Highly efficient fluoride extraction from simulant leachate of spent potlining via La-loaded chelating resin. An equilibrium study

Abstract

Spent potlining (SPL) hazardous waste is a potentially valuable source of fluoride, which may be recovered through chemical leaching and adsorption with a selective sorbent. For this purpose, the commercially available chelating resin Purolite S950+ was loaded with lanthanum ions, to create a novel ligand-exchange sorbent. The equilibrium fluoride uptake behaviour of the resin was thoroughly investigated, using NaF solution and a simulant leachate of SPL waste. The resin exhibited a large maximum defluoridation capacity of 187 ± 15 mg g from NaF solution and 126 ± 10 mg g from the leachate, with solution pH being strongly influential to uptake performance. Isotherm and spectral data indicated that both chemisorption and unexpected physisorption processes were involved in the fluoride extraction and suggested that the major uptake mechanism differed in each matrix. The resin demonstrates significant potential in the recovery of fluoride from aqueous waste-streams.

Development of a Combined Leaching and Ion-Exchange System for Valorisation of Spent Potlining Waste

“…Therefore, pH was adjusted to 3.0 to minimise any precipitation. Our equilibrium work suggested this would result in a minimal decrease in resin performance [28].…”

“…The data suggested there was no increase in leaching efficiency between the two size fractions, which would be advantageous industrially, as coarser grinding of the SPL would require less energy input. The approximate composition of the SPL material, derived from the leaching data can be compared to values quoted by Holywell and Bréault [1] (Table S3), which is often referenced in the literature as being an accurate range [28,38]. The apparent concentrations of Al Fe, Ti and Mg were considerably lower than expected, although it should be noted that our values are based on the total leachable content under the conditions stated and should not be considered total quantification values.…”

“…A small amount of precipitation appears to be inevitable, upon mixing the caustic and acidic leachates. It would not be feasible to treat acidic and caustic streams individually with La-MTS9501 resin, as it is completely ineffective at extreme pHs [28]. However, it is desirable to avoid loss of fluoride from the leachate by precipitation of impure cryolite, before it enters the ion-exchange system.…”

“…NaOH pellets were purchased from Fisher Scientific. Puromet™ MTS9501 was kindly donated by Purolite and converted into La-loaded form (which will be referred to as La-MTS9501) by the procedure previously reported [28].…”

“…However, key information is seen in Figures S1-S2. The adsorbent has extracted fluoride from a simulated SPL leachate with an efficiency of 126 mg g −1 via a unique complexation reaction between La centres and aqueous aluminium hydroxyfluorides (AHFs) [28]. It was also observed to load efficiently in simulated industrial conditions using a mini resin column [29].…”