Effective Adsorption of Congo Red from Aqueous Solution Using Fe/Al Di-Metal Nanostructured Composite Synthesised from Fe(III) and Al(III) Recovered from Real Acid Mine Drainage

Abstract

This study presents the first known exploration of Congo red dye (CR) adsorption by a polycationic Fe/Al Di-metal nanostructured composite (PDFe/Al) synthesised using Fe(III) and Al(III) recovered from authentic acid mine drainage (AMD). The PDFe/Al successfully removed CR from the aqueous solution. The mineralogical, microstructural, and chemical properties of the synthesised PDFe/Al adsorbent (before and after adsorption) were studied using state-of-the-art analytical instruments. The optimum conditions were observed to be 100 mg·L−1 CR, 1 g of the PDFe/Al in 500 mL adsorbate solution, 20 min of shaking, pH = 3–8, and a temperature of 35 °C. At optimised conditions, the PDFe/Al showed ≥99% removal efficacy for CR dye and an exceptionally high Langmuir adsorption capacity of 411 mg·g−1. Furthermore, a diffusion-limited adsorption mechanism was observed, with two distinct surfaces involved in the adsorption of CR from an aqueous solution. It was determined that the adsorption of CR induced internal strain and deformation within the matrices and interlayers of the PDFe/Al which resulted in a marked increase in the adsorbent pore surface area and pore volume. The remarkably high adsorption capacity could be attributed to the high surface area. A regeneration study showed that the adsorbent could be reused more than four times for the adsorption of CR. The findings from this study demonstrated the feasibility of recovering valuable minerals from toxic and hazardous AMD and demonstrated their potential for the treatment of industrial wastewaters.

Rapid Removal of Cr(VI) from Aqueous Solution Using Polycationic/Di-Metallic Adsorbent Synthesized Using Fe3+/Al3+ Recovered from Real Acid Mine Drainage

“…These results are consistent with that observed previously for Congo Red adsorption [2]. As indicated in Figure 4, the plot for 2θ values for PDFe/Al before and after Cr( adsorption shows a clear shift in 2θ values of 0.66° thus confirming internal adsorpt induced strains as previously reported in Muedi et al 2022 [2]. The increased total surface area implies that the adsorbed chemical has the potential to enhance the adsorbent's surface area, indicating the material's potential for subsequent usage after Cr(VI) ion adsorption.…”

“…It is clear that a significant increase in both the internal surface area and volume was observed The total surface area of the raw PDFe/Al was reported to be around 37.5841 m 2 /g, which then changed to 95.5269 m 2 /g after Cr(VI) adsorption, while an eight-fold increase in internal pore volume (0.003 cm 3 /g to 0.02 cm 3 /g) was observed after Cr(VI) adsorption. These results are consistent with that observed previously for Congo Red adsorption [2]. As indicated in Figure 4, the plot for 2θ values for PDFe/Al before and after Cr( adsorption shows a clear shift in 2θ values of 0.66° thus confirming internal adsorpt induced strains as previously reported in Muedi et al 2022 [2].…”

“…As indicated in Figure 4, the plot for 2θ values for PDFe/Al before and after Cr(VI) adsorption shows a clear shift in 2θ values of 0.66 • thus confirming internal adsorption induced strains as previously reported in Muedi et al 2022 [2].…”

“…The PDFe/Al was synthesized using the method previous described [1,2]. A known AMD volume was reacted with 30% NaOH at a pH = 4.5 to selectively precipitate trivalent Fe and Al as -OOH compounds and the mixture was stirred for 30 min at room temperature with an overhead stirrer.…”

“…Despite the socio-economic benefits provided by the gold and coal industries, the mining of these commodities is notorious for inducing significant environmental degradation [1,2]. Mining entails the excavation of large quantities of rock to obtain the targeted minerals or minerals.…”