# Cationic and Anionic Dye Adsorption on a Natural Clayey Composite
###### Abstract  
One of the main challenges for environmental sciences today is the effective treatment of dye-laden industrial effluents. This work aimed to study the potential of an untreated (natural occurring clayey composite) red clay (RC) for the adsorption of a cationic dye Basic Navy Blue 2 RN (CNB) and anionic dye Drimaren Yellow CL-2R (ADY). We evaluated the effect of pH, dye concentration, and adsorbent concentration on the removal effectiveness to study the absorption process. Also, we studied the adsorption process by analyzing the feasibility of several known adsorption isotherms and kinetic models. The results show that at a pH of less than 4, the CNB and ADY removal percentages were 97% and 96%, respectively. At a pH greater than 8, the CNB and ADY removals were 75% and 25%, respectively. The CNB adsorption happened by chemisorption of a monolayer on iron-containing particles (IPs). In congrast, the ADY adsorption occurred by monolayer physisorption on kaolinite particles (KPs) and Na, K-rich Laumontite particles (LPs). The Langmuir isotherm model fits very well with CNB experimental data. The Temkin model shows the best fit between the isotherm function and the ADY dye-adsorption data. The pseudo-second-order kinetic model fits the CNB and ADY dye-adsorption data on RC particles. The heterogeneous composition of naturally occurring clay favors different adsorption mechanisms and opens an avenue for the separation process's engineering. clayey composite; adsorption isotherm; adsorption kinetic; anionic dye adsorption; dye adsorption; basic navy blue 2 RN; cationic dye adsorption; dimaren yellow CL-2R +
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to be mutagenic and genotoxic chemical agents. Therefore, the discharge of dyes on water bodies is a significant environmental contamination source [4; 7]. Dyes tend to sequester metal and may cause microtoxicity to fish and other organisms [1]. At present, around 100,000 dyes exist and are toxic beyond the threshold level. This number is gradually increasing and constitutes a threat to the biosphere. As such, it is crucial to treat colored effluents for the removal of dyes [8]. Dyes organic compounds are based on functional groups such as the chromophore group (NR\({}_{2}\), NHR, NH\({}_{2}\), COOH, and OH) and auxochromes (N\({}_{2}\), NO, and NO\({}_{2}\)) [3]. There are different dyes: acid, basic, disperse, direct, reactive, solvent, sulfur, and vat dyes, amount others [1; 3]. Several treatment methods have been developed to treat colored effluents: biological treatment, membrane separation, chemical oxidative processes, electrochemical processes, and adsorption processes [9]. However, one factor to consider within the existing alternatives is the treatments' high investment and operating costs, energy expenditure, and the waste generated [10]. The adsorption process is a promising technique to treat wastewater, which utilizes natural materials as an adsorbent. It is regarded as eco-friendly and economical to operate. The adsorbent in the highest demand is activated carbon, due to its adsorption capacity [11], because of its large specific surface area [12]. However, active carbon has some drawbacks, primarily related to its high cost and complicated regeneration process [13]. Alternatively, dye removal by clay has shown promising results. Clays are suitable adsorbent materials for the adsorption of various pollutants because of their: high surface area, porosity, thermal stability, specific active sites, high cation exchange capacity, easy availability, and attractive adsorptive properties [14]. Clay refers to a material that: (1) occurs naturally on the earth's surface, (2) is composed primarily of colloidal grains of minerals, (3) forms a viscous, plastic mass when mixed with water, and (4) hardens and holds its shape when dried or baked. The natural-pristine clays' constituents are mineral clays and associated minerals. Mineral clay provides plasticity, e.g., kaolinite, montmorillonite, illite, and vermiculite. It hardens when dried or fired.