Low-cost preparation of ethylene glycol-modified micro-nano porous calcium carbonate with excellent removal of Cadmium in wastewater

Abstract

Contamination, migration, and bioaccumulation of cadmium ion [Cd(II)] in aquatic environments seriously threaten human health and ecological systems. Although eliminating Cd(II) via an adsorption process is a promising strategy, developing cost-effective, efficient, and eco-friendly adsorbents, particularly those enabling safe cadmium disposal, remains a huge challenge. In this work, a novel adsorbent, ethylene glycol - modified micro-nano porous calcium carbonate (EG-NCaC), is fabricated from natural limestone via a mechanical activation-calcination-precipitation process. Compared to the traditional NCaC, both grain sizes and aggregation of the EG-NCaC (50–150 nm) can be reduced. When EG-NCaC with 1.0 g L⁻¹ is applied for simulated wastewater treatment (concentration: 50 mg L⁻¹ pH: 6.0), the removal efficiency of Cd(II) reached 98.90 % after 60 min adsorption. Adsorption isotherm matched well with the Langmuir model, with the maximum theoretical Cd(II) adsorption capacity (q_m) of 75.20 mg g⁻¹ at 298 K. Kinetic studies are fitted well with pseudo-first-order and pseudo-second-order models. The Elovich model proves that Cd(II) can be adsorbed rapidly by the EG-NCaC in the initial adsorption and strong Cd(II) binding. Intra-particle diffusion analysis suggested that the adsorbed Cd(II) can be transported to the inner EG-NCaC via pore diffusion until equilibrium. However, coexisting ions and organic impurity significantly affected adsorption efficiency. Furthermore, conventional acid-base post-treatment processes were inappropriate for the recycle application of the EG-NCaC, whereas the Cd(II)-saturated adsorbent can be utilized as ceramic additives. This study provides valuable theoretical and technical insights for the effective removal of Cd(II) from aquatic environments and the safe disposal of cadmium.