This work concerns the elimination of the organic pollutant; Bemacid Red (BR), a rather persistent dye present in wastewater from the textile industry in western Algeria, by adsorption on carbon from an agricultural waste in the optimal conditions of the adsorption process. An active carbon was synthesized by treating an agro-alimentary waste, the date stones that are very abundant in Algeria, physically and chemically. Sample after activation (SAA) with phosphoric acid was highly efficient for the removal of BR. The characterization of this porous material has shown a specific surface area that exceeds 900 m2/g with the presence of mesopores. The iodine value also indicates that the activated carbon obtained has a large micro porosity. The reduction of the infrared spectroscopy (FTIR) bands reveals that the waste has been synthesized and activated in good conditions. Parameters influencing the adsorption process have been studied and optimized, such as contact time, adsorbent mass, solution pH, initial dye concentration and temperature. The results show that for a contact time of 60 min, a mass of 0.5 g and at room temperature, the adsorption rate of the BR by the SAA is at its maximum. Pseudo-first-order, pseudo-second-order and intraparticle diffusion models were studied to analyse adsorption kinetics. The result shows the adsorption kinetic is best with the pseudo-second-order model. In this study, Langmuir, Freundlich and Temkin isotherms were investigated for adsorption of BR onto SAA. The Freundlich and Temkin isotherms have the highest correlations coefficients. The suggested adsorption process involves multilayer adsorption with the creation of chemical bonds. The mechanism of adsorption of BR by SAA is spontaneous and exothermic, and the Gibbs free energy values confirm that the elimination of the textile dye follows a physisorption.