Effect of anions species on copper removal from wastewater by using mechanically activated calcium carbonate.

In this work, the wastewater containing sulfate ions, nitrate ions or chloride ions was used to investigate the performance of anions in copper removal by mechanically activated calcium carbonate. The copper removal from wastewater containing sulfate anion achieved almost 99% with the CaCO3/Cu molar ratio of 1:1. However, the copper removal from wastewater containing nitrate and chloride anions are lower than 20% and 35%, respectively. The precipitations from wastewater containing different anions were analyzed by using XRD, FTIR, SEM-EDS and XPS, respectively. Cu (II) in wastewater containing sulfate anion is precipitated in the form of posnjakite. The nitrate anion precipitates as gerhardtite, whereas chloride anion as atacamite and botallackite. The solubility of precipitation plays a decisive role in copper removal so that sulfate anions have a superior effect on Cu (II) precipitation due to relatively stable posnjakite with the lowest solubility, suggesting that this method using mechanically activated calcium carbonate is more suitable and effective for the wastewater containing sulfate anion.