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 low sulfur content, yet its effectiveness is limited by its 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@P^bm) exhibited a markedly improved Cd(II) adsorption capacity (43.77 mg g⁻¹), which was 1.83 times than that of ball-milled natural pyrite without phosphate modification (FeS^bm₂, 23.93 mg g⁻¹). The adsorption process fitted well with the pseudo-second-order kinetic model and Langmuir isotherm, indicating a monolayer adsorption process predominantly controlled by chemisorption. Characterizations revealed that the Cd(II) adsorption mechanisms on FeS₂@P^bm involved electrostatic attraction, surface complexation, and chemical precipitation. The phosphate modification altered the surface functional groups and surface potential of FeS₂@P^bm, facilitating the chemical and electrostatic adsorption of Cd(II). Additionally, FeS₂@P^bm 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 metal removal from wastewater.