Build-up of phosphorus, an important nutrient, in environmental waters can lead to diminished water quality. Orthophosphate (PO4) is the most bioavailable source of phosphorus and is a key target for remediation efforts. Trivalent lanthanum (La) is known to effectively bind PO4. At least one commercial La-containing product has been developed and evaluated for PO4 removal in field settings. However, few studies used controlled experiments to examine the impact of background water matrix constituents, such as alkalinity and pH, on the performance of these materials. This study aimed to evaluate the impact of pH and dissolved inorganic carbon (DIC) on (1) the effectiveness of two La-containing materials, La2(CO3)3 and La-modified bentonite, on PO4 removal and (2) La leaching into water. Batch experiments were conducted at pH 6 and 8 and with DIC additions of 0, 12, and 60 mg/L as C. Aqueous concentrations of PO4 and La were measured over time until equilibrium was reached. Equilibrium-model and experimental results revealed that PO4 removal did not measurably vary at the tested pH and DIC treatments. However, the removal kinetics for La2(CO3)3 were pH-dependent. At pH 8, the reaction was slower, regardless of DIC, 250% more time to reach 80% removal. Additionally, equilibrium-model and experimental results revealed that La leaching decreased with increasing DIC. Overall, increased DIC did not measurably impact PO4 removal and decreased La leaching, while increasing pH led to slower PO4 removal and increased La leaching such that La levels in filtrate were above 4 ug/L La, the level at which ecotoxicological concerns arise.

Phosphate removal by lanthanum-containing materials: Effect of alkalinity and pH on treatment effectiveness

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.