Acidic Waste Research Articles

One-step synthesis of short columnar α-calcium sulfate hemihydrate from titanium white waste acid

The waste sulfuric acid solution emerged as a main emission substance from titanium dioxide production is called titanium white waste acid (TWWA). The disposal of TWWA has been a concern due to its potential impact on the environment. A green way including one-step preparation and purification stages of α-calcium sulfate hemihydrate (α-HH) from TWWA and lime mud via a neutralization reaction in the hydrothermal pressure apparatus was developed. The preferred experimental conditions were obtained, i.e., lime mud/TWWA/sodium citrate ratio: 16/16/1, 140 ℃, 0.5 MPa, reaction time: 10 min. The recovery rate of α-HH in the whole process was 89.5%. The method presented high efficiency and selectivity in conversion to a short-columnar-shaped α-HH under addition of 3.40 × 10−2 mol/L sodium citrate as a crystal modifier. The structure and composition of the obtained α-HH products were confirmed by XRD, TGA, and SEM. Compared with titanium gypsum, the obtained short columnar α-HH with hexaprismatic morphology showed excellent mechanical properties. According to GB/T 9776 − 2008 “Calcined gypsum”, the compressive strength of 7 days of the cemented short-columnar α-HH was about 6.35 MPa, which it meets the strength requirements for building gypsum.

The Functionalized N-Rich Covalent Organic Framework for Palladium Removal from Nuclear Wastewater.

Efficiently adsorbing Pd(II) from acidic radioactive waste liquid is crucial for ensuring the safety of the radioactive waste vitrification process and significantly alleviating the scarcity of precious metals. However, the stability and selectivity of most current adsorbents are limited, hindering their practical application under acidic conditions. To address these limitations, a covalent organic framework (DHTP-TPB COF) was prepared with a high nitrogen content, leveraging the high affinity of its soft ligand N with palladium to achieve high selectivity. This work demonstrated that DHTP-TPB COF exhibits rapid adsorption kinetics, with equilibrium achieved within 10 min. The framework also boasts a high adsorption capacity of 142.8 mg/g and impressive reusability in 1.0 M nitric acid. Moreover, the DHTP-TPB COF displays excellent selectivity for Pd(II), even in the presence of 13 interfering ions. By combining FT-IR, XPS spectroscopy, and DFT theoretical calculations, the dense N sites in the framework have a strong affinity for Pd(II), resulting in exceptional adsorption performance that was confirmed. The findings of this study highlight the potential of COFs with robust linkers and customized functional groups to effectively and selectively capture Pd(II) under harsh environmental conditions of high-level liquid waste.

Efficient Extraction and Separation of Scandium from Scandium-Bearing Solid Waste and Acid by Synergistically Leaching Followed by Solvent Extraction.

The solid waste and waste acid generated during the production of titanium dioxide contain considerable amount of scandium, which are valuable secondary resources. In this study, the titanium dioxide waste acid was used to leach the scandium-containing solid waste, and the leached solution was pretreated for iron removal by reduction-crystallization process. After that, scandium was recovered from the leached solution by using the P204-TBP co-extraction system. The process parameters were investigated systematically. The results showed that iron powder reduction-crystallization for iron removal at molar ratio of Fe:Fe3+ = 0.25 was most suitable for subsequent extraction, and the scandium extraction efficiency could reach 100% using 15% P204-5% TBP at 25 °C with A/O = 8. This study provided a novel process for treating scandium-bearing solid waste with scandium-bearing waste acid, showing great potential for industrial application.

