Novel Application of Mineral By-Products Obtained from the Combustion of Bituminous Coal–Fly Ash in Chemical Engineering

Abstract

The aim of this work was the chemical modification of mineral by-products obtained from the combustion of bituminous coal (FA) treated with hydrogen peroxide (30%), used as an adsorbent for the removal of Cr(III) and Cd(II) ions and crystal violet (CV) from a mixture of heavy metal and organic dye in a solution containing either Cr(III)–CV or Cd(II)–CV. Fourier transform infrared (FT-IR), thermogravimetric analysis (TG), scanning electron microscopy–energy dispersive spectroscopy (SEM-EDS), and X-ray diffraction (XRD) analyses suggested that the mechanism of Cr(III)–CV or Cd(II)–CV sorption onto FA–H2O2 includes ion-exchange and surface adsorption processes. The effect of pH on the adsorption equilibrium was studied. The maximum adsorption was found for pH values of 9. The values of the reduced chi-square test (χ2/degree of freedom (DoF)) and the determination coefficient R2 obtained for the sorbate of the considered isotherms were compared. Studies of equilibrium in a bi-component system by means of the extended Langmuir (EL), extended Langmuir–Freundlich (ELF), and Jain–Snoeyink (JS) models were conducted. The estimation of parameters of sorption isotherms in a bi-component system, either Cr(III)–CV or Cd(II)–CV, showed that the best-fitting calculated values of experimental data for both sorbates were obtained with the JS model (Cr(III) or CV) and the EL model (Cd(II) or CV). The maximum monolayer adsorption capacities of FA–H2O2 were found to be 775, 570 and 433 mg·g−1 for Cr, Cd and CV, respectively. Purification water containing direct Cr(III) or Cd(II) ions and CV was made with 90%, 98% and 80% efficiency, respectively, after 1.5 h. It was found that the chemical enhancement of FA from coal combustion by H2O2 treatment yields an effective and economically feasible material in chemical engineering for the treatment of effluents containing basic dyes and Cr(III) and Cd(II) ions.