Electrochemical Recognition of Selective Mercury Adsorption on Minerals

Abstract

Mercury species are highly toxic contaminants of the environment, and their dissemination in aquatic media is governed by sorption processes on both organic (including biological) and inorganic particles. An electrochemical method is provided for the direct monitoring of the selective binding of inorganic mercury(II) to the surface hydroxyl groups of some minerals (silica, goethite, pyrite) by using carbon paste electrodes modified by these mineral particles. After accumulation from aqueous solutions at open circuit, anodic stripping voltammetry was performed with the electrode immersed in a detection cell containing typically 0.2 M HNO 3 in order to desorb and measure the amount of previously adsorbed mercury. Several experimental parameters were optimized with a silica-modified electrode to ensure quantitative and reproducible results, including the electrode composition, the accumulation time, and the voltammetric detection mode. Mercury adsorption was studied as a function of pH and chloride concentration. It was found that only the soluble mercury-(II) species with hydroxyl moieties (HgOH + , Hg(OH) 2 , HgOHCl) were able to adsorb on these minerals by reacting with their surface hydroxyl groups. Moreover, in a rather low pH region (4-7), this reaction was extremely selective for mercury over other soluble metal species. The electrochemical monitoring, though mainly controlled by kinetics, gave significant insight in the adsorption processes as far as equilibrium states were rapidly reached.

RETRACTED: Amazon silicates modified by organofunctionalization for use in removing Hg(II) from aqueous medium: A thermodynamic approach

“…The metallic ion could be suffering hydrolysis, starting at pH higher that 5.0, forming Hg(OH) + species, which promotes a diminution of the adsorption capacity, because the diminution of the formal charge of the metallic ion. Besides that, at pH around 8.0, a slight decomposition of the adsorbents could takes place [18][19][20][21][22]. The following equations for metal ions as a function of pH have been expected (Eqs.…”

“…The solid adsorption capacities for the metal halide by the modified smectite and zeolite samples depend on the nature of the complex formed on the structure of silicates and also on the affinity of the mercury cation for the particular attached ligand [19] and on the number of reactive groups anchored in the silicate structures. The maximum adsorption capacity, N max f , for mercury halide on modified silicates is listed in Table 1.…”

Organic/inorganic hybrid nanospheres based on hyperbranched poly(ethylene imine) encapsulated into silica for the sorption of toxic metal ions and polycyclic aromatic hydrocarbons from water

“…Silica by itself has been extensively studied as heavy metal ion sorbent from water [32,33]. The sorption has been described as a process governed by the electrostatic attractions between the positively charged metal ions and the negatively charged silica.…”

Electroanalysis with Pure, Chemically Modified and Sol-Gel-Derived Silica-Based Materials

“…In ammoniacal medium, silanol groups are deprotonated to give the corresponding silanolates that are able to form ion pairs with positively charged metal complexes as CuNH 3 2 4 or HgNH 3 2 4 [97,145], while the nonionized silica surface was found to adsorb Hg II species from diluted solutions if they were in the form of HgOH , HgOHCl, or Hg(OH) 2 [146]. In ammoniacal medium, silanol groups are deprotonated to give the corresponding silanolates that are able to form ion pairs with positively charged metal complexes as CuNH 3 2 4 or HgNH 3 2 4 [97,145], while the nonionized silica surface was found to adsorb Hg II species from diluted solutions if they were in the form of HgOH , HgOHCl, or Hg(OH) 2 [146].…”