Catalytic synthesis of DHHB using solid acids

Abstract DHHB (Diethylamino hydroxybenzoyl hexyl benzoate) is a widely regarded UV absorber with a high degree of safety, excellent efficiency and good solubility characteristics. In the conventional method of DHHB synthesis, H2SO4 is not effective as a catalyst. To address this drawback, we synthesized solid acid (sulfonic acid group-modified ion exchange resin) catalysts to replace H2SO4 by suspension polymerization modification and optimized the process. The experimental results showed that the yield of DHHB could reach 85% at 110 °C for 10 h, and the conversion of DHHB could be maintained above 90% after 10 cycles of the catalyst. SEM, FT-IR characterization and analysis of the solid acid catalysts before and after use revealed that the catalysts did not show any significant changes. The use of solid acid not only improves the yield of DHHB and reduces the energy consumption in the experimental process, but also the solid acid is simple to recover, recycled and has less waste acid. This experiment successfully explored a green and economic synthesis method for synthesizing DHHB.

Synthesis of Ferrocenyl Chalcone-Containing Aminourea Schiff Bases and Their Detection on Tryptophan.

In this paper, 1-phenyl-3-ferrocenylenone aminourea Schiff bases were synthesized by a novel method. A multifunctional molecular probe (Probe A) of 1-phenyl-3-ferrocenylenone, carbon-based solid acid, aminourea, and anhydrous ethanol was synthesized by adding them to a vessel at elevated temperatures and refluxing for the synthesis of a multifunctional molecular probe (Probe A) of 1-phenyl-3-ferrocenylenone aminourea Schiff base, and it was found that it recognizes tryptophan (Trp) in solution, and that the catalyst can be reused more than five times after recycling. This method is characterised by low cost, high efficiency, green environment and no waste acid. Fluorescence and UV spectra show that probe A specifically recognizes tryptophan (Trp) without interference by other amino acids or pH and time does not affect it within 45min. The lowest limit of detection for Trp was 1.307 × 10- 4 mol/L for probe A. The binding ratios of probe A to Trp were measured to be 1:1 by Job's plotting method, respectively. The complexation constant of probe A with Trp was found to be 2.733 × 107 L/mol according to the Benesi-Hildebrand equation. The bonding mechanism was explored through IR spectroscopy and ¹H NMR titration.

Anti-seepage performance and oxygen barrier performance of the three-layered landfill cover system comprising neutralized slag under extreme climate conditions

For acidic industrial solid wastes, an effective cover system is needed to reduce the rainwater infiltration and oxygen intrusion, thus reducing the generation of acid mine drainage (AMD) from wastes. A three-layered cover using low-permeability neutralized slag (abbreviated as TCNS) at the bottom of the traditional capillary barrier cover is proposed, in line with the novel concept of “waste protecting waste”. This study investigates the anti-seepage performance and oxygen barrier performance of TCNS under extreme climate conditions, through laboratory column test and numerical simulations. The results show that the water content of the neutralized slag (NS) layer remained stable (i.e., changed by less than 0.02) under either extremely wet condition or extremely dry condition. Under extremely wet condition (i.e., heavy rainfall corresponding to a 50-year return period), no water percolation was observed at the cover bottom; under extremely dry conditions, oxygen diffusion was greatly impeded, e.g., after 208 days of column test, the SO42− concentration in the AMD of the exposed (i.e., uncovered) waste rock was 4.6 times higher than that of the waste rock covered by TCNS. Numerical simulations considering two realistic climate conditions (i.e., humid and arid) showed that TCNS were effective in controlling water percolation and oxygen intrusion. The saturated permeability coefficient (ks) and initial saturation degree (Se) of the NS layer have significant effects on the performance of TCNS, i.e., decreasing ks or increasing Se can effectively reduce the water percolation and oxygen flux. In sum, TCNS is an effective barrier for controlling water percolation and oxygen intrusion, even in extreme climate conditions. Consequently, it can effectively minimize AMD leakage and thus reduce geological disasters such as groundwater contamination.

