Complex-forming Ligands Research Articles

Genetic Association between Granites and Mineralization at the Gindi Akwati Cassiterite–Sulfide Deposit, North-Central Nigeria: Insights from Mineralogy, Fluid Inclusions, and Sulfur Isotopes

The cassiterite–sulfide mineralization occurs within quartz veins and greisenized Precambrian Older Granite around the Gindi Akwati region at the Ropp complex’s western boundary, north-central Nigeria. The intrusion of Jurassic Younger granite porphyry sheared the marginal parts of the Older Granite and the mylonitized zone created pathways for fluids that escaped during the late-stage consolidation of Jurassic biotite granite. The biotite granites are highly differentiated (K/Rb < 200), peraluminous (A/CNK > 1), high-K, and have high Sn concentrations (average = 117 ppm). The intrusion of Jurassic granite porphyry forced Older Granite interaction with ore-bearing fluid that escaped from Jurassic biotite granite under low oxygen fugacity at or below the NNO buffer. The above fluid–rock interaction caused mass changes in host granite during greisenization and redistributed ores in the vicinity of the shears. This suggests that chloride ions take the form of significant complex-forming ligands and efficiently sequestrate, transport, and deposit ore metals (Sn, Zn, Fe, and Cu) locally within the greisenized granites and quartz veins. The redox potential of the ores probably gave a false impression of metal zoning with a relatively higher abundance of the oxide ore than the sulfides at the surface. The alteration mineralogy (quartz-, topaz-, lepidolite-, and fluorite-bearing assemblages) coupled with S isotope and fluid inclusion systematic data suggests the hydrothermal history of “greisens” and veins started with hot (homogenization temperature ≥300 °C), low to moderate salinity (average = 4.08 wt. % NaCl), low density (≤0.6 g/cm3) fluids and ≥ 200 bar trapping pressure. The sulfide isotopic composition (δ34SV-CDT = −1.30 to + 0.87 ‰) is very similar to typical magmatic fluids, indicating late-magmatic to early post-magmatic models of mineralization related to the anorogenic granite intrusions.

The effect of citric acid on the catalytic oxidation of Mn(II) on ferrihydrite surface

Surface-catalyzed Mn(II) oxidation is an important process for abiotic formation of various Mn (oxyhydr)oxides in nature. Previous research has shown that some complex-forming ligands (e.g., citric acid, desferrioxamine B, and tartrate) can significantly bind with Mn(II) to promote its homogeneous oxidation by dissolved O2. However, there is little to no understanding of the role played by complex-forming ligands in abiotic interfacial oxidation of Mn(II). In this study, the adsorption and oxidation of Mn(II) on ferrihydrite (Fh) surface at a range of citric acid (CIT) concentrations was investigated using batch kinetic studies combined with X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and wet chemistry analyses. The presence of CIT substantially inhibited the adsorption and oxidation of Mn(II) on Fh, whereas oxidized Mn generated certainly enhanced the degradation of CIT. However, at a high concentration of CIT (> 1 mM), the oxidation kinetics of Mn(II) were slightly accelerated due to ligand-promoted homogeneous oxidation. Moreover, the presence of CIT remarkably altered the distribution and composition of Mn(II) oxidation products by inhibiting the formation of hausmannite on Fh surface and the following auto-catalytic oxidation. At low CIT concentration (< 1 mM), the oxidation products were mostly coated on Fh surface with weaker crystallinity and higher Mn AOS, resulting in stronger reactivity. When CIT concentrations were above 1 mM, Mn(II) oxidation products were mainly distributed in the bulk solution as soluble Mn(III)-CIT/ox complexes, thereby enhancing the mobility of redox active Mn. These results suggested that CIT improved the redox activity of oxidation products and migration of active Mn in the environment although it inhibited Mn(II) oxidation on mineral surfaces.

