The synthesis and characterization of AlPO 4 hollow microspheres of uniform size, and the sorption properties for Pb 2+ , Cd 2+ , Cu 2+ , and Zn 2+

Ion-imprinted chitosan prepared without cross-linking agent for efficient selective adsorption of Al(III) from rare earth solution

In the aqueous phase, ion-imprinted materials exhibit excellent selective adsorption properties for specific ions, but their complicated preparation process and large amount of crosslinker consumption limit their application. In this study, ion-imprinted chitosan (IIP-CS) was prepared by a simple one-step hydrothermal method without a cross-linking agent for the efficient adsorption of trace amounts of Al(III) from a rare earth solution. The structures and morphology of IIP-CS were analyzed by FT-IR, SEM, and XRD. The Al(III) adsorption characteristics of IIP-CS were investigated under various preparation processes and adsorption conditions. It was found that the optimum mass ratio of IIP-CS is 3 : 1 and pH is 3 and the adsorption capacity reaches up to 40.36 mg g-1. In addition, three different isothermal models-Temkin, Freundlich, and Langmuir-were used to analyze the equilibrium adsorption of IIP-CS in aqueous solution. The results obtained are consistent with the Langmuir model. The adsorption process of Al(III) on IIP-CS follows a pseudo-secondary kinetic model, suggesting that electron sharing or exchange between IIP-CS and Al(III) is a key factor affecting its adsorption rate. IIP-CS shows high selectivity coefficients for Al(III) in mixtures of La(III), Y(III), and Gd(III), which are 792.50, 163.26, and 55.16, respectively. The mechanism of action is the formation of a complex via amidation between Al(III) and IIP-CS. IIP-CS is an adsorbent with excellent regeneration and selective adsorption performance in aqueous solution.

Preparation of chitosan mesoporous membrane/halloysite composite for efficiently selective adsorption of Al(III) from rare earth ions solution through constructing pore structure on substrate

The removal of impurity Al(III) from rare earth ion solution by selective adsorption method was one of the challenging tasks. Herein, calcination and acid dissolution treatment were used to construct the pore structure for the halloysite substrate (Hal-650-H) and provide conditions for the formation of the chitosan mesoporous membrane to prepare composite (Hal-H-2CS). The selective adsorption properties and mechanism of the Hal-H-2CS for Al(III) in the rare earth ion solution were studied. The results showed that the formation of mesoporous structures for chitosan provided abundant sites for the adsorption of Al(III). Hal-H-2CS showed remarkable selective adsorption properties for Al(III) in a wide pH range and the binary mixtures with high content of Al(III) or La(III). The maximum adsorption capacity of Al(III) was 106 mg/g, while the adsorption capacity of La(III) was only 1.41 mg/g at pH 4.0. In addition, the Hal-H-2CS exhibited excellent regeneration and structural stability. The remarkable selective properties of Hal-H-2CS was achieved by the synergistic effect between chitosan mesoporous membrane and Hal-650-H, the main adsorption sites were the OH, NH2, CONH2 of chitosan and the oxygen sites of the Hal-650-H. This work provides a new strategy for the design and preparation of outstanding selective adsorbent for Al(III).

Experimental and numerical study on Zn and Pb migration in the farmland soil under wastewater irrigation conditions

Long-term wastewater irrigation may lead to the accumulation, transformation, and migration of heavy metals in the farmland soil, increasing the risk of groundwater pollution. However, it is currently uncertain whether using wastewater for irrigation would lead to the migration of heavy metals zinc (Zn) and lead (Pb) into deeper layers of soil, in the local undeveloped wastewater irrigation farmland. In this study, the migration characteristics of Zn and Pb from irrigation wastewater in local farmland soil were investigated through a series of experiments including adsorption experiments, tracer, and heavy metals breakthrough experiments, as well as numerical simulations using HYDRUS-2D software. The results revealed that the Langmuir adsorption model, CDE model, and TSM model were effective in fitting the required adsorption and solute transport parameters for the simulations. Furthermore, both the soil experiments and simulation results showed that in the test soil, Pb had a stronger affinity for adsorption sites than Zn, while Zn exhibited greater mobility than Pb. After 10 years of wastewater irrigation, it was found that Zn had migrated to a maximum depth of 32.69 cm underground and Pb had only migrated to 19.59 cm. Despite their migration, the two heavy metals have not yet reached the groundwater zone. Instead, they had accumulated to higher concentrations in the local farmland soil. Moreover, the proportion of active forms of Zn and Pb decreased after flooded incubation. The present results can improve understanding of the environmental behavior of Zn and Pb in the farmland soil and can be used as a basis for risk assessment of Zn and Pb polluting groundwater.