Upcycling acid waste gas containing H2S and CO2 into syngas and sulfur by non-thermal plasma coupled with Zn-Mo/Al2O3 catalyst

Synergistic conversion of H2S and CO2 into syngas and sulfur in one step, not only achieves harmless treatment, but also produces valuable chemicals, which is an ideal strategy for waste gas upcycling. Nevertheless, due to the kinetic inertia and high thermodynamic stability of H2S and CO2, the process of the reaction has not received enough attention. Non-thermal plasma has advantages over thermal processes in the process of enhanced conversion owning to its non-equilibrium properties. Herein, a novel method of non-thermal plasma coupled by Zn-Mo/Al2O3 catalyst was demonstrated for the simultaneous conversion of H2S and CO2. Furthermore, compared to the single component catalysts (ZnS/Al2O3 and MoS2/Al2O3), the Zn-Mo/Al2O3 catalysts with different Zn/Mo ratios had excellent catalytic performance. In particular, the ZM(4/4) catalyst showed complete conversion of H2S and approximately 62 % of CO2 conversion, with the highest energy efficiency of 0.95 mmol/kJ and 120 h long-term stability. Meanwhile, the mechanism of the synergistic reaction between non-thermal plasma and catalysis was revealed by means of in-situ optical emission spectrometry. This study offers a new strategy for catalyst design for the highly efficient conversion of H2S-CO2 acid waste gas via plasma-catalytic method, and highlights the synergy between Zn-Mo/Al2O3 catalyst and non-thermal plasma to promote catalytic performance.

Simultaneous precipitation removal of fluoride ion and chloride ion from smelting waste acid using renewable remover

Purification and reuse is a potential method of smelting waste acid disposal. High concentrations of fluoride and chloride in waste acid are harmful impurity and must be removed. Previous studies have shown that fluoride removal with rare earth and chloride removal with bismuth have similar cyclic process of "precipitation removal-agent regeneration" and similar reaction conditions. In this paper, a method of simultaneous precipitation removal of F− and Cl− from waste acid using La(OH)3 and Bi2O3 as a mixed remover was proposed, and the mixed remover is regenerated by sodium hydroxide solution for the recycling of the remover. Thermodynamic analysis of La3+-Bi3+-F−-Cl−-H2O system verified the feasibility of simultaneous removal. The experimental results showed that under the optimum reaction conditions, the removal efficiencies of F− and Cl− were 93.67 % and 96.47 %, respectively, and the concentrations of F− and Cl− in the solution after removal were 66.70 mg/L and 71.10 mg/L, respectively. Under the optimum conditions, the regeneration efficiencies of La(OH)3 and Bi2O3 were 96.80 % and 96.95 %, respectively. The proposed process has the advantages of no waste output, short process, and low energy consumption and provides an environmentally friendly method of removing fluoride and chloride from waste acid.

A novel potato peels waste β-cyclodextrin biocomposite for the efficient uptake of diuron and glyphosate herbicides.

A novel biocomposite (FPPW-β-CD) was prepared by a simple and sustainable method involving fine potato peel waste, β-cyclodextrin (β-CD), and green citric acid through the crosslinking reaction. The polymer was characterized using SEM, FTIR, XRD, TGA, and DSC analyses. The adsorbent performance was evaluated about the glyphosate and diuron adsorption from the aqueous solution. Pesticide removal was investigated regarding the influence of solution pH, temperature, and initial concentration of contaminants. Also, it highlights the main interactions involved in the adsorption phenomenon based on the pH effect and characteristics of adsorbent and adsorbate molecules. The maximum adsorption capacity values according to the Sips model were higher than 2000µgg-1. The pseudo-second-order and general-order models described the kinetic data well. Thermodynamic parameters indicated that pesticide removal was spontaneous and favorable. The magnitude of enthalpy variation values (27.37kJmol-1 and - 100.79kJmol-1) revealed that the glyphosate and diuron adsorption occurred through the physisorption and chemisorption, respectively. The novel biocomposite is a promising green adsorbent for the uptake of micropollutant pesticides in aqueous solutions at concentrations of µg L-1.

