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 °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 AsO43- concentration compared to untreated samples. Through chemical adsorption, S600 demonstrated superior adsorption capability for AsO2-/AsO43-/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 cadmium- arsenic contaminants through eco-friendly activation.