# Cationic and Anionic Dye Adsorption on a Natural Clayey Composite
###### Abstract
The associated minerals do not impart plasticity to clay, e.g., micas, quartz, feldspars, and others: iron oxide; hydroxides such as magnetite, hematite, maghemite, goethite; and aluminum hydroxides such as corundum, gibbsite, boehmite, diaspores. Therefore, natural clays are a mixture of weathered minerals that give rise to unique clayy composite materials. These differences among the clays provide an opportunity to investigate the adsorption potential of these naturally occurring clayy composites as multifunctional adsorbents of pollutants like dyes. Clays have shown the potential to remove dyes in aqueous solutions [4]. Bentonite removed 88% of acid dyes [15]. Dolomite (CaMg(CO\({}_{3}\))\({}_{2}\)) rich natural clay removed 90% of methylene blue [14]. Smetite-rich natural clay removed 80% of acid brow 75 [16]. Natural red clay removed 96% of bright green dye [17]. The adsorption capacity of clays generally results from a net negative charge on the structure of minerals. This negative charge gives clays the capability to adsorb positively charged molecules [18]. Comparatively, clay adsorbents are more cost-effective than active carbon and other organic adsorbents for effluent treatment [3]. Moreover, clay adsorbents reduce costs ten to more times than other adsorbents (Table 1). Even though many studies deal with clay material as adsorbents, a great deal of work still needs to be done [1; 3; 19]. There exists a wide variety of dyes, and their removal is based on various factors, which include: adsorbate (dye)-adsorbent (clay) relationships \begin{table}
\begin{tabular}{c c c c} \hline
**Adsorbent** & **USD 5/kg** & **Adsorbent** & **USD 5/kg** \\ \hline Bentonite & 0.05–0.3 & Active carbon & 0.8–1.1 \\ Red mud & 0.025 & Chitin & 15–20 \\ Clinoptiolite & 0.14–0.29 & Chitosan & 16–10 \\ Natural zeolite & 0.08 & Cross-linked chitosan & 5–10 \\ \hline \end{tabular}
\end{table} 
Table 1: The effective cost of effluent treatment with clay and other adsorbents [3]. (interactions), adsorbate molecular size, and the role of functional groups on both adsorbate as well as adsorbent. More detailed work on these interactions is needed for the studies to correlate and compare [1]. Composite materials made up of nanomaterial, bio-material, and mineral clay can improve the dye removal effectiveness. However, their cost still hampers practical application. Clayey composites are low-cost adsorbents with unique properties and structural diversity, offering superior performance versus individual clay mineral counterparts. This research aimed to study a clayy composite--naturally occurring red clay--from Ecuador's Amazonia region as a multifunctional adsorbent to treat dye-laden textile industrial effluents. We selected as adsorbate a cationic dye (Basic Navy Blue 2 RN) and an anionic dye (Drimaren Yellow CL-2R) to achieve this objective. We evaluated the effect of pH, adsorbate (dye), and adsorbent (red clay) 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.