Lanthanum-modified sepiolite adsorbent for efficient phosphate removal

Excessive phosphorus in surface water leads to eutrophication that adversely impacts the water quality, ecosystem and human health. La modified bentonite is a highly effective and safe adsorbent for phosphate removal. In this study, sepiolite (SEP) is used as an alternative carrier for preparation of La modified SEP (La-MT-SEP) as a phosphate adsorbent. The adsorption kinetics follows the Pseudo-second-order kinetic model, and the adsorption isotherm fits well with the Langmuir model. The adsorption process consists of electrostatic attraction, inner-sphere complexation, and the formation of stable LaPO 4 phase. The maximum adsorption capacity reaches 74.3 mg/g at 298 K. La-MT-SEP exhibits La utilization efficiencies above 90 % and high phosphate adsorption capacity within a broad pH range of 3.7–8.2. The adsorption is favored under weakly acidic conditions and further enhanced by the coexistence of anions. As a result, La-MT-SEP demonstrates efficacy in remediation of natural eutrophic surface water. Compared to lanthanum-modified bentonite, La-MT-SEP has higher specific surface area and exhibits high La utilization at higher La loading. • La-modified sepiolite shows high phosphate adsorption capacity over wide pH range. •The near unity P/La ratio indicates high utilization of the active La sites. •La@sepiolite is highly selective for phosphate adsorption, yielding stable LaPO 4 . •Excellent phosphate removal performance is demonstrated in natural eutrophic water.