沉水植物黑藻对沉积物磷吸附动力学的影响

在室内模拟条件下,通过吸附动力学实验,研究了沉水植物黑藻对沉积物吸附磷动力学模型拟合和吸附速度的影响,并从有机质和铁铝氧化物含量的角度,讨论了沉水植物黑藻对沉积物吸附磷动力学的影响机理。初步得出如下结论:(1)一级反应动力学模型虽然从模型拟合的角度达到了极显著水平,但不能真实地反映沉水植物对沉积物吸附磷动力学过程的影响。其余三个模型均能很好地反映,其中抛物线扩散模型的拟合效果最好,修正的Elovich模型和双常数速率模型的拟合效果较好。种植沉水植物与否并不影响这一趋势;(2)沉水植物黑藻提高了沉积物吸附磷的强度和速度,特别是提高了0～0.5h内的吸附速度,沉水植物影响有机质和铁铝氧化物含量是增强沉积物吸附磷强度和速度的重要机理。     

A radiotracer study on the kinetics of gold sorption by mineral surfaces

Aqueous solutions with about 10 ppt¹⁹⁵Au and [HCl] of 10^–2.3 and 10^–1.3 m were exposed to solid minerals for several months. The gold uptake with time was observed by time-stepped sampling and radiochemical Au analysis. Sorbants were polished thick sections of quartz, pyrite, pyrrhotite and elemental gold, as well as crushed grains and sawed mineral cubes of quartz and pyrite (all randomly oriented). The kinetics of gold sorption strongly varied with the surface area of the sorbents, the type of mineral and the pH of the solution. Mineral-specific differences in reaction rates were observed only at experimental pH values around 2.3, where sorption on pyrrhotite and elemental gold was much more rapid than by quartz and pyrite. At pH around 1.3 gold sorption was rapid on all minerals. This finding is thought to reflect the gold speciation, i.e. neutral hydroxo-gold complexes above pH 1.5, for which only chemisorption is possible, versus dominantly AuCl ₄ ^– below pH 1.5, where unspecific electrostatic interaction enhances reaction rates with all protonated mineral surfaces.     

Binary gas sorption/desorption experiments on a bituminous coal: Simultaneous measurements on sorption kinetics,volumetric strain and acoustic emission

There is still no clear understanding of the specific interactions between coal and gas molecules. In this context sorption–desorption studies of methane and carbon dioxide, both in a single gas environment and gas mixtures, are of fundamental interest. This paper presents the results of unique simultaneous measurements of sorption kinetics, volumetric strain and acoustic emission (AE) on three tetragonal coal samples subjected to sorption of carbon dioxide and methane mixtures. The coal was a high volatile bituminous C coal taken from the Budryk mine in the Upper Silesia Basin, Poland. Three different gas mixtures were used in the sorption tests, with dominant CO₂, with dominant CH₄ and a 50/50 mixture.The experimental set-up was designed specially for this study. It consisted of three individual units working together: (i) a unit for gas sorption experiments using a volumetric method, (ii) an AE apparatus for detecting, recording and analysing AE, and (iii) a strain meter for measuring strains induced in the coal sample by gas sorption/desorption. All measurements were computer aided.The experiments indicated that the coal tested showed preferential sorption of CH₄ at 2.6 MPa pressure and exhibited comparable affinities for CH₄ and CO₂ at higher pressures (4.0 MPa). The results of chromatographic analysis of the gas released on desorption suggested that the desorption of methane from the coal was favoured. The relationship between the volumetric strain and the amount of sorbed gas was found to be non-linear. These results were contrary to common opinions on the coal behaviour. Furthermore, it appeared that the swelling/shrinkage of coal was clearly influenced by the network of fractures. Besides, the AE and strain characteristics suggested common sources of sorption induced AE and strain.The present results may have implications for the sequestration of carbon dioxide in coal seams and enhanced coalbed methane recovery (ECBM).     

