Sorption Kinetics for Dye Removal From Aqueous Solution Using Natural Clay

The kinetics of the adsorption of Congo red onto natural clay has been studied in an agitation batch adsorber. The Furusawa model has been used to determine the external transfer coefficient for the system and the effect of several experimental variables have been investigated: these include agitation, initial dye concentration, clay mass and clay particle size. The mass transfer coefficient has been correlated with the system variable by the following equation:  kf = A(variable)B. Keywords: dyes, adsorption,  mass transfer, cla

RESPONSE SURFACE OPTIMIZATION AND MODELING OF AMMONIUM CHLORIDE ACTIVATION PROCESS OF BENTONITE

Ce travail a consisté en l‟optimisation et la modélisation de l‟activation d‟une bentonite avec le chlorure d‟ammonium en utilisant la méthode des plans d‟expériences, et en particulier la méthodologie de surface de réponse (RSM). Un plan central composite orthogonal (CCOD), a permis la détermination de l‟influence des effets simultanés et de l‟interaction des paramètres opératoires sur la surface spécifique (SBET). Les paramètres étudiés sont la température de l'activation (50-90°C), le temps de contact (2-6h), le rapport massique liquide/solide (4-7g/g) et la concentration de la solution d‟activation (1-2 mol L-1).Les valeurs optimales des paramètres d‟activation donnant une surface spécifique maximale ont pu être déterminées (température : 98.28°C, temps du contact : 6.828 h, rapport massique liquide/solide : 4.627 g/g, concentration de la solution d‟activation : 0.793 mol L-1). La surface spécifique de l‟argile activée sous ses conditions optimales étant de 87.545 m²g-1 et elle est en bonne adéquation avec la valeur prédite par le modèle (89.9 m²g-1). Le modèle de second ordre obtenu pour la surface spécifique de la bentonite activée est en bonne adéquation avec les résultats expérimentaux. Le traitement d‟une bentonite tunisien avec une solution de chlorure d'ammonium provoque une augmentation de la surface spécifique de 47.3 à 87.545 m² g-1 correspondant à une augmentation de 85%

Glyphosate adsorption onto porous clay heterostructure (PCH): kinetic and thermodynamic studies

The synthesis of PCH from natural bentonite produces a porous heterostructure material effective for the adsorption of glyphosate from water. The adsorption process takes place through an interaction between the silanol group of montmorillonite and/or the PCH adsorbent with the functional groups of glyphosate. The glyphosate adsorption isotherms, recorded for all the studied samples, have been established to be of Langmuir type. The kinetic of the herbicide adsorption on the PCH was best described by the pseudo-second-order model. With the increase in temperature from 25 to 50 °C, the sorption capacities of the materials studied towards glyphosate increased. The process of glyphosate adsorption was found to be endothermic and spontaneous in nature, as indicated by positive values of ΔH and negative values of ΔG. According to the results obtained, the herbicide sorption was more effective in a basic environment. The maximum amount of adsorbed glyphosate is almost doubled with PCH from 13.5 mg/g of natural clay to 27.5 mg/g of PCH.This study was partially funded by project RTI2018-099668-BC22 of Ministerio de Ciencia, Innovación y Universidades, and project UMA18-FEDERJA-126 of Junta de Andalucía and FEDER funds. Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature and Funding for open access charge: Universidad de Málaga / CBUA

ADSORPTION DE NITROBENZENE PAR UNE ARGILE NATURELLE ET UNE ARGILE ACTIVEE

Le nitrobenzène est un intermédiaire de synthèse important utilisé pour la production industrielle des colorants, des matières plastiques, des pesticides, des explosifs et des produits pharmaceutiques. Il est présent sous forme des traces dans les effluents liquides issues de ces industries et constitue donc une pollution potentielle pouvant dégrader la faune et la flore, d’où la nécessité de trouver des techniques de traitement afin de minimiser les  concentrations résiduelles de ce produit toxique dans les effluents avant rejets dans l’environnement.  L’objectif de ce travail est l’étude de traitement des solutions synthétiques aqueuses de nitrobenzène par adsorption sur une argile naturelle et activée en batch.  L’argile activée a été obtenue par l’attaque avec une solution métallique (Chlorure ferrique, FeCl3). L’équilibre a été atteint après 8 heures d’agitation pour l’argile naturelle et 4 heures pour l’argile activée.  Les isothermes d’adsorption correspondantes suivent respectivement le modèle de Dubinin-Radushkevich pour l’argile naturelle et de Langmuir pour l’argile activée. Les rendements maximaux d’adsorption de nitrobenzène par l’argile naturelle et l’argile activée sont respectivement 37,5 % et 50 %  à des concentrations initiales allant de 6,5 à 246 mg/L

