorporating the solutes permeabilities determined experimentally, effectively described the system performance, especially for HCl and B, albeit slightly overestimating the other TEs’ transport.

Techno-Economic Study on the Application of Reverse Osmosis Technology in the Process of Boiler Feed Water Demineralization PT Puncak Jaya Power 3x65 MW

The quality of boiler feed water in a Coal Power Plant generation (PLTU) needs to be considered to avoid corrosion and deposits (scale) on process equipment. Decreased water quality causes several disturbances as such disruption of power plant operations and also regeneration of the ion exchange unit is required quite frequently. This study aims to evaluate the performance of boiler feed water demineralization system with the addition of RO unit and the effect of implementing RO system on chemical consumption in demineralizer regeneration process, as well as determine long-term economic benefits. The research was conducted in the demineralization building area of PLTU PT Puncak Jaya Power 3x65 MW, a power plant owned by PT Freeport Indonesia, located in Amamapare Village, Timika, Papua. This research is divided into two phases: technical evaluation based on research data that will be optimized using the Water Application Value Engine® (WAVE) software, and economic evaluation. Good results are obtained by adding an RO unit to the boiler feed water demineralization unit. Its application allows reducing operating costs and implementing higher level water treatment automation. The chosen RO module configuration is 2 stages with 6 vessels, offering several advantages: % recovery = 70%, high average flux = 22.5 Liters/m2/hour, longer membrane life with the additional filter, reduced load in the first stage. The results of the economic evaluation indicate that the reduction in chemical consumption for ion exchange regenerant will yield 218% return on investment (ROI) with an amortization period of two years.

Decomposition of PFOA in IEX regeneration wastewater: Comparison of UV/sulfur-based processes, key parameters and submicellar aggregates on degradation kinetics

The ultraviolet/sulfite (UV/S) destruction of perfluorooctanoic acid (PFOA) in seven solutions, representing ion exchange (IEX) regeneration wastes, was investigated, where Na2SO4, Na2SO3 and NaCl were the most promising regenerants in degrading PFOA. A complete degradation and 94.7 % defluorination of 10 ppm PFOA were achieved in 10 % (1.7 M) NaCl regenerant containing waste within fluence of 248 J.cm−2. Among the four investigated key parameters (pH, sulfite dose, temperature, and initial PFOA concentration), an unexpected trend was observed for the effect of PFOA initial concentration on degradation efficiency. At outset of process, higher initial PFOA concentrations led to substantial decrease in PFOA concentration, but this trend reversed as the process continued. This drop in concentration is explained based on the fast aggregation of PFOA as revealed in molecular dynamic simulations and thermodynamic calculation. The reactivity of aggregates toward eaq- was three orders of magnitude less than that of monomers. Incorporating aggregation into the kinetic model led to a noteworthy improvement in the model prediction of PFOA concentration profiles, closely aligned with the experimental data. Neglecting aggregation kinetics in models can lead to an overestimation of the required fluence for PFOA degradation, with significant cost implications for large-scale treatment system design. This study underscores the critical and often underestimated issue of PFAS aggregation and its profound implications for the effectiveness of UV/S treatment in addressing IEX regeneration wastes.

Sustainable mainstream deammonification by ion exchange and bioregeneration via partial nitritation/anammox

The partial nitritation and anammox (PN/A) process has gained popularity for the treatment of nitrogen removal in wastewater due to significant energy savings and its potentially much lower CO2 footprint. However, the treatment of mainstream municipal wastewater by PN/A has been limited mainly due to its unsuitable composition. In this research, we apply ion exchange using a zeolite column to selectively remove and concentrate ammonium from mainstream municipal wastewater. After an absorption phase, the ion exchange column is regenerated using a brine solution. The ammonium rich brine is “bioregenerated” in a PN/A reactor where ammonium is converted to nitrogen gas allowing the brine to be reused in another cycle of ion exchange regeneration. To successfully remove ammonium from the spent brine, anammox and ammonia oxidizing bacteria (AOB) were first cultivated in separate reactors under hypersaline conditions (4.0 %) and later combined in a single PN/A reactor. After continuous operation with sea water, the PN/A reactor treated recirculating brine from the ion exchange column for 48 cycles of ammonium absorption and bioregeneration with minimal blowdown. The various cations of the regenerant solution were stable except for calcium that reached very high values upwards of 3000 mg/L as Ca2+ and finally caused PN/A reactor failure due to mineral precipitation. The buildup of high concentrations of calcium in the regenerant was addressed in two ways: 1) 20 % regenerant replacement per cycle, and 2) precipitation of CaCO3 via the addition of sodium carbonate. Both methods were applied to 30 absorption and bioregeneration cycles each and shown to be effective in keeping calcium concentrations from accumulating in the regenerant allowing for stable PN/A reactor operation.

