Performance and Mechanisms of Cd(II) Removal by Phosphate-Modified Natural Pyrite

Abstract

Natural pyrite possesses inherent advantages for heavy metal immobilization due to its natural abundance and reductive sulfur content, yet its effectiveness is limited by a low surface area and scarce active sites. Herein, a straightforward phosphate modification strategy via ball-milling was employed to enhance the cadmium removal performance of natural pyrite. The obtained phosphate-modified natural pyrite (FeS2@Pbm) exhibited a markedly improved Cd(II) adsorption capacity (43.77 mg/g), which was 1.83 times higher than that of ball-milled natural pyrite without phosphate modification (FeS2bm, 23.93 mg/g). The adsorption process fitted well with the pseudo-second-order kinetic model and the Langmuir isotherm, indicating a monolayer adsorption process predominantly controlled by chemisorption. Characterizations revealed that the Cd(II) adsorption mechanisms on FeS2@Pbm involved electrostatic attraction, surface complexation, and chemical precipitation. The phosphate modification altered the surface functional groups and surface potential of FeS2@Pbm, facilitating the chemical and electrostatic adsorption of Cd(II). Additionally, FeS2@Pbm exhibited substantial potential for the removal of multiple metal ions, including As(III), Pb(II), Cu(II), Ag(I), Hg(II), and Zn(II). This study offers a unique strategy for fabricating highly cost-effective mineral adsorbents through phosphate modification via ball-milling, enabling effective heavy metals removal from wastewater.