A new alkali-activated binder prepared from dolomite waste and diatom frustules: Insights into the mechanical performance and Mn(VII) treatment

A new alkali-activated binder with a high mechanical strength was prepared via mixing up 5, 10, and 15 wt% of purified diatom (PD) with dolomite waste (DW) in a DW/PD mixture and sodium silicate (7.5 wt% of Na2O) activation. The formed alkali-activated DW/PD with 10 wt% PD exhibited the highest compressive strength (51.51 MPa) compared to the 36.3 MPa and 41.4 MPa of those with 5.0 wt% PD and 15.0 wt% PD, respectively. The characterization of the binder with the optimal mechanical performance (DW/PD-AAC) was performed by X-ray diffraction (XRD, Fourier transform infrared (FTIR) spectrometry, field-emission scanning electron microscopy (FESEM), and zeta potential techniques and this sample was employed in the removal of Mn(VII) from aqueous solutions. The physicochemical study of the Mn(VII) adsorption orientation and mechanism at 25 - 45 degrees C was performed via the integration of adsorption experiments and statistical physics modeling. The Freundlich and the advanced double layer adsorption models fitted well the Mn(II) adsorption process. The number of removed Mn(VII) ions per active site (n) ranged from 0.75 to 0.87, which reflected a group of horizontal and vertical ion anchoring at all temperatures. The Mn(VII) adsorption capacity at saturation (Q(sat)) increased from 322.03 to 364.12 mg/g (i.e., endothermic interaction). Energetically, the Mn(VII) adsorption onto the developed binder was ruled by physical interactions (i.e., triangle E < 40 kJ/mol). The calculated Gibbs free energy, entropy, and internal energy showed the spontaneous nature of Mn(VII) adsorption process. The compressive strength and adsorption performance indicated that DW/PD-AAC is a strong and promising adsorbent for removing hazardous water pollutants.