Aranda Mastin technology (AMT) is an emerging industry focused on the extracting aluminum from secondary sources, amid the decline of traditional bauxite resources. However, the cost-effectiveness of AMT operations remains challenged by the limited added value of its by-products. This study investigates the potential of utilizing acid-leached residues from Egyptian kaolin as low-cost adsorbents for removing methylene blue (MB) from aqueous solutions. Four mineral acids—HCl, HNO3, H2SO4, and H3PO4—were evaluated for their effectiveness in direct kaolin dealumination under varying experimental conditions, including concentration, temperature, stirring time, and solid/liquid ratio. Optimal conditions were found to be: 7 mol L−1 acid concentration, 100 °C, > 240 min of reaction time, and a 1/20 solid/liquid ratio. The leaching efficiency followed the order: H3PO4 > H2SO4 > HCl > HNO3. X-ray diffraction (XRD) analysis confirmed amorphization due to dealumination in the residues from H3PO4 and H2SO4. The specific surface area (SBET) of the residues increased in the order: H2SO4 > HCl > H3PO4 residues. Despite this, the highest dye removal efficiency (84.1%) was observed with residue treated using H3PO4, followed by HCl then with H2SO4 was the lowest efficiency. Adsorption kinetic studies followed the pseudo-second-order model for both H3PO4 and HCl residues, with high correlation coefficients (0.997–0.999), suggesting a heterogeneous adsorption mechanism. Additionally, the adsorption data for H3PO4-treated residue fit both the Langmuir and Freundlich isotherm models, indicating the coexistence of monolayer and multilayer adsorptions. When the removal efficiency was tested in MB-spiked seawater samples across various salinities and pH values (7.84–8.5), it remained consistently high (89.4–91.8%). These results highlight that while both H3PO4 and H2SO4 leaching effectively promote dealumination, only H3PO4-derived residues exhibit significant adsorption potential—making them suitable for cost-effective water treatment applications in addition to their role in aluminum recovery.

Optimizing direct acid leaching of Egyptian kaolin for aluminum extraction and value-added adsorbent production for water treatment applications

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2025年10月29日

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Elsayed A. Drweesh,
Eman A. M. Elzahany,
Ahmed Tawfik,
Adel I. M. Akarish,
Khaled S. Abou-El-Sherbini

摘要

Aranda Mastin technology (AMT) is an emerging industry focused on the extracting aluminum from secondary sources, amid the decline of traditional bauxite resources. However, the cost-effectiveness of AMT operations remains challenged by the limited added value of its by-products. This study investigates the potential of utilizing acid-leached residues from Egyptian kaolin as low-cost adsorbents for removing methylene blue (MB) from aqueous solutions. Four mineral acids—HCl, HNO₃, H₂SO₄, and H₃PO₄—were evaluated for their effectiveness in direct kaolin dealumination under varying experimental conditions, including concentration, temperature, stirring time, and solid/liquid ratio. Optimal conditions were found to be: 7 mol L⁻¹ acid concentration, 100 °C, > 240 min of reaction time, and a 1/20 solid/liquid ratio. The leaching efficiency followed the order: H₃PO₄ > H₂SO₄ > HCl > HNO₃. X-ray diffraction (XRD) analysis confirmed amorphization due to dealumination in the residues from H₃PO₄ and H₂SO₄. The specific surface area (S_BET) of the residues increased in the order: H₂SO₄ > HCl > H₃PO₄ residues. Despite this, the highest dye removal efficiency (84.1%) was observed with residue treated using H₃PO₄, followed by HCl then with H₂SO₄ was the lowest efficiency. Adsorption kinetic studies followed the pseudo-second-order model for both H₃PO₄ and HCl residues, with high correlation coefficients (0.997–0.999), suggesting a heterogeneous adsorption mechanism. Additionally, the adsorption data for H₃PO₄-treated residue fit both the Langmuir and Freundlich isotherm models, indicating the coexistence of monolayer and multilayer adsorptions. When the removal efficiency was tested in MB-spiked seawater samples across various salinities and pH values (7.84–8.5), it remained consistently high (89.4–91.8%). These results highlight that while both H₃PO₄ and H₂SO₄ leaching effectively promote dealumination, only H₃PO₄-derived residues exhibit significant adsorption potential—making them suitable for cost-effective water treatment applications in addition to their role in aluminum recovery.