坡缕石/氧化铝复合材料对磷的吸附动力学和热力学

以坡缕石粘土为原料,通过溶胶-凝胶法制备坡缕石/氧化铝复合材料,通过静态吸附实验研究了复合材料吸附水中磷的动力学特征、吸附平衡和热力学参数,探讨了吸附机理。结果表明,复合材料对磷有较好的吸附作用,吸附过程能较好地符合准二级动力学方程,吸附速率常数随初始浓度的增大而减小,随温度的升高有所增大;吸附平衡能较好地符合Langmuir方程和D-R方程,吸附过程吸热,ΔG为-25~-21 kJ/mol,是物理吸附和化学吸附并存的过程。     

Effect of organic matter on DOM sorption on lake sediments

The effect of organic matter on the sorption of dissolved organic matter (DOM) on lake sediments is critical to understanding the fate and transport of contaminants at the sediment–water interface in lake ecosystems. Results indicate that DOM sorption on sediment is largely due to ligand exchange between the DOM and hydroxyl groups, and the amount of DOC sorbed is a linear function of added DOC. With increasing organic matter content the sediment has lower binding strength, higher releasing ability for DOM, and the higher amount of DOM sorbed by sediment naturally. There was no clear difference before and after the sediment was treated with H₂O₂, but the constant b implied that after the sediments were treated DOC release was promoted. Organic matter in the sediment tends to impede the sorption of DOC and results in a remarkable decrease in DOC sorption rates.     

Effect of organic acids and fluoride on the dissolution kinetics of hydrous alumina. A model study using the rotating disc electrode

The dissolution of aluminium oxide was studied with an oxide film covered rotating disc aluminium electrode. This allows us to make measurements under conditions of well defined mass transport under conditions representative of those found in natural waters (conc. of Al, organic acids and fluoride), and permits us to distinguish between surface-controlled and transport-controlled rates.Under steady-state conditions, the dissolution current is a direct measure of the flux of dissolving Al ions at the aqueous interface of the amorphous hydrous oxide film.At pH 3–6 and in presence of organic ligands, dissolution is controlled by a surface process, i.e. the rate of detachment of surface complexes. Fluoride ions in concentrations ≥ 10^?6 M increase dramatically the dissolution rate: at pH = 4 the process is controlled by convertive diffusion of F^? from the solution to the surface (k_F- = (3.6 ± 0.5) × 10^?2cms^?1). Competitive and reversible adsorption of organic ligands (10^?6 ? 10^?2M) displacing fluoride slows down the rate of detachment of the surface complex which becomes the rate-limiting step. The affinity of ligands for the Al₂O₃ surface sites increases in the sequence: formate ~ chloride ~ carbonate < acetate < sulphate < salicylate < fumarate < maleate < malonate ? oxalate ? fluoride ≤ citrate.The results are compared with simulated weathering experiments and interpreted in terms of the surface complexation model.     

Processes and kinetics of Cd2+ sorption by a calcareous aquifer sand

The rate of Cd²⁺ sorption by a calcareous aquifer sand was characterized by two reaction steps, with the first step reaching completion in 24 hours. The second step proceeded at a slow and nearly constant rate for at least seven days. The first step includes a fast adsorption reaction which is followed by diffusive transport into either a disordered surface film of hydrated calcium carbonate or into pore spaces. After 24 hours the rate of Cd²⁺ sorption was constant and controlled by the rate of surface coprecipitation, as a solid solution of CdCO₃ in CaCO₃ formed in recrystallizing material. Desorption of Cd²⁺ from the sand was slow. Clean grains of primary minerals, e.g. quartz and aluminosilicates. sorbed much less Cd²⁺ than grains which had surface patches of secondary minerals, e.g. carbonates, iron and manganese oxides. Calcite grains sorbed the greatest amount of Cd²⁺ on a weight-normalized basis despite the greater abundance of quartz. A method is illustrated for determining empirical binding constants for trace metals at in situ pH values without introducing the experimental problem of supersaturation. The binding constants are useful for solute transport models which include a computation of aqueous speciation.     

Trend and mechanisms of transformation of natural sorption barriers in acid soils under phosphate loading

The current status of studies on chemisorption of phosphate anions on soil aluminum(iron)-bearing sorbents has been analyzed. The theoretical possibility of the formation of soluble phosphorus compounds during chemisorption was supported by experiments. It was shown that a decrease in efficiency of aluminum (iron)-bearing mineral and humus-mineral sorbents is related to the peculiar transformation of their phosphatized surfaces with formation of soluble metallophosphate anionic complexes. Mechanisms of the decrease in the efficiency of soil sorbents and their destruction are considered.     