Rates of Abiotic MnII Oxidation by O2: Influence of Various Multidentate Ligands at High pH

Oxidation of manganous manganese (MnII) is an important process driving manganese cycles in natural aquatic systems and leading to the formation of solid-phase MnIII,IV (hydr)oxide products. Previous research has shown that some simple ligands (e.g., phosphate, sulfate, chloride, fluoride) can bind with MnII to make it unreactive to oxidation by dissolved oxygen. However, there is little to no understanding of the role played by stronger, complex-forming ligands in MnII oxidation reactions. The objective of this study was to evaluate the rates of abiotic MnII oxidation by O2 in the presence of low concentrations of several complex-forming model ligands (pyrophosphate, tripolyphosphate, ethylenediaminetetraacetic acid, oxalate) in bicarbonate-carbonate buffered laboratory solutions of pH 9.42, 9.65, and 10.19. The influence of increasing ligand concentrations on observed autocatalytic profiles of MnII oxidation was investigated, and initial oxidation rates were linked quantitatively to the initial MnII speciation in experimental solutions. Observed rates of MnII oxidation decreased with increasing ligand concentration for all four ligands tested. However, the profiles observed with time and the magnitudes of decrease in initial oxidation rates were different for the different ligands. Likely explanations for these observations include the denticity of the tested ligands, the relative strength of the ligands to complex MnII versus MnIII, and the ability of some ligands to enhance the reduction of MnIII back to MnII on a time scale comparable to the forward homogeneous MnII oxidation reaction.

Carbonate Form of Mg,Al-Layered Double Hydroxides for Concentrating Eu(III) and Its Subsequent Analytical Determination in Natural Aqueous Media

The efficiency of the sorption of Eu(III) by various forms of Mg,Al- and Zn,Al-layered double hydroxides (LDH) from model and natural waters at various pH was estimated for concentrating this metal ions and its subsequent spectrophotometric determination. It was found that the almost complete extraction of Eu(III) is reached on the carbonate form of Mg,Al-LDH by a deposition mechanism because of the formation of poorly soluble compounds of this element (carbonate and hydroxide of Eu(III) at pH ≥ 6.2, which correlates with the calculated Eu(III) speciation in aqueous solution in the presence of carbonate ions. The distribution coefficients of Eu(III) are 1.4 × 106 cm3/g (the pH of the initial solution is ≥7.0; the pH of the solution after the sorption is ≥ 6.87), which is indicative of a high efficiency of this sorbent with respect to this metal ion. For Mg,Al- and Zn,Al-LDH intercalated with organic complex-forming ligands—citrate and ethylenediaminetetraacetate ions, the dominant mechanism Eu(III) extraction from aqueous media is the complex formation. The distribution coefficients of Eu(III) on these sorbents are (0.26—22.71) × 103 cm3/g. For concentrating Eu(III) and its spectrophotometric determination in natural waters, it was proposed to use the carbonate form of Mg,Al-LDH with its subsequent decomposition by a nitric acid solution after the sorption. It was shown that the major components of natural waters and the constituents of this sorption materials do not affect the correctness and accuracy of the determination of Eu(III) by this method with arsenazo III (at pH 2.6 ± 0.1). The linearity range of the calibration graph is 1–50 μg Eu(III) in 50 cm3 of the final solution cm3 (λ = 650 nm). The proposed method of concentrating and determining Eu(III) was tested on samples of model, tap, and surface waters (the sorbent weight is 0.100 g, and the water sample volume is 500 cm3).

Elucidation of Chemical Species and Reactivity at Methylammonium Lead Iodide and Cesium Tin Bromide Perovskite Surfaces via Orthogonal Reaction Chemistry

We quantified the chemical species present at and reactivity of the (100) face of tetrahedral single-crystal methylammonium lead iodide, MAPbI3(100), and polycrystalline cesium tin bromide, CsSnBr3. For these ABX3 perovskites, experiments utilized the orthogonal reactivity of the A+-site cation, the B2+-site cation, and the X–-site halide anion. Ambient pressure exposure to BF3 solutions probed the reactivity of interfacial halides. Reactions with p-trifluoromethylanilinium chloride probed the exchange reactivity of the A+-site cation. A complex-forming ligand, 4,4′-bis(trifluoromethyl)-2,2′-bipyridine, probed for interfacial B2+-site cations. Fluorine features in X-ray photoelectron spectroscopy (XPS) quantified reaction outcomes for each solution-phase species. XPS revealed adsorption of BF3, indicating surface-available halide anions on both MAPbI3(100) and on CsSnBr3. Temperature-programmed desorption quantified a ∼200 kJ mol–1 desorption activation energy from MAPbI3(100) and a ∼215 kJ mol–1 desorpti...

