Removal of organic phosphorus from water by CaLa–LDH adsorption: Performance and mechanism

Water pollution from phosphonates is receiving increasing attention and adsorption is a promising treatment method. In this work, CaLa – layered double hydroxide (CaLa – LDH) was used to adsorb phosphonates (1-hydroxyethane-1,1-diphosphonic acid, HEDP) from water, demonstrating an excellent theoretical maximum adsorption capacity of 89.41 mg-P/g at pH 3.0. The pseudo-second-order kinetic model accurately describes the adsorption process of CaLa – LDH for HEDP, implying that the adsorption process was governed by chemisorption. The heterogeneous adsorption of the CaLa – LDH was confirmed by the Sipes model. Among co-existing ions (SO42−, Cl−, NO3−, CO32−, PO43−, Ca2+, and Mg2+), CO32− and PO43− hindered adsorption. Characterization analysis showed that the adsorption mechanisms may involve electrostatic attraction, chemisorption, ion exchange, and complexation. Additionally, the CaLa – LDH adsorbent can be reused up to four times, with adsorption capacity recovering to over 90%. During the fifth cycle, adsorption capacity decreased to 41%. The CaLa – LDH was applied to remove phosphorus from the actual leachate concentrate, with satisfactory results confirming its potential for actual wastewater treatment.