Phosphate-loaded industrial wastewaters have resulted in numerous environmental issues that have hard hit the Gulf of Gabes-Tunisia, making the environmental protection one of the most compelling priorities. Consequently, this study aimed first to compare the amounts of phosphate adsorbed by two types of Tunisian activated clays. The second goal was to assess and optimize the phosphate removal efficiency of these clays, using Box-Behnken design (BBD) under response surface methodology. Results showed that the highest adsorption amounts of 130.16 mg g-1 , 125.42 mg g-1 were yielded for Jebel Haidoudi clay and Douiret clay, respectively. These values demanded an initial phosphate concentration of 300 mg L-1 , a contact time of 5 h, and a pH of 2). Thus, kinetic and isotherm studies of phosphate elimination from synthetic solutions demonstrated that for both activated clays, the pseudo-second-order and Langmuir equation fitted very well the experimental data, respectively. These results indicate that phosphate adsorption might be mainly a chimisorption phenomenon and a monolayer process. All these findings confirmed that both activated clays could be considered as a competent, cost-effective, efficient and ecological alternative for the elimination of phosphate from industrial wastewaters. PRACTITIONER POINTS: Activated clay could be adopted as an efficient and cost-effective adsorbent. The optimum conditions were nominated as 300 mg L-1 of initial phosphate concentration, 5 h contact times and pH = 2. The probable uptake mechanism of phosphate followed predominantly the acid-base interaction and hydrogen bond.
Keywords: Box-Behnken; activated clays; optimization; phosphate; removal.
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