Exchange of Adsorbed Pb(II) at the Rutile Surface: Rates and Mechanisms

Abstract

The dynamics of Pb­(II) at mineral surfaces affect its mobility in the environment. Pb­(II) forms inner- and outer-sphere complexes on mineral surfaces, and this adsorbed pool often represents a large portion of the bioaccessible Pb in contaminated soils. To assess the lability of this potentially reactive adsorbed Pb­(II) pool at metal oxide surfaces, we performed Pb­(II) isotope exchange measurements between dissolved Pb­(II) enriched in 207Pb and natural isotopic abundance Pb­(II) adsorbed to rutile at pH 5, 6, and 7. We find that ∼95% of the adsorbed lead is exchangeable. An initially fast exchange (<1 h) is followed by a slower exchange that occurs on a time scale of hours to days. Pb LIII-edge extended X-ray absorption fine structure spectra indicate that similar binding mechanisms are present at all pH values and Pb­(II) loadings, implying that differences in exchange rates across the pH range examined are not attributable to changes in the coordination environment. The slower exchange at pH 5 may be associated with interparticle and intraparticle diffusion resulting from particle aggregation. These findings demonstrate that the dissolved Pb­(II) pool can be rapidly replenished by adsorbed Pb­(II) if this pool is drawn down incrementally by biological uptake or a shift in chemical conditions.

Irreversible Trace Metal Binding to Goethite Controlled by the Ion Size

“…The intrinsic rates of adsorption−desorption reactions are quite rapid, often with characteristic times <1 s. 33−36 Rates of adsorption−desorption observed in most macroscopic studies are mass transfer limited and thus slower. 17,19,32 Prior work demonstrates that isotopic exchange between adsorbed and dissolved pools occurs in 1−5 days because of such limitations. 32 The aim of this study is to identify how aging influences labile fractions and rates of trace metal adsorption−desorption at the goethite surface.…”

“…17,19,32 Prior work demonstrates that isotopic exchange between adsorbed and dissolved pools occurs in 1−5 days because of such limitations. 32 The aim of this study is to identify how aging influences labile fractions and rates of trace metal adsorption−desorption at the goethite surface. Three divalent metal cations (Ni(II), Zn(II), and Cd(II)) were selected to represent a range of ionic radii: 0.69, 0.74, and 0.95 Å, respectively, compared to 0.645 Å for Fe(III).…”

Efficient Removal of Pb2+ from Water by Bamboo-Derived Thin-Walled Hollow Ellipsoidal Carbon-Based Adsorbent

“…Lead ion (Pb 2+ ) is one of the most toxic and frequently exposed heavy metals in the environment. − It can disturb the distribution and contents of trace metal elements (e.g., Fe and Zn) in the human body and destroy the enzyme system of the human body, thus causing diseases like autonomic nerve dysfunction, anemia, nausea, and dizziness. Furthermore, Pb 2+ are easily bound by albumin protein, thus leading to detrimental effects in the body .…”

“…In addition to the direct harm to the human body, Pb 2+ also pollutes the water, destroys the growth of aquatic animals and plants, shows strong accumulation in the soil, penetrates into the root systems of plants, affects the growth and development of plants, and reduces plant chlorophyll, thus hindering plant photosynthesis which in turn affects the entire ecosystem . Therefore, efficiently removing Pb 2+ from water has become a hot topic in sustainable chemistry and engineering. − …”

“…Many water treatment technologies have been developed for removing heavy metals from water, including solvent extraction, chemical precipitation, ion exchange, electrochemical treatment, coagulation-flocculation, membrane filtration, and adsorption. − Among these technologies, adsorption is particularly attractive, as it is low cost, easy to control, and highly efficient in removing various heavy metals including Pb 2+ from water. − Carbon-based materials, e.g., carbon nanotubes and carbon fibers, have been widely used as adsorbents for removing heavy metals from water. − For example, Ma et al found that the adsorption of Pb 2+ on carbon nanotubes reached equilibrium within 30 min, and the adsorption capacity of carbon nanotubes for Pb 2+ was 73.4 mg g –1 . They proposed that the adsorption kinetics of Pb 2+ on carbon nanotubes was well fitted into the pseudo-second-order model .…”