Mechanism and kinetics of scorodite formation in arsenic-bearing solutions using Fe(OH)3 as a solid iron source

Recently, solid iron sources have been used for scorodite synthesis in arsenic-bearing wastewater from nonferrous metallurgy. Immobilising arsenic-solution as scorodite via iron hydroxide (Fe(OH)3) solid iron source is an important method for controlling arsenic pollution. The evolution behavior of scorodite during its formation in high arsenic solution have been rarely investigated. In this paper, the mechanism and kinetics of scorodite formation using Fe(OH)3 in arsenic-bearing solution were investigated. This work was divided into three parts. Firstly, the influencing parameters were investigated, revealing that the dissolution of Fe(OH)3 and scorodite generation accelerated at lower initial pH and higher reaction temperature. Increasing Fe/As ratio delayed scorodite crystallisation, which was in turn enhanced by elevating arsenic concentration. Secondly, the mechanism of scorodite formation was investigated, revealing that Fe(OH)3 underwent acidic dissolution to form a precursor. Subsequent scorodite formation had a ΔrGmθ ranging from −69.39 kJ·mol−1 to −15.64 kJ·mol−1. Residual As was absorbed and converted into Fe(OH)3@scorodite. Thirdly, the chemical kinetics were investigated, showing that activation energy (Ea) for Fe(OH)3 dissolution was 72.54 and 105.37 kJ·mol−1 at Stages I and II, respectively, whereas it was 105.97 kJ·mol−1 for residual As absorption-conversion at Stage III outweighing the Ea of As-Fe coprecipitation. The restrictive steps were Fe(OH)3 dissolution and residual arsenic absorption-conversion. This proposed method can be applied for environment-friendly treatment of 10－40 g/L of arsenic-bearing industrial effluent for scorodite formation. Overall, this research confirmed the formation of scorodite via Fe(OH)3 and can potentially provide feasible schemes for eliminating arsenic-bearing acidic waste, dust, and anode slime from nonferrous metallurgical processes.

Recycling valuable metals from spent cathode material by in-situ thermal reduction combined with electrochemical leaching

In-situ thermal reduction is a promising technology that realizes the reduction of high-valence metals in spent lithium-ion batteries (LIBs) through its reductive substances. However, the subsequent simple acid leaching cannot adapt to all thermal reduction products, especially elemental Ni and Co, resulting in low leaching efficiency and high acid consumption. In this work, in-situ thermal reduction combined with electrochemical-enhanced leaching technology was provided for extracting valuable metals from spent LIBs with minimum chemical consumption. Results show that after thermal reduction, the layered structure of LiNi1/3Co1/3Mn1/3O2 was fully broken, yielding acid-soluble components including Ni, Co, NiO, CoO, MnO, Li2CO3, and LiAlO2, all achieved without external reductants. During the electrochemical leaching, the acidic solution produced by water electrolysis and electrochemical oxidation synergistically promoted the leaching of valuable metals, and finally, 99.02 % Li, 96.34 % Ni, 98.28 % Co and 99.24 % Mn were leached from the roasted cathode product. Compared with traditional acid leaching, the proposed electrochemical method has advantages in the dissolution of elemental Ni and Co. Moreover, the whole process does not consume any external acids or bases, and there is no emission of waste acid. The findings of this work help to reduce reagent consumption in the spent LIBs recycling process and provide an effective, adaptable, and green method for leaching thermal reduction products.

One-step utilizing of waste acidic Cu-containing etching solution to prepare hierarchical Cu-ZSM-5 for efficient flue gas Hg0 removal

Developing mercury adsorbents could mitigate environmental risk of mercury pollution. In this study, waste acidic Cu-containing etching solution from PCBs etching industry was utilized for the simultaneous porosity etching and Cu/Cl sites loading to prepare WA-ZSM for Hg0 removal via a one-step method. WA-ZSM synthesized with different waste acid concentrations exhibited over 94 % Hg0 removal efficiency within 60 min. The long-term stability of 5WA-ZSM under 110 μg/m3 Hg0 within 300 min was higher than 90 %. The dealumination process significantly affected the formation of micropores and Cu loading into the pore structure. The EFAl-Al3+ and “Si-O-Cu” structures formed by dealumination greatly enhanced the strong acid sites and the Cu sites improved the medium strong acidity. Isolated [Cu-OH]+ sites and [Cu–O-Cu]2+ sites are the main active sites in Hg0 removal. This method successfully synthesizes low-cost, high-efficiency Hg0 adsorbents using hazardous wastes, presenting a significant advancement in sustainable waste utilization and mercury pollution control.

