scholarly journals Investigations of mechanism of Ca2+ adsorption on silica and alumina based on Ca-ISE monitoring, potentiometric titration, electrokinetic measurements and surface complexation modeling

Adsorption ◽  
2020 ◽  
Author(s):  
Karolina Szymanek ◽  
Robert Charmas ◽  
Wojciech Piasecki
Keyword(s):  
Electrostatic Interactions ◽  
Surface Species ◽  
Mineral Surface ◽  
Surface Complexation Modeling ◽  
Surface Complexes ◽  
Mononuclear Complexes ◽  
Alkaline Earths ◽  
Calcium Complexes ◽  
Tetranuclear Complexes ◽  
Proton Surface Charge

Abstract Research on Ca2+ adsorption onto the mineral surface is of significant importance with regard to geochemical processes. Sverjensky (Geochim Cosmochim Acta 70(10), 2427–2453, 2006) assumed that alkaline earths form two types of surface species on oxides: tetranuclear (> SOH)2(> SO−)2_M(OH)+ and mononuclear > SO−_M(OH)+. To look into the above assumption we investigated calcium adsorption on SiO2 and Al2O3 because they are the most widespread minerals in the environment. We have determined the proton surface charge, electrokinetic potential and metal adsorption as a function of pH. The Ca2+ uptake and concentration in the system were monitored by the calcium ion-selective electrode (Ca-ISE). The Ca-ISE measurements indicated a similar affinity of Ca2+ for both materials despite their differently charged surface, negative for silica and mainly positive for alumina. This may suggest that simple electrostatic interactions are not the primary driving force for calcium adsorption, and that solvation of calcium ions at the surface may be crucial. We have analyzed our experimental data using the 2-pK triple-layer model (2-pK TLM). Three calcium complexes on the mineral surface were reported. Two of them were the same for both oxides, i.e. the tetranuclear ($$>$$ >  SOH)2($$>$$ >  SO−)2_Ca2+ and mononuclear complexes > SO−_CaOH+. Additionally, minor contribution from >SOH…Ca2+ for silica was assumed. In the case of Al2O3 the hydrolyzed tetranuclear complexes ($$>$$ >  SOH)2($$>$$ >  SO−)2_CaOH+ at pH > 7.5 occurred based on the modeling results. Two types of surface complexes suggested by Sverjensky allowed for the correct description of proton and calcium uptake for alumina. However, the electrokinetic data excluded hydrolyzed tetranuclear surface species for this oxide.

scholarly journals Antimony (V) Adsorption at the Hematite–Water Interface: A Macroscopic and In Situ ATR-FTIR Study

Soil Systems ◽  
2021 ◽  
Vol 5 (1) ◽  
pp. 20
Author(s):  
Jerzy Mierzwa ◽  
Rose Mumbi ◽  
Avedananda Ray ◽  
Sudipta Rakshit ◽  
Michael E. Essington ◽  
...  
Keyword(s):  
Iron Oxide ◽  
Adsorption Mechanism ◽  
Surface Complexation ◽  
Outer Sphere ◽  
Surface Complexation Modeling ◽  
Surface Complexes ◽  
Ph Values ◽  
Oxide Minerals ◽  
Complexation Mechanism

The environmental mobility of antimony (Sb) is largely unexplored in geochemical environments. Iron oxide minerals are considered major sinks for Sb. Among the different oxidation states of Sb, (+) V is found more commonly in a wide redox range. Despite many adsorption studies of Sb (V) with various iron oxide minerals, detailed research on the adsorption mechanism of Sb (V) on hematite using macroscopic, spectroscopic, and surface complexation modeling is rare. Thus, the main objective of our study is to evaluate the surface complexation mechanism of Sb (V) on hematite under a range of solution properties using macroscopic, in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopic, and surface complexation modeling. The results indicate that the Sb (V) adsorption on hematite was highest at pH 4–6. After pH 6, the adsorption decreased sharply and became negligible above pH 9. The effect of ionic strength was negligible from pH 4 to 6. The spectroscopic results confirmed the presence of inner- and outer-sphere surface complexes at lower pH values, and only outer-sphere-type surface complex at pH 8. Surface complexation models successfully predicted the Sb (V) adsorption envelope. Our research will improve the understanding of Sb (V) mobility in iron-oxide-rich environments.

