Effective Removal of Fe (III) from Strongly Acidic Wastewater by Pyridine-Modified Chitosan: Synthesis, Efficiency, and Mechanism

A novel pyridine-modified chitosan (PYCS) adsorbent was prepared in a multistep procedure including the successive grafting of 2-(chloromethyl) pyridine hydrochloride and crosslinking with glutaraldehyde. Then, the as-prepared materials were used as adsorbents for the removal of metal ions from acidic wastewater. Batch adsorption experiments were carried out to study the impact of various factors such as solution pH value, contact time, temperature, and Fe (III) concentration. The results showed that the absorbent exhibited a high capacity of Fe (III) and the maximum adsorption capacity was up to 66.20 mg/g under optimal experimental conditions (the adsorption time = 12 h, pH = 2.5, and T = 303 K). Adsorption kinetics and isotherm data were accurately described by the pseudo-second-order kinetic model and Sips model, respectively. Thermodynamic studies confirmed that the adsorption was a spontaneous endothermic process. Moreover, the adsorption mechanism was investigated using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results revealed the pyridine group forms a stable chelate with iron (III) ions. Therefore, this acid-resistant adsorbent exhibited excellent adsorption performance for heavy metal ions from acidic wastewater compared to the conventional adsorbents, helping realize direct decontamination and secondary utilization.

Bipyridine containing poly(amic-acid)s: Synthesis, characterization, and sorption behavior toward the Ni (II) ions

New poly(amic-acid)s sorbents, bearing bipyridine chelating groups, were synthesized by reaction of benzophenonetetracarboxylic dianhydride (BTDA) with different percentages of 4,6-bis(4-aminophenyl)-2,2′-bipyridine (BAPB), and 1,4-phenylene diamine (PPD) and were characterized by FTIR and 1HNMR spectroscopies. Because of the imidization of these poly(amic-acid)s after about 10% weight loss, their thermal stability was raised to about 500°C. The glass transition temperatures of these polymers were in the range of 154–166°C. The sorption of Ni(II) by these sorbents from the aqueous solutions was investigated by varying different parameters such as the contact time, pH, and sorbent dosage. Results indicated that the optimum efficiencies of these sorbents toward Ni(II) were at 25°C, at pH = 4 and after about 75 min. According to the Langmuir equation, the maximum uptake capacity ( qm) of PAA30/70 as a best sorbent for nickel was 14.66 mg.g−1. The modeling results confirmed the pseudo-second-order sorption for the metal ion. The morphology of these sorbents before and after sorption of Ni(II) was investigated using Scanning Electron Microscopy and the results confirmed the porous structure of these sorbents.

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Effects of Electronegativity and Hydration Energy on the Selective Adsorption of Heavy Metal Ions by Synthetic NaX Zeolite

The adsorption capacity of synthetic NaX zeolite for Pb²⁺, Cd²⁺, Cu²⁺ and Zn²⁺ in single and multi-component systems were investigated. The effects of electronegativity and hydration energy on the selective adsorption, as well as potential selective adsorption mechanism of the NaX zeolite for Pb²⁺, Cd²⁺, Cu²⁺ and Zn²⁺ were also discussed. The maximum adsorption capacity order of the heavy metals in the single system was Pb²⁺ > Cd²⁺ > Cu²⁺ > Zn²⁺, and this could be related to their hydration energy and electronegativity. The values of the separation factors (α) and affinity constant (K_EL) in different binary systems indicated that Pb²⁺ was preferentially adsorbed, and Zn²⁺ presented the lowest affinity for NaX zeolite. The selective adsorption capacities of the metals were in the order, Pb²⁺ > Cd²⁺ ≈ Cu²⁺ > Zn²⁺. The trend for the selective adsorption of NaX zeolite in ternary and quaternary systems was consistent with that in the binary systems. Pb²⁺ and Cu²⁺ reduced the stability of the Si-O-Al bonds and the double six-membered rings in the NaX framework, due to the high electronegativity of Pb²⁺ and Cu²⁺ than that of Al³⁺. The selective adsorption mechanism of NaX zeolite for the high electronegative metal ions could mainly result from the negatively charged O in the Si-O-Al structure of the NaX zeolite, hence heavy metal ions with high electronegativity display a strong affinity for the electron cloud of the oxygen atoms in the Si-O-Al. This study could evaluate the application and efficiency of zeolite in separating and recovering certain metal ions from industrial wastewater.

Highly selective removal of Ni(II) from plating rinsing wastewaters containing [Ni-xNH3-yP2O7]n complexes using N-chelating resins

Inorganic complexants, such as ammonia (AA) and pyrophosphate (PP), are often present alongside heavy metal ions in alkaline plating rinsing wastewater. We investigated the removal capacity of Ni(II) from waters containing [Ni-xNH₃-yP₂O₇]ⁿ complexes by chelating and ion-exchange resins in sole and dual-ligand systems. D463 (containing iminodiacetic groups) and PAMD (possessing polyamine groups) exerted superior performance under all conditions. Ni(II) adsorption on D463 decreased with AA and PP by 10.3% and 64.4%, respectively. Conversely, the adsorption on PAMD increased by 57.3% and 75.8%, respectively. PAMD exhibited high selectivity toward anionic [Ni-PP] species over free PP. More Ni(II) was captured by PAMD in the dual-ligand systems than sole systems, while the case for D463 was opposite. As confirmed by species tracking and DFT/XPS analyses, complexes breaking-Ni²⁺ capture was the dominant mechanism for D463, while the dual-site (non-charged and protonated amines) interactions with NiP₂O₇^2- on PAMD promoted its adsorption. The tandem combination D463-PAMD was the optimal mode to remove the most Ni(II). The actual wastewater test demonstrated that >210 BV effluent met the limit of 0.1 mg Ni(II)/L and the eluent contained 15 g Ni(II)/L. This study guides the application of chelating adsorption processes in the advanced treatment of plating rinsing wastewaters.