Zirconium titanium phosphonates for enhanced lanthanide recovery from acidic wastes

Metal phosphonates show promise for recovery of valuable lanthanide (Ln) elements from acidic waste streams due to their selectivity, high capacity, fast kinetics and chemical stability. To optimise these properties, a balance is needed between free phosphonate groups available to bind Ln and P-O-metal linkages to provide stability. This work demonstrates how astute choice of metal precursors can be used to control the phosphonate structure and maximise both sorption and stability. Relative to single metal zirconium phosphonate, mixed metal zirconium titanium phosphonate sorbents had more free phosphonate groups and greater porosity, increasing Ln capacity by 30 % and the kinetic rate constant by 90 %. Acid stability was also improved upon Ti inclusion. Use of metal propoxide and tert-butoxide precursors were also compared, revealing different reactivities with Zr versus Ti. Specifically, the tert-butoxide precursor increased P-O-Zr linkages and acid stability with Zr, but increased formation of leachable P-O-Na2 groups in the presence of Ti that decreased acid stability. The optimised zirconium titanium phosphonate sorbent used metal propoxide precursors and a Zr:Ti molar ratio of 1:1 to achieve (1) selectivity for Ln over Co, Sr and Cs, (2) sorption capacity of approximately 70 mg Eu/g, (3) fast kinetics with > 99 % sorption in 10 min and (4) retention of 60 % sorption capacity after contact with 5 M nitric acid. The enhanced chemical stability, capacity and kinetics achieved via incorporating Ti drastically improves the practicality of these sorbents for Ln recovery from acidic leachates of magnets, phosphors and other wastes.

Fabrication of high-performance pervaporation desalination composite membranes with study of its acid-base stability

In the process of industrial production will produce a lot of acid and alkaline waste liquid, how to effectively treat acid and alkali waste liquid is an important topic at present. At present, there are some problems about the treatment of acid and alkali waste liquid, such as large investment, complicated process and low efficiency. Pervaporation has the characteristics of mild operating conditions and no influence of osmotic pressure threshold, so it has great application potential in the concentration, reuse and reduction of acid and alkali waste liquid. However, at present, conventional pervaporation dense membrane materials cannot maintain long-term stability in strong acid and alkali environment, in order to achieve this performance, we use perfluorosulfonic acid resin with good acid and alkali resistance as the dense layer substrate. PFSA/PTFE/PP composite membrane was prepared by spraying process, and the final prepared composite membrane had a pure water flux of 45 ± 1.2 kg/(m2∙h) at 70 ℃. The acid and alkali resistance of the intrinsic membrane and the composite membrane was evaluated, and it was found that the feed liquid was concentrated to 20 wt% after 19 h long concentration operation at 70℃ and starting liquid was 5 wt% H2SO4 and 5 wt% NaOH. The retention rate of acid and alkali can be maintained above 99.9 %. During the concentration of H2SO4 solution, the dense layer structure is affected, and the pure water flux of the composite membrane is reduced, eventually maintaining around 32 kg/(m2∙h). In the process of concentrating NaOH solution, the pure water flux of the composite membrane increased first and then decreased, and the final pure water flux of the membrane remained near 40 kg/(m2∙h).

Garnet-Based Solid Li-Metal Batteries Operable under High External Pressure with HCOOH-Induced Electron-Blocking and Lithiophilic Interlayer.

