Adsorption behavior of orange waste gel for some rare earth ions and its application to the removal of fluoride from water

A new type of adsorbent for rare earth metal ions was prepared from orange waste by simple method of saponification reaction with lime water. Adsorption test of rare earth metals ions such as Sm(III), Ho(III), La(III), Sc(III) and Lu(III) suggested that these rare earth metals ions were effectively adsorbed on this adsorbent. Adsorption of fluoride ion was investigated using this adsorbent after being loaded with above-mentioned rare earth metal ions. It was found that fluoride adsorption was fast and dependent on solution pH. The maximum adsorption capacity for fluoride was evaluated as 0.60, 0.92, 1.06 and 1.22 mmol/g for Sc(III), Ho(III), La(III) and Sm(III) loaded adsorbent, respectively. Fluoride ions were successfully removed below the environmental standard by the use of small amount of La(III) loaded adsorbent. Adsorbed fluoride was successfully eluted by using NaOH solution.

► Novel application of orange waste for the adsorption of rare earth metal ions.
► EDX showed that cation exchange reaction between Ca2+ and tested RE metal ion.
► The trace concentration of fluoride ion was effectively removed by RE-loaded orange waste.
► Loaded fluoride could be successfully desorbed by alkali solution.