Waste glass as a source for green synthesis of mesoporous adsorbent for efficient removal of heavy metals

Abstract

Mesoporous analcime Adsorbent (MaA) was cogently synthesized in a hydrothermal reaction where a waste silica glass powder was mixed into NaOH solution. The satisfactory reaction properties were achieved by regulating the conditioning time (Ct), reaction temperature (Rt), and relative ratio of the reactants (Rr = SiO₂:Na₂O). XRF, XRD, SEM, BET, FTIR, AFM, TG and TEM analysis formed part of the selected samples. The prepared MaA adsorbent was then applied to treat Pb²⁺, Cd²⁺ and Cu²⁺ ions, thus effectively allowing the physicochemical properties (pH, temperature and contact duration), on the adsorption amount to be examined. Upon completion, the results indicated that the initial pH as well as the contact duration had notable effect on the adsorption amount. Conversely, the temperature change had an insignificant effect on the equilibrium adsorption amount. In addition, a dosage of 0.1 g of MaA, concentration of 1000 mg/L, pH ranging from 6 to 8, and temperature of about 25 °C were found to be the optimum process conditions for the adsorption of the examined heavy metals, whereas difference in contact time was recorded as follows: 1 h for Pb²⁺ and Cu²⁺ ions with adsorption amounts of 75.081 mg/g and 74.054 mg/g, respectively; and 3 h for Cd²⁺ ion with adsorption equal to 75.530 mg/g. In the analysis of the trend, the coefficients of correlation (R² = 0.99) of the Langmuir isotherm model were increasingly consistent compared to Freundlich isotherm model (R² from 0.10 to 0.55), thus indicating that the process to be a homogeneous monomolecular layer adsorption. Moreover, the kinetic aspects were similarly consistent in relation to quasi-secondary kinetic equation, which then further established that the process was primarily controlled by ion exchange, extra-particle, intra-particle, and liquid film diffusion. In addition, research on the potential reusability of MaA adsorbent after being employed to treat heavy metals was also performed. The crystalline phase of the composite after subjected to high temperature indicated wollastonite (CaSiO₃) and gregoryite (Na₂CO₃) as the main mineralogical phases. These minerals are beneficial in the preparation of functional building materials by promoting a sustainable solution for the full recycling of waste glass and contributing to efficient solid waste management and environment protection.