Impact of thermal treatment of calcium silicate-rich slag on the removal of cadmium from aqueous solution

The problem of wastewater treatment and inorganics removal and the waste management including slags is of great importance nowadays. Three types of treated calcium silicate-rich slags were tested. The impact of thermal treatment of slag in air (SA), under NH3 atmosphere (SN), and in the presence of flux (SF) at different temperatures (500-1000 degrees C) on removal of cadmium from aqueous solution was investigated. The treatment had the impact on slag characteristics. In the slag samples thermally treated in air, SiO2, clinopyrexene, larnite, CaSiO3, Ca3SiO5, Ca8Si5O18, and olivine crystalline phases were formed. A very similar trend was observed for the slag samples heat treated under NH3 atmosphere except the formation of wollastonite at 1000 degrees C. Depending on the flux employed in the thermal treatment of slag, various crystalline phases were formed. Each alkaline earth metal chloride (CaCl2, SrCl2, and BaCl2) flux affected differently. Potassium, iron, magnesium, aluminum, silicon, calcium, and lead are the main elemental components of the slag. The slag sample thermally treated with CaCl2 flux showed the highest potential for Cd(II) adsorption followed by the SN sample series. The results strictly indicate the complex mechanism of Cd(II) adsorption onto the slag materials considering both chemical adsorption (a pseudo-second order) and intraparticle diffusion. Cd(II) adsorption proceeded according to the Langmuir, Temkin or Freundlich models. The best results can be obtained using a low-cost slag adsorbent thermally treated under NH3 atmosphere. (C) 2018 Elsevier Ltd. All rights reserved.