Efficient conversion of granite powder: synthesis of zeolite A for Cu(II) adsorption from acidic electropainting wastewater

Abstract

As a silicon‑aluminum-rich solid waste, granite powder (GP) requires expanded utilization methods to mitigate the environmental impact caused by its storage. Given its compositional similarity to zeolites, non-adsorptive GP can be converted into highly active materials with strong adsorption capacity for heavy metal removal from wastewater. Building upon this potential, this study innovatively employed an alkali-hydrothermal synergistic method to convert GP into zeolite A (GPA) for Cu(II) adsorption in acidic electroplating wastewater. GPA was synthesized by mixing sodium hydroxide and sodium aluminate with GP, followed by calcination and hydrothermal crystallization. The optimal preparation parameters were identified: an alkali-to-GP mass ratio of 0.4, a Si/Al ratio of 1.12, a calcination temperature of 700 °C, and a crystallization time of 4 h. Response surface analysis revealed that the alkali-to-GP mass ratio had the most significant impact on adsorption performance. The results of batch experiments showed that the removal rate of GPA for 100 mg/L Cu(II) solution is 98.79 % at pH 3 and 25 °C. The theoretical maximum adsorption capacity was 134.6 mg/g. The removal mechanism was confirmed by adsorption kinetics and isotherm modeling, and the elimination of Cu(II) by GPA was a synergistic processing effect, which mainly relied on ion exchange (with Na⁺ and H⁺ as the main active sites) and hydroxyl complexation. GPA exhibited significant potential for treating acidic copper-containing electroplating wastewater, providing an efficient and sustainable approach for GP valorization in environmental applications.