Kinetic research on ion exchange regeneration of quaternary ammonium-based CO2 sorbent for direct air capture

To satisfy the Paris Agreement's 1.5 °C goals, direct air capture (DAC) has become an increasingly crucial technology. However, the ultralow partial pressure of CO2 in ambient air contributes to a low desorption rate and high regeneration energy consumption. In this study, we proposed a fast regeneration method for CO2 sorbents based on an ion exchange process. Utilizing an alkaline solution rich in hydroxide (OH–) ions, the quaternary ammonium (QA)-based ion exchange resin can be changed from carbonate (CO32–) to OH– form, which directly captures CO2 from ambient air. The results showed that the working capacity of the sorbents in the OH– form was 1.85 mmol⋅g−1, which was double that of the CO32– form (0.88 mmol⋅g−1). The kinetics showed that the ratio of OH–/HCO3– at inlet, concentration, and external diffusion influence the desorption rate of CO32– because of the ion exchange reaction. With a high ratio of OH–/HCO3– at inlet, 1 M alkaline solution, and 3 mL⋅s−1 cyclic flow rate, the desorption time of the sorbents was approximately 20 min. Finally, because the energy consumption of the entire process comprises mainly electric energy required to regenerate the alkaline solution after ion exchange, it is expected to establish an electrochemical DAC system to utilize renewable energy efficiently.

A new pretreatment approach for applying high-recovery reverse osmosis desalination to highly scaling brackish groundwater

A new approach is presented for pretreating very hard, divalent-ion-laden brackish-water, to allow applying reverse-osmosis desalination at reasonable recovery-ratio and competitive cost. The approach consists of a cation-exchange step applied on the raw-water to reduce the divalent-cation concentrations thereby enabling operation at high recovery (>80 %) without chemical scaling. For cost-effectiveness, the exhausted ion-exchange regeneration solution undergoes nanofiltration separations to recover the NaCl, enabling multi-cycle usage. The process was exemplified on brackish groundwater from New-Mexico's National-Desalination-Research-Facility. Two treatment alternatives were considered for the exhausted regeneration brine, consisting of several NF in series (alternative 1) and additional NF-retentate treatment (alternative 2). Following simulation and selection of alternative 1, empirical-evaluation and cost-assessment ensued. The results showed that when the regeneration-solution contained total-hardness < 2 % of the total-cation concentration (eq/eq), the cation-exchange breakthrough curves did not deteriorate. To maintain this criterion the exhausted regeneration-solution should undergo 3–4 sequential NF passes after each regeneration cycle. This approach enables operating the BWRO plant with RR = 81 % at additional cost of ∼US$0.4/m3 (CAPEX+OPEX), which ∼doubles the overall brackish desalination cost, but also produces more desalted water and much less retentate. The approach is competitive when the brackish water is laden with divalent ions and the retentate discharge-cost is high.

Physicochemical model for simulating the chemical processes during the crystallization of minerals from spent ion exchange regenerant

Traditionally, industrial processes produce wastes that, even though often containing useful materials, are discarded, contributing to environmental pollution and depletion of natural resources. An example of such wastes are brines, flows of concentrated salts, produced in water treatment processes, which are now routinely discharged into receiving water bodies. Brines however can also be considered as flows of reusable materials which should be recovered, and the Zero Brine cooperation project aims to develop processes for that purpose. For a demineralized water production plant in the port of Rotterdam (the Netherlands), a closed water processing cycle was proposed to treat the large volume of spent Ion Exchange (IEX) regenerant brine which, apart from recovering demineralized water, is also intended to produce magnesium (Mg2+) and calcium (Ca2+) salts, with the highest purity possible, from the otherwise discharged brine. The process scheme includes nanofiltration (NF) for separating mono- and multivalent ions, followed by sequential chemical precipitation of Mg2+ and Ca2+ ions from the NF concentrate, and production of demineralized water by evaporation of the NF permeate. The concentrate of monovalent ions produced in the evaporator, essentially a concentrated sodium chloride solution, in its turn might be reused for IEX regeneration. Part of the supernatant of the sequential precipitation may be fed to the evaporator as well, but bleeding the other part of this supernatant is essential in order to maintain process stability, avoid accumulation of minor pollutants, and reduce scaling. In this study, various scenarios to operate the process were modeled, using PHREEQC and Excel. According to the simulation results, recovery of ≈97% of Mg2+ and Ca2+ is possible, the latter with a higher purity than the former. The main factors affecting the results are the concentration of carbonate present in the spent IEX regenerant, as well as characteristics of the NF membrane and the dosing of sodium hydroxide in the sequential precipitation steps. The results of the simulations were used for the design and operation of a pilot plant, comprising all mentioned process steps.