Geochemical characteristics of the Arabshah kaolin deposit, Takab geothermal field, NW Iran

The Arabshah kaolin deposit (Takab geothermal field, NW Iran) is the product of alteration of Miocene dioritic rocks. According to mineralogical data, the rock-forming minerals in this deposit include kaolinite, quartz, muscovite-illite, pyrophyllite, accompanied by lesser amounts of rutile, chlorite, anatase, albite, gypsum, nontronite, and pyrite. Consideration of elemental ratios and geochemical indices such as TiO2, Nb + Cr, Ti + Fe, Sr + Ba, and La + Ce + Y demonstrated that both hypogene and supergene processes played a significant role in the development of this deposit. The mass change calculations revealed that elements like Zr, Ga, Hf, REEs, and Th which are normally immobile in ordinary alteration processes had both incremental and decremental trends during the development of this deposit. The Eu and Ce anomaly values (normalized to chondrite) in kaolinized samples vary within the range of 0.65–1.13 and 0.91–1.05, respectively. It seems that the variation of negative Eu anomaly values was controlled by kaolinization of feldspars by hypogene solutions and by scavenging of this element by Fe oxides and hydroxides (formed during oxidation of hypogene pyrite by supergene solutions). Variation of Ce anomalies also unravels the effective role of reducing hypogene fluids and to some extent of supergene solutions during kaolinization. Combination of the results obtained from mineralization considerations, mass change calculations of elements, and correlation coefficients illustrate that distribution and concentration of major, minor, and rare earth elements during kaolinization at Arabshah were affected by the function of factors such as changes in physico-chemical conditions of altering solutions (e.g., Eh and pH), adsorption, accessibility to complex-forming ligands, water-rock ratios, existing in resistant (to alteration) mineral phases, and scavenging by Fe and Mn oxides.

Preparation and properties of amylose complexes prepared from hexadecylamine and its hydrochloride salt

Amylose inclusion complexes were prepared from jet-cooked aqueous mixtures of high amylose corn starch and 1-hexadecylamine (HDA). Slow-cooling produced torus/disc-shaped spherulites, whereas aggregates of smaller spherulites were obtained by rapid-cooling in ice. The morphologies and 61V X-ray diffraction patterns of these spherulites were similar to those of spherulites obtained previously with palmitic acid, indicating that spherulite morphology is influenced largely by the hydrophobic structure of the carbon chain of the complex-forming ligand and to a lesser extent by the nature of the more polar head group. Water soluble, cationic amylose inclusion complexes were prepared by adding an aqueous solution of the HCl salt of HDA to a jet-cooked dispersion of high amylose starch. The cationic nature of these HDA·HCl complexes suggests possible applications as flocculating agents for water purification and as retention aids in papermaking.

Reuse of washing effluent containing oxalic acid by a combined precipitation–acidification process

This study aims at evaluating the reuse feasibility of effluent produced by the soil washing of mine tailings with oxalic acid. Alkaline chemicals such as NaOH, Ca(OH)2, and Na2CO3 are used for the precipitation of arsenic and heavy metals in the effluent containing oxalic acid. All of the target contaminants are removed with very high efficiency (up to 100%) at high pH. The precipitation using NaOH at pH 9 is determined to be the most cost-effective method for the removal of arsenic as well as heavy metals in the effluent. The effluent decontaminated by NaOH is consecutively reused for the soil washing of raw mine tailings, resulting in considerable efficiency. Furthermore, even more arsenic and heavy metals are extracted from raw mine tailings by acidifying the decontaminated effluent under the alkaline condition, compared with direct reuse of the decontaminated effluent. Here, the oxalic acid, which is a weak complex-forming ligand as well as a weak acid, has noticeable effects on both soil washing and effluent treatment by precipitation. It extracts efficiently the contaminants from the mine tailings without adverse change of soil and also makes possible the precipitation of the contaminants in the effluent unlike strong chelating reagent. Reuse of the washing effluent containing oxalic acid would make the existing soil washing process more environment-friendly and cost-effective.

Computer optimization of background electrolyte composition in the separation of metal ions by capillary electrophoresis.

