Chitosan (CS) modified with ethylenediamine tetraacetic acid (EDTA) was further modified with the zeolite imidazole framework (ZIF-8) by in situ growth method and was employed as adsorbent for the removal of rare-earth elements (REEs). The material (EDTA–CS@ZIF-8) and ZIF-8 and CS were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and nitrogen adsorption/desorption experiments (N2- Brunauer–Emmet–Teller (BET)). The effects of adsorbent dosage, temperature, the pH of the aqueous solution, contact time on the adsorption of REEs (La(III), Eu(III), and Yb(III)) by EDTA–CS@ZIF-8 were studied. Typical adsorption isotherms (Langmuir, Freundlich, and Dubinin–Radushkevich (D-R)) were determined for the adsorption process, and the maximal adsorption capacity was estimated as 256.4 mg g−1 for La(III), 270.3 mg g−1 for Eu(III), and 294.1 mg g−1 for Yb(III). The adsorption kinetics results were consistent with the pseudo-second-order equation, indicating that the adsorption process was mainly chemical adsorption. The influence of competing ions on REE adsorption was also investigated. After multiple cycles of adsorption/desorption behavior, EDTA–CS@ZIF-8 still maintained high adsorption capacity for REEs. As a result, EDTA–CS@ZIF-8 possessed good adsorption properties such as stability and reusability, which have potential application in wastewater treatment.
In this work, low-cost ceramic membranes (CMs) were prepared from ultrafine starting powders such as kaolin, clay, and starch by a dry compaction method. The ceramic membranes were sintered at different temperatures and times and were characterized by XRD, XRF, TG-DTA, SEM-EDS, N2-BET, water absorption, compressive strength, and pure water flux. The optimal membrane, sintered at 1000 °C for 3 h, possessed water absorption of 27.27%, a compressive strength of 31.05 MPa, and pure water flux of 20.74 L/h m2. Furthermore, chitosan crosslinked with glutaraldehyde was coated on the surface of the ceramic membrane by the dip coating method, and the pore size of the chitosan-coated ceramic membrane (CCCM) was 16.24 nm. Eventually, the separation performance of this membrane was assessed for the removal of chromium(VI) from aqueous solution. The ultrafine filtration of Cr(VI) was studied in the pH range of 2–7. The maximum removal of Cr(VI) was observed to be 71.25% with a pH of 3. The prepared CCCM showed good membrane properties such as mechanical stability and ultrafine structure, which have important applications for the treatment of wastewater including such heavy metals.
In this study, the sorptions of Cu(II), Pb(II), and Cr(VI) on amine-functionalized activated carbon were investigated. Coal from the Tavantolgoi deposit of Mongolia was used as a precursor for the modification. After the coal carbonization, the char was activated with heated steam at different times (120, 180, and 240 min) and several temperatures (800ºC and 850ºC). The activated carbon at 850ºC for 240 min was used for the treatment with 3-aminopropyltriethoxysilane (APTES). The interactions between metal ions and functional groups on the sorbent surface were confirmed by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) coupled with X-ray energy dispersive spectroscopy (EDS). The influence of various parameters such as pH (2-7), contact time (0.5-6 h), temperature (25ºC, 35ºC, 45ºC, and 55ºC), initial concentration of heavy metals ions (10, 25, and 50 mg/L), and common cations (Na + , K + , Ca 2+ , Mg 2+ ) was investigated. The optimum pH for Cu(II), Pb(II), and Cr(VI) sorption on the modified activated carbon was chosen as 4, 3, and 3, respectively. The sorption capacity was increased from 6.15 to 9.88 mg/g and 17.1 mg/g to 19.0 mg/g when increased the temperature from 25ºC to 55ºC for Cu(II) and Cr(VI) adsorption, respectively (initial concentration of metal ions were 50 mg/L). But the sorption capacity was decreased from 3.13 mg/g to 2.69 mg/g when increased the temperature from 25ºC to 55ºC for Pb(II) adsorption. The thermodynamic parameters such as enthalpy (ΔHº), entropy (ΔSº), and Gibb's free energy (ΔGº) were estimated, and the results confirmed that all sorption processes are spontaneous and thermodynamically favorable. The sorption capacity was decreased when the amount of Na + , K + , Ca 2+ , or Mg 2+ increased from 0 to 200 mg/L, and a remarkable decrease in sorption capacity was observed for Pb(II) adsorption. The order of adsorption capacity of modified activated carbon for metal ions was Cr(VI) Cu(II) Pb(II). The sorption mechanism was discussed for the processes.
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