## 1 Introduction  
The water demand doubles globally every two decades, due to the rapid increase of populations, industrial activities, and the decrease of rainfall [1]. The exploration of safe water sources to overcome the scarcity of water has been a global challenge for many countries [2]. Waste water reclamation and recycling were proposed as an alternative way to reduce the water demand in irrigation, industries, and domestic uses [3]. The textile industry presented an important share in total water consumption, as during dyeing processes about 20-40% of these dyes remain in the effluents [4] The presence of dyesin effluents causes a lot of pollution in water. Many dyes are carcinogenic and affect the life of aquatic organisms [5; 6]. Many physical and chemical processes for color removal have been applied, including coagulation and flocculation, biosorption, photo-decomposition and ultrafiltration, oxidizing agents, membrane, and electrochemical. The advantages and disadvantages of each technique have been extensively reviewed [7]. The adsorption process is an efficient and economic process for removing dyes, pigments, and other colorants, particularly for its initial low cost, simplicity, ease of operation, and insensitivity towards toxic substances [8; 9]. Many types of adsorbents are effective in removing color from aqueous effluents, with activated carbon as the most commonly used one in industrial wastewater treatment systems, mainly because of its large specific surface area [10; 11]. However, its major drawback is its relatively high cost. This has encouraged many researchers to search for cheaper substitutes, such as coal, fly ash, silica gel, wool wastes, agricultural wastes, oak leaves, wood wastes, sewage sludge, and clay materials [9; 10; 11; 12]. Clays, such as sepiolite, bentonite, montmorillonite, and smectite are being considered as alternative low-cost adsorbents with high chemical and mechanical stability, small particle sizes, lamellar structures, and negatively charged surfaces. This makes them good cation adsorbents with large specific surface areas for ion exchange or electrostatic attraction. The chemical nature and pore structure usually determine the sorption ability of clays [13; 14; 15]. To enhance their removal properties, the modification of clay minerals could be achieved by different physical or chemical methods. The type of modification affects the removal properties of the obtained materials. For instance, the acid activation process, based on chemical alteration of the starting clay minerals, led either to an improvement or reduction of the removal properties for basic dyes [15; 16; 17; 18]. Modification of clay minerals was done by insertion of an alkyl-ammonium cation or cationic surfactant into the interlamellar spacing. These are called as organoclays. These organoclays have a lower thermal stability due to the decomposition of organic molecules in the range of 200 to 400 \({}^{\circ}\)C and were used for the removal of acidic dyes [19]. The pillaring process was proposed to modify the chemical composition and enhance the thermal stability of the starting clay minerals. It consisted of maintaining the clay sheets, separated apart after introducing the polyoxocation metal cations, and was followed by calcination of the obtained materials. This process would introduce additional adsorption sites between the clay sheets and make them accessible to the dye cations [20]. The calcination of raw clay was proposed as an alternative way to modify its adsorption properties [21; 22]. In addition, this method was used to regenerate spent clays after the removal process [23]. The calcination temperature was in the range of 200 to 500 \({}^{\circ}\)C. Above this temperature, the layered structure was collapsed and the clay mineral was transformed to an amorphous silica phase that exhibited low adsorption capacity [22]. Thus, further calcination of clay minerals at higher temperatures between 800 to 1000 \({}^{\circ}\)C was not undertaken.