Preparation and solubility of northupite from brine and its adsorption properties for Cu(II) and Cd(II) in seawater

The mineral northupite Na₃Mg(CO₃)₂Cl was synthesized from a solar Adriatic seawater brine pond to which Na₂CO₃ was added at 373°K. The precipitated northupite had a surface area (P) of 6.0 ± 0.4 m²g⁻¹, and the thermodynamic solubility product was estimated to be log K Na₃Mg(CO₃)₂Cl = −4.8 ± 0.3 at 25°C. This value was used to calculate the interfacial energy (σ = 50 erg cm⁻²) for the homogeneous nucleation of northupite. The solubility constant determined in this study has been used to examine the saturation state of Mahega Lake and Lake Katwe (Uganda). The waters from Lake Katwe were found to be supersaturated with respect to northupite.The adsorption of Cu and Cd onto northupite particles was studied in seawater. Both metals are strongly adsorbed. Adsorption constants and the specific area of northupite occupied by Cd and Cu using Langmuir adsorption isotherms and equilibrium constants for surface complex formation have been determined.     

Lead(II) complexation by fulvic acid: how it differs from fulvic acid complexation of copper(II) and cadmium(II)

Pb²⁺, like Cu²⁺, forms strong complexes with fulvic acids (Cd²⁺-fulvate complexes are much weaker), but Pb-fulvate precipitates at a much lower mole ratio of metal ion to fulvic acid than either Cu-fulvate or Cd-fulvate does. Physical association of Pb²⁺ with Pb-fulvate solids as well as complexation by sites still available in the precipitates probably causes the increased removal of free Pb²⁺ from solution after precipitation begins.     

Adsorption of copper(II) from aqueous solution by Beidellite

Dry lakes, degraded sandy grasslands, abandoned farmland and mobile dunes which are widely distributed throughout the arid areas of northern China have been investigated in this work. Gain-size distribution of the surface sediments of Manas lake in Junggar basin, Juyan lake in the Alxa plateau, Zhuye lake in Minqin basin and most deserts (such as Mu Us desert, Otindag desert, Horqin desert and Hulun Buir desert) in China have been analyzed. The results show clay with particle sized <10 μm on the surface sediments of dry lakebed and sandy grassland developed from dry lakebed, respectively, account for >60% and ∼50% of the total mass. Since the tiny particles on the surface of abandoned farmland are blown away easily and rapidly, the content of clay particles in Minqin basin is <14%. The grain-size distribution of mobile dunes in northern China mainly consists of particles >63 μm and few particles <10 μm. Consequently, although sand/dust storms originate primarily in the western deserts, the gobi areas of the Alxa plateau, the north and east of Hexi Corridor and in central Mongolia, the widely distributed dry lakebeds, sandy grasslands and abandoned farmland adjacent to the deserts also contribute to aeolian dusts. Hence, the material sources for sand dust storm in East Asia include inland deserts, but also dry lakes, sandy grasslands and abandoned farmland, which are widely distributed throughout the arid inlands of northern China.     

Surface complexation model for multisite adsorption of copper(II) onto kaolinite

We measured the adsorption of Cu(II) onto kaolinite from pH 3-7 at constant ionic strength. EXAFS spectra show that Cu(II) adsorbs as (CuO₄H_n)ⁿ⁻⁶ and binuclear (Cu₂O₆H_n)ⁿ⁻⁸ inner-sphere complexes on variable-charge ≡AlOH sites and as Cu²⁺ on ion exchangeable ≡X--H⁺ sites. Sorption isotherms and EXAFS spectra show that surface precipitates have not formed at least up to pH 6.5. Inner-sphere complexes are bound to the kaolinite surface by corner-sharing with two or three edge-sharing Al(O,OH)₆ polyhedra. Our interpretation of the EXAFS data are supported by ab initio (density functional theory) geometries of analog clusters simulating Cu complexes on the {110} and {010} crystal edges and at the ditrigonal cavity sites on the {001}. Having identified the bidentate (≡AlOH)₂Cu(OH)₂⁰, tridentate (≡Al₃O(OH)₂)Cu₂(OH)₃⁰ and ≡X--Cu²⁺ surface complexes, the experimental copper(II) adsorption data can be fit to the reactions

     

