Effect of some physical and chemical parameters on fluoride removal by nanofiltration

Abstract

In natural waters, fluoride ions are necessary and beneficial for the human being. At higher level of F − in water, it is toxic and detrimental to human health, leading to serious problems such as dental and skeleton fluorosis. According to the World Health Organization, the acceptable concentrations of fluoride in potable water are in the range of 0.7-1.5 mg L −1 . Various treatment technologies for fluoride removal from water have been used such as ion exchange, adsorption and membrane processes. In the present study, removal of fluoride ions from aqueous solutions was investigated using a polyamide thin film composite nanofiltration membrane denoted as HL 2514 T from Osmonics Company. Through this membrane, the mechanism of transport was investigated. The KedemKatchelsky model was applied in order to determine phenomenological parameters σ and P s , respectively, the reflection coefficient of the membrane and the solute permeability of ions. The convective and diffusive parts of the mass transfer were quantified. The retention of monovalent and bivalent salts by this membrane shows that it is negatively charged. In the second part, retention of fluoride anions was investigated. Results show that the retention of fluoride by HL membrane exceeds 80%. The influence of the chemical parameters (feed concentration and ionic strength) and the physical parameters (applied pressure and recovery) on the elimination of fluoride was studied.

Factors affecting fluoride and natural organic matter (NOM) removal from natural waters in Tanzania by nanofiltration/reverse osmosis

“…Fluoride retention by NF/RO is generally governed by steric effects (size exclusion) and electrical effects (charge repulsion, Donnan exclusion and dielectric exclusion) (Shen and Schäfer, 2014). A variety of parameters, including feed compositions, membrane characteristics and operational conditions, lead conditions to be more conducive to the dominant effect of one mechanism over the other (Bejaoui et al, 2011;Mnif et al, 2010;Richards et al, 2010;Shen and Schäfer, 2014).…”

Phenol removal from water by AG reverse osmosis membrane

“…Table 4 shows that the values of P s depend on the nature of the anion. High values of r were obtained by Mnif et al [22] using a thin film composite (TFC) polyamide membrane for NaCl and Na 2 SO 4 salts. The reflection coefficient r is a characteristic of the convective transport of the solute.…”

“…The reflection coefficient r is a characteristic of the convective transport of the solute. Hydration energies of different electrolytes [22]. High values of r were obtained by Mnif et al [22] using a thin film composite (TFC) polyamide membrane for NaCl and Na 2 SO 4 salts.…”

“…When one considers the exclusion model of Donnan which involves electrostatic forces [22], the decrease in the charge of the membrane triggers, therefore, a decrease in the retention of the negatively charged ions as the electrostatic effect of membrane-aqueous solution is weakened and consequently this exclusion model effect is reduced.…”

“…It is worth to note that for the determination of phenomenological parameters, the model of Kedem-Katchalsky was used and is detailed in our previous work [22].…”