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Safe drinking water is a necessity for every human being, but clean water is scarce and not easily available due to natural geochemical factors or industrial pollutant activity. Many issues involving water quality could be greatly improved using clays as adsorbents. We highlight for the first time, the uptake of fluoride from natural water by Lapon...
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... around 24.0 and 29.5°2θ low intensity peaks are also observed, which are due to the partial crystallization of the surfactant HDPy. To understand how the Laponite surface is modified, Fourier transform infrared spectroscopy (FTIR) was used for the characterization of raw and modified Laponites at a measuring range between 400 and 4,000 cm À1 (Figure 4). ...
Citations
... min 1/2 ), and C (g/g) a constant associated with diffusion resistance Adsorption isotherm models, namely, Langmuir and Freundlich adsorption isotherm models, were used to give more insight into the relationship between the adsorbate concentration and the solid phases in the aqueous solution at equilibrium. 15 The nonlinear mathematical expressions of the Langmuir and Freundlich isotherm models are shown in Equation 6 and Equation 7, respectively. 14 ...
Contamination of water and food with cyanotoxins poses human health risks, and hence the need for sensitive early warning tools to monitor these in water. A composite of glutaraldehyde-crosslinked chitosan and multi-walled carbon nanotubes (ChMWCNTs) was synthesised and tested for potential use as a solid-phase adsorption toxin tracking (SPATT) adsorbent for monitoring microcystins (MCs) in fresh water. The composite was characterised by Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller theory and scanning electron microscopy. Batch adsorption experiments to assess the effect of contact time, adsorbent dosage and initial microcystin-LR (MC-LR) concentration were conducted. The composite was found to be efficient in adsorbing MC-LR, showing 97% removal and a maximum adsorption capacity of 4.639 μg/g under optimised conditions of 5 μg/L of MC-LR, adsorbent dose of 0.03 g/5 mL and 30 min contact time. The adsorption kinetics were better explained by a pseudo-second-order model, inferring chemisorption adsorption. The isotherm data better fitted the Langmuir isotherm model, thus inferring monolayer surface adsorption. For desorption, 100% methanol was the most effective, with an efficiency of 84.71%. The composite effectively adsorbed and desorbed three congeners of MCs (–LR, –RR and –YR) when tested in raw dam water, regardless of its lower maximum adsorption capacity compared to those of other adsorbents used for similar purposes.
Significance:
• Monitoring of microcystins is problematic in large reservoirs and rivers.
• Chitosan can be crosslinked and modified to enhance its adsorption properties.
• Composites of chitosan and carbon nanotubes efficiently adsorb and desorb microcystins.
• This study is possibly the first to apply a chitosan-based sorbent in solid-phase toxin tracking (SPATT) to be used as an early warning tool in passive monitoring of microcystins in water resources.
Open data set: https://doi.org/10.6084/m9.figshare.20992291.v1
... Previous studies have demonstrated that coal, as a biological organic rock, contains kaolinite, calcite, and other minerals in addition to organic matter. These constituents are capable of reducing the levels of anions, cations, and heavy metal ions in water [16,17]. It is hypothesized that the substantial decrease in NO − 3 concentrations during the early stages of water-coal interactions can be attributed to the rapid adsorption of coal. ...
... The results of NO − 3 adsorption in residual coal under different conditions are shown in Figure 4. Previous studies have demonstrated that coal, as a biological organic rock, contains kaolinite, calcite, and other minerals in addition to organic matter. These constituents are capable of reducing the levels of anions, cations, and heavy metal ions in water [16,17]. It is hypothesized that the substantial decrease in NO − 3 concentrations during the early stages of water-coal interactions can be attributed to the rapid adsorption of coal. ...
... Therefore, an adsorption experiment was conducted to investigate the effect of various factors (additional amount of residual coal, adsorption time, and initial concentration of NO Previous studies have demonstrated that coal, as a biological organic rock, contains kaolinite, calcite, and other minerals in addition to organic matter. These constituents are capable of reducing the levels of anions, cations, and heavy metal ions in water [16,17]. It is hypothesized that the substantial decrease in NO The effect of coal dosage on the adsorption and removal of NO − 3 in the mine water by coal is shown in Figure 4a. ...
