Activated calcium-rich serpentine tailings and their superefficient removal for arsenite, arsenate and cadmium

In heavy metal treatment, cost-effective serpentine tailings as adsorbents were in accordance with the objectives of low-carbon development. But both untreated and calcined serpentine showed limited adsorption capacity for arsenic (As) and cadmium (Cd) ions. Here, naturally calcium-rich serpentine tailings associated with dolomite were chosen. Chemical-free thermal activation resulted in the expansion of specific surface area and activation of Si-OH, Mg-OH and CaCO3. Thermal conversion analyses and comparative experimental results identified S600 (the sample activated at 600 degrees C) as the optimal product. S600 maintained similar adsorption capacity under wide initial pH and efficiently removed over 98 % trace contaminants in potable water and reservoir water. Incorporating S600 diminished the release of Cd in soil pore water and improved long-term stability. With a surface water depth of 1.5-2 cm, S600-treated samples exhibited a 29.47 % decrease in combined AsO2- and AsO4 3- concentration compared to untreated samples. Through chemical adsorption, S600 demonstrated superior adsorption capability for AsO2- /AsO4 3-/ Cd2+ at 178.37/383.87/855.87 mg/g (determined by Sips model) compared to natural serpentine (0.23/3.77/14.35 mg/g). The surface complexation, partial oxidation-reduction, ion exchange and co-precipitation process were the primary mechanisms of adsorption. This study proposed that serpentine showed potentiality as an adsorbent for the long-term treatment of cadmiumarsenic contaminants through eco-friendly activation.