A multiple model approach for evaluating the performance of time-lapse capsules in trapping heavy metals from water bodies

This article applies multiple approaches for evaluating the effect of operating factors on the adsorption of heavy metals from watershed using time-lapse capsules.

Highly efficient removal of Cu(ii) by novel dendritic polyamine–pyridine-grafted chitosan beads from complicated salty and acidic wastewaters

In this study, dendritic polyamine chitosan beads with and without 2-aminomethyl pyridine were facilely prepared and characterized. Compared to CN (without the pyridine function), more adsorption active sites, larger pores, higher nitrogen content, higher specific surface area, and higher strength could be obtained for CNP (with the pyridine function). CNP microspheres afforded a larger adsorption capacity than those obtained by CN for different pH values; further, the uptake amounts of Cu(ii) were 0.84 and 1.12 mmol g⁻¹ for CN and CNP beads, respectively, at pH 5. The CNP microspheres could scavenge Cu(ii) from highly acidic and salty solutions: the maximum simulated uptake amount of 1.93 mmol g⁻¹ at pH 5 could be achieved. Due to the strong bonding ability and weakly basic property of pyridine groups, the adsorption capacity of Cu(ii) at pH 1 was 0.75 mmol g⁻¹ in highly salty solutions, which was comparative to those obtained from the commercial pyridine chelating resin M4195 (Q_Cu(II) = 0.78 mmol g⁻¹ at pH 1). In addition, a distinct salt-promotion effect could be observed for CNP beads at both pH 5 and 1. Therefore, the prepared adsorbent CNP beads can have promising potential applications in the selective capturing of heavy metals in complex solutions with higher concentrations of H⁺ and inorganic salts, such as wastewaters from electroplating liquid and battery industries.

Dendritic polyamine chitosan (CNP) beads containing 2-aminomethyl pyridine were facilely prepared for the efficient removal of Cu(ii) ions from highly acidic and salty solutions.

Preliminary study on the dynamics of heavy metals in saline wastewater treated in constructed wetland mesocosms or microcosms filled with porous slag

This study aims to evaluate the practical potential of using constructed wetlands (CWs) for treating saline wastewater containing various heavy metals. The results demonstrated that CWs growing Canna indica with porous slag as substrate could efficiently remove heavy metals (Cu, Zn, Cd, and Pb) from saline wastewater at an electrical conductivity (EC) of 7 mS/cm, especially under low influent load. Salts with salinity level (characterized as EC) of 30 mS/cm suppressed the removal of some heavy metals, dependent on heavy metal species and their influent concentrations. The presence of salts in CWs can improve the accumulation of Cu, Zn, and Pb in plant tissues as compared to control treatment, irrespective of metal concentrations in solution. The influence of salts on Cd accumulation depended on both salinity levels and Cd concentrations in solution. Although more heavy metals were accumulated in roots than in shoots, the harvesting of aboveground plant materials is still efficient addition for heavy metal removal due to the greater biomass and growth rate of aboveground plant material. Furthermore, replacing all plants instead of preserving roots from harvested plants in CWs over a period of time is essential for heavy metal removal, because the continued accumulation by roots can be inhibited by the increasing accumulated heavy metals from saline wastewater.

Efficient and synergistic removal of tetracycline and Cu(II) using novel magnetic multi-amine resins

A series of magnetic multi-amine resins (MMARs, named E1D9-E9D1) was proposed for the removal of tetracycline (TC) and Cu(II) in sole and binary solutions. Results showed that the N content of the resins increased sharply from 1.7% to 15.49%, and the BET surface areas decreased from 1433.4 m²/g to 8.9 m²/g with methyl acrylate ratio increasing from E1D9 to E9D1. Their adsorption capacities for TC and Cu(II) could reach 0.243 and 0.453 mmol/g, respectively. The adsorption isotherms of TC onto MMARs transformed from heterogeneous adsorption to monolayer-type adsorption with DVB monomer ratio in resin matrix decrease, suggesting the dominant physical adsorption between TC and benzene rings. TC adsorption capacity onto E9D1 was higher than that onto E7D3 when the equilibrium concentration of TC exceeded 0.043 mmol/L because the electrostatic interaction between negatively charged groups of TC and protonated amines of adsorbents could compensate for the capacity loss resulting from BET surface area decrease. In the binary system, the electrostatic interaction between negatively charged TC-Cu(II) complex and protonated amines of adsorbents was responsible for the synergistic adsorption onto E7D3 and E9D1. The XPS spectra of magnetic resins before and after adsorption were characterized to prove the probable adsorption mechanisms. This work provides alternative adsorbent for the efficient treatment of multiple pollution with different concentrations of organic micropollutants and heavy metal ions.