Applicability of granite and quartzite residues in the development of porous adsorbents for effective organic pollutant removal

Abstract In this work, granite and quartzite residues were converted into amorphous materials through an alkaline fusion process employing KOH as the activating agent. Structural characterization confirmed the significant loss of crystallinity in both precursors, while textural analysis indicated a marked improvement in the pore structure, particularly in the quartzite-derived material. Among the synthesized adsorbents, the amorphized quartzite (AQZ) demonstrated superior adsorption performance compared to the amorphized granite (AGR). The adsorption of crystal violet (CV) onto AQZ was optimized using experimental design, with pH 9 and an adsorbent dosage of 0.9 g L⁻ 1 identified as the most favorable conditions. Kinetic studies showed that the system reached equilibrium within 90 min. Isotherm evaluation revealed a maximum adsorption capacity of 86.24 mg g⁻ 1 at 298 K, confirming the high efficiency of AQZ. Thermodynamic parameters indicated that the adsorption process is spontaneous, exothermic, and thermodynamically favorable, with electrostatic attraction identified as the predominant interaction mechanism. AQZ retained satisfactory adsorption efficiency after four consecutive regeneration cycles. These findings demonstrate that alkaline fusion is a viable strategy for transforming ornamental stone residues into a reusable adsorbent for treating CV-contaminated wastewater.