Electrically regenerated ion-exchange technology: Leveraging faradaic reactions and assessing the effect of co-ion sorption

Capacitive deionization (CDI) technologies have the potential to become cost-competitive alternatives to reverse osmosis for the treatment of brackish waters. In this study, we report our findings on the effect of co-ion sorption and faradaic side reactions on our ion exchange resin functionalized desalination electrodes which passively capture salt and reject it upon charging. This system, which we previously reported on and refer to as electrically regenerated ion exchange (ERI), avoids the use of expensive ion exchange membranes in an effort to save costs. Surprisingly, we find that, compared to a reference CDI system, ERI electrodes capture salt most effectively at low applied voltages (0.5 mg/cm3 at 0.8 V). Both CDI and ERI systems also seem to suffer from co-ion sorption effects which negatively impact salt adsorption. However, Faradaic side reactions at higher voltages (1 V and 1.2 V) which we track via pH measurements, serve as a detriment to CDI but seem to facilitate the functionality of ERI.

Reverse Osmosis Treatment of Wastewater for Reuse as Process Water-A Case Study.

The aim of this work was to purify mixed wastewater from three different production processes in such a manner that they could be reused as process water. The maximum allowed concentrations (MAC) from the Environmental Standards for emissions of substances released into surface water were set as target concentrations. Wastewaters contained solid particles, sodium, aluminium, chloride, and nitrogen in high amounts. Quantitatively, most wastewaters were generated in the production line of alumina washing. The second type of wastewater was generated from the production line of boehmite. The third type of wastewater was from regeneration of ion exchangers, which are applied for feed boiler water treatment. The initial treatment step of wastewater mixture was neutralisation, using 35% HCl. The precoat filtration followed, and the level of suspended solids was reduced from 320 mg/L to only 9 mg/L. The concentrations of ions, such as aluminium, sodium and chlorides remained above the MAC. Therefore, laboratory reverse osmosis was applied to remove the listed pollutants from the water. We succeeded in removal of all the pollutants. The concentration of aluminium decreased below 3 mg/L, the sodium to 145 mg/L and chlorides to 193 mg/L. The concentration of nitrate nitrogen decreased below 20 mg/L.

Field demonstration of coupling ion-exchange resin with electrochemical oxidation for enhanced treatment of per- and polyfluoroalkyl substances (PFAS) in groundwater

This pilot-scale field demonstration evaluated the remediation of poly- and perfluoroalkyl substances (PFAS) from groundwater contaminated with aqueous film-forming foam (AFFF) from a coupled regenerable ion exchange resin (IXR) and electrochemical oxidation (EO) treatment train. A pilot-scale IXR system was used that incorporates a novel resin regeneration process, and recovers and reuses the majority of the regenerant solution using distillation. The pilot system removed PFAS from ∼1,000,000 L (approximately 260,000 gallons) of contaminated groundwater from a fire training area, and treated effluent from the IXR system was non-detect for PFOA and PFOS. The concentrated waste stream (i.e., still bottom) from IXR was treated on-site by an EO system with Ti4O7 electrodes, achieving 80–98% destruction of PFOA and PFOS. The surface area normalized first-order rate constants (kSA) were 3.96 × 10−7 m s−1 and 7.92 × 10−7 m s−1 for PFOA and PFOS, respectively, with short-chain perfluoroalkyl acids (PFAAs) identified as intermediate degradation products. Based on the fluoride recovered and PFAS mass loss measured at the end of EO treatment, fluoride release ratios were 130% for still bottom sample 1 (SB1) and 215% for still bottom sample 2 (SB2), indicating mineralization of unquantified fluorinated compounds in the waste stream. Overall, the electric energy consumed per order of magnitude reduction in concentration (EE/O) for treating PFOA and PFOS in groundwater by the IXR-EO treatment train was 0.131–0.161 kWh/m3 for PFOA and 0.071–0.094 kWh/m3 for PFOS, which was orders of magnitude lower than the reported EE/O values for stand-alone electrochemical treatment. The results of this field demonstration show the promise of coupling regenerable IXR with EO for cost-effective removal, concentrating, and destroying PFAS from groundwater.