Removal of caffeine by oxidized biochar

2020 ◽  
Author(s):  
Ioannis Anastopoulos ◽  
Ioannis Pashalidis ◽  
Artis Robalds
Keyword(s):  
Contact Time ◽  
Electrostatic Interactions ◽  
Plant Biomass ◽  
Freundlich Isotherm ◽  
Outer Sphere ◽  
Initial Step ◽  
Order Kinetic ◽  
Surface Complexes ◽  
Order Kinetic Model ◽  
Repulsive Forces

<p>Oxidized biochar from plant biomass (OBPM) was used to remove caffeine (CF) from aqueous solutions. Among examined parameters that affect adsorption, pH was found to play the most important role. By increasing the initial pH from 2 to 4, the adsorption capacity of CF was increased, whereas for pH above 4, a decline of the adsorption efficiency was noticed. The effect of contact time was also investigated in the range of 1 – 150 minutes and results indicated that the adsorption process consists of two steps. The initial step was relatively fast most probably, because a large number of adsorption surface sites was available, and with proceeding contact time the adsorption rate declined. The latter could be attributed to the decreasing number of vacant sites and to the development of repulsive forces between the free CF molecules and the occupied OBPM surface. The experimental data were best fitted by the pseudo-second order kinetic, compared to pseudo-first order kinetic model and the Freundlich isotherm model better fitted the data. The raise of temperature from 25 to 50 °C affected negatively the CF removal, indicating the exothermicity of the adsorption. Finally, FTIR spectroscopic data and investigations on the effect of ionic strength indicated that the adsorption mechanism is mainly based on electrostatic interactions and the formation of outer sphere surface complexes.</p><p><strong> </strong></p>

QUANTUM CHEMISTRY STUDIES ON THE Fe-Hg INTERACTIONS AND 31P NMR IN [Fe(CO)3(RPhPpy)2 (HgCl2)] (R = Me, Et, Ph)

2011 ◽  
Vol 10 (01) ◽  
pp. 53-63
Author(s):  
XUAN XU ◽  
QIN-YU LI ◽  
LIANG FANG ◽  
ZHONG-MIN SU
Keyword(s):  
Charge Transfer ◽  
Electron Density ◽  
Electrostatic Interactions ◽  
Density Functional ◽  
Chemical Shifts ◽  
Binuclear Complexes ◽  
Functional Theory ◽  
Nmr Chemical Shifts ◽  
Orbital Interactions ◽  
Mononuclear Complexes

In order to study the effects of R group on Fe-Hg interactions and 31P NMR, the structures of mononuclear complexes [Fe(CO)3(RPhPpy)2] (1: R = Me; 2: R = Et; 3: R = Ph) and binuclear complexes [Fe(CO)3(RPhPpy)2(HgCl2)] (4: R = Me; 6: R = Et; 6: R = Ph) were calculated by density functional theory (DFT) PBE0 method. Moreover, the 31P NMR chemical shifts were calculated by PBE0-GIAO method. The replacement of Ph group in Ph2Ppy ligands with Me or Et group results in higher stabilities and stronger Fe-Hg interactions. The stabilities of binuclear complexes follow the order of 5 > 4 >6. Although the electrostatic interactions in 5 are weaker, the weaker repulsion interactions and stronger orbital interactions lead to the highest stability. The strength of Fe → Hg interactions, which mainly attribute to σFe-P → nHg and σFe-C → nHg charge-transfer interactions, follows the order of 5 > 4 > 6. The 31P NMR chemical shifts in mononuclear complexes 1 ~ 3 or binuclear complexes 4 ~ 6 increase with the increase of electron-withdrawing effect of R group following the order of Me < Et < Ph. Due to Fe → Hg interactions, the charge-transfer from R groups towards the P , Fe and Hg atoms increases the electron density on P nucleus in binuclear complexes. Besides, the stronger σFe-C → nP charge-transfer in binuclear complexes can also increase the electron density of P nucleus. As a result, compared with corresponding mononuclear complexes, the 31P chemical shifts in binuclear complexes show some reduction.