Facile preparation of MoS2@Kaolin composite by one-step hydrothermal method for efficient removal of Pb(II)

MoS₂@Kaolin was prepared by facile one-step hydrothermal method for the efficient adsorption of Pb(II) from aqueous solution. XRD, TG, SEM, BET, XPS and FTIR were used to characterize the phase and structure of composite before and after the adsorption of Pb(II). The results showed that MoS₂ nanosheets were successfully assembled on kaolinite surface to form MoS₂@Kaolin, and the adsorption capacity of the MoS₂@Kaolin is 1.74 and 16.95 times than that of single MoS₂ and kaolinite, respectively. MoS₂@Kaolin composite exhibited a fast adsorption rate for Pb(II) and an excellent adsorption efficiency for Pb(II) in a wide pH range (2-5.5). The adsorption process followed the Langmuir isotherm model and maximum adsorption capacity was 280.39 mg/g. The adsorption kinetics of MoS₂@Kaolin composite to Pb(II) fitted well with the pseudo-second-order kinetics models, which showed that the adsorption process was controlled by chemical sorption. MoS₂@Kaolin showed excellent regeneration and maintained high selectivity adsorption with co-existence metal ions. The adsorption mechanism was that the Pb(II) reacted with the S atoms on surface of MoS₂@Kaolin under oxidation conditions provided by molybdenum disulfide to form the insoluble compound β-Pb₃O₂SO₄ in aqueous solution. MoS₂@Kaolin was an adsorbent for Pb(II) in aqueous solution with excellent adsorption properties and application potential.

Synthesis and characterization of γ-MnO2/chitosan/Fe3O4 cross-linked with EDTA and the study of its efficiency for the elimination of zinc(II) and lead(II) from wastewater

In this research, a novel γ-MnO₂/chitosan/Fe₃O₄ nanocomposite was synthesized and modified by ethylenediaminetetraacetic acid (EDTA) for the separation and simultaneous elimination of Zn(II) and Pb(II) ions from aqueous solutions in a batch system. The magnetic nanocomposite was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and elemental analysis (EDAX). The results demonstrated that the magnetic nanocomposite was successfully synthesized and cross-linked. The predominant influential experimental parameters including pH, contact time, initial concentration, and temperature were analyzed in relation to the adsorption capacity. The experimental data were well converged with the double exponential kinetic model. Also, the results were well matched with the Langmuir isotherm, where the maximum adsorption values were 310.4 and 136 mg g^-1 for Pb(II) and Zn(II), respectively. On the other hand, in the binary-component system, the Langmuir-Freundlich model dominated the experimental data. The thermodynamic results (ΔG° < 0, ΔH° > 0, and ΔS° > 0) within the temperature range of 25-40 °C showed that the nature of adsorption by the nanocomposite for both ions was spontaneous and endothermic and was favored at higher temperatures. The simultaneous removal of two ions, the excellent magnetic separation, and the high efficiency in reuse (five effective recovery cycles) indicated the high capability of the EDTA-modified γ-MnO₂/chitosan/Fe₃O₄ nanocomposite in the treatment of industrial effluents from Pb(II) and Zn(II).

Simultaneous removal of Pb2+, Cu2+ and Cd2+ ions from wastewater using hierarchical porous polyacrylic acid grafted with lignin

In PAA-g-lignin, phase separation, caused by the difference in expansion properties between lignin and polyacrylic acid, is used to build a porous hydrogel. In this study, PAA-g-APL was produced by grafting polyacrylic acid with acid-pretreated alkali lignin. Acid-pretreated alkali lignin acts as a hierarchical pore-forming agent that enhances the simultaneous adsorption capacities for Pb²⁺, Cu²⁺ and Cd²⁺ ions from wastewater. Notably, PAA-g-APL acted as a selective adsorbent for Pb²⁺ ions has an excellent selective removal coefficient α (20.22) in contaminated wastewater contained Cu²⁺ ions. Its molar partition coefficient for Pb²⁺ ions (68 %) is higher than that for either Cu²⁺ ions (28.6 %) or Cd²⁺ ions (3.4 %). At equilibrium, the total adsorption capacities of PAA-g-APL for Pb²⁺, Cu²⁺ and Cd²⁺ were 1.076 mmol g^-1, 0.3233 mmol g^-1 and 0.059 mmol g^-1, respectively. The experimental kinetic data fitted well to a pseudo-second order model and to an intra-particle-diffusion model. The Freundlich isotherm model gave the best fit with the experimental equilibrium data. The ΔG° for PAA-g-APL is < 0, indicating that the adsorption of heavy metal ions is a spontaneous process. This study provides a highly promising candidate for the treatment of wastewater contaminated with a mixture of heavy metals.