**1. Introduction**

Synthetic dyes have been used in several industrial sectors such as the automotive sector, the textile industries, leather tanning, plastics, aper, and photoelectrochemical cells and therefore, A significant amount of water is used [1]. Wastewater laden with dyes is usually dumped in sewers, rivers, and nearby lagoons. Such treatment affects the water quality, the aquatic ecosystem and the biodiversity of the environment [2, 3]. Wastewater treatment is necessary before it is released into the environment [4]. Likewise, wastewater treatment has been proposed as a solution to obtain good quality water for agricultural and industrial applications [5, 6]. The literature reports several techniques for the treatment and depollution of textiles effluents. It is important to mention, among them, the membrane filtration techniques [7], coagulation / flocculation [8], electro- coagulation [9], oxidation techniques [10] and aerobic biological processes and anaerobes [11, 12]. The search for other effective methods is necessary because these previously described processes have financial limitations and design complexities.

The adsorption process is used for water treatment, however, the high price of adsorbent materials, remains a constraint [13, 14].

Among the proposed solutions include using adsorbents from agricultural residues, for example, the waste material of corn cob, palm fruit parts, the chestnut peel, almond shell, rice husk, orange, and lime peels, pine fruit shells, and others [15, 16].

The clay minerals and the waste produced by the phosphate industries have been used for the retention of textiles dyes [16–21]. The phosphate rocks is Tunisia is considered among the top countries that produce phosphate rocks [22]. Tunisia is ranked among the top phosphate-producing countries. The Natural phosphate (NP) is an abundant product extracted from phosphate rocks and made up of a carbonated fluoroapatite with important substitution of phosphate by carbonate [23]. The literature reveals the existence of a few studies related to the adsorption of some dyes in polluted textile water or adsorption of basic dyes and reactive dyes using natural phosphates (NP) [24–26].

The calcination (heat treatment) of natural phosphate rocks was described in the literature for upgrading the calcareous phosphate ores [27], and to propose other applications than direct synthesis of fertilizers, such the production of pure chemicals, soft drinks and pharmaceutical products [28].

Although the properties of the calcined materials were well documented for the synthesis of fertilizers, however, there are no attempts to describe their usage for the elimination of dyes from polluted water.

Also, the phosphate rocks are converted into phosphoric acid by the addition of sulfuric acid through the socalled wet process [29]. The production of phosphoric acid resulted in the formation of huge amount of wastes by products such as phospohogypsum [30]. Some evaluation of theses wastes were proposed in the treatment of polluted water and some research activities have studied their utility as removal agents of some dyes and heavy metal ions from aqueous solutions [31–40].
