Adsorption of Ni²⁺ from aqueous solution by functionalized coal particles with dithiocarbamate

Shenfu coal particles with a mean diameter of 71.55 μm were modified to contain functional surface groups by chemically grafting dithiocarbamate (DTC) onto the coal particles using γ-aminopropyltriethoxysilane as a coupler. The properties of Ni²⁺ adsorption using the functionalized coal particles were studied using batch experiments and compared with adsorption using the original coal particles. The mechanisms of coal particle modification and adsorption are discussed. Results show that the process of Ni²⁺ adsorption onto the functionalized coal particles follows pseudo-second-order kinetics. The adsorption isotherm of Ni²⁺ on functionalized coal particles can be described by the Langmuir model. The amount of saturated monomolecular layer adsorption (Q⁰) onto the functionalized coal particles for Ni²⁺ was found to be 82.37 mg/g, which is much higher than that found for the original coal particles. The related thermodynamic parameters, ΔH and ΔG of Ni²⁺ adsorption onto functionalized coal particles were negative, indicating that the process is exothermic and spontaneous. The Fourier transform infrared spectroscopy (FTIR) spectrum analysis illustrated that the DTC grafted onto the surface of the coal particles and successfully reacted with Ni²⁺ from the aqueous solution. The specific surface area analysis showed that the specific surface area of functionalized coal particles was 7.9126 mg/g, which was much higher than that of original coal particles (2.0618 mg/g). The scanning electron microscopy (SEM) analysis showed that the surfaces of functionalized coal particles were rougher than original coal particles. The paper concludes that functionalized coal with chelating groups is an efficient way to improve the adsorption capacity of coal used for removing heavy metal ions from aqueous solutions.