Competitive adsorption of three anionic orange-type dyes (i.e., methyl orange, orange II, orange G) and three inorganic anions (HPO42–, SO42–, CrO42–) onto Mg–Al layered double hydroxide (LDH) from bisolute aqueous solutions has been studied in view of potential application of the sorption-based technology in dye removal from textile wastewater effluents. The individual solute affinities for the LDH sample were inferred from the calorimetry measurements of the cumulative enthalpy of displacement in single-solute systems, thus leading to the following affinity order: CrO42– ≈ SO42– < OG2– ≈ HPO42– < OII– ≪ MO–. The individual and composite adsorption isotherms from bisolute aqueous solutions were determined by a solution depletion technique and supplemented by XRD studies on the well-defined adsorption systems corresponding to selected points on isotherms. Based on the shape of the individual adsorption isotherms for a dye and inorganic anion, it was possible to distinguish three different competition sche...

How Does Competition between Anionic Pollutants Affect Adsorption onto Mg–Al Layered Double Hydroxide? Three Competition Schemes

The co-occurrence of various pollutants in industrial effluents is one of the most difficult problems the researchers have to face in the field of Environmental Remediation. In this context, the main objective of the present Ph.D. thesis has been to improve the comprehension of the sorption mechanisms involved in the competitive retention of selected organic dyes and inorganic species at the Solid-Liquid interface by using some model sorbents.The manuscript reports the results of advanced sorption studies made by combining several experimental techniques, mainly including kinetic and equilibrium adsorption measurements, XRD diffraction, as well as isothermal titration calorimetry. Three Azo dyes differing in the molecular size, electric charge, and hydrophobic/hydrophilic character, i.e., Methyl Orange (MO), Orange II (OII), and Orange G (OG), were selected for the purpose of this work. Two types of solid materials possessing positively charged surface sites were considered as model sorbents: layered double hydroxide structures based on Mg and Al (molar Mg:Al ratio of 2) with either nitrate (Mg-Al-LDH-NO3) or chloride counter-ions (Mg-Al-LDH-Cl) localized in the interlayer space, on the one hand, and strongly basic anion-exchange resin, Amberlite® IRN-78, on the other hand. The impact of carbonate(IV), sulfate(VI), chromate(VI), and hydrogen phosphate(V) oxyanions on the retention capacity of model sorbents towards the three dyes was also investigated thoroughly.In the first step, the single-component adsorption onto three sorbents was analyzed in regards with the detailed mechanism of retention. In all cases, an ion-exchange pathway between the pristine compensating anions (NO3-, Cl-, OH-) or anions coming from the ambient atmosphere (e.g., carbonates) and the oncoming anionic species was identified as the principal retention mechanism. In the case of LDH sorbents, this anion exchange was accompanied by the intercalation of the adsorbing species within the interlayer space with the concomitant changes in the layered structure, as inferred from the XRD study of the LDH samples loaded with the appropriate solute species. The retention of monovalent MO anions, both from the single-solute and bi-solute solutions, was found to exceed the anionic exchange capacity (AEC) of the LDH samples, which was ascribed to the dye adsorption on the external surface paralleled by the co-adsorption of sodium cations. The adsorption capacity was demonstrated to depend strongly on the hydrophilic-hydrophilic character of the dye units and their capacity of generating lateral interactions (e.g., pi-stacking) with other adsorbed species within the LDH structure. The use of isothermal calorimetry allowed the unusual shape of the curve representing the cumulative enthalpy of displacement to be attributed to the formation of OII aggregates/fibers induced by the presence of Mg and Al cations originating from the partial dissolution of the LDH sample. Competitive adsorption of dye and selected inorganic anions on the three model sorbents was studied in the second step in view of increasing the efficiency of dyes removal by optimizing experimental conditions. One of the main achievements was to categorize the dye uptake schemes in the presence of inorganic anions in regards with the shape of the experimental adsorption isotherms and to correlate them with the individual adsorbate affinities for the LDH sample, as inferred from the calorimetry measurements of the cumulative enthalpy of displacement in single-solute systems. The discussion on the mechanisms of dye retention in the single- and multi-component systems was supplemented by experimental studies of such applicative aspects of sorption phenomena as kinetics, reversibility, and selectivity.Keywords: Layered double hydroxides, anion-exchange resin, Methyl Orange, Orange II, Orange G, Cr(VI), inorganic anions, single-solute and multi-solute adsorption, XRD study, isotherm titration calorimetry.

https://tel.archives-ouvertes.fr/tel-01331366/document

Thermodynamic and structural study of the mechanism of competitive retention of azo dyes and inorganic anions at the solid-liquid interface with the use of such model sorbents as mineral oxides, anionic clays, and organic exchangers

In this paper we are describing a green cycle process. The first step was a novel hydrotalcite-like compound (HTLC) synthesized by a co-precipitating method, under standard ambient temperature and pressure, using chemical industry wastewater rich in divalent and trivalent cations, activated by a thermal treatment and finally characterized by scanning electron microscopy (SEM), energy dispersive X-ray fluorescence (EDS) and thermogravimetric analysis (TGA). The second step was a series of batch sorption tests performed with this activated HTLC and untreated underground sulfurous water from the state of Puebla, Mexico. The HTLC calcined at 500°C/3 h exhibited the best sorption ability for ions, demonstrated a decrease of the hardness and sulfate ions to below the regional legal standards for drinking water. Once inactive after being used in water treatment, the sorbed ions were removed by ion exchange in a carbonate-containing solution, resulting in an 80% recycling of the material which upon activation demonstrated a retained capacity for water treatment. This recyclability suggests the exciting possibility of this novel compound as an efficient “green” technology in water treatment processes.

https://file.scirp.org/pdf/GSC_2013051510022430.pdf

Juan M. López Oglesby

Papers

Green Cycle: Sulfate Sorption from Natural Water on Anionic Clay Compound Obtained from Industry Wastewater