International audienceDefluoridation of groundwater is of major concern in several places around the world, such as North and East Africa, India and China. In this paper, removal of fluoride from model solutions and a Tunisian groundwater sample was performed using calcite particles in the presence of acetic acid in batch experiments. After 1 h decantation, dead-end microfiltration was further used to retain the fluorite (CaF2) precipitates present in the supernatant. At 5 mg L-1 fluoride concentration, removal efficiency was found to increase from 17.4% without acid to 30.4% with 0.1 M acetic acid. The increase in fluoride removal with acetic acid was mainly attributed to the renewal of the area available for adsorption on the calcite particles. At the fluoride concentration of 50 mg L-1, the removal efficiency was equal to 9.5% without acid and 94.3% with the addition of 0.1 M acetic acid. The removal of fluoride was attributed to precipitation as a result of higher supersaturation in the solution. Optimum parameters were selected for the defluoridation of a Tunisian groundwater sample with initial fluoride concentration around 2.7 mg L-1. The final F- concentration after treatment with calcite in the presence of 0.1 M acetic acid was found equal to 1.2 mg L-1, which was below the standard of the World Health Organisation.Keyword

Valorisation of pine cone as an efficient, low-cost, and eco-friendly biosorbent for the removal of heavy metals from aqueous solutions is evaluated. The morphology and surface chemistry of the biosorbent are characterized by scanning electron microscopy, energy-dispersive elemental analysis, and Fourier transform infrared spectroscopy, revealing the presence of carboxylic and alcoholic functional groups that interact with metal ions. The effect of the contact time, pH, amount of adsorbent, and initial metal concentration in the adsorption is studied, resulting in removal percentages for Cd(II), Cu(II), Pb(II), and Cr(VI) (metal concentration of 5 mg L^-1) of 82.24%, 93.71%, 94.67%, and 88.8%, respectively ([ ], 2 g L^-1 of adsorbent), except for Cr(VI) ([ ], 10 g L^-1). The equilibrium data of Pb(II) and Cd(II) were found to follow the Langmuir-Freundlich model, with maximum adsorption capacities of 100.01 and 78.73 mg g^-1, respectively, whereas Cu(II) followed the Langmuir model with 33.55 mg g^-1. Cr(VI) adsorption data also fitted the Langmuir model, and the maximum adsorption capacity was 57.36 mg g^-1. Adsorption data was obtained at pH 5.4 for divalent metal ions and at pH 2 for Cr(VI) and in a range of metal concentrations ranging from 1 to 500 mg L^-1 at 298.2 K. The presence of the three metal ions in the solution does not affect the percentage of the target metal ion adsorbed, proving the absence of competition between them and showing the pine cone to be an efficient adsorbent to treat multimetal effluents allowing water reuse.