Apatite and Phillipsite as Sequestering Agents for Metals and Radionuclides

ABSTRACT Laboratory and greenhouse studies were conducted to quantify apatite and phillipsite (zeolite) sequestration of selected metal contaminants. The laboratory batch study measured the sorption of aqueous Co2+, Ba2+, Pb2+, Eu3+, and UO22+ Apatite sorbed more Co2+, Pb2+, Eu3+, and UO22+ from the spike solution than phillipsite, resulting in distribution coefficients (Kd values) of >200 000 L kg−1 Phillipsite was more effective than apatite at sorbing aqueous Ba2+ Results from the laboratory study were used to design the greenhouse study that used a soil affected by a Zn–Pb smelter from Pribram, Czech Republic. Two application rates (25 and 50 g kg−1) of phillipsite and apatite and two plant species, maize (Zea mays L.) and oat (Avena sativa L.), were evaluated in this study. There was little (maize) to no (oat) plant growth in the unamended contaminated soil. Apatite and, to a slightly lesser extent, phillipsite additions significantly enhanced plant growth and reduced Cd, Pb, and Zn concentrations in all analyzed tissues (grain, leaves, and roots). The sequestering agents also affected some essential elements (Ca, Fe, and Mg). Phillipsite reduced Fe and apatite reduced P and Fe concentrations in oat tissues; however, the level of these elements in oat leaves and grains remained sufficient. Sequential extractions of the soil indicated that the Cd, Pb, and Zn were much more strongly sorbed onto the amended soil, making the contaminants less phytoavailable.