Intensification of a Neutralization Process for Waste Generated from Ion Exchange Regeneration for Expansion of a Chemical Manufacturing Facility

Waste generated during regeneration of Ion Exchanger (IX), used for deionizing water, needs to be neutralized before it can be discharged back to a clean water source. An efficient and novel process is disclosed that minimizes the neutralization volume and chemicals required for pH adjustment. The currently employed neutralization setups in the industry are environmentally unsustainable. Various neutralization setups were studied for treating waste generated from IX regeneration. From the collected plant data, the treatment requirements of waste streams generated during regeneration of IX beds were analyzed. An efficient neutralization setup was developed to lower the operating and capital costs by eliminating the need of some equipment and by lowering the neutralization volume. The new process results in considerable savings compared to currently used processes in the industry and is environmentally benign. The improved neutralization setup proposed in this work has achieved a 63% reduction in volume of IX regeneration waste stream; a 62% reduction in the capital cost; 23% reduction in chemical usage; and a 55% reduction in operating cost. The achieved improvements are quite significant, which are bound to immensely benefit the chemical industries that require demineralized water for their operation.

Ammonia recovery from brines originating from a municipal wastewater ion exchange process and valorization of recovered nitrogen into microbial protein

A hollow fibre membrane contactor (HFMC), and two vacuum thermal stripping processes, a rotary evaporator (VTS) and multi-component system (MVTS) were compared for their ability to recover ammonia (NH3) from ion exchange (IEX) regeneration brines. The IEX was a 10 m3/day demonstration scale plant fed with secondary municipal wastewater. The 10% potassium chloride regeneration brine was used multiple times leading to ammonium (NH4+-N) saturation (up to 890 mg N/L). When treating the saturated IEX brine, the highest NH3 mass transfer coefficient for the HFMC, MVTS and VTS were 0.6, 0.7 and 0.1 h−1, respectively, compared to values between 1.7 and 3.5 h−1, when treating a synthetic solution. The highest NH3 recovery was obtained with the HFMC (99.8%) and the ammonium sulphate produced was characterised for impurities, presenting high quality. Concentrated ammonium (NH4+-N) solutions (0.5–3.1 g N/L) were obtained from the MVTS and VTS processes. To further valorise the recovered NH4+-N solution produced from the MVTS process, this was used as a substrate for microbial protein (MP) production. Limited differences were observed for production rate (specific growth rate 0.092–0.40 h−1), protein yield (0.021–0.18 g protein/g acetate-CODconsumed) and protein content (0.073–0.87 g protein/g cell dry weight) between recovered and commercial nitrogen (N) sources, indicating that recovered N from IEX can serve as a substrate for MP production. This study demonstrates a comprehensive N management solution for wastewater applications, leading to a range recovered products. These combined technologies can contribute to the local economy, whilst delivering to the ambitious NET-ZERO and circular economy targets.

Ion exchange resin derived magnetic activated carbon as recyclable and regenerable adsorbent for removal of mercury from flue gases

Regenerable ion exchange resin derived magnetic activated carbon (Fe/AC) was prepared to remove mercury from flue gases at 120–180 °C under a high space velocity of 240000 h−1, in this study. The Fe/AC showed higher mercury removal efficiency than those of either magnetic activated carbon without activation or commercial coconut-activated carbon. The optimum temperature for removal of mercury from flue gases was determined to be 120 °C and the existence of SO2 in flue gases promoted the mercury removal efficiency of Fe/AC. Mercury compounds of HgS (metacinnabar), HgO, HgS (cinnabar) and HgSO4 were found over spent adsorbents. The HgO was generated through the reaction of mercury with lattice oxygen and chemisorbed oxygen, while the formation of HgS was due to the reaction between mercury, FeS and sulfur over the adsorbent. The lattice oxygen could oxidize SO2 to SO3, which further reacted with mercury to form HgSO4. The Fe/AC presented excellent regeneration and reuse ability, the mercury removal efficiency of which showed a great increase even after 5 runs of regeneration. The crystalline structure of Fe/AC changed remarkably after regeneration and the FeS over Fe/AC was converted to Fe3O4. The above excellent properties suggest that Fe/AC might be a promising adsorbent to remove mercury from flue gases.

