The Effects of Temperature on the Hydrothermal Synthesis of Hydroxyapatite-Zeolite Using Blast Furnace Slag

Characterization of the Physical, Chemical, and Adsorption Properties of Coal-Fly-Ash–Hydroxyapatite Composites

(1) Hydroxyapatite (HAp), which can be obtained by several methods, is known to be a good adsorbent. Coal fly ash (CFA) is a commonly reused byproduct also used in environmental applications as an adsorbent. We sought to answer the following question: Can CFA be included in the method of HAp wet synthesis to produce a composite capable of adsorbing both heavy metals and dyes? (2) High calcium lignite CFA from the thermal power plant in Bełchatów (Poland) was used as the base to prepare CFA–HAp composites. Four types designated CFA–HAp1–4 were synthesized via the wet method of in situ precipitation. The synthesis conditions differed in terms of the calcium reactants used, pH, and temperature. We also investigated the equilibrium adsorption of Cu(II) and rhodamine B (RB) on CFA–HAp1–4. The data were fitted using the Langmuir, Freundlich, and Redlich–Peterson models and validated using R2 and χ2/DoF. Surface changes in CFA–HAp2 following Cu(II) and RB adsorption were assessed using SEM, SE, and FT-IR analysis. (3) The obtained composites contained hydroxyapatite (Ca/P 1.67) and aluminosilicates. The mode of Cu(II) and RB adsorption could be explained by the Redlich–Peterson model. The CFA–HAp2 obtained using CFA, Ca(NO3)2, and (NH4)2HPO4 at RT and pH 11 exhibited the highest maximal adsorption capacity: 73.6 mg Cu/g and 87.0 mg RB/g. (4) The clear advantage of chemisorption over physisorption was indicated by the Cu(II)–CFA–HAp system. The RB molecules present in the form of uncharged lactone were favorably adsorbed even on strongly deprotonated CFA–HAp surfaces.

Hydroxyapatite nanoparticle functionalized activated carbon particle electrode that removes strontium from spiked soils in a unipolar three-dimensional electrokinetic system

Biohazard performance of Sr radionuclide can be significantly magnified by its release from the contaminated sedimentation. In this study, hydroxyapatite nanoparticle-functionalized activated carbon electrode (AC-HAP) was synthesized and stacked to the cathode compartment of the electrokinetic (EK) system to develop a unipolar three-dimensional (3D) electrochemical process for Sr²⁺ removal from spiked soils. Sr²⁺ adsorption by AC-HAP can be fitted by the pseudo-first-order and pseudo-second-order kinetic models and the Langmuir, Freundlich, and Temkin isotherm models. The largest monolayer adsorption capacity of AC-HAP of 69.49 mg g^-1 was evaluated in the pH range of 10-12 and at 40 °C. 3D EK further intensified the adsorption process of AC-HAP and the corresponding Sr²⁺ removal from aqueous environments. Voltage gradients and proposing time had a significant effect on the migration and transmission of Sr²⁺ in the electrolyzer. The influence of competitive ions on Sr²⁺ removal in the stock solutions followed Al³⁺ < Mg²⁺ < K⁺ < Na⁺ < Ca²⁺ while followed Al³⁺ < Na⁺ < K⁺ < Mg²⁺ < Ca²⁺ in 3D EK. The first three cycles for AC-HAP had taken roughly 50% of the reusability percentage. Sr²⁺ removal from spiked samples in 3D EK was achieved by acid dissolution, electromigration, and selective uptake on particle electrode.

The Effects of NaOH Concentration on the Hydrothermal Synthesis of a Hydroxyapatite–Zeolite Composite Using Blast Furnace Slag

This study investigated the effect of NaOH concentration on the assemblage, crystallinity, and dimension of crystalline phases in hydroxyapatite–zeolite composites made with blast furnace slag. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy measurement, scanning electron microscopy (SEM), and nitrogen adsorption–desorption tests were conducted to characterize the synthesized composites. In addition, the cesium adsorption potential of the synthesized composites was evaluated to assess the feasibility of using hydroxyapatite–zeolite composites synthesized from blast furnace slag. The composite samples using a 3 M NaOH solution showed the formations of Na-P1 and Faujasite (FAU) zeolites along with hydroxyapatite, which led to the highest adsorption capacity for cesium (44.90 mg/g).