Polarized XANES and EXAFS spectroscopic investigation into copper(II) complexes on vermiculite

Interaction of heavy metals with clay minerals can dominate solid-solution reactions in soil, controlling the fate of the metals in the environment. In this study we used powdered and polarized extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray absorption near edge spectroscopy (XANES) to investigate Cu sorbed on Llano vermiculite and compare the results to reported Cu sorption mechanism on Wyoming (WY) smectite and reduced South African (SA) vermiculite. Analysis of the Cu K-edge spectra revealed that Cu sorbed on Llano vermiculite at high ionic strength (I) has the greatest degree of covalent bond character, followed by Cu sorbed on montmorillonite at high I, and Cu sorbed on reduced SA vermiculite at high I. Cu sorbed on clay minerals at low I has the least covalent character. EXAFS data from Cu sorbed Ca- and K-equilibrated Llano vermiculites showed the presence of a second-shell Al, Si, or Mg backscatterer at 3.02 Å. This distance is consistent with Cu sorbing via a corner-sharing monodentate or bidentate bond. Polarized XANES and EXAFS results revealed that the angle between the Cu atom and the mineral sorption sites is 68° with respect to the [001] direction. From the bond angle and the persistence of the second-shell backscatterer when the interlayer is collapsed (K-equilibration), we conclude that Cu adsorption on the Llano vermiculite is not occurring in the interlayer but rather Cu is adsorbing onto the edges of the vermiculite. Results from this research provide evidence that Cu forms inner-sphere and outer-sphere complexes on clay minerals, and does not form the vast multinuclear surface precipitates that have been observed for Co, Zn, and Ni.     

Factors controlling copper solubility and chalcopyrite deposition in the Sungun porphyry copper deposit, Iran

The Sungun porphyry copper deposit is hosted in a Diorite/granodioritic to quartz-monzonitic stock that intruded Eocene volcanosedimentary and Cretaceous carbonate rocks. Copper mineralization is associated mainly with potassic alteration and to a lesser extent with sericitic alteration. Based on previously published fluid inclusion and isotopic data by Hezarkhani and Williams-Jones most of the copper is interpreted to have deposited during the waning stages of orthomagmatic hydrothermal activity at temperatures of 400 to 300 °C. These data also indicate that the hydrothermal system involved meteoric waters, and boiled extensively. In this work, thermodynamic data are used to delineate the stability fields of alteration and ore assemblages as a function of fS₂, fO₂ and pH. The solubility of chalcopyrite was evaluated in this range of conditions using recently published experimental data. During early potassic alteration (>450 °C), Copper solubility is calculated to have been >50 000 ppm, whereas the copper content of the initial fluid responsible for ore deposition is estimated, from fluid inclusion data, to have been 1200–3800 ppm. This indicates that initially the fluid was highly undersaturated with respect to chalcopyrite, which agrees with the observation that veins formed at T > 400 °C contain molybdenite but rarely chalcopyrite. Copper solubility drops rapidly with decreasing temperature, and at 400 °C is approximately 1000 ppm, within the range estimated from fluid inclusion data, whereas at 350 °C it is only 25 ppm. These calculations are consistent with observations that the bulk of the chalcopyrite deposited at Sungun is hosted by veins formed at temperatures of 360 ± 60 °C. Other factors that, in principle, may reduce chalcopyrite solubility are increases in pH, and decreases in fO₂ and aCl⁻. Our analysis shows, however, that most of the change in pH occurred at high temperature when chalcopyrite was grossly undersaturated in the fluid, and that the direction of change in fO₂ increased chalcopyrite solubility. We propose that the Sungun deposit formed mainly in response to the sharp temperature decrease that accompanied boiling, and partly as a result of the additional heat loss and decrease in aCl⁻, which occurred as a result of mixing of acidic Cu-bearing magmatic waters with cooler meteoric waters of lower salinity. Received: 8 July 1998 / Accepted: 8 April 1999     

Adsorption of copper (II) on mesoporous silica: the effect of nano-scale confinement