Despite good compatibility with Li metal, garnet solid electrolytes suffer from severe electron-attack-induced Li-metal penetration and large interfacial resistance. Here, a formic acid (HCOOH)-induced electron-blocking and lithiophilic interlayer is created via a spontaneous reaction with surface Li2CO3 contamination on the garnet electrolyte (LLZTO) pellet. Unlike previous methods that involved immersing LLZTO in acidic solutions, this study employs a volatile small-molecule organic acid that is easily removable, condensed, and recyclable, thus circumventing the environmental drawbacks associated with acid waste. The Li symmetric cell assembled with HCOOH-treated LLZTO exhibits a low interfacial impedance (3 Ω cm2) and a high critical current density (1.7 mA cm-2) at room temperature, enabling the cell to cycle continuously for over 1000 h at 0.2 mA cm-2. Furthermore, under a stacking pressure of 2 MPa, stable lithium plating/stripping was achieved at a current density of 0.3 mA cm-2 with the assistance of HCOOH treatment. Additionally, the battery paired with a LiFePO4 cathode delivers a high capacity of 151.7 mAh g-1 at 1 C and maintains 88.5% of the initial capacity after 500 cycles, suggesting the feasibility of this interfacial engineering strategy for garnet-based solid Li-metal batteries.

Recovery of Zinc and Rhenium for the Production of Zinc Perrhenates

This study outlines findings from an investigation into the development of a hydrometallurgical process for manufacturing various forms of zinc perrhenate, entirely from waste from recycling and from the Zn–Pb industry. Scraps of Re-bearing Ni-based superalloys and acidic waste, circulating zinc solutions generated during the production of Zn by the electrolytic method and which contain >45 g/dm3 of Zn, Na, Mn, and Mg, were used in the research. In the publication, the conditions for the production of three types of zinc perrhenate, i.e., Zn(ReO4)2·4H2O, Zn(ReO4)2, and Zn(ReO4)2·2H2O, are presented. As a result of the analysis of the obtained results, it was concluded that to obtain the above-mentioned forms of zinc perrhenate, zinc carbonate can be used, precipitated from acidic, waste, and multi-component solutions after their prior neutralization to pH 4.0 and partial purification from Mn, Mg, and Na using metallurgical zinc oxide. Zinc carbonate should be precipitated using Na2CO3 at pH 6.3 and subsequently purified from other impurities, i.e., Mg, Na, and Mn, using aqueous ammonia solutions. As a result, zinc carbonate was obtained, which was used in a reaction with an aqueous solution of HReO4 to produce zinc perrhenate. The precipitated forms of Zn(ReO4)2 were obtained by appropriately drying the crude and hydrated Zn(ReO4)2 to obtain its tetrahydrate, dihydrate, and anhydrous forms, respectively, using drying temperatures of 55, 135, and 185 °C. The developed technology has been submitted for a patent and is an example of a technology founded on the principles of sustainable development, with a particular emphasis on the minimalization of loss of rhenium and zinc at all stages of its realization.

Thermodynamic and Experimental Studies of Selective Decomposition of Diopside in Ti-Bearing Blast Furnace Slag.

Titanium-bearing blast furnace slag (TBFS) is formed during the smelting of vanadium-titanium magnetite ore, containing more than 10 wt % Ti. The metal resource in TBFS has not yet been utilized because of the difficulty of extracting the objective phase from the complex eutectic. In this work, thermodynamic and experimental studies of selective leaching of diopside phase in TBFS in 20 wt % H2SO4 were conducted. The Gibbs free energy of reaction with H2SO4 calculated by applying a mechanical mixture model was in the order of Ti-bearing diopside < MgAl2O4 < Ti-rich diopside < CaTO3. The extraction rate of Ti ions was controlled by the leaching temperature and leaching time in 20 wt % H2SO4. The extraction rate of Ti reached as high as 0.50 under optimal conditions. The diopside phases in TBFS were completely decomposed, while the perovskite (CaTiO3) was almost unaffected by 20 wt % H2SO4. The experimental results agreed with the trend of thermodynamic calculations, supporting their validity. The hydrolysis of TiOSO4 showed the possibility of obtaining high-purity TiO2. This work shows the selective leaching of the diopside phase in TBFS and suggests an environmentally friendly method for utilizing Ti-bearing blast furnace slag and waste acid.

