Facile synthesis and characterization of a magnetic biosorbent derived from sodium alginate and activated graphite schist: Experimental and statistical physics analysis for Mn(VII) remediation.

H2O2-modified graphite schist (GS) and sodium alginate (SA) interface was loaded by Fe3O4 nanoparticles (MNPs) to prepare a magnetic biosorbent that was employed in removing Mn(VII) from solutions. The prepared GS/SA/MNPs adsorbent was investigated using a variety of techniques, including elemental mapping, TEM, XPS, FTIR, FESEM, EDX, XRD, XPS, and zeta potential. An experimental study supported by statistical physics calculations was carried out to obtain a new outline of the Mn(VII) uptake mechanism. The classical Freundlich and the statistical physical double-layer models adequately described the Mn(VII) uptake process at pH 3.0 and a temperature of 25-55 °C. The removed number of Mn ions (such as Mn+7 and Mn+2) per GS/SA/MNPs active site ranged from 0.70 to 0.84, indicating a mixed adsorption orientation driven by surface complexation and attraction forces mechanisms. The adsorption energies (∆E) calculated by the double-layer model ranged from 18.79 to 24.94 kJ/mol, suggesting that the interaction between Mn(VII) and GS/SA/MNPs was controlled by physical forces. Increasing the adsorption capacity at saturation (Qsat) from 333.14 to 369.52 mg/g with temperature proposed an endothermic capture process. Thermodynamic functions clarified the viability and spontaneity of Mn(VII) uptake on the GS/SA/MNPs adsorbent.

Sodium alginate-modified alkali-activated eggshell/Fe3O4 nanoparticles: A magnetic bio-based spherical adsorbent for cationic dyes adsorption.

Herein, a mixture of eggshell (ES) and magnetite nanoparticles (MNPs) was alkali-activated using NaOH/Na2SiO3 solution and then, impregnated with sodium alginate (SA) to prepare a magnetic bio-based adsorbent (namely SAAES/SA/MNPs) for the decontamination of water containing basic dyes, in particular, methylene blue (MB) and crystal violet (CV). The physicochemical properties of magnetic spheres of SAAES/SA/MNPs were characterized using XRD, FTIR, FESEM, EDX, elemental mapping, TEM, and zeta potential techniques. Dye adsorption equilibrium was studied experimentally at pH 8.0 and 25-55 °C, and a statistical physics multilayer model was applied to understand the removal mechanism of these dyes including the adsorption orientations on the adsorbent surface. The number of adsorbed dye molecules per functional group (n) of this bio-based adsorbent ranged from 0.70 to 0.91, indicating the presence of vertical and horizontal adsorption orientations for these organic molecules at all tested solution temperatures. The calculated saturation adsorption capacities (Qsat) were 332.57-256.62 mg/g for CV and 304.47-240.62 mg/g for MB, and an exothermic adsorption was observed for both adsorbates. The estimated adsorption energies (∆E) were < 25 kJ/mol, confirming that the SAAES/SA/MNPs-dye interactions were governed by physical forces as electrostatic interactions. This bio-based adsorbent was effectively regenerated using ethanol and it can be reused showing a removal of 71 and 74 % of MB and CV, respectively, after fourth adsorption-desorption cycles. Overall, the results of this article suggest the attractive performance of SAAES/SA/MNPs for removing basic dyes from aqueous solutions, thus highlighting the promising potential of this magnetic bio-based adsorbent for sustainable wastewater treatment at an industrial level.

Repurposing carbonate-based waste for producing an innovative binder: optimization and characterization.

This study reports the full recycling of dolomite waste (DW) in the fabrication of a novel cementitious material through a facile and eco-efficient method. The proposed technique includes mixing different alkali-activators (i.e., NaOH and Na2SiO3) with DW powder, followed by curing at room temperature. Based on the alkali-activator type, sodium oxide concentration, and curing time, the formulated mixtures yield a wide range of compressive strengths. When DW powder is mixed with different contents of NaOH (2.5, 5, and 7.5 wt.% Na2O), the resulting hardened materials exhibited modest compressive strengths (less than 11 MPa) due to the formation of the gaylussite Na2CO3·CaCO3·5H2O phase. Concerning the other chemical activator (Na2SiO3), a significant improvement in the compressive strengths of the resulted hardened materials was detected. This was ascribed to the formation of calcium silicate hydrate, with a high binding capacity, through the exchange reaction between Na2SiO3 and CaCO3 inside DW. The sample activated with Na2SiO3 (silica modulus of 1.5) equivalent to Na2O of 7.5 wt.% offered the highest 90-day compressive strength (34 MPa). At silica modulus lower or higher than 1.5, a noticeable decrease in the performance of the hardened materials was observed, which could be attributed to the alter in binding phase composition. Overall, the present work presented a new approach in utilizing the available and low cost carbonate-based wastes as main precursors in the family of promising alkali-activated materials.