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We explain here that the authors of the article cited in the title have misrepresented the species of As(III) and As(V) in solutions and, in particular, have neglected their speciation as a function of pH. Their discussion of (ad)sorption mechanisms is therefore unsatisfactory, especially since organic matter (flower waste) and the presence of iron oxyhydroxides should be taken into account. Furthermore, the modeling of (ad)sorption kinetics and isotherms was based on linearized equations, whereas the corresponding nonlinear equations should have been used. Therefore, we believe that the authors of the original article should make corrections and additions to it. This Letter to the Editor is motivated by a concern to avoid the dissemination of approximate or even incorrect concepts in the scientific literature, which could mislead novice researchers.

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New sorption isotherms for heterogeneous sorbents are derived by combining a Gamma distribution of binding constants with a local isotherm defined by a Langmuir or Hill equation. The new "Gamma isotherms" are expressed as Stieltjes transforms of the distribution and involve generalized exponential integrals. The related energy distributions are asymmetric and present a peak corresponding to the mean binding constant. The advantages of the new isotherms are (1) at low pressures or concentrations, with a Langmuir local isotherm, the global "Gamma-Langmuir" isotherm retrieves Henry's law; (2) contrary to the power Freundlich or hypergeometric Freundlich global isotherms, these Gamma isotherms do not need a redefinition of the standard state; (3) with a Hill local isotherm, the global "Gamma-Hill" isotherm allows a separate estimation of the cooperativity and heterogeneity parameters; and (4) the condensation approximation is a good approximation if the local isotherm is Hill and displays a high degree of cooperativity. The Gamma-Langmuir model is applied to three examples from the literature, with rather different Gamma distributions.

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This correspondence critically examines and rectifies modeling deficiencies identified in a recent article published in this journal. Our analysis covers a range of models and issues, including the Temkin isotherm, the Flory-Huggins isotherm, the pseudo-first-order kinetic model, the pseudo-second-order kinetic model, the intraparticle diffusion model, the Elovich kinetic model, and the computation of thermodynamic parameters. The elucidation and correction of these modeling issues contribute to a more accurate and reliable understanding of the studied phenomena, thereby enhancing the scientific rigor of the subject paper.

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This work explores the effect of humic acids (HA) fractionation on the sorption ability of a natural zeolite (NYT)-HA adduct. HA were extracted from compost, fractionated via the pH fractionation method, and characterized via UV-Vis spectroscopy and gel permeation chromatography. The HA samples were immobilized onto NYT via thermal treatment. The resulting adducts (NYT-HA) were tested for their ability to remove methylene blue (MB) from an aqueous solution. It was found that the sorption performance of NYT-HA strongly depends on the chemical characteristics of humic acids. Sorption capacity increased with the molecular weight and hydrophobicity degree of the HA fractions. Hydrophobic and π-π interactions are likely the primary mechanisms by which MB interacts with HA. The sorption kinetic data conform to the pseudo-second-order model. The Freundlich isotherm model adequately described the sorption equilibrium and revealed that the uptake of MB onto NYT-HA is endothermic in nature.

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The name of Herbert Freundlich is commonly associated with a power relationship for adsorbed amount of a substance (Cads) against the concentration in solution (Csln), such that Cads = KCslnn; this isotherm (together with the Langmuir isotherm) is considered to be the model of choice for correlating the experimental adsorption data of micropollutants or contaminants of emerging concern (pesticides, pharmaceuticals, and personal care products), but it also concerns the adsorption of gases on solids. However, Freundlich's 1907 paper was a "sleeping beauty", which only started to attract significant citations from the early 2000s onward; moreover, these citations were too often wrong. In this paper, the main steps in the historical developments of Freundlich isotherm are identified, along with a discussion of several theoretical points: (1) derivation of the Freundlich isotherm from an exponential distribution of energies, leading to a more general equation, based on the Gauss hypergeometric function, of which the power Freundlich equation is an approximation; (2) application of this hypergeometric isotherm to the case of competitive adsorption, when the binding energies are perfectly correlated; and (3) new equations for estimating the Freundlich coefficient KF from physicochemical properties such as the sticking surface or probability. From new data treatment of two examples from the literature, the influence of several parameters is highlighted, and the application of linear free-energy relationships (LFER) to the Freundlich parameters for different series of compounds is evoked, along with its limitations. We also suggest some ideas that may be worth exploring in the future, such as extending the range of applications of the Freundlich isotherm by means of its hypergeometric version, extending the competitive adsorption isotherm in the case of partial correlation, and exploring the interest of the sticking surfaces or probabilities instead of KF for LFER analysis.

