Trace determination of fluoride using lanthanum hydroxide supported on alumina

Abstract

Lanthanum hydroxide supported on alumina has been studied to sorb fluoride ion from aqueous solutions. The adsorbent is effective in decreasing fluoride ion concentration from 7 mM to 0.003 mM in the pH range 5.7–8.0. The rate constant for sorption was found to be 6x10‐2 min‐1. The sorption of fluoride is Langmuir type and its capacity is 0.82 m M F‐/g of the adsorbent. The sorption selectivity shows that fluoride removal is affected by the presence of phosphate and sulphate but not affected by chloride, bromide iodide and nitrate ions. Alumina impregnated with lanthanum hydroxide has adsorption capacity in the range 0.340–0.365 mM/g. The removal of fluoride from industrial waste water is more than 96%. Fluoride ion sorbed can be eluted from the adsorbent with 10 mL of 0.1 M NaOH and the column can be reused after being conditioned with 10 mL of 1 mM hydrochloric acid. Results obtained by batch as well column methods are in good agreement with each other.