Abstract
Heavy metals have caused serious environmental issues, which are enriched during open-cast coal mining. It is urgent to develop sustainable remediation materials to protect and restore the contaminated soil and aquifers in mining areas. The feasibility of applying Pisha sandstone (PS) and Na+-modified Pisha sandstone (Na-PS) for adsorption of heavy metals was evaluated. Na-PS exhibited maximum Cd(II) and Cu(II) removal rates of 65.9% and 99.8%, respectively, exceeding the corresponding values for PS (8.2% and 1.3%, respectively) in 1 × 10−3 M solution. Efficient heavy metals adsorption occurred in the pH range 5.0–6.0. The adsorption of Cu(II) and Cd(II) on PS and Na-PS was characterized by kinetic models and adsorption isotherms and was well represented by pseudo-second-order kinetics (R2 > 0.99) and the Langmuir and Freundlich isotherm models. The values of the thermodynamic parameters indicated that the interactions were spontaneous endothermic reactions. Binary solutions adsorption isotherms indicated that the linearity of the adsorption amount and initial concentration of Cu(II) and Cd(II) was better in certain ranges and the adsorbents were selective towards Cu(II) rather than Cd(II). Therefore, PSs can be used as excellent adsorbents for Cu(II) and Cd(II) remediation from contaminated surface water.
Highlights
Heavy metal contamination in open-cast coal mining areas has attracted great attention due to the serious effect of heavy metal toxicity and water acidification on plants and soil
All chemicals used in this work were of analytical reagent grade and were utilized without further purification. e chemical composition and morphology of Pisha sandstone (PS) and Na+-modified Pisha sandstone (Na-PS) were characterized by X-ray diffraction (XRD) using Cu Kα radiation (D8 Advance A25, Bruker, Germany) and field emission scanning electron microscopy (FESEM) (S-4800, Hitachi, Japan)
Characterization of PS and Na-PS. e surface morphology and elemental content of PS and Na-PS were determined as shown in Figure 1. e SEM images of the PSs clearly showed that some sheet-like substances existed on the surface of both clays.; Previous studies indicated that these substances are montmorillonite [26]. e XRD patterns indicated the mineral phases, which mainly include quartz, calcite, feldspar, and montmorillonite, as shown in Figure 1(c). e high crystallinity of quartz means that the PSs have high chemical stability
Summary
Heavy metal contamination in open-cast coal mining areas has attracted great attention due to the serious effect of heavy metal toxicity and water acidification on plants and soil. Heavy metals could be removed in several ways including biosorption, chemical precipitation, electrolysis, adsorption, ultrafiltration, reverse osmosis, and ion exchange from aqueous solutions [4,5,6,7]. Among these methods, adsorption has been considered a promising method because this technique is generally easy to operate and cost-effective for the immobilization of heavy metals even at low concentrations [8]. Padrovaet al. [12] found that the industrial synthetic adsorbents (e.g., Nanofer 25 and Nanofer 25S) are toxic to the soil microorganisms. erefore, natural adsorbents, naturally formed or derived from natural materials with insignificant risks to the environment, have attracted the attention of researchers again due to their
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