Scanning Electron Microscope Study of Bacteria on Mineral Surfaces

1976 ◽  
Vol 34 ◽  
pp. 130-131
Author(s):  
V.K. Berry
Keyword(s):  
Oxidation Reaction ◽  
Electron Microscope Study ◽  
Elemental Sulfur ◽  
Thiobacillus Ferrooxidans ◽  
Physical Contact ◽  
Metal Sulfides ◽  
Low Grade ◽  
Mineral Surfaces ◽  
Mineral Surface ◽  
Scanning Electron Microscope Study

There are two strains of bacteria viz. Thiobacillus thiooxidansand Thiobacillus ferrooxidanswidely mentioned to play an important role in the leaching process of low-grade ores. Another strain used in this study is a thermophile and is designated Caldariella .These microorganisms are acidophilic chemosynthetic aerobic autotrophs and are capable of oxidizing many metal sulfides and elemental sulfur to sulfates and Fe2+ to Fe3+. The necessity of physical contact or attachment by bacteria to mineral surfaces during oxidation reaction has not been fairly established so far. Temple and Koehler reported that during oxidation of marcasite T. thiooxidanswere found concentrated on mineral surface. Schaeffer, et al. demonstrated that physical contact or attachment is essential for oxidation of sulfur.

Immunogold and immunoblot studies on a cell surface protein found in primary mesenchyme cells and in the cortical secretory vesicles of the sea urchin egg

1987 ◽  
Vol 45 ◽  
pp. 832-833
Author(s):  
G.L. Decker ◽  
M.C. Valdizan
Keyword(s):  
Cell Surface ◽  
Sea Urchin ◽  
Surface Protein ◽  
Egg Cell ◽  
Secretory Vesicles ◽  
Cell Surface Protein ◽  
Surface Complexes ◽  
Mesenchyme Cells ◽  
Lowicryl K4m ◽  
Primary Mesenchyme Cells

A monoclonal antibody designated MAb 1223 has been used to show that primary mesenchyme cells of the sea urchin embryo express a 130-kDa cell surface protein that may be directly involved in Ca2+ uptake required for growth of skeletal spicules. Other studies from this laboratory have shown that the 1223 antigen, although in relatively low abundance, is also expressed on the cell surfaces of unfertilized eggs and on the majority of blastomeres formed prior to differentiation of the primary mesenchyme cells.We have studied the distribution of 1223 antigen in S. purpuratus eggs and embryos and in isolated egg cell surface complexes that contain the cortical secretory vesicles. Specimens were fixed in 1.0% paraformaldehyde and 1.0% glutaraldehyde and embedded in Lowicryl K4M as previously reported. Colloidal gold (8nm diameter) was prepared by the method of Mulpfordt.

Template mediated crystal engineering

1994 ◽  
Vol 52 ◽  
pp. 480-481
Author(s):  
Brigid R. Heywood ◽  
S. Champ
Keyword(s):  
Crystal Engineering ◽  
Electrostatic Interactions ◽  
Alkyl Chain ◽  
Crystallographic Axis ◽  
Two Dimensional ◽  
Engineering Process ◽  
Solution Interface ◽  
Extensive Program ◽  
Geometric Homology ◽  
Long Alkyl Chain

Recent work on the crystallisation of inorganic crystals under compressed monomolecular surfactant films has shown that two dimensional templates can be used to promote the oriented nucleation of solids. When a suitable long alkyl chain surfactant is cast on the crystallisation media a monodispersied population of crystals forms exclusively at the monolayer/solution interface. Each crystal is aligned with a specific crystallographic axis perpendicular to the plane of the monolayer suggesting that nucleation is facilitated by recognition events between the nascent inorganic solid and the organic template.For example, monolayers of the long alkyl chain surfactant, stearic acid will promote the oriented nucleation of the calcium carbonate polymorph, calcite, on the (100) face, whereas compressed monolayers of n-eicosyl sulphate will induce calcite nucleation on the (001) face, (Figure 1 & 2). An extensive program of research has confirmed the general principle that molecular recognition events at the interface (including electrostatic interactions, geometric homology, stereochemical complementarity) can be used to promote the crystal engineering process.

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