FLUORIDE REMOVAL FROM COAL COKE PRODUCTION WASTEWATER BY ADSORPTION ONTO BOVINE BONE CHAR
wastewater treatment; fluoride; adsorption; bovine bone char, steel industry.
Fluoride has become a challenge for some industrial sectors such as steel, due to its high load over some processes, which requires specific treatment for removal. In this context, this study aimed at investigating the adsorption capacity of bovine bone char to remove fluoride from real coke production wastewater. Central Composite Design (CCD) as well as a Mixture Design were performed to set the best conditions of pH and solid / liquid ratio to improve fluoride percentage removal and bone char adsorptive capacity. Desirability method was used for optimization of the results. Bovine bone char, particle size 12 to 32 mesh (0.5 to 1.4 mm), mesoporous structure, showed great potential for fluoride removal from steel wastewater, especially under previous acid pre-treatment. A 75% increase in its surface area (145.91 m².g- 1), compared to non-treated bone char (83.33 m².g-1), allowed greater access of fluoride onto the active sites for hydroxyapatite (HAP) phosphate exchange. At 20.0 g pre- treated bovine bone char.Kg- 1 effluent, adsorptive capacity achieved 3.24 mg.g-1, representing an increase of 42%, compared to non-treated bone char. Equilibrium was well represented by Freundlich model, revealing the formation of multiple heterogeneous layers on bone char surface. Adsorption kinectis was favored (as it was possible to remove up to 75% of fluoride in the first hour of adsorbent-adsorbate contact) and pseudo-second order modeled. Thermodynamics parameters estimation indicates an endothermic (ΔH = + 28.357 KJ. mol-1), spontaneous (ΔG = -15,291 KJ.mol-1; ΔG = - 17,052 KJ.mol-1; ΔG = -18,212 KJ.mol-1) and entropy favored (ΔS = + 0.146 kJ. mol- 1.K-1) process.