Cross-linked poly(vinyl alcohol) nanofibers were dipped in alternating solutions of aqueous lanthanum acetate and alkali metal carbonates (for up to 10 cycles) to precipitate lanthanum carbonate. Only sodium carbonate yielded Na-La double-metal carbonates and lanthanum carbonate hydroxide as the cycles of precipitation increased. Potassium and cesium carbonates yielded lanthanite phases that removed more P than inorganics derived from Na2CO3 (212 and 157 mg P g(-1) nanofiber, respectively, at pH 7 after 110 h). The lanthanum carbonate from Na2CO3 and K2CO3 showed the greatest potential for P removal when exposed to groundwater for more than 24 h. Among the phase and pH-dependent mechanisms of P removal, lanthanite transformed to lanthanum phosphate at neutral pH and phosphate ions exchanged with carbonate ions. Hydration of crystalline phases (synthesized from Na2CO3 and Cs2CO3) was accompanied by phosphate ion sorption at pH 10. Within 24 h, phosphate ion sorption was higher at pH 10 than pH 7, indicating that ion exchange between phosphate and carbonate at pH 7 occurs relatively slower than diffusion of hydrated phosphate ions at pH 10. Selective P removal of the developed lanthanum carbonate mineralized nanofibers will help develop novel water purification technology that can be used in contaminated sites.