Mechanisms of orthophosphate removal from water by lanthanum carbonate and other lanthanum-containing materials

• Published in: The Science of the total environment 2022-05, Vol.820, p.153153-153153, Article 153153
• Main Authors: Zhi, Yue, Paterson, Alisa R., Call, Douglas F., Jones, Jacob L., Hesterberg, Dean, Duckworth, Owen W., Poitras, Eric P., Knappe, Detlef R.U.
• Format: Article
• Language: English
• Subjects: Adsorption; Lanthanum - chemistry; Lanthanum carbonate; Lanthanum containing material; Mineral precipitation; Phosphates - chemistry; Phosphorus removal; Wastewater treatment; Water; Water Pollutants, Chemical
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.153153

Removing phosphorus (P) from water and wastewater is essential for preventing eutrophication and protecting environmental quality. Lanthanum [La(III)]-containing materials can effectively and selectively remove orthophosphate (PO4) from aqueous systems, but there remains a need to better understand the underlying mechanism of PO4 removal. Our objectives were to 1) identify the mechanism of PO4 removal by La-containing materials and 2) evaluate the ability of a new material, La2(CO3)3(s), to remove PO4 from different aqueous matrices, including municipal wastewater. We determined the dominant mechanism of PO4 removal by comparing geochemical simulations with equilibrium data from batch experiments and analyzing reaction products by X-ray diffraction and scanning transmission electron microscopy with energy dispersive spectroscopy. Geochemical simulations of aqueous systems containing PO4 and La-containing materials predicted that PO4 removal occurs via precipitation of poorly soluble LaPO4(s). Results from batch experiments agreed with those obtained from geochemical simulations, and mineralogical characterization of the reaction products were consistent with PO4 removal occurring primarily by precipitation of LaPO4(s). Between pH 1.5 and 12.9, La2(CO3)3(s) selectively removed PO4 over other anions from different aqueous matrices, including treated wastewater. However, the rate of PO4 removal decreased with increasing solution pH. In comparison to other solids, such as La(OH)3(s), La2(CO3)3(s) exhibits a relatively low solubility, particularly under slightly acidic conditions. Consequently, release of La3+ into the environment can be minimized when La2(CO3)3(s) is deployed for PO4 sequestration. [Display omitted] •We studied mechanisms of PO4 removal by La2(CO3)3 and other La-containing materials.•PO4 removal occurred primarily by precipitation of LaPO4.•PO4 removal rates increased with decreasing solution pH.•La2(CO3)3 selectively removed PO4 from wastewater.•Low solubility of La2(CO3)3(s) minimizes release of soluble La into the environment.