Étude cinétique de l’adsorption du rouge de Congo sur une bentonite

L’avancement industriel et technologique à l'échelle mondiale a introduit des polluants de natures diverses dans l'eau. Les polluants peuvent être des contaminants organiques et des métaux lourds. Leur présence dans des effluents industriels où l'eau potable est un problème de santé publique en raison de leur absorption et, par la suite, leur accumulation dans l’organisme humain. Les règlements de pollution de l'eau exigent que les industries textiles réduisent considérablement la quantité de colorants dans leurs rejets. L'adsorption, procédé de traitement des eaux usées, exploite la capacité de quelques solides pour concentrer certaines substances sur leurs surfaces. Généralement, l’adsorbant le plus utilisé pour le traitement des effluents textiles est le charbon activé. La capacité de la bentonite pour enlever la couleur a été reconnue il y a quelque temps. Dans ce travail, nous avons étudié la cinétique d’adsorption d’un colorant acide, le rouge de Congo, en solution aqueuse sur un matériau argileux naturel (bentonite) dans un processus en lots. La concentration initiale du colorant était de 30 mg•L‑1 déterminée par une méthode spectrophotométrique. L’influence de certains paramètres, comme la vitesse d’agitation, la masse d’argile en solution, la concentration initiale du colorant et la granulométrie a été étudiée. Les résultats ont montré pour la vitesse d’adsorption : (i) une augmentation avec la vitesse d’agitation et la masse d’argile et, (ii) une décroissance avec la concentration initiale en colorant et la granulométrie. Cinq modèles de transport externe ont été étudiés et ont montré que l’ordre de grandeur du coefficient, kf, se trouve dans la gamme de 10‑5 à 10‑4•ms‑1.Industrial growth and technological advancement have led globally to the introduction of pollutants of diverse nature into water bodies. Such pollutants include dyes, organic contaminants and heavy metals. Their presence in industrial effluents or drinking water is a public health problem, due to their absorption and possible accumulation in living organisms. Water pollution regulations require textile dye industries to reduce substantially the amount of colour in their effluents. Adsorption, as a wastewater treatment process, exploits the ability of some solids to concentrate certain substances from solution onto their surface. The most commonly used adsorbent for the treatment of textile effluents is activated carbon. The ability of bentonite to remove colour was recognized some time ago. Batch adsorption experiments are used easily in the laboratory for the treatment of small volumes of effluents. Batch adsorption provides certain preliminary information such as the pH for maximum adsorption, the maximum initial dye concentration, the particle size for optimum adsorption, the mass of adsorbent, the temperature and time of the separation process. Experiments were conducted in this study using bentonite. The dye used in all experiments was Congo red. The initial dye concentration was 30 mg•L‑1 and was determined spectrophotometrically at the wavelength of maximum absorbance. The time required to reach equilibrium was about 2 h. The effect of agitation, initial dye concentration, mass of adsorbent and mean particle diameter were investigated. It appears that the rate of dye removal: (i) increased with the agitation speed and mass of adsorbent and, (ii) decreased with the initial dye concentration and the particle size. Five models for external transport were used to calculate the external mass transfer coefficient, kf, and the results showed that this coefficient is in the range of 10‑5-10‑4•ms‑1

The aid of calorimetry for kinetic and thermal study

International audiencePhosphoric acid, a non-renewable chemical, is used in different industries. Production of this chemical from natural phosphate can be done by two routes: wet process and thermal process. The nature of the natural phosphate, i.e., its chemical composition, plays an important role in the kinetics and thermodynamics of phosphoric acid production. Thus, the establishment of a kinetic model, based on reaction mechanism, for the dissolution of natural phosphate is cumbersome due to the presence of impurities. Besides, one should use an online analytical method because the dissolution reaction is fast. The dissolution of two natural phosphates with different percentages of phosphorus pentoxide (P2O5), phosphate samples (28 mass% of P2O5) from Gafsa region (Tunisia) and phosphate samples (18 mass% of P2O5) from Cheketma-Kasserine region (Tunisia), was studied from a kinetic and thermal aspect. Experiments were performed by using a Tian—Calvet calorimeter. Two acid solutions were used for the dissolution: one with phosphoric acid (S1) and the other a mixture of phosphoric and sulfuric acid (S2). For both natural phosphates, it was found that in case of using S1 solution the heat released due to the dissolution was lower than in case of using solution S2. This difference was explained by the precipitation of monohydrate sulfate calcium to its dihydrate form. By using a granulometry distribution lower than 500 μm, heat released during the dissolution of both phosphates by S1 was similar, i.e., − 230 J g−1, and the same observation was done by using S2 solution, i.e., between − 300 and − 350 J g−1. We have demonstrated that granulometry distribution plays an important role, and by using a granulometry lower than 120 μm for Cheketma-Kasserine region phosphate, the heat released during the dissolution was higher, i.e., − 400 J g−1 with solution S2. Avrami model was found to describe the precipitation of calcium sulfate, and three distinguished domains were obtained by using Gafsa region phosphate compared to two domains with Cheketma-Kasserine region phosphate

Sorption Isotherms and Thermodynamic Properties of Pomegranate Peels

Convective drying is the most widely used technique to stabilize by-products in the food industry, permitting later processing. A thorough knowledge of the relationship between moisture content and water activity allows the optimization of not only drying operations, but the settings of storage conditions. Thus, the thermodynamic properties of pomegranate peels were determined during the desorption process. Experimental sorption isotherms at 20, 30, 40 and 50 °C showed type II Brunauer behavior. Eight different theoretical and empirical equations were fitted to the experimental results; the theoretical GAB model and the empirical Peleg model were the ones that achieved the best fit (R2 of 0.9554 and 0.974, respectively). The Clausius–Clapeyron equation and the enthalpy–entropy compensation theory were used to determine the thermodynamic parameters. The isosteric heat determined from the sorption isotherms decreased regularly as the equilibrium moisture content rose (from 8423.9 J/mol at 0.11 kgH2O/kg d.m. to 3837.7 J/mol at 0.2 kgH2O/kg d.m.). A linear compensation was observed between enthalpy and entropy, which indicated an enthalpy-controlled sorption process