Adsorption of Co²⁺ and Cr³⁺ in Industrial Wastewater by Magnesium Silicate Nanomaterials

In this paper, two flower-like magnesium silicate nanomaterials were prepared. These and another two commercial magnesium silicate materials were characterized using a scanning electron microscope, the N₂ adsorption–desorption method, and other methods. The structure–activity relationship between the adsorption performance of these four magnesium silicate materials and their specific surface area, pore size distribution, and pore structure was compared. The results showed that the 3-FMS modified by sodium dodecyl sulfonate (SDS) had the largest specific surface area and pore size, the best adsorption performance, and the largest experimental equilibrium adsorption capacity (q_e,exp) for Co²⁺, reaching 190.01 mg/g, and Cr³⁺, reaching 208.89 mg/g. The adsorption behavior of the four materials for Co²⁺ and Cr³⁺ both fitted the pseudo-second-order kinetic model and Langmuir adsorption model, indicating that chemical monolayer uniform adsorption was the dominant adsorption process. Among them, the theoretical adsorption capacity (q_m) of 3-FMS was the highest, reaching 207.62 mg/g for Co²⁺ and 230.85 mg/g for Cr³⁺. Through further research, it was found that the four materials mainly removed Co²⁺ and Cr³⁺ through electrostatic adsorption, surface metal ions (Mg²⁺), and acidic groups (-OH and -SO₃H) exchanging with ions in solution. The adsorption performance of two self-made flower-like magnesium silicate materials for Co²⁺ and Cr³⁺ was superior to that of two commercial magnesium silicates.