Mechanically activated calcium carbonate and zero-valent iron composites for one-step treatment of multiple pollutants

The growing presences of conventional and emerging contaminants make the wastewater treatment increasingly difficult and expensive on a global scale. ZVI tends to be an expectable material for the detoxification of some difficult contaminants such as chlorinated solvents and nitroaromatics. In this work, together use with calcium carbonate (CaCO3), which serves as a green supporter to ZVI and also direct participant toward the purification process, has been carried out by cogrinding to give a synergistic effect, particularly for treating multiple pollutants including both inorganic and organic compositions. Based on a set of analytical methods of XRD, FTIR, SEM, XPS, and other test methods, the activation mechanism of the ball milling process and the removal performances of the prepared composites were examined. The results prove that the mechanically activated calcium carbonate and ZVI composite samples exhibited extremely high removal capacity on a variety of pollutants contaminated water. The decolorization of azo dyes is mainly attributed to the breaking of chromogenic functional group nitrogen and nitrogen double bonds, and the removal mechanism of aromatic series occurs through a hydrogenation substitution reaction. As to the inorganic pollutant removals, besides the efficient heavy metal ion precipitations, phosphate and fluoride ions are co-precipitated through the formation of fluorapatite to achieve a simultaneous and synergistic removal effect. Under the optimal reaction conditions, the concentration of PO43- is reduced from 250 to 0 mg/L, and that of F- is reduced from 51.07 to 1.20 mg/L. The prepared composite sample of ZVI rand calcium carbonate allowed simultaneous removals of both inorganic and organic pollutants, simplifying the remediation process of complicated multiple contaminations.

Automated summary

The presence of various conventional and emerging contaminants has made wastewater treatment increasingly difficult and expensive globally. In this study, a composite material of zero-valent iron (ZVI) and calcium carbonate (CaCO3) was used to achieve a synergistic effect in treating multiple pollutants. The activation mechanism of the ball milling process and the removal performance of the prepared composites were examined using various analytical methods. The results showed that the composite samples exhibited extremely high removal capacity for a variety of pollutants. Azo dyes were decolorized through the breaking of nitrogen and nitrogen double bonds, while inorganic pollutants were removed through efficient heavy metal ion precipitation and co-precipitation of phosphate and fluoride ions.