Abstract

The objective of this study was to investigate the production of activated carbons (AC) from cashew shells, and millet stalks and their efficiency in fluoride retention. These agricultural residues are collected from Senegal. It is known that some regions of Sénégal, commonly called the groundnut basin, are affected by a public health problem caused by an excess of fluoride in drinking water used by these populations. The activated carbons were produced by a combined pyrolysis and activation with water steam; no other chemical compounds were added. Then, activated carbonaceous materials obtained from cashew shells and millet stalks were called CS-H₂O and MS-H₂O respectively. CS-H₂O and MS-H₂O show very good adsorbent features, and present carbon content ranges between 71 % and 86 %. The BET surface areas are 942 m² g^-1 and 1234 m².g^-1 for CS-H₂O and MS-H₂O respectively. A third activated carbon produced from food wastes and coagulation-flocculation sludge (FW/CFS-H₂O) was produced in the same conditions. Carbon and calcium content of FW/CFS-H₂O are 32.6 and 39.3 % respectively. The kinetics sorption were performed with all these activated carbons, then the pseudo-first equation was used to describe the kinetics sorption. Fluoride adsorption isotherms were performed with synthetic and natural water with the best activated carbon from kinetics sorption, Langmuir and Freundlich models were used to describe the experimental data. The results showed that carbonaceous materials obtained from CS-H₂O and MS-H₂O were weakly efficient for fluoride removal. With FW/CFS-H₂O, the adsorption capacity is 28.48 mg.g^-1 with r² = 0.99 with synthetic water.

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