Nano-scale spatial confinement can alter chemistry at mineral–water interfaces. These nano-scale confinement effects can lead to anomalous fate and transport behavior of aqueous metal species. When a fluid resides in a nanoporous environments (pore size under 100 nm), the observed density, surface tension, and dielectric constant diverge from those measured in the bulk. To evaluate the impact of nano-scale confinement on the adsorption of copper (Cu²⁺), we performed batch adsorption studies using mesoporous silica. Mesoporous silica with the narrow distribution of pore diameters (SBA-15; 8, 6, and 4 nm pore diameters) was chosen since the silanol functional groups are typical to surface environments. Batch adsorption isotherms were fit with adsorption models (Langmuir, Freundlich, and Dubinin–Radushkevich) and adsorption kinetic data were fit to a pseudo-first-order reaction model. We found that with decreasing pore size, the maximum surface area-normalized uptake of Cu²⁺ increased. The pseudo-first-order kinetic model demonstrates that the adsorption is faster as the pore size decreases from 8 to 4 nm. We attribute these effects to the deviations in fundamental water properties as pore diameter decreases. In particular, these effects are most notable in SBA-15 with a 4-nm pore where the changes in water properties may be responsible for the enhanced Cu mobility, and therefore, faster Cu adsorption kinetics.     

Molecular-level modes of As binding to Fe(III) (oxyhydr)oxides precipitated by the anaerobic nitrate-reducing Fe(II)-oxidizing Acidovorax sp. strain BoFeN1

Sorption of contaminants such as arsenic (As) to natural Fe(III) (oxyhydr)oxides is very common and has been demonstrated to occur during abiotic and biotic Fe(II) oxidation. The molecular mechanism of adsorption- and co-precipitation of As has been studied extensively for synthetic Fe(III) (oxyhydr)oxide minerals but is less documented for biogenic ones. In the present study, we used Fe and As K-edge X-ray Absorption Near Edge Structure (XANES), extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, Mössbauer spectroscopy, XRD, and TEM in order to investigate the interactions of As(V) and As(III) with biogenic Fe(III) (oxyhydr)oxide minerals formed by the nitrate-reducing Fe(II)-oxidizing bacterium Acidovorax sp. strain BoFeN1. The present results show the As immobilization potential of strain BoFeN1 as well as the influence of As(III) and As(V) on biogenic Fe(III) (oxyhydr)oxide formation. In the absence of As, and at low As loading (As:Fe ≤ 0.008 mol/mol), goethite (Gt) formed exclusively. In contrast, at higher As/Fe ratios (As:Fe = 0.020-0.067), a ferrihydrite (Fh) phase also formed, and its relative amount systematically increased with increasing As:Fe ratio, this effect being stronger for As(V) than for As(III). Therefore, we conclude that the presence of As influences the type of biogenic Fe(III) (oxyhydr)oxide minerals formed during microbial Fe(II) oxidation. Arsenic-K-edge EXAFS analysis of biogenic As-Fe-mineral co-precipitates indicates that both As(V) and As(III) form inner-sphere surface complexes at the surface of the biogenic Fe(III) (oxyhydr)oxides. Differences observed between As-surface complexes in BoFeN1-produced Fe(III) (oxyhydr)oxide samples and in abiotic model compounds suggest that associated organic exopolymers in our biogenic samples may compete with As oxoanions for sorption on Fe(III) (oxyhydr)oxides surfaces. In addition HRTEM-EDXS analysis suggests that As(V) preferentially binds to poorly crystalline phases, such as ferrihydrite, while As(III) did not show any preferential association regarding Fh or Gt.     

Modeling the adsorption of Cd (II), Cu (II), Ni (II), Pb (II) and Zn (II) onto montmorillonite

The adsorption of five toxic metallic cations, Cd(II), Cu(II), Ni(II), Pb(II) and Zn(II), onto montmorillonite was investigated as a function of pH and ionic strength and a two-site surface complexation model was used to predict the adsorption data. The results showed that in the lower pH range, 3∼6 for Cd, Cu, Ni and Zn, and 3∼4.5 for Pb, the adsorption was greatly affected by ionic strength, while in the higher pH range, the adsorption was not. In the lower pH range, the metallic cations were mainly bound through the formation of outer-sphere surface on the permanently charged basal surface sites (≡X⁻), while in the higher pH range the adsorption occurred mainly on the variably charged edge sites (≡SOH) through the formation of inner-sphere surface complexes. Acid-base surface constants and metal binding constants for the two sites were optimized using FITEQL. The adsorption affinity of the five metallic cations to the permanently charged sites of montmorillonite was Pb > Cu > Ni ≈ Zn ≈ Cd, while that to the variable charged sites was Pb ? Cu > Zn > Cd > Ni.     

