Study of adsorption performance and adsorption mechanism for U(VI) ion on modified polyacrylonitrile fibers

Alkaline Hydrolysis of Waste Acrylic Fibers Using the Micro-Water Method and Its Application in Drilling Fluid Gel Systems

Filtrate reducer is a drilling fluid additive that can effectively control the filtration loss of drilling fluid to ensure the safe and efficient exploitation of oilfields. It is the most widely used treatment agent in oilfields. Due to its moderate conditions and controllable procedure, alkaline hydrolysis of high-purity waste polyacrylonitrile has been utilized for decades to produce filtrate reducer on a large scale in oilfields. However, the issues of long hydrolysis time, high viscosity of semi-finished products, high drying cost, and tail gas pollution have constrained the development of the industry. In this study, low-purity waste acrylic fiber was first separated and purified using high-temperature hydroplastization, and the hydrolyzed product was obtained using alkaline hydrolysis with the micro-water method, which was called MW-HPAN. The hydrolysis reaction was characterized using X-ray diffraction, scanning electron microscopy, infrared spectroscopy, and thermogravimetric analysis, and the elemental analysis showed a hydrolysis degree of 73.21%. The experimental results showed that after aging at 180 °C for 16 h, the filtration volume of the freshwater base slurry with 0.30% dosage and 4% brine base slurry with 1.20% dosage was 12.7 mL and 18.5 mL, respectively. The microstructure and particle size analysis of the drilling fluid gel system showed that MW-HPAN could prevent the agglomeration of clay and maintain a reasonable particle size distribution even under the combined deteriorating effect of high temperature and inorganic cations, thus forming a dense filter cake and achieving a low filtrate volume of the drilling fluid gel system. Compared with similar commercially available products, MW-HPAN has better resistance to temperature and salt in drilling fluid gel systems, and the novel preparation method is promising to be extended to practical production.

Impact of treatment chemicals on the morphology and molecular structure of microfibers and microplastic films in wastewater

This study investigated the impact of commonly used treatment chemicals on the morphology and molecular structure of microfibers (MFs) and microplastic films (MPFs) to determine whether significant changes could occur during wastewater treatment. MFs and MPFs were exposed to sodium hypochlorite (NaOCl), hydrogen peroxide (H2O2), calcium hydroxide (Ca(OH)2, pH 11), sodium hydroxide (NaOH, pH11), and hydrochloric acid (HCl, pH 3) at typical doses and exposure times used at wastewater treatment plants. Scanning electron microscopy (SEM) analysis and attenuated total reflectance-Fourier-transform infrared (ATR-FTIR) were used to examine any morphological or chemical changes after the treatment. Morphological changes were observed in the form of cracks, and increased roughness was revealed in the SEM and 3-D surface images. The results showed that MFs were more resistant to surface degradation than MPFs. Moreover, intensity peaks of ATR-FTIR revealed some partial dislodgement of the bonds in both MFs and MPFs after chemical treatment, but the overall polymer structure remained intact. The changes that occur on the surface of MFs and MPFs during chemical treatment can impact their fate, removal, and transportation behavior both at the treatment plant and after discharge to the environment.

Purification performance of modified polyacrylonitrile fiber-activated carbon fiber filter for heavy metal ions

A heavy metal ion adsorbent (HFPANF) with high surface area was obtained from polyacrylonitrile fibers with fibrillation and alkali hydrolysis, and an activated carbon fiber filter was prepared by using HFPANF as the binder. The surface area of polyacrylonitrile was 48.64 m²/g due to fibrillation, which also led to the carboxyl content of the HFPANF up to 3.4 mmol/g. Batch adsorption experiments on Cu²⁺ and Pb²⁺ showed that the adsorption capacities of HFPANF for Cu²⁺ and Pb²⁺ were 47.5 mg/g and 54.3 mg/g. The adsorption kinetics showed that the adsorption reached equilibrium at 90 min and that the adsorption followed the pseudo-second order model. It indicates that the adsorption process is chemisorption. HFPANF formed a single tooth chelate with Cu and a double tooth chelate with Pb. HFPANF-ACF filter was prepared by wet molding technique. When the HFPANF content was 30%, the filter reached a compressive strength of 15.37 MPa and its maximum flux was 180 L/h. 2.5 mg/L of Cu and Pb were used for dynamic adsorption experiments and the heavy metal removal rate was still above 95% after filtering 600 L. The pressure drop of HFPANF-ACF filter was much smaller compared with that of GAC filter due to the combined effect of fibrillated nanofibers and ACF, which can improve the filtration efficiency of the filter.

Green Hydrogel-Biochar Composite for Enhanced Adsorption of Uranium

Uranium is the backbone of the nuclear fuel used for energy production but is still a hazardous environmental contaminant; thus, its removal and recovery are important for energy security and environmental protection. So far, the development of biocompatible, efficient, economical, and reusable adsorbents for uranium is still a challenge. In this work, a new orange peel biochar-based hydrogel composite was prepared by graft polymerization using guar gum and acrylamide. The composite's structural, morphological, and thermal characteristics were investigated via Fourier transform infrared (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) methods. The composite's water absorption properties were investigated in different media. The performance of the prepared composite in adsorbing uranium (VI) ions from aqueous media was systematically investigated under varying conditions including solution's acidity and temperature, composite dose, contact time, and starting amount of uranium. The adsorption efficiency increased with solution pH from 2 to 5.5 and composite dose from 15 to 50 mg. The adsorption kinetics, isotherms, and thermodynamics parameters were analyzed to get insights into the process's feasibility and viability. The equilibrium data were better described through a pseudo-second-order mechanism and a Langmuir isotherm model, indicating a homogeneous composite surface with the maximum uranium (VI) adsorption capacity of 263.2 mg/g. The calculated thermodynamic parameters suggested that a spontaneous and endothermic process prevailed. Interference studies showed high selectivity toward uranium (VI) against other competing cations. Desorption and recyclability studies indicated the good recycling performance of the prepared composite. The adsorption mechanism was discussed in view of the kinetics and thermodynamics data. Based on the results, the prepared hydrogel composite can be applied as a promising, cost-effective, eco-friendly, and efficient material for uranium (VI) decontamination.

Facile preparation and adsorption performance of low-cost MOF@cotton fibre composite for uranium removal

A novel composite MOF@cotton fibre (HCF) was prepared and characterized by FTIR, SEM, XPS and TGA. The effect of various parameters on the adsorption efficiency, such as the solution pH, contact time, initial U(VI) concentration and temperature, was studied. The maximal sorption capacity (Qm) is 241.28 mg g-1 at pH 3.0 for U(VI) according to the Langmuir isotherm adsorption model, and the kinetic and thermodynamic data reveal a relatively fast entropy-driven process (ΔH0 = 13.47 kJ mol-1 and ΔS0 = 75.47 J K-1 mol-1). The removal efficiency of U(VI) by HCF is comparable with that of pure cotton fibre and as-prepared MOF (noted as HST). However, the HST composite with cotton fibre significantly improved the treatment process of U(VI) from aqueous solutions in view of higher removal efficiency, lower cost and faster solid-liquid separation. Recycling experiments showed that HCF can be used up to five times with less than 10% efficiency loss.