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Subject: search.filters.subject.Calcium silicate hydrate

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    Calcium silicate hydrate–embedded porous concrete for efficient phosphate removal and recovery in concentrated eluates
    (2026-01-01)
    Wongniramaikul, Worawit
    ;
    Choodum, Aree
    ;
    Pasitsuparoad, Pakorn
    ;
    Cotchim, Suparat
    ;
    Phawachalotorn, Chanadda
    Phosphate remediation and recovery from wastewater remain challenging due to limitations in adsorbent stability and real–world applicability. This study presents a sustainable porous concrete–calcium silicate hydrate (PC–CSH) column engineered for continuous–flow phosphate removal and resource recovery. Synthesized CSH nanoparticles were incorporated into a porous cement matrix, and comprehensive characterization confirmed the formation of calcium phosphate phases, including hydroxyapatite (HAP), CaHPO₄, and Ca(H₂PO₄)₂. The results indicate that surface-induced microprecipitation, driven by Ca²⁺ and OH⁻ released from both added and in situ–formed CSH, is the dominant removal mechanism. Externally added nanoparticles contributed 40.05% of total uptake, while the remainder originated from CSH generated during cement hydration. Breakthrough analysis showed that increasing column height enhanced longevity, whereas higher influent phosphate concentration and flow rate accelerated saturation. Under optimal conditions (7.5 cm column, 50 mg L⁻¹ phosphate, 10 mL min⁻¹ flow), the system achieved >99% removal with a total adsorption capacity of 3599.7 mg. The nonlinear Yoon–Nelson model best described the breakthrough behavior. Application to real municipal wastewater (initial phosphate 4.57 mg L⁻¹) achieved 99.3% removal with minimal influence from coexisting anions (SO₄²⁻, NO₃⁻, CO₃²⁻). Phosphate was efficiently recovered using 0.5 M HCl (100.4% desorption), and performance was restored by reloading fresh PC–CSH slurry. The column retained 73.9% phosphate removal efficiency after four adsorption–desorption cycles with real wastewater, demonstrating excellent reusability and practical potential. Overall, the PC–CSH column offers a robust, semi–regenerable platform for sustainable phosphate mitigation and recovery in wastewater treatment.
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    Magnetic calcium silicate hydrate–oyster shell waste nanocomposite for phosphate removal and recovery: RSM-based optimization, mechanism, and real water application
    (2025-09-01)
    Boonkanon, Chanita
    ;
    Wongniramaikul, Worawit
    ;
    Phawachalotorn, Chanadda
    ;
    Limwongsakorn, Somsak
    ;
    Choodum, Aree
    Magnetic nanocomposites offer an effective strategy for phosphate removal from wastewater, preventing eutrophication and enabling phosphate recovery for reuse as fertilizer—supporting a zero-waste approach. In this study, a novel hybrid nanocomposite composed of magnetized calcined oyster shell waste and calcium silicate hydrate (M-COS-CSH) was synthesized through a simple process completed within 5.2 h. Response Surface Methodology was employed for optimization: a Central Composite Design determined the optimal FeCl₃ and COS ratios, while a Box–Behnken Design optimized adsorption conditions including adsorbent dose (20–100 mg), initial phosphate concentration (10–90 mg L<sup>−1</sup>), contact time (15–75 min), and pH (3−11). Under optimal conditions (60 mg adsorbent, 10 mg L<sup>−1</sup> phosphate, 45 min, pH 6.28), M-COS-CSH achieved a predicted maximum removal efficiency of 97.30 %. An experimental removal efficiency of 98.06 % ± 0.19 % was obtained under the same conditions without pH adjustment (pH 6.84), offering a cost advantage. The adsorption process closely followed the Langmuir isotherm model (R<sup>2</sup> = 0.9963), with a maximum adsorption capacity of 161.29 mg g<sup>−1</sup>, and was best described by the pseudo-second-order kinetic model (R<sup>2</sup> = 1.0000). Characterization suggested a mechanism involving surface microprecipitation and inner-sphere complexation. Thermodynamic analysis confirmed the process to be endothermic and spontaneous (ΔG°: −9.97 to −10.84 kJ mol<sup>−1</sup>; ΔH°: 3.00 kJ mol<sup>−1</sup>; ΔS°: 43.52 J mol<sup>−1</sup> K<sup>−1</sup>). M-COS-CSH achieved phosphate removal ranging from 70.81 % ± 2.47 % to 94.24 % ± 0.39 % in real water samples. Even in the presence of competing anions at fivefold phosphate concentration, removal efficiency remained high (93.58 % ± 0.32 %), confirming the material's strong selectivity and suitability in complex matrices.