Solvent and Catalyst-Free Depolymerization of Polylactic Acid Waste to Lactide Enabled by Dry Steam

Solvent and Catalyst-Free Depolymerization of Polylactic Acid Waste to Lactide Enabled by Dry Steam

Semi-Interpenetrating Polymer Network Anion Exchange Membranes Based on Quaternized Polybenzoxazine and Poly(Vinyl Alcohol-Co-Ethylene) for Acid Recovery by Diffusion Dialysis.

Acid recovery from acidic waste is a pressing issue in current times. Chemical methods for recovery are not economically feasible and require significant energy input to save the environment. This study reported a semi-interpenetrating polymer network (semi-IPN) anion exchange membranes (AEMs) for acid recovery by diffusion dialysis with excellent dimensional stability, high oxidation stability, good acid dialysis coefficient (UH +) and high separation factor (S). Semi-IPN AEMs are prepared by ring-open cross-linked quaternized polybenzoxazine (AQBZ) with poly(vinyl alcohol-co-ethylene), where AQBZ is obtained by Mannich reaction and Menshutkin reaction. All four proportions of semi-IPNs exhibit clear micro-phase separation, which is conducive to ion transport. The water uptake (WU) of the four semi-IPNs ranges from 14.2 % to 19.2 %, while the swelling ratio (SR) remains between 8.7 % and 11.3 %. These results indicate that the cross-linked structure in the designed semi-IPNs effectively control swelling and ensure dimensional stability. The thermal degradation temperature (Td5) of semi-IPN4:6 to semi-IPN7:3 varies from 309 °C to 289 °C, with an oxidation stability weight loss rate (WOX) ranging from 91.5 % to 93.5 %, demonstrating excellent thermal stability and oxidation stability. The semi-IPNs also show good UH + values ranging from 11.9-16.3*10-3 m/h and high S values between 38.6 and 45.9, indicating the promising potential of the semi-IPNs.

Nucleobase-mediated hydrogen bonding crosslinked highly sulfonated poly(ether ether ketone) electrodialysis membranes for efficient waste acid recovery

Electrodialysis is a promising technology for waste acid recovery with the advantages of low energy consumption and high efficiency. In this work, two nucleobase-modified highly sulfonated poly(ether ether ketone) with adenine (SPEEK-50A) and thymine (SPEEK-50T) were successfully synthesized. Then, a series of blending SPEEK-50Ax/50Ty membranes with varying molar ratios of these two functionalized SPEEKs were fabricated by solution casting. The hydrogen bonding crosslinked structure of ‘A-T base pairs’, as well as the acid-base interactions between the incorporated nucleobases and SO3H groups of the polymer backbone, not only enhanced the mechanical properties and thermal stability of the blending membranes, but more importantly, it successfully addressed the over-swelling issue of highly sulfonated SPEEK membrane. The SPEEK-50Ax/50Ty membranes exhibited tensile strengths between 59.3 and 72.3 MPa, which is 2.2–2.6 times that of the pristine SPEEK membrane. And the water uptake of the blending membranes reduced from 116 % to 14.6–19.2 %, while the swelling ratio decreased from 27.1 % to 5.86–6.60 %. The proton affinity of the multiple basic N atoms in nucleobases, as well as the ‘A-T base pairs’ hydrogen bonding network and acid-base interactions between nucleobases and SO3H groups, all can serve as effective proton transport channels. Additionally, the charge repulsion effect of protonated nucleobases and the crosslinking structure is beneficial to the permselectivity. Therefore, the fabricated blending SPEEK-50Ax/50Ty membranes exhibited superior H+ flux (1.66–1.73 mmol m−2 s−1) and enhanced H+/Fe2+ permselectivity (40.3–43.2). The SPEEK-50A0.5/50T0.5 membrane demonstrated a H+ flux of 1.70 mmol m−2 s−1 and a H+/Fe2+ permselectivity of 43.2, which is 2.8 times that of the pristine SPEEK membrane, surpassing both commercially available and recently reported membranes. Therefore, the nucleobase-modified blending SPEEK-50Ax/50Ty membranes might be potential candidates for the efficient recovery of acid from pickling wastewater.