红壤中矿物表面对腐殖质吸附萘的影响

矿物表面可改变土壤腐殖质对疏水性有机污染物的结合能力。采用红壤和高岭石分别与胡敏酸结合制备得到的两种复合体对萘的吸附等温线非线性显著,其n=0.76或0.74,并且有机碳归一化吸附分配系数的实验值Koacds是采用Kow计算得出的理论值Koc的5倍以上,表明红壤、高岭石均对腐殖质吸附萘有强化作用,且红壤较之高岭石对腐殖质吸附萘的影响稍强些。主要原因是,红壤中除了高岭石外,还有与腐殖质结合力很强的铁氧化物,而且很可能是吸附态腐殖质组成结构形态发生了有利于对萘吸附的改变。     

Effect of contaminant carbonaceous matter on the sorption of gold by pyrite

The effect of carbon or graphite coating on the adsorption of gold cyanide on pyrite was investigated with pure pyrite and a pyrite concentrate. In the carbon or graphite contaminated pyrite systems carbon and graphite not only acted as gold sorbents, but also enhanced gold adsorption on pyrite. The carbon coating enhanced gold adsorption on pyrite to a larger extent, in comparison with the graphite coating. The carbon or graphite coating on pyrite reduced the negativity of the pyrite surfaces, and hence improved the physical adsorption of gold cyanide on pyrite. In addition, the highly conductive coating of carbon or graphite on pyrite could enhance electron transfer in the electrochemical reactions occurring in the chemical adsorption of gold and gold reduction on pyrite. The preg-robbing by pyrite or the graphite-coated pyrite was reduced and further eliminated at higher cyanide concentrations. However, gold adsorption on the carbon-coated pyrite could not be prevented even at higher cyanide concentrations due to gold adsorption on the carbon coating. In comparison with pure pyrite, the pyrite concentrate had a higher capacity adsorbing gold, due to the presence of carbonaceous matter in the pyrite concentrate. Fine grinding intensified the smearing of carbon or graphite on the mineral particles, resulting in a larger extent of enhancement in the preg-robbing of the concentrate by the carbon or graphite coating.A diagnostic elution of the preg-robbing pyrite samples indicated that the reduction of gold at the pyrite surfaces was the dominant mechanism for gold adsorption on pyrite, followed by physical and chemical adsorption. Surface topological studies by SEM/EDX showed that gold adsorbed at defect sites on pyrite surfaces. For the pyrite with a 5% carbon coating, gold was observed to adsorb not only at the defect sites, but also at the smooth surfaces with carbon present. For the pyrite with a 5% graphite coating, carbon was also found at the pyrite surfaces, but gold was only detected at the defect sites. XPS studies revealed that part of the gold physically and chemically adsorbed on pyrite or pyrite coated with carbon or graphite. Some gold cyanide was reduced at the pyrite surfaces, with the sulphide ions of pyrite being oxidised to elemental sulphur.     

Effect of contaminant carbonaceous matter on the sorption of gold by pyrite

The effect of carbon or graphite coating on the adsorption of gold cyanide on pyrite was investigated with pure pyrite and a pyrite concentrate. In the carbon or graphite-contaminated pyrite systems carbon and graphite not only acted as gold sorbents, but also enhanced gold adsorption on pyrite. The carbon coating enhanced gold adsorption on pyrite to a larger extent, in comparison with the graphite coating. The carbon or graphite coating on pyrite reduced the negativity of the pyrite surfaces, and hence improved the physical adsorption of gold cyanide on pyrite. In addition, the highly conductive coating of carbon or graphite on pyrite could enhance electron transfer in the electrochemical reactions occurring in the chemical adsorption of gold and gold reduction on pyrite. The preg-robbing by pyrite or the graphite-coated pyrite was reduced and further eliminated at higher cyanide concentrations. However, gold adsorption on the carbon-coated pyrite could not be prevented even at higher cyanide concentrations due to gold adsorption on the carbon coating. In comparison with pure pyrite, the pyrite concentrate had a higher capacity adsorbing gold, due to the presence of carbonaceous matter in the pyrite concentrate. Fine grinding intensified the smearing of carbon or graphite on the mineral particles, resulting in a larger extent of enhancement in the preg-robbing of the concentrate by the carbon or graphite coating.A diagnostic elution of the preg-robbing pyrite samples indicated that the reduction of gold at the pyrite surfaces was the dominant mechanism for gold adsorption on pyrite, followed by physical and chemical adsorption. Surface topological studies by SEM/EDX showed that gold adsorbed at defect sites on pyrite surfaces. For the pyrite with a 5% carbon coating, gold was observed to adsorb not only at the defect sites, but also at the smooth surfaces with carbon present. For the pyrite with a 5% graphite coating, carbon was also found at the pyrite surfaces, but gold was only detected at the defect sites. XPS studies revealed that part of the gold physically and chemically adsorbed on pyrite or pyrite coated with carbon or graphite. Some gold cyanide was reduced at the pyrite surfaces, with the sulphide ions of pyrite being oxidised to elemental sulphur.     