Surface complexation modelling of Cd(II), Cu(II), Ni(II), Pb(II) and Zn(II) adsorption onto kaolinite

Proton binding constants for the edge and basal surface sites of kaolinite were determined by batch titration experiments at 25 °C in the presence of 0.1 M, 0.01 M and 0.001 M solutions of NaNO₃ and in the pH range 3-9. By optimizing the results of the titration experiments, the ratio of the edge sites to the basal surface sites was found to be 6:1. The adsorption of Cd(II), Cu(II), Ni(II), Zn(II) and Pb(II) onto kaolinite suspensions was investigated using batch adsorption experiments and results suggested that in the lower pH range the metallic cations were bound through non-specific ion exchange reactions on the permanently charged basal surface sites (X⁻). Adsorption on these sites was greatly affected by ionic strength. With increasing pH, the variable charged edge sites (SOH) became the major adsorption sites and inner-sphere specifically adsorbed monodentate complexes were believed to be formed. The effect of ionic strength on the extent of adsorption of the metals on the variable charged edge sites was much less than those on the permanently charged sites. Two binding constants, log K_(X2Me) and log K_(SOMe), were calculated by optimizing these constants in the computer program FITEQL. A model combining non-specific ion exchange reactions and inner-sphere specific surface complexations was developed to predict the adsorption of heavy metals onto kaolinite in the studied pH range. Linear free energy relationships were found between the edge site binding constants and the first hydrolysis constants of the metals.     

The aqueous solubility of trichloroethene (TCE) and tetrachloroethene (PCE) as a function of temperature

Using a flexible Au bag autoclave and a precision high-pressure liquid chromatography pump to control pressure, the liquid–liquid aqueous solubilities of TCE and PCE were measured as a function of temperature from 294 to 434 K (at constant pressure). The results were used to calculate the partial molal thermodynamic quantities of the organic liquid aqueous dissolution reactions: ΔḠ_soln, ΔH̄_soln, ΔS̄_soln and ΔC̄_{p soln}. Calculated values for these quantities at 298 K for TCE are: ΔḠ_soln=11.282 (±0.003) kJ/mol, ΔH̄_soln=−3.35 (±0.07) kJ/mol, ΔS̄_soln=−49.07 (±0.24) J/mol K, and ΔC̄_{p soln}=385.2 (±3.4) J/mol K. Calculated values for these quantities at 298 K for PCE are: ΔḠ_soln=15.80 (±0.04) kJ/mol, ΔH̄_soln=−1.79 (±0.58) kJ/mol, ΔS̄_soln=−59.00 (±1.96) J/mol K and ΔC̄_{p soln}=354.6 (±8.6) J/mol K. These thermodynamic quantities may be used to calculate the solubility of TCE and PCE at any temperature of interest. In the absence of direct measurements over this temperature range, the Henry's Law constants for TCE and PCE have been estimated using the measured aqueous solubilities and calculated vapor pressures.     

The solubility of rhodochrosite (MnCO3) and siderite (FeCO3) in anaerobic aquatic environments

Natural groundwaters are often reported to be highly supersaturated with the carbonate minerals siderite (FeCO₃) and rhodochrosite (MnCO₃). The kinetics of precipitation and dissolution were determined in the light of new determinations of the solubility products of siderite and rhodochrosite. Laboratory experiments showed that the precipitation kinetics of siderite and rhodochrosite were much slower than that of calcite, and also much slower than their dissolution kinetics. Experiments with supersaturated solutions failed to reach steady state within 474 days in the case of siderite, whereas steady state for rhodochrosite was reached after 140 days. Suspensions of siderite and rhodochrosite crystals reached steady state after 10 and 80 days, respectively. The solubility product of siderite (−log K_S0(FeCO₃)) was 11.03 ± 0.10 for dried crystals and 10.43 ± 0.15 for wet crystals. For rhodochrosite the solubility product (−log K_S0(MnCO₃)) was 11.39 ± 0.14 for dried crystals and 12.51 ± 0.07 for wet crystals. The solubility product determined from supersaturated solutions was −log K_S0(MnCO₃)=11.65 ± 0.14. The observed slow precipitation kinetics of siderite and rhodochrosite might explain the apparent supersaturation that is often reported for anaerobic aquatic environments.     