Resilience and life cycle assessment of ion exchange process for ammonium removal from municipal wastewater

This study was completed to understand the resilience of an ion exchange (IEX) process for its ability to remove variable ammonium (NH4+-N) loads) and to prove its environmental benefits through a life cycle assessment (LCA). The tertiary 10 m3/day demonstration scale IEX was fed with variable NH4+-N concentrations (<0.006–26 mg NH4+-N /L) naturally found in municipal wastewater. Zeolite-N was used as ion exchange media and regeneration was completed with 10% potassium chloride (KCl). The influent NH4+-N concentration impacted the ion exchange capacity, which ranged from 0.9–17.7 mg NH4+-N/g media. When the influent concentration was <2.5 mg NH4+-N/L, the Zeolite-N released NH4+-N (up to 12%). However, the exchange increased up to 62% when the influent NH4+-N load peaked, confirming the resilience of the process. A 94% regeneration efficiency was obtained with fresh regenerant, however, with the increase of the mass of NH4+-N on the media, the regeneration efficiency decreased. An optimisation of the volume of brine and regeneration contact time is suggested. To further measure the benefits of the IEX process, an LCA was conducted, for a 10,000 population equivalent reference scenario, and compared with traditional nitrification-denitrification WWTP. The LCA revealed that IEX with regenerant re-use and NH4+-N recovery through a membrane stripping process resulted in reductions of: 25% cumulative energy demand; 66% global warming potential and 62% marine eutrophication potential, when compared to traditional WWTP. This work demonstrated that the IEX process is an efficient and an environmentally benign technology that can be widely applied in WWTPs.

Removal of Poly- and Per-Fluorinated Compounds from Ion Exchange Regenerant Still Bottom Samples in a Plasma Reactor.

"High-concentration" and "low-concentration" bench-scale batch plasma reactors were used to effectively degrade per- and polyfluoroalkyl substances (PFAS) at a high concentration (∼100 mg/L) and a low concentration (<1 μg/L), respectively, in ion exchange (IX) regenerant still bottom (SB) solutions. In the SBs, numerous PFAS were detected with a wide concentration range (∼0.01 to 100 mg/L; total oxidizable precursors (TOP) ∼4000 to 10000 mg/L). In the "high-concentration" plasma reactor, the concentrations of PFAS precursors and long-chain perfluoroalkyl acids (PFAAs) (≥6C for PFSAs and ≥8C for perfluorocarboxylic acids (PFCAs)) were decreased by >99.9% in 2 h, and short-chain PFAAs (<6C for perfluorocarboxylic acids (PFSAs) and <8C PFCAs) were decreased by >99% in 6 h of treatment. Subsequently, a "low concentration" plasma reactor was used to remove additional PFAAs. In this reactor, the addition of CTAB (cetrimonium bromide, a cationic surfactant) caused short-chain PFAAs, other than PFBA, to be removed to below detection limits in 90 min of treatment time. Overall, >99% of the TOP present in SBs was removed during the treatment. Fluorine recovery of 47 to 117% was obtained in six SB samples. Energy requirement (EE/O) for the treatment of PFOA and PFOS from SBs ranged from 380 to 830 kWh/m3.

Low energy consumption electrically regenerated ion-exchange for water desalination.

A new regeneration method of ion exchange resin named Adjacent Bed Electrically Regenerated Ion-exchange (ABERI) was proposed to eliminate the environmental impact of traditional chemical regeneration and improve the economy of replacing chemical regeneration with electrical regeneration. The desalting operation of ABERI was the same as the conventional mixed bed. When the resins were exhausted, anion and cation resins were separated and then packed in a dedicated regenerator adjacently. The resins were regenerated by the H+ and OH- ions produced from a pair of electrodes installed on both sides of the resin bed. By optimizing the regeneration time, current, and feed water flow rate, the energy consumption of ABERI was 0.38 kWh/m3 water; that is, 54% of that of another electrical regeneration technology, membrane-free electrodeionization (MFEDI). Compared with MFEDI, the quality and quantity of purified water produced after regeneration were improved. In ABERI, the average conductivity and the volume (times of bed volumes) of the purified water are 0.9 μS/cm and 109; that is, 75 and 133% of that of MFEDI, respectively. The preliminary economic analysis showed that ABERI offers the potential to regenerate ion exchange resin in an eco-friendly and cost-effective manner.

