| Abstract [eng] |
Water pollution is one of the top environmental problems in industrialised regions of the world. Due to their unique properties, heavy metals in water can cause developement of cancer, hormone imbalances and organ failure. One of the most commonly used methods for the treatment of heavy metals is heterogeneous adsorption. Microporous aliuminophosphate zeotypes with a signature neutral structure are considered as potential adsorbents suitable for water treatment. Two synthesis methods for obtaining crystalline zeotypes, microwave hydrothermal and ionothermal, are used in the project study. The crystalline composition and particle morphology of the resulting products are evaluated by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy diffraction spectroscopy (EDS). Thermal properties are analysed by the simultaneous thermal analysis (STA) method and surface area is assessed by the Brunauer-Emeth-Teller (BET) method. The XRD results showed that the target AEL structure type AlPO-11 ceotypes were obtained, the SEM images show the characteristic rhombohedral syngony of AEL and the EDS results show a neutrality-confirming ratio of aluminium to phosphorus atoms close to unity. The adsorption properties of AlPO-11 in aqueous solutions of Pb2+ are compared with those of the NaA zeolite; it is found that the adsorption profile of both adsorbents is close to the type I adsorption isotherm, indicating microporous adsorption. Adsorption equilibrium and kinetic isotherm models are used to determine the process mechanism. The Langmiur, Freundlich, Temkin, Dubinin-Radushkevich and Tóth models are used to study adsorption equilibrium. The Langmiur and Tóth models are the most suitable for describing the processes occurring on AlPO-11 and NaA adsorbents. The adsorption capacity of AlPO-11 adsorbent is more reliably determined by the nonlinear Tóth model, qmTo = 391,53 mg/g, and that of NaA by the nonlinear Langmiur model, qmL = 736,33 mg/g. The values of the Temkin model parameter bT indicate that the energy of interactions on the surface of the AlPO-11 adsorbent is significantly lower than for NaA, indicating stronger interactions of the adsorbent with the zeolite. The pseudo-first-order, pseudo-second-order, Elovich and internal particle diffusion (IPD) methods were chosen to study the kinetics. The IPD model was found to be inadequate to describe both systems as the interactions are multistationary. The pseudo-second-order and Elovich models indicating chemisorption are the most appropriate for both adsorbents. The nature of the adsorption was found to be mathematically defined as having irreversible chemical interactions, but this nature may be determined by the presence of micropores in the adsorbent structure. Based on all the results, AlPO-11 adsorbent is considered to have physisorption as the main mechanism, while adsorption on NaA is considered to be governed by an ion-exchange mechanism. |
