Adsorption of aqueous Pb(II), Cu(II), Zn(II) ions by amorphous tin(VI) hydrogen phosphate: an excellent inorganic adsorbent

Abstract

Amorphous tin(VI) hydrogen phosphate (ATHP) was synthesized using the liquid phase precipitation method and served as an adsorbent to remove Pb(II), Cu(II), and Zn(II) from aqueous solutions. The ATHP was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption-desorption techniques. Adsorption properties were evaluated as a function of pH, reaction time, concentration of reactants, and salinity. Their equilibrium adsorption data were modeled using Freundlich, Langmuir, and Dubinin-Kaganer-Radushkevich isotherms, respectively. The results revealed that adsorption equilibrium reached within 180 min. ATHP indicated good adsorption even below the pH ZPC , and best adsorption at pH 5 for Pb(II) and Cu(II) and at pH 5.5 for Zn(II) was observed. Equilibrium data fitted better to the Langmuir model for Pb(II) and Cu(II) and fitted better to the Freundlich model for Zn(II). The saturated adsorption capacities deduced from the Langmuir model were 2.425, 1.801, and 0.600 mmol/ g for Cu(II), Pb(II), and Zn(II), respectively, indicating an adsorption affinity order of Cu [ Pb [ Zn. There is a negative correlation between the concentration of NaCl and adsorption capacity of ATHP, yet ATHP still exhibited excellent adsorption having an adsorption capacity of 19.35, 15.16, 6.425 mg/g when the concentration of NaCl was 0.6 mol/L. The free energy (E) was 12.33, 10.70, and 14.74 kJ/mol for Pb(II), Cu(II), and Zn(II), respectively. An adsorption mechanism based on ion exchange between heavy metal ions and H ? in the ATHP is proposed. Furthermore, the used ATHP was regenerated by HCl solution and the adsorbent was used repeatedly.

A Way to Close the Loop: Physicochemical and Adsorbing Properties of Soybean Hulls Recovered After Soybean Peroxidase Extraction

“…Indeed, the hulls behavior toward aluminum resulted very peculiar: Al(III) has the lowest ionic radius (then, less steric hindrance) and a strong positive charge (3+), but it was not sequestrated by SBH-B and 1 h was not a sufficient contact time to allow an efficient adsorption. This occurrence can be justified by taking into account the solvation degree: smaller ions with high density charge are more solvated and less rapidly attracted by the adsorbent surface (Zhu et al, 2016 ). In general, a complex frame of factors connected to the adsorbate nature influences the adsorption effectiveness, as valence, electronegativity, hydration radii, hydration enthalpies, solubility of the cations (Zhu et al, 2016 ) and hard—soft, acid–bases affinity [according to Pearson's principle (Alfarra et al, 2004 )].…”

“…This occurrence can be justified by taking into account the solvation degree: smaller ions with high density charge are more solvated and less rapidly attracted by the adsorbent surface (Zhu et al, 2016 ). In general, a complex frame of factors connected to the adsorbate nature influences the adsorption effectiveness, as valence, electronegativity, hydration radii, hydration enthalpies, solubility of the cations (Zhu et al, 2016 ) and hard—soft, acid–bases affinity [according to Pearson's principle (Alfarra et al, 2004 )]. Moreover, it is worth to underline that the modifications induced by SBP extraction, including a lowering of the surface's negative charge, did not compromise the adsorptive properties of hulls, but rather improved them in some cases.…”

Removal of Cd(II) and Cu(II) from Aqueous Solution by Na+-Modified Pisha Sandstone

“…Na +modified PS effectively increased the Cd(II) and Cu(II) sorption amounts (12.81 and 21.37 mg•g − 1 , respectively). e selective adsorption of the PS adsorbents to Cd(II) or Cu(II) was dependent on the electronegativity and the hydrated ionic radius [46]; higher electronegativity and hydrated ionic radius exhibited better metal uptake [47,48]. In addition, compared with other adsorbents such as kaolinite and bentonite (6.8 and 10.8 mg•g − 1 for Cu(II) and 4.4 and 11 mg•g − 1 for Cd(II), respectively) [24,25,41,49], the PSs showed superior adsorption capacity to Cd(II) and Cu(II), which further confirmed their attractive potential for applications in adsorption of heavy metals.…”

The Simultaneous Removal of Zinc and Cadmium from Multicomponent Aqueous Solutions by Their Sorption onto Selected Natural and Synthetic Zeolites

“…As a result, it may be expected to have competition for the sorption sites. However, those two elements differ in other properties considered crucial for sorption onto zeolites, namely [37,62,63] (2) Hydrolysis constant, for Zn 2+ K a = 9.0 and for Cd 2+ pK a = 10.1;…”