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<p>Phosphoric acid activation of Fe-rich copper slag (CS) fines has been understudied due to the rapid setting of the geopolymer caused by the exothermic reaction between Fe<sup>2+</sup> and H<sub>3</sub>PO<sub>4</sub>. Conversely, fly ash (FA) takes longer to set and exhibits low strength due to its inadequate aluminium content, making it less preferred as a sole binding material. Hence, this study investigates the interactions that control the strengthening of the blend of CS and FA in different proportions of 0%, 20%, 50%, and 100% in the acid-activated geopolymer paste. The compressive strength results indicate the influence of iron sialate O–Fe–Si–O– in aluminium silicate, with structural units Si–O–P–O–Si– or Si–O–Al–O–P–. The lowest strength of 1–3&#xa0;MPa was found in sole FA binders, but strength significantly increased in CS-FA blends, notably C<sub>1</sub>F<sub>4</sub> (21.24&#xa0;MPa) and C<sub>1</sub>F<sub>1</sub> (16.72&#xa0;MPa). Beyond these proportions, strength decreased due to flash setting, hindering CS particle dissolution. XRD, FTIR, SEM-EDAX, and EPR supported these findings. The higher strength is attributed to the formation of mixed gel and new crystalline phases, such as hydrated iron phosphate, calcium phosphate, and berlinite, which contribute to matrix densification. An EPR signal at a g<sub>eff</sub> value of 2.0 confirmed iron phosphate aggregates after acid excitation. This study suggests that CS and FA can create a high-strength geopolymer paste matrix showcasing their recyclability.</p>

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A Study on the Influence of the Composition of the Fe-Rich Copper Slag on the Production and Structure of Silico-Aluminophosphate Fly Ash Geopolymer

  • 期刊论文

  • 发表日期：

    2025年4月5日

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  • Manivannan Muthusamy,
  • Vanitha Nandhiraman,
  • Jeyalakshmi Ramaswamy

摘要

Phosphoric acid activation of Fe-rich copper slag (CS) fines has been understudied due to the rapid setting of the geopolymer caused by the exothermic reaction between Fe2+ and H3PO4. Conversely, fly ash (FA) takes longer to set and exhibits low strength due to its inadequate aluminium content, making it less preferred as a sole binding material. Hence, this study investigates the interactions that control the strengthening of the blend of CS and FA in different proportions of 0%, 20%, 50%, and 100% in the acid-activated geopolymer paste. The compressive strength results indicate the influence of iron sialate O–Fe–Si–O– in aluminium silicate, with structural units Si–O–P–O–Si– or Si–O–Al–O–P–. The lowest strength of 1–3 MPa was found in sole FA binders, but strength significantly increased in CS-FA blends, notably C1F4 (21.24 MPa) and C1F1 (16.72 MPa). Beyond these proportions, strength decreased due to flash setting, hindering CS particle dissolution. XRD, FTIR, SEM-EDAX, and EPR supported these findings. The higher strength is attributed to the formation of mixed gel and new crystalline phases, such as hydrated iron phosphate, calcium phosphate, and berlinite, which contribute to matrix densification. An EPR signal at a geff value of 2.0 confirmed iron phosphate aggregates after acid excitation. This study suggests that CS and FA can create a high-strength geopolymer paste matrix showcasing their recyclability.