The effect of organics on lead sorption onto Apatite II™

Training activities at firing ranges, both civilian and military, deliver large quantities of Pb bullets into range soils where the physical and geochemical properties of the soil can influence Pb transport. Some best management practices (BMPs) developed for range managers include the addition of phosphate amendments, such as apatite, to immobilize Pb and other metals associated with firing ranges. In this study, the effect of the organic matter content of apatite II™ on its metal sorption properties was investigated. Batch and column experiments were conducted using mechanically, enzymatically, and thermally-treated forms of Apatite II™ to sorb soluble Pb. In batch experiments, mechanically and enzymatically-treated Apatite II™ reduced soluble Pb concentrations from 29% to 96%, depending on the age of the Apatite source. Thermally-treated Apatite II™ consistently reduced soluble Pb concentrations in solution by more than 90%, regardless of aging. The mechanically and enzymatically-treated Apatite II™ produced significantly higher dissolved organic carbon (DOC) and biochemical oxygen demand (BOD) concentrations while undergoing aging. This contrasts with the thermally-treated Apatite II™ that produced very low to non-detectable levels of DOC and BOD while aging. To determine the effects of thermal treatment on performance efficiencies, studies were performed using 500 mg L⁻¹ Pb solutions in columns packed with Apatite II™ that had been preheated at various temperatures for 2 h. The column study showed Pb loading of the Apatite II™ at different thermal treatments that ranged from 10.5% to 16.8% Pb by weight of substrate. The Pb loading capacity (by weight of substrate) increased as the treatment temperature of the Apatite II™ increased.     

Effect of pH and organic ligands on the kinetics of smectite dissolution at 25 °C

Forward dissolution rates of Na-Montmorillonite (Wyoming) SWy-2 smectite (Ca_0.06Na_0.56)[Al_3.08Fe(III)_0.38Mg_0.54] [Si_7.93 Al_0.07]O₂₀(OH)₄ were measured at 25 °C in a mixed-flow reactor equipped with interior dialysis compartment (6-8 kDa membrane) as a function of pH (1-12), dissolved carbonate (0.5-10 mM), phosphate (10⁻⁵ to 0.03 M), and nine organic ligands (acetate, oxalate, citrate, EDTA, alginate, glucuronic acid, 3,4-dihydroxybenzoic acid, gluconate, and glucosamine) in the concentration range from 10⁻⁵ to 0.03 M. In organic-free solutions, the Si-based rates decrease with increasing pH at 1 ? pH ? 8 with a slope close to −0.2. At 9 ? pH ? 12, the Si-based rates increase with a slope of ∼0.3. In contrast, non-stoichiometric Mg release weakly depends on pH at 1 ? pH ? 12 and decreases with increasing pH. The empirical expression describing Si-release rates [R, mol/cm²/s] obtained in the present study at 25 °C, I = 0.01 M is given by

     

红柱石微粉对高铝矾土熟料制品的补强作用

高铝矾土熟料制品是除粘土制品之外使用范围最广、用量最大的耐火材料,在各种工业窑炉中都有广泛应用。生产铝矾土熟料制品一般采用不同粒级的铝矾土熟料与塑性粘土为原料,用倒焰窑烧成时,烧成温度为１４３０～１４５０℃,保温４０ｈ;用隧道窑烧成时,烧成温度为１５５０～１５６０℃。其工艺关键是控制二次莫来石化产生的体积效应。当制品的Ａｌ２Ｏ３含量在７０％以下时,铝矾土熟料制品的高温性能取决于莫来石晶相与液相间的数量比例。Ａｌ２Ｏ３含量越高,制品中莫来石含量越高,玻璃相相应减少,制品的高温性能越好。在生产中提高…     