Low‐voltage and ion‐free‐reverse‐migration electrically regenerated mixed‐bed ion exchange for MEG desalination

AbstractAn improved electrical regeneration method of ion exchange was proposed to enhance the feasibility of applying ion exchange for mono‐ethylene glycol (MEG) desalination and simplify the existing MEG regeneration process in deepwater gas fields. Compared with the latest electrical regeneration process named membrane‐free electrodeionization (MFEDI), this method required lower voltage, did not consume high purity water, and eliminated ion backward migration in principle. These improvements were achieved by changing the electric field direction and the flow direction from parallel in MFEDI to perpendicular during ion exchange regeneration step. In this work, a pair of commercial ruthenium oxide‐coated titanium electrodes was installed on both sides of the cuboid experimental setup. The mixed resins consisting of strong‐base and weak‐acid resins were filled between the electrodes. In water flow and direct current electric field, the resins were regenerated successfully. The feasibility of efficient regeneration with high conductivity feed water (3–200 μS/cm) was verified. After regeneration of the resin bed for 1 h at a voltage lower than 73 V, 33.83% of NaCl in 5.16 bed volume (BV) simulated rich MEG liquid was removed. After 15 cycles of repeated operation, the performance of the resins remained stable. These results provide the possibility to reclaim MEG in deepwater gas fields through a simpler method.

Electro-assisted regeneration of pH-sensitive ion exchangers for sustainable phosphate removal and recovery

Removal and recovery of phosphate from wastewater can minimize deleterious environmental impacts and supplement fertilizer supply. Hybrid anion exchangers (HAIX, with doped ferric oxide nanoparticles (FeOnp)) can remove phosphate from complex wastewaters and recover concentrated phosphate solutions. In this study, we integrate HAIX with a weak acid cation exchanger (WAC) to enrich phosphate and calcium in mild regenerants and precipitate both elements for recovery. We demonstrated an electro-assisted regeneration approach to avoid strong acid and base input. Based on demonstrated pH sensitivities of both materials, electrochemically produced mild electrolytes (pH 3 and pH 11), which are 100–1000 times less concentrated than typical regenerants, preserved 80% WAC and 50% HAIX capacities over five batch adsorption-regeneration cycles. FeOnp in HAIX facilitated regeneration due to pH sensitivity and their likely distribution on the resin particle surface, which reduced intraparticle diffusion path length. In column tests, repeatable phosphate removal (> 95%) from synthetic wastewater (3 mg P/L) was achieved with 20 kWh/kg P specific energy consumption. After removal, a similar 50% HAIX regeneration efficiency as batch experiments was achieved. In spent regenerant, more than 95% phosphorus was recovered as hydroxyapatite. This novel approach enhances ion exchange by minimizing chemical inputs.

Fluoride sorption from aqueous solution using Al(OH)3-modified hydroxyapatite nanosheet

In this study, Al(OH)3-hydroxyapatite nanosheet (Al(OH)3-nHAP), an adsorbent of high defluoridation capacity, was prepared based on the nano hydroxyapatite (nHAP) with lattice defect (4% calcium deficiency) brought by the addition of EDTA. And the composite was characterized by XRD, TEM-EDS, FT-IR and N2 adsorption method. The effects of adsorbent dosage, pH value, initial fluoride concentration and co-existing ions to the adsorption behaviors were studied, and then kinetics, isotherms, thermodynamics, ion exchange rate, regeneration and dissolution were investigated. The maximum defluoridation capacity of Al(OH)3-nHAP nanosheet were 141.84, 171.88 and 194.2 mg/g at 298, 308 and 318 K in neutral condition with the initial fluoride concentration of 200 mg/L. The high defluoridation capacity was due to the high Al/Ca atomic ratio (1.44). The nHAP with lattice defect might help Al atoms to dope into the nHAP. About 22.14% of Al atoms was doped into the lattice of nHAP and 77.86% was loaded on the surface of nHAP by modifying. Ca9.6(PO4)6(OH)1.2 and 8.5156Al(OH)3-Ca7.5792Al2.4208(PO4)6(OH)4.4208 was proposed as the chemical formula of nHAP and Al(OH)3-nHAP synthesized in this study via calculations. The adsorption performance followed the Pseudo-second-order kinetic model and Freundlich isotherm model, which was a spontaneous and endothermic process. The removal efficiency of regenerated Al(OH)3-nHAP nanosheet always stayed above 81.32% and showed good stability during the four cycles. The concentrations of Al3+, Ca2+ and F− in dissolution experiment were 0.01, 2.11 and 0.56 mg/L, respectively, indicating its safety and stability.