Selective recovery of heavy metals from wastewater by mechanically activated calcium carbonate: Inspiration from nature

Abstract

In nature, the calcium carbonate shows different interactions with different metal ions. Inspiration from this natural phenomenon, in this work, the selective recovery of heavy metals from wastewater by mechanically activated calcium carbonate was investigated. The changes in Ca2+ concentration, pH value and metals uptake ratio of solution showed that M2+ (M = Cu, Mn, Zn and Ni) were endowed with different migration rules, resulting in the various interaction with the calcium carbonate in metal-bearing solution. The combination of XRD, SEM, and stereomicroscope affirmed that the adsorbed M2+ rarely change the lattice structure of calcium carbonate, while the adsorbed Cu2+ and Zn2+ could convert the mineral phase from calcium carbonate to posnjakite and hydrozincite, respectively. As a result of phase transition, 15% Cu2+ and 6% Zn2+ were uptaken with initial concentration of 1 mM for 100 min, however, the unsatisfactory recovery prevented the efficient recycling of metal. The mechanically activated calcium carbonate had a superior solubility at the solid/liquid interface, promoting mineral phase transformation on the premise of weak displacement adsorption. Hence, the uptake ratio of Cu2+ and Zn2+ were significantly increased to 99% and 53% at the same condition. Finally, Cu2+ was recovered from polymetallic systems from complex environment with high precision. The concept of selective recycling in this research guides the development of innovative processes from natural information.