The influence of pH on the kinetics, reversibility and mechanisms of Pb(II) sorption at the calcite-water interface

Pb(II) sorption experiments with calcite powders were conducted in suspensions equilibrated at atmospheric PCO_2(g) and ambient temperature at pH 7.3, 8.2 and 9.4. Pb fractional sorption was low at pH 7.3 and 9.4 relative to pH 8.2, and correlated well with PbCO₃⁰_(aq) speciation. Desorption experiments conducted for initial sorption times ranging from 0.5 h to 12 d reveal an almost completely reversible process at pH 8.2, attributed to the dominance of an adsorption mechanism, with slight and pronounced irreversibility at pH 7.3 and 9.4 respectively. Similarities in X-ray absorption near edge spectra (XANES) for 24 h and 12 d pH 7.3 and 9.4 sorption samples indicate no effect of initial sorption time. Results from linear combination (LC) fits of XANES spectra for samples sorbed at pH 9.4 confirm ∼75% adsorbed and ∼25% coprecipitated components. The coprecipitated fraction was attributed to the non-exchangeable metal observed in desorption experiments. At pH 7.3, ∼95% adsorbed and ∼5% coprecipitated components were obtained. A comparison of results from desorption experiments and LC-XANES alludes to an irreversibly bound adsorbed component for the pH 9.4 12 d sorption sample. Extended X-ray absorption fine structure spectroscopy (EXAFS) analysis of pH 7.3 and 9.4 12 d sorption samples confirms the presence of both adsorbed and coprecipitated metal. At pH 7.3 a first-shell Pb-O bond length of 2.38 Å is intermediate between that of adsorbed (2.34 Å) and coprecipitated (2.51 Å) Pb. At pH 9.4, two first-shell Pb-O distances at 2.35 Å and 2.51 Å were obtained, indicative of the occurrence of both adsorption and coprecipitation and a larger coprecipitated fraction relative to that at pH 7.3, consistent with LC-XANES results. We propose that the disparity in the fraction of coprecipitated metal with pH may be linked to the ability of sorbed Pb to inhibit near-surface dynamic exchange of Ca and CO₃ species, which dictates step advance and retreat. Less effective inhibition of step motion at pH 9.4, due to lower fractional sorption, combined with highest rates of dynamic exchange results in a significant fraction of coprecipitated Pb at this pH. At low pH, though fractional sorption is also low, lower rates of exchange prohibit significant coprecipitation. At pH 8.2, effective inhibition of surface processes due to higher fractional sorption and lower rates of exchange compared to pH 7.3 and 9.4 preclude detectable coprecipitation. Other factors such as changes in surface speciation and solubility of the Pb-Ca solid solution with pH may also come into play. Overall, this study presents evidence for the influence of pH on Pb sorption mechanisms, and addresses the efficiency of Pb immobilization in calcitic systems.     

Small angle X-ray scattering mapping and kinetics study of sub-critical CO2 sorption by two Australian coals

Time- and position-resolved synchrotron small angle X-ray scattering data were acquired from samples of two Australian coal seams: Bulli seam (Bulli 4, R_o = 1.42%, Sydney Basin), which naturally contains CO₂ and Baralaba seam (R_o = 0.67%, Bowen Basin), a potential candidate for sequestering CO₂. This experimental approach has provided unique, pore-size-specific insights into the kinetics of CO₂ sorption in the micro- and small mesopores (diameter 5 to 175 Å) and the density of the sorbed CO₂ at reservoir-like conditions of temperature and hydrostatic pressure.For both samples, at pressures above 5 bar, the density of CO₂ confined in pores was found to be uniform, with no densification in near-wall regions. In the Bulli 4 sample, CO₂ first flooded the slit pores between polyaromatic sheets. In the pore-size range analysed, the confined CO₂ density was close to that of the free CO₂. The kinetics data are too noisy for reliable quantitative analysis, but qualitatively indicate faster kinetics in mineral-matter-rich regions.In the Baralaba sample, CO₂ preferentially invaded the smallest micropores and the confined CO₂ density was up to five times that of the free CO₂. Faster CO₂ sorption kinetics was found to be correlated with higher mineral matter content but, the mineral-matter-rich regions had lower-density CO₂ confined in their pores. Remarkably, the kinetics was pore-size dependent, being faster for smaller pores.These results suggest that injection into the permeable section of an interbedded coal-clastic sequence could provide a viable combination of reasonable injectivity and high sorption capacity.     