The coal pillar dam of underground reservoirs and residual coal in goaves have a direct impact on the quality of mine water. In this paper, the coal pillar dam of an underground reservoir and residual coal in the goaf and mine water in the Daliuta coal mine are used as research objects. The adsorption mechanism of residual coal with respect to NO3− in mine water was analyzed by carrying out adsorption experiments. The composition and variation of organic matter in mine water at different times were simulated using three-dimensional fluorescence spectrum analysis. The influence of residual coal and microorganisms in underground reservoirs on the change in NO3− contents in mine water was explored. Moreover, the mechanism of NO3− changes in the water body was clarified. The results showed that the concentration of NO3− in the water first decreased and then increased, showing a downward trend as a whole. The adsorption of NO3− by residual coal led to a decrease in its concentration, which conformed to a pseudo-second-order kinetic model and Freundlich isothermal adsorption model, indicating that the adsorption process of NO3− by residual coal is mainly carried out via chemical adsorption and multi-layer adsorption. The increase in NO3− concentration was caused by the hydrolysis of tryptophan and other protein-like substances in the water into nitrate under the action of microorganisms.
Fluoride concentrations in drinking water above permissible levels and incidences of fluorosis among people have been
reported from many parts of the world including India. Low-cost and biodegradable adsorbents are the preferred choice for
the removal of fluoride from an aqueous medium. In the present study, zinc-aluminium layered double hydroxide (LDH)
supported on sugarcane bagasse (raw and acid-treated) has been synthesized, characterized, and investigated for the
defluoridation of water. The SEM micrographs of the supported adsorbents show good dispersion of the LDH particles on
the support material. The defluoridation capacity of the LDH is enhanced by supporting it on bagasse. The adsorption
capacity of supported adsorbents increased by 3-fold than the unsupported LDH adsorbent. The adsorption data have been
well fitted to the Freundlich isotherm model indicating physical and multi-layer adsorption. The maximum fluoride
adsorption capacity has been found to be 8.85 mg/g with 76.3% fluoride removal when the initial fluoride concentration is
11-12 mg/L. The pseudo-second-order kinetic model has been found suitable to explain the fluoride adsorption kinetics on
the supported LDH adsorbents. The present study reveals that the bagasse-supported LDH adsorbent has a high potential for
defluoridation of water.
The cleaning of water polluted by toxic geogenic compounds is challenging and demands novel, sustainable and low-cost adsorbents. To address this environmental problem, agricultural wastes functionalized with lanthanum have been studied for the depollution of arsenate and fluoride in aqueous solution. A simple and straightforward approach was utilized to anchor lanthanum on the surface of avocado seed, cauliflower stem, and macadamia nut shell wastes with the aim of effectively removing these toxic water pollutants and avoiding the microorganism growth on the biomass and its degradation during prolonged equipment operation. The adsorption mechanism using these modified biomass samples was endothermic and multi-ionic, involving up to two arsenate and three fluoride ions that can interact with the biomass surface functionalities. The simultaneous adsorption of these pollutants was antagonistic, and the co-anion concentration inhibited the adsorption of target geogenic pollutants. Overall, the fluoride adsorption properties of these modified lignocellulosic wastes were better than those for arsenate. The antibacterial activity of the lanthanum-modified biomass samples may enable for their use in packed-bed columns for long-term water treatment processes. The adsorption and antimicrobial properties of these functionalized biomass residues are promising for the implementation of efficient and economic processes for purifying water contaminated by arsenate and fluoride.
This work aims to study caffeine removal from an aqueous solution through adsorption on laponite. Experimental analysis of adsorption in batch scale was performed to verify the influence of pH (2 to 10), the concentration of solid adsorbent (0.5 to 5.0 g L⁻¹), and the contact time (1 to 150 min). The adsorption equilibrium was analyzed using Bayesian Information Criteria metric statistics to define the isotherm model of caffeine removal. The Bayesian Markov Chain Monte Carlo technique estimated the main isotherm parameters. The thermodynamics tests were performed at three different temperatures (303, 313, and 323 K) using concentrations from 10 to 4000 g L⁻¹. The results showed that the kinetics study at pH 4 and 5 g L⁻¹ of laponite was efficient, exceeding 90% of caffeine removal even in a short period of adsorption time (after 1 min). The equilibrium state was reached at about 20 min of contact time. Redlich-Peterson and Sips were the isotherm models that best fit the experimental data. The thermodynamics study suggested that the caffeine adsorption on laponite was spontaneous, exothermic, and mainly was governed by physisorption. The results showed that adsorption is a suitable method for removing emerging pollutants like caffeine. Furthermore, laponite is a promising material to remove them.
Article Highlights
• Laponite is mesoporous and there was no change in structure after adsorption
• Parameters from the isotherms studied shows smooth dependence of the temperature
• The Sips and Redlich-Peterson isotherm models best described the experimental data