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Consideration is now being given to the use of metal coagulants to remove turbidity from drinking water and wastewater. Concerns about the long-term impact of non-biodegradable sludge on human health and the potential contamination of aquatic systems are gaining popularity. Recently, alternative biocoagulants have been suggested to address these concerns. In this study, using a 1 M sodium chloride (NaCl) solution, the active coagulating agent was extracted from Pinus halepensis Mill. Seed, and used for the first time to remove Congo red dye, the influence of numerous factors on dye removal was evaluated in order to make comparisons with conventional coagulants. The application of biocoagulant was shown to be very successful, with coagulant dosages ranging from 3 to 12 mL L-1 achieving up to 80% dye removal and yielding 28 mL L-1 of sludge. It was also found that biocoagulant is extremely pH sensitive with an optimum operating pH of 3. Ferric chloride, on the other hand, achieved similar removal rate with higher sludge production (46 mL L-1) under the same conditions. A Fourier Transform Infrared Spectroscopy and proximate composition analysis were undertaken to determine qualitatively the potential active coagulant ingredient in the seeds and suggested the involvement of proteins in the coagulation-flocculation mechanism. The evaluation criteria of the Support vector machine_Gray wolf optimizer model in terms of statistical coefficients and errors reveals quite interesting results and demonstrates the performance of the model, with statistical coefficients close to 1 (R = 0.9998, R2 = 0.9995 and R2 adj = 0.9995) and minimal statistical errors (RMSE = 0.5813, MSE = 0.3379, EPM = 0 0.9808, ESP = 0.9677 and MAE = 0.2382). The study findings demonstrate that Pinus halepensis Mill. Seed extract might be a novel, environmentally friendly, and easily available coagulant for water and wastewater treatment.

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Two flaws in concepts were identified and discussed in the paper ("Removal of Pb(II) from contaminated waters using cellulose sulfate/chitosan aerogel: Equilibrium, kinetics, and thermodynamic studies". J. Environ. Manag. 286, 112167; https://doi.org/10.1016/j.jenvman.2021.112167). In the literature, the Radke-Prausnitz model is expressed in different forms, but some of them are incorrect. The first flaw is related to the nonlinear form of the Radke-Prausnitz model. The nonlinear form of this three parameters model is expressed correctly as [Formula: see text] . The units of two parameters are ARP (L/kg) and BRP [(mol/kg)/(mol/L)ß] by considering qe (mol/kg) and Ce (mol/L). The limitation for its exponent is 0≤ ß ≤ 1. This model is developed by two authors (Radke and Prausnitz). The correct paper (DOI: 10.1021/i160044a003) cited as reference of this model is "Radke, C.J., Prausnitz, J.M., 1972. Adsorption of organic solutes from dilute aqueous solution of activated carbon. Ind. Eng. Chem. 11, 445-451". The second is the misconception about the unit of the Langmuir constant (KL; L/mg). The correct unit of KL is litre per milligram of adsorbate (i.e., Pb ions), not litre per milligram of adsorbent (the cellulose sulfate/chitosan aerogel material as reported by Najaflou and co-workers. They proposed a new equation [KL (L/mg) × m/V (mg/L)] to convert the Langmuir constant and then applied it to calculate the thermodynamic parameters of the adsorption process. The m/V is a solid/liquid ratio (g/L or kg/L). However, this conversion and application are mistakes that were thoroughly discussed in this paper. The correction is KEqo=1γAdsorbate×KLLmol×ComolL, with C° (1 mol/L by definition) being the standard state of solute and γAdsorbate (dimensionless) being the activity coefficient of adsorbate in solution. To avoid unexpected mistakes, the present authors suggest that researchers should have a correct citation (citing the original reference instead of using secondary references) and check the consistency of units (i.e., the constants of adsorption models) carefully.

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In this discussion, we highlight that the terms sorption and adsorption are often confused and misused in many articles. Even if one thought their formal definition is well known, this does not appear to be the case. We recommend encouragement to adopt the word adsorption only when fully supported by appropriate data and using the sorption terminology when it is more speculative, typically in complex solid/fluid natural systems.

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The study mentioned in the title of this comment paper contains some calculations/results that disagree with some basic chemistry concepts. These misleading calculations include (i) both kinetic and isotherm modelling through linear equations, and (ii) calculating the thermodynamic parameters for the adsorption processes. Thus, we run through the correct way to make these calculations. In our opinion, it is very confusing to continue to disseminate erroneous methods as applied in the original paper.

