Porous vaterite and cubic calcite aggregated calcium carbonate obtained from steamed ammonia liquid waste for Cu2+ heavy metal ions removal by adsorption process

Abstract

Removal of copper ions (Cu2+) from wastewater has garnered significant interest due to the growing environmental concerns. In order to address such issues, porous vaterite and cubic calcite aggregated CaCO3 is successfully prepared from steamed ammonia liquid waste (CaCl2) and (NH4)2CO3 (Ca2+/CO2−3M ratio = 5) via a simple precipitation method conducted at room temperature. The physicochemical properties of CaCO3 are studied using conventional material characterization techniques. Furthermore, the possible formation mechanism of the as-obtained CaCO3 is also discussed in this work. The effects of the CaCO3 quantity, pH, temperature, reaction duration, and initial Cu2+ solution concentration on the Cu2+ adsorption by CaCO3 are also investigated. A high Cu2+ removal rate, i.e., as high as 99%, is achieved with the use of CaCO3 (1000 mg·L−1). After the adsorption process, the residual Cu2+ concentration is less than 0.5 mg/L (from an initial Cu2+ concentration of 500 mg·L−1), which meets the discharge standard for industrial waste. The adsorption kinetics of the process can be expressed by a pseudo-second-order model, with a R2 of 0.9992. Langmuir adsorption model can be used to express the equilibrium adsorption of the as-prepared CaCO3, with a R2 of 0.9967. The obtained sediment after adsorption process is characterized with XRD, XPS, SEM, SEM-EDS, TEM, TEM-SEAD, EDS, and EDAX elemental mapping. Based on the collective results, Cu2+ removal mechanism by the aggregated CaCO3 in aqueous solution is based on two simultaneous process, i.e., adsorption and ion exchange chemical precipitation.