The iterative regression design developed earlier for high performance liquid chromatography (HPLC) has been applied successfully to the optimization of the separation of 11 metal ions by capillary electrophoresis. The parameters used for optimization were pH (over the range 3.5-5.0) and the concentration of 2-hydroxyisobutyric acid (HIBA) (2-20 mM) used as the complex-forming ligand added to the background electrolyte. Five initial experiments were performed and the response surface was calculated using the relative resolution product as criterion. Three additional experiments were sufficient to establish a stable optimum, with which all 11 metal ions were separated and well spread in the electropherogram. The total analysis time was less than 5 min.

Antimony electrodes

Antimony electrodes are clinically useful because of their low cost and simple construction; they have no glass to break. There is only a few hundred ohms resistance between an antimony pH electrode and the reference electrode so that the voltage generated can be recorded with simple low-impedance recorders linked to microcomputers. We used antimony pH electrodes with silver-silver chloride electrodes applied to the skin to measure the gastric pH in vivo and obtained erroneously high values. Using an ion-permeable dialysis chamber to surround electrodes in vivo, we showed that the discrepancy was caused by interference from gastric transmucosal potential difference. To circumvent the interference, we used a combination electrode constructed by embedding a monocrystalline antimony electrode and a silver-silver chloride reference electrode in dental acrylic. Antimony pH electrodes calibrated with commercial pH buffers also gave erroneous readings in HCl solutions of known pH. The erroneous readings were due, in part, to organic complex-forming ligands or organic salts such as potassium phthalate present in commercial buffer solutions. Accurate pH calibration can be obtained with citrate or acetate buffers or by using a normogram to correct for the errors introduced with commercial buffers. The combination antimony pH electrode has a number of potential clinical and research applications and simplifies obtaining accurate and reliable pH data in vivo.

The use of a surface complexation model to describe the kinetics of ligand-promoted dissolution of anorthite

The dissolution of anorthite (CaAl 2Si 20 8) in the presence of fluoride and oxalate was studied under controlled pH and CO 2 conditions. The dissolution of anorthite in the absence of complex-forming ligands was nearly pH independent between pH 5 and 9. The presence of complex-forming ligands resulted in a dissolution rate that increased linearly with decreasing solution pH. The dissolution data were modeled using the theory that the reaction rate is proportional to the surface concentration of activated sites. Surface activated sites are formed by the adsorption of protons and complexing ligands. On anorthite, the proton-promoted activated sites are probably Si centered and the ligand-promoted activated sites Al centered. Two surface chemistry models were combined in order to describe the overall reaction. At pH values less than 4.2, the rate of the proton-promoted dissolution was linearly proportional to Γ 4, where Γ is the surface concentration of adsorbed protons. The rate of the ligand-promoted dissolution was found to be linearly related to the surface concentration of adsorbed ligand. These findings suggest that for most natural systems, pH and complexing ligands have a synergistic effect on feldspar dissolution. The observation in nature that Ca-rich plagioclase feldspars are less resistant to weathering than Na-rich feldspars can be attributed to the increased reactivity of organic ligands towards Ca-rich feldspars. The increased reactivity is attributed to the higher proportion of Al in the Ca-feldspars.

Application of asv for trace metal speciation: Part V. The pseudo-polarography of zinc by RGCE

The pseudo-polarographic properties of Zn 2+ are described. It has been shown that the pseudo-polarograms of a quasi-reversible redox reaction can be recorded. The results were compared with square-wave polarographic measurements and with the theoretical predictions. The main reason for recording pesudo-polarograms is the possibility of measuring the dependence of their half-wave potentials on the concentration of a certain complex-forming ligand at vrey low metal concentration. The stability constants of zinc chloride complexes, at a zinc concentration of 1 × 10 −8 mol/dm 3, were calculated and compared with literature data. Pseudo-polarography improves the possibility of verifying experimentally the chemical models of trace metal speciation in natural waters.