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There have been numerous environmental geochemistry studies using chemical, geological, ecological, and toxicological methods but each of these fields requires more subject specialist rigour than has generally been applied so far. Field-specific terminology has been misused and the resulting interpretations rendered inaccurate. In this paper, we propose a series of suggestions, based on our experience as teachers, researchers, reviewers, and editorial board members, to help authors to avoid pitfalls. Many scientific inaccuracies continue to be unchecked and are repeatedly republished by the scientific community. These recommendations should help our colleagues and editorial board members, as well as reviewers, to avoid the numerous inaccuracies and misconceptions currently in circulation and establish a trend towards greater rigour in scientific writing.

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The use of synthetic hydroxyapatites (HAps) in biomedical and environmental applications is well warranted given that they have been shown to behave as an excellent bio-compatible material in human teeth and bones. In this paper, a series of HAps doped and co-doped with two metal cations (zinc and magnesium) has been successfully synthesized by means of the precipitation method using CaCl2, Na2HPO4, ZnCl2 and MgCl2 aqueous solutions as reagents. The synthesized samples have been characterized using Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray fluorescence spectroscopy (XRF). All samples prepared using over 10 mol% of Zn and Mg ions were identified as HAp. However, the presence of metal cations caused a significant increase in their crystallite sizes (30-50 nm) along with the appearance of a second phase (scholzite, whitlockite). The XRF spectra indicated the presence of Ca, P, Zn and Mg in the powders prepared with a high Metal/P ratio (1.7-2). The antimicrobial activity of these nanopowders has been tested in vitro against five bacteria (Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa as Gram-negative; Staphylococcus aureus and Bacillus subtilis as Gram-positive) and two fungal strains (Candida albicans and Aspergillus niger). The outcomes revealed that these nanopowders exhibited strong antimicrobial activity, starting at 15 mol% of Zn and/or Mg.

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The influence of temperature upon the hydrolysis of phenyl acetate, catalysed by purified human serum arylesterase/paraoxonase (E. C. 3.1.8.1), was studied in the temperature range 10 °C-40 °C by spectrophotometry in TRIS buffer, pH 8.0, using both initial rate analysis and progress curve analysis. The kinetic parameters (catalytic constant k(cat); Michaelis constant K(m); product inhibition constant K(p)) were determined by nonlinear regression. All parameters increased with temperature, but the ratios k(cat)/K(m) and K(p)/K(m) remained practically constant. Binding of both substrate and reaction product (phenol) was exothermic. A negative entropic term accounted for about 50% of the enthalpy change for both the binding and catalytic steps. Thermodynamic analysis suggested that: (1) the rate-limiting step is the nucleophilic attack of the carbonyl group of the substrate by a water molecule, (2) the active site is preorganized with no induced fit, (3) the enzyme-bound calcium plays an important role in stabilizing both the substrate and the transition state. The practical implications of these results are discussed.

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Due to its simple and inexpensive synthesis, a new amorphous hydrous manganese oxide (AMO) has been studied as a possible chemical stabilizing agent for soils contaminated with metals. Preliminary experiments evaluating the stability of AMO in pure water have reported only minor dissolution (5.70% and 0.24% depending on the w/v ratio). Sorption kinetics have shown fast metal adsorption, especially for Pb. The sorption capacities of AMO for Cu, Cd, Pb, and Zn have been described and compared with synthetic birnessite for pH 4 and 5.5. Both oxides show similar sorption capacities at pH 4 despite the fact that birnessite characteristics (pH of zero point charge, specific surface area and cation exchange capacity) are more favorable for metal sorption. Moreover, the pH adsorption-edges show that the AMO is more pH-dependent than birnessite.

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The aim of this study is to investigate how the presence of Cu influences tebuconazole (Teb) sorption onto contrasting soil types and two important constituents of the soil sorption complex: hydrated Fe oxide and humic substances. Tebuconazole was used in commercial form and as an analytical-grade chemical at different Teb/Cu molar ratios (1:4, 1:1, 4:1, and Teb alone). Increased Cu concentrations had a positive effect on tebuconazole sorption onto most soils and humic substances, probably as a result of Cu-Teb tertiary complexes on the soil surfaces. Tebuconazole sorption increased in the following order of different Teb/Cu ratios 1:4>1:1>4:1>without Cu addition, with the only exception for the Leptosol and ferrihydrite. The highest K f value was observed for humic substances followed by ferrihydrite, the Cambisol, the Arenosol, and the Leptosol. The sorption of analytical-grade tebuconazole onto all matrices was lower, but the addition of Cu supported again tebuconazole sorption. The Teb/Cu ratio with the highest Cu addition (1:4) exhibited the highest K f values in all matrices with the exception of ferrihydrite. The differences in tebuconazole sorption can be attributed to the additives present in the commercial product. This work proved the importance of soil characteristics and composition of the commercially available pesticides together with the presence of Cu on the behavior of tebuconazole in soils.

