Functionalized Silica Fume for Efficient Cd2+ Removal from Aqueous Solutions

The rapid development of the silicon industry has led to the massive production of silica fume (SF), while its improper disposal poses environmental risks and represents a waste of resources. Unlike conventional methods that require dissolution and high-pressure treatment, this study pioneers a low-cost direct-functionalization strategy that preserves the inherent microsphere structure of SF, using calcination for carbon removal and activation for surface hydroxylation. The activated SF was synthesized into TACA-APTES-SF by reacting with 3-aminopropylethoxysilane (APTES) and 1,3-Thiazole-2-carbaldehyde (TACA). SEM, FT-IR, and XPS were used to characterize these samples, revealing amino groups and sulfur groups grafted onto the SF surface successfully. The adsorbent demonstrated highly effective adsorption of Cd²⁺ ions. Throughout five reuse cycles, TACA-APTES-SF maintained a high removal efficiency for Cd²⁺ in aqueous solution. The adsorption kinetics confirmed to the pseudo-second-order model, while the adsorption isotherm results aligned with the Langmuir model, which collectively suggests that the adsorption process was chemical and monolayer in nature. Comparative XPS and FT-IR analyses of TACA-APTES-SF and TACA-APTES-SF-Cd indicated that adsorption mechanisms involved electrostatic and coordination reactions between hydroxyl-, amino-, and sulfur-containing groups and Cd²⁺ ions. This study therefore proposes a straightforward and cost-effective approach for the high-value utilization of SF.