The concentration of Cu(II), Pb(II) and Zn(II) from aqueous solutions by particulate algal matter

Experimental studies of the reactions of Cu(II), Pb(II), and Zn(II) in aqueous solutions with organic matter derived from fresh samples of the green filamentous algae Ulothrix spp. and the green unicellular algae Chlamydomonas spp. and Chlorella vulgaris show that, under suitable conditions, a significant proportion of the metals is removed from solution by sorption onto the particulate organic matter of the algal suspension.The metal sorption is strongly suppressed by H⁺ but is only marginally influenced by the proportion of whole cells in the suspension and by complexing of metals in solution by the soluble organic matter. The presence of relatively small amounts of the cations Na⁺ and Mg²⁺ in solution reduces the sorption of Zn(II) to near zero, but Pb(II) and Cu(II) sorption occurs to an appreciable extent even in strong brines. This may be a means for the selective precipitation of Pb(II) from brines rich in Pb(II) and Zn(II).Metal “saturation” values indicate that particulate algal matter of the type used in these experiments could sorb sufficient quantities of metal to form an ore deposit if a weight of organic matter of similar order of magnitude to that of the inorganic sediments in the deposits was available. However, the metal sorption is an equilibrium reaction, and the experimentally determined “enrichment factors” suggest that the “saturation” values could be approached only in solutions whose metal contents were initially at least two orders of magnitude above those of normal seawater.     

Composition and U-Pb isotopic age determinations (SHRIMP II) of the ophiolitic assemblage from the Shaman paleospreading zone and the conditions of its formation (North Transbaikalia)

The Upper Riphean Shaman ophiolitic assemblage was first distinguished and described in the territory of North Transbaikalia. Ophiolites found within a narrow suture (Shaman paleospreading zone) are represented by serpentinized ultrabasites with numerous plagiogranite veins having a U-Pb age of 971 ± 14 Ma, gabbros (939 ± 11 Ma), and basalts (892 ± 16 Ma). The ophiolite section also contains dikes of diabases and gabbro-diabases, siliceous-terrigenous stratum (black shale) of Upper Riphean age. The fragments of island-arc complexes (differentiated volcanites, gabbro-diorites, granites) of the Kelyan island-arc system are also found within the Shaman zone. The presence of Upper Riphean ophiolites in Baikalides of North Transbaikalia testifies to the formation of oceanic crust of the marginal spreading basins in the Precambrian Paleo-Pacific Ocean and the emerging Paleoasian Ocean.     

Adsorption of Lead (II) and Zinc (II) from Aqueous Solution by Bituminous coal

Activated carbons have been proven to be effective adsorbents for the removal of Pb (II) and Zn (II) dissolved in aqueous media. The study of adsorption of Pb (II) and Zn (II) on two different size fractions from a composite coal sample of Maghara coal mine, C₆₃ (63–125 μm) and C₂₅₀ (125–250 μm) is presented in this paper. C₆₃ and C₂₅₀ were treated in water solutions of 50 mM lead and zinc acetates. X-ray photoelectron spectroscopy (XPS) was used to characterize the starting and treated coal surfaces. The high surface area and surface functional groups (carboxy and phenolic) enable activated bituminous coal of Maghara to act as efficient adsorbents for removing dissolved Pb (II) and Zn (II) in alkaline medium.     

Metal ion complex formation constants of some sedimentary humic acids with Zn(II), Cu(II) and Cd(II)

Metal ion complex formation constants were determined for several sedimentary humic acids (SHA) derived from a fresh water lake and several coastal marine environments, using a method based on size exclusion chromatography. Only one type of binding site was observed in all cases, and conditional log K_f values of between 5 and 7 (at pH 8, I = 0.01 M) were found. Elemental composition of the SHA was similar to soil HA, except that nitrogen content was significantly higher in the SHA. Other chemical properties of the SHA were consistent with those reported by other workers. While spectroscopic measurements indicated that the SHA may have contained significant amounts of polysaccharide compounds which were not removed by conventional separation and purification procedures, analysis indicated only very low levels of polysaccharides were present in the SHA.