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This study investigates the column leaching of a soil contaminated mainly with Cr and Ni by using two chelants: citric acid (biodegradable) and EDTA (non-biodegradable) followed with water rinse. The chelants lead to Cr and Ni leaching, in addition to major elements (Ca, Fe, Mg, Al, Mn and Zn) showing the dissolution of soil mineral constituents. EDTA leaches more major elements and Ni than citric acid related to the respective stability of metal-chelant complexes; citric acid leaches more Cr than EDTA, certainly because of a substitution reaction with Cr(VI). In the case of alternating chelant/water applications, leaching occurs during the chelant applications, but also during water applications. In the case of chelant/water applications followed by continuous water application, both Cr and Ni leach over time. This increased mobility could be due to the residual chelant present in soil as well as to the dissolution/mobilization of mineral or organic soil fractions.

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The redox potential (Eh) is a key parameter for controlling the release of elements from solid materials. Nevertheless, this parameter is seldom taken into account during risk assessment studies within any regulatory framework. We studied the incidence of redox changes to the solid materials using two batch procedures: i) a gradient of redox conditions obtained using sodium ascorbate solutions at various concentrations; ii) N(2) bubbling in water. These experiments were performed on two Mn-rich slag samples coming from a pyrometallurgical plant that recycles alkaline batteries. Both samples differed slightly in their chemical composition and solid characterization (i.e. presence of Mn oxide) and presented different behaviours. The present study focused on the release of the main slag elements (i.e. Mn and Si) chosen as indicators of the dissolution of primary silicate phases. Solid phase analyses (SEM-EDS and XRD) were coupled with the monitoring of elements in leachates in order to understand their behaviour and the mechanisms involved. The results indicated that the solid composition plays an important role in the release mechanisms. The presence of Mn oxide enhanced the mobilization of Mn in the greatest reducing conditions (-320 ± 5 mV/SHE), to the extent that 42% of the total Mn was leached. This demonstrated the significance in studying the solid phases (using SEM-EDS and XRD) before and after any leaching experiment. From a laboratory practice point of view, it was easier to use sodium ascorbate and allowed, in our case, greater reducing conditions to be reached.

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A Mn-rich slag sample coming from a pyrometallurgical plant recycling alkaline batteries was submitted to environmental conditions during one year. After crushing, the slag was buried in topsoil and the leachate was periodically collected in order to monitor the leached amounts of metallic elements (ME). Results evidenced a low release of the slag constituents (Mn: < 0.01%). The SEM/EDS investigations did not show alteration features supposing a weak dissolution of the primary phases (tephroite, bustamite and leucite). The modification of the pH induced by the slag enhanced the mobility of soil components and of the organic matter, particularly in the vicinity of the soil/slag contact zone. This suggested that the slag indirectly influenced the ME mobility through the organic matter and colloidal transports. The comparison with a classical laboratory column test evidenced the underestimation of the leached amounts due to the differences of operational conditions.

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The aim of this study is to evaluate the influence of organic matter on arsenic removal by coagulation/flocculation on both a model water with low mineral content and a natural water sample. Ferric chloride was used as coagulant at concentrations avoiding the preoxidation step usually required to oxidize As(III) and increase its removal. Arsenic removal was accomplished by combining evaluation of arsenic residual concentrations and speciation analysis with zeta potential measurements. A preliminary study evaluated the influence of coagulant dose, coagulation pH, and organic matter on As(III) and As(V) removal. The main conclusions were: (i) As(III) removal depended on coagulant dose and on the number of sites available on hydroxide surfaces rather than on coagulation pH; (ii) As(V) removal depended on the zeta potential of colloidal suspension and was more influenced than As(III) by coagulation pH and the presence of organic matter; (iii) organic matter removal followed As(V) removal. This allowed determination of adsorption as the main mechanism occurring during As(V) and organic matter removal and supposing precipitation/coprecipitation as an important As(III) removal mechanism. Adsorption on preformed ferric hydroxide flocs experiments allowed then confirmation of these hypotheses.

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