Effect of orthophosphate on the dissolution kinetics of biogenic magnesian calcites

The dissolution behavior of two biogenic Mg-calcites, the echinoid, Tripneustes (12 mol% MgCO₃), and the red alga, Neogoniolithon (18 mol% MgCO₃ plus brucite), was studied using free-drift methods in distilled water and phosphate-spiked solutions at 25°C and P_CO2 = 1 atm. Small concentrations of phosphate strongly inhibit dissolution rates. Inhibition increases with increased phosphate levels and with approach toward saturation. Near saturation, dissolution rates are reduced by 10³ by the presence of 0.6 μmol adsorbed-P/m². The magnitude of phosphate inhibition is similar to that observed for low-Mg calcite, and like calcite, the mechanism of inhibition is probably by adsorption of P at surface kink sites. Phosphate appears to inhibit removal of Mg and Ca equally during Mg-calcite dissolution. Rates of brucite dissolution are unaffected by phosphate.Mg-calcites containing >8.5 mol% MgCO₃ should be thermodynamically unstable relative to aragonite in most natural waters. Recent work, however, shows that in contrast to its effect on the behavior of Mg-calcites. phosphate does not inhibit aragonite dissolution. The presence of phosphate might thus reverse the relative stability of these two minerals during diagenesis of shallow marine carbonate sediments.     

Influence of phosphate on the oxidation kinetics of nanomolar Fe(II) in aqueous solution at circumneutral pH

The oxygenation kinetics of nanomolar concentrations of Fe(II) in aqueous solution have been studied in the absence and presence of millimolar concentrations of phosphate over the pH range 6.0-7.8. At each phosphate concentration investigated, the overall oxidation rate constant varied linearly with pH, and increased with increasing phosphate concentration. A model based on equilibrium speciation of Fe(II) was found to satisfactorily explain the results obtained. From this model, the rate constants for oxygenation of the Fe(II)-phosphate species FeH₂PO₄⁺, FeHPO₄ and FePO₄⁻ have been determined for the first time. FePO₄⁻ was found to be the most kinetically reactive species at circumneutral pH with an estimated oxygenation rate constant of (2.2 ± 0.2) × 10 M⁻¹ s⁻¹. FeH₂PO₄⁺ and FeHPO₄ were found to be less reactive with oxygen, with rate constants of (3.2 ± 2) × 10⁻² M⁻¹ s⁻¹ and (1.2 ± 0.8) × 10⁻¹ M⁻¹ s⁻¹, respectively.     

Kinetics of oxytetracycline sorption on magnetite nanoparticles

Iron oxide nanoparticles (nano-Fe) have been widely used in environmental remediation, including that of emerging contaminants, such as antibiotics. Magnetite nanoparticles (nano-Fe₃O₄) have been reported to form on the outer surface of nano-Fe and have the potential to be a good sorbent for certain antibiotics. This study reports, for the first time, the kinetics and thermodynamics of adsorption of a common tetracycline group antibiotic, oxytetracycline (OTC), on nano-Fe₃O₄. Batch sorption kinetics were evaluated by varying initial OTC concentration (0.25–2 mM), nano-Fe₃O₄ concentration (2.5–20 g L^?1), pH (3.8–7.6), temperature (5, 15, 35 °C), and ionic strength (0.01–0.5 M KCl) to derive thermodynamic and kinetic constants. Results show that OTC sorption kinetics is rapid and increases with increasing temperature. The derived thermodynamic constants suggest a surface chemical-controlled reaction that proceeds via an associative mechanism. Results indicate the potential of developing a nano-magnetite-based remediation system for tetracycline group of antibiotics.