RESUMO
The remediation of arsenic contamination in potable water is an important and urgent concern, necessitating immediate attention. With this objective in mind, the present study investigated arsenic removal from water using batch adsorption and fixed-bed column techniques. The material employed in this study was a waste product derived from the treatment of groundwater water for potable purposes, having a substantial iron composition. The material's properties were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Fourier-transformed infrared spectroscopy (FT-IR). The point of zero charge (pHPZC) was measured, and the pore size and specific surface area were determined using the BET method. Under static conditions, kinetic, thermodynamic, and equilibrium studies were carried out to explore the influencing factors on the adsorption process, namely the pH, contact time, temperature, and initial arsenic concentration in the solution. It was found that the adsorption process is spontaneous, endothermic, and of a physical nature. In the batch adsorption studies, the maximum removal percentage was 80.4% after 90 min, and in a dynamic regime in the fixed-bed column, the efficiency was 99.99% at a sludge:sand = 1:1 ratio for 380 min for a volume of water with arsenic of ~3000 mL. The kinetics of the adsorption process conformed to a pseudo-second-order model. In terms of the equilibrium studies, the Sips model yielded the most accurate representation of the data, revealing a maximum equilibrium capacity of 70.1 mg As(V)/g sludge. For the dynamic regime, the experimental data were fitted using the Bohart-Adams, Thomas, and Clark models, in order to establish the mechanism of the process. Additionally, desorption studies were conducted, serving as an essential step in validating the practical applicability of the adsorption process, specifically in relation to the reutilization of the adsorbent material.
RESUMO
In recent years, during industrial development, the expanding discharge of harmful metallic ions from different industrial wastes (such as arsenic, barium, cadmium, chromium, copper, lead, mercury, nickel, selenium, silver, or zinc) into different water bodies has caused serious concern, with one of the problematic elements being represented by selenium (Se) ions. Selenium represents an essential microelement for human life and plays a vital role in human metabolism. In the human body, this element acts as a powerful antioxidant, being able to reduce the risk of the development of some cancers. Selenium is distributed in the environment in the form of selenate (SeO42-) and selenite (SeO32-), which are the result of natural/anthropogenic activities. Experimental data proved that both forms present some toxicity. In this context, in the last decade, only several studies regarding selenium's removal from aqueous solutions have been conducted. Therefore, in the present study, we aim to use the sol-gel synthesis method to prepare a nanocomposite adsorbent material starting from sodium fluoride, silica, and iron oxide matrices (SiO2/Fe(acac)3/NaF), and to further test it for selenite adsorption. After preparation, the adsorbent material was characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The mechanism associated with the selenium adsorption process has been established based on kinetic, thermodynamic, and equilibrium studies. Pseudo second order is the kinetic model that best describes the obtained experimental data. Also, from the intraparticle diffusion study, it was observed that with increasing temperature the value of the diffusion constant, Kdiff, also increases. Sips isotherm was found to best describe the experimental data obtained, the maximum adsorption capacity being ~6.00 mg Se(IV) per g of adsorbent material. From a thermodynamic point of view, parameters such as ΔG0, ΔH0, and ΔS0 were evaluated, proving that the process studied is a physical one.
RESUMO
This study aims to remove arsenic from an aqueous medium by adsorption on a nanocomposite material obtained by the sol-gel method starting from matrices of silica, iron oxide and NaF (SiO2/Fe(acac)3/NaF). Initially, the study focused on the synthesis and characterization of the material by physico-chemical methods such as: X-ray diffraction, FT-IR spectroscopy, Raman spectroscopy, atomic force microscopy, and magnetization. Textural properties were obtained using nitrogen adsorption/desorption measurements. The zero load point, pHpZc, was also determined by the method of bringing the studied system into equilibrium. In addition, this study also provides a comprehensive discussion of the mechanism of arsenic adsorption by conducting kinetic, thermodynamic and equilibrium studies. Studies have been performed to determine the effects of adsorbent dose, pH and initial concentration of arsenic solution, material/arsenic contact time and temperature on adsorption capacity and material efficiency. Three theoretical adsorption isotherms were used, namely Langmuir, Freundlich and Sips, to describe the experimental results. The Sips isotherm was found to best describe the experimental data obtained, the maximum adsorption capacity being ~575 µg As(III)/g. The adsorption process was best described by pseudo-second order kinetics. Studies have been performed at different pH values to establish not only the optimal pH at which the adsorption capacity is maximum, but also which is the predominantly adsorbed species. The effect of pH and desorption studies have shown that ion exchange and the physiosorption mechanism are implicated in the adsorption process. From a thermodynamic point of view, parameters such as ΔG°, ΔH° and ΔS° were evaluated to establish the mechanism of the adsorption process. Desorption studies have been performed to determine the efficiency of the material and it has been shown that the material can be used successfully to treat a real-world example of deep water with a high arsenic content.
