Cadmium removal from wastewater by sponge iron sphere prepared by charcoal direct reduction

Sponge iron sphere (SIS), made of concentrated iron powder and possessed high activity and intension, was prepared through the process of palletizing, roasting and direct reduction by charcoal. The sponge iron sphere could remove most of Cd2+ from wastewater. The results showed the Cd2+ removal followed the first order reaction. Initial pH value played an important role in Cd2+ removal. With original initial pH, Cd2+ removal decreased to the minimum and then increased slightly with the rising of original concentration. The removal rate constant was −0.1263 and −0.0711 h−1, respectively, under the Cd2+ concentration of 50 and 200 mg/L. When the initial pH was adjusted to 3.0, the removal rate constant could increase to −9.896 and −4.351 h−1, respectively. The removal percentage almost reached to 100% when Cd2+ concentration was below 100 mg/L. While Cd2+ concentration was above 100 mg/L, Cd2+ removal percentage decreased slightly. In dynamic experiments, the column filled with sponge iron sphere exhibited favorable permeability. There was no sphere pulverization and conglutination between spheres. In contrast to the static state experiments, the Cd2+ removal percentage in dynamic state experiment was lower, and the removal Cd2+ quantity was 1.749 mg/g.