Lead and zinc removal from aqueous solutions by aminotriphosphonate-modified converted natural phosphates

Apatite particles prepared from natural phosphate rock and grafted with nitrilotris(methylene)triphosphonate (NTP) were evaluated for Pb2+ and Zn2+ sorption from aqueous solutions. Sorption capacities as high as 640 mg g−1 and 300 mg g−1 could be obtained for the highest organic content (10 wt.%). Analysis of the sorption isotherms using Langmuir, Freundlich and Dubinin–Kaganer–Radushkevich models revealed that Pb2+ ions have a larger affinity for apatite (sorption energy ≈ 8 kJ mol−1) than for NTP so that organo-modified surfaces led to a heterogenous adsorption process. In contrast, Zn2+ interacts weakly (sorption energy ≈ 1 kJ mol−1) and similarly with the mineral surface and the organic moieties following a homogenous sorption process. Such an association of organic metal ligands with reactive apatite surfaces within porous materials appears as a promising strategy to obtain efficient adsorbents at low cost and limited environmental impact.

► Aminotriphosphonate–apatite nanoparticles were prepared from phosphate rocks.
► Adsorption kinetics and isotherms were studied for aqueous Pb2+ and Zn2+.
► Organics decrease access to apatite surface but provide additional binding sites.