The coordination chemistry of weathering: I. Dissolution kinetics of δ- Al2O3 and BeO

The dissolution kinetics of most slightly soluble oxides and silicates are controlled by chemical processes at the surface. The reaction controlling steps can be interpreted in terms of a surface coordination model. In dilute acid solutions, in the absence of complex-forming ligands, the dissolution kinetics are controlled by the surface bound protons. The rate of the proton-promoted reaction of δ- Al 2 O 3 is R H = k H ( C H 3) 3 where C h 3 is the proton concentration per unit area on the oxide surface. The mechanism can be described by the attachment of three protons to the reaction site prior to the detachment of an Al species into the solution. The dissolution rate of BeO is proportional to (C H 2) 2. For δ- Al 2 O 3 at pH ⩽ 3.5 dissolution rate is independent of pH; at this pH maximum surface concentration of protons is reached. The organic ligand-promoted dissolution, R L , is of first order with respect to concentration of surface chelates: R L = k L {M ▪L} where {M ▪L} is the concentration of surface chelates per unit area. Detachable surface complexes result from surface coordination of metal ions of the hydrous oxides with bidentate ligands. Especially efficient are bidentate ligands that form mononuclear surface complexes. The sequence of rate constants shows that five- and six-membered chelate rings (oxalate, catechol, malonate and salicylate) enhance the dissolution reactions to a greater extent than seven-membered rings (phthalate, succinate). Monodentate ligands (benzoate ion), though readily adsorbed, do not enhance dissolution rates. However, they can inhibit dissolution by displacing ligands that catalyze this reaction.

Ion-selective determination of total metal ion concentration in an excess of complexing ligand using the standard additions method

An ion-selective potentiometric determination of total calcium and silver ion in the presence of an excess of complex-forming ligands, nitrilotriacetic acid and sodium thiosulphate, respectively, is described. A standard additions method with a Philips plastic calcium and solid-state silver ion-selective electrodes was used. This method has been applied to 1 mg l–1 of calcium and 10–3–10–5 mol l–1 silver solutions containing an ionic strength adjustor and an excess of complex-forming ligand. Calcium measurements in solutions containing an excess of ligand and other complexing ions are reported, e.g., HPO42– and NO3–. This method has also been applied to the determination of total silver in black and white photographic paper containing 0.8 g m–2 of silver. Dissolution of the paper's silver in an excess of thiosulphate is followed by a standard additions procedure. Suitable conditions for calcium and silver determinations are reported and advantages gained in precision of measurement, electrode sensitivity and speed of analysis are discussed.

Effects of some complex-forming ligands on the potential of antimony pH-sensors

The E vs. pH relationship for oriented monocrystalline antimony electrodes was studied in various ionic media, containing no buffer or one of several common buffer substances, and the stability of the electrode potential with time was investigated. Several makes of commercially available polycrystalline antimony electrodes were also studied. The results indicate that tris(hydroxymethyl)aminomethane may be used for calibration of antimony electrodes, but most other commonly used buffer substances, e.g., orthophosphate, yield erroneous results. Monocrystalline antimony electrodes are preferable to polycrystalline ones, especially when measurements are made in unstirred solutions. The long-term stability of monocrystalline electrodes is superior to that of polycrystalline ones.

Anodic stripping voltammetry with the florence mercury film electrode. determination of copper, lead and cadmium in sea water

The use of the rotating glassy carbon electrode mercury plated in situ for anodic stripping voltammetry has been investigated. The choice of electrode material is discussed. The effect of instrumental parameters on the stripping response for copper, lead and cadmium in sea water is studied, the results being in accordance with the theory of thin film electrodes. The variation in the observed sensitivity for the three metals in sea water is discussed in terms of complex-forming ligands. Lastly the performance of the film electrode is compared to that of the hanging mercury drop electrode.

Uber metallcarbonyle—LXXVI zur kenntnis des rutheniumcarbonyljodids

Under certain conditions the polymeric, diamagnetic ruthenium carbonyl iodide Ru(CO) 2J 2 will react with complex-forming ligands (X) having a free electron pair. In this way, with N-bases such as pyridine, o-phenanthroline and also with triphenylphosphine, -arsine, -stibine, and tri- cyclohexyl-phosphine, compounds of the RuX 2(CO) 2J 2 type are formed which are non-electrolytes. With potassium cyanide K 2[Ru(CO) 2(CN) 2J 2] a complex compound showing ionic structure is obtained. On the other hand, aromatic isonitriles form tetra isonitrile compounds, e.g. Ru( pCNC 6H 4OCH 3) 4J 2, by total substitution of carbon monoxide. It is characteristic that stable complex ruthenium carbonyl iodides can only be obtained by using ligands that are bound to the metal by a mesomeric double bond.