Precipitate flotation. V. Extractive solvent sublation

The new technique of precipitate flotation of the second kind is unique amongst flotation processes in that it requires no surfactant. This does have the disadvantage that the floated material is not supported on the surface and tends to redisperse into the solution. A layer of immiscible organic solvent containing either a surfactant, a complexing agent, or the original precipitant, leads to solubilisation and retention of the floated material. As this is quantitative, spectrophotometric examination of the organic layer may provide a means of analysis for the ion originally precipitated. Complete removal from solutions as dilute as 10^?5 M is possible.     

Ion flotation of dichromate and of complexed cyanide: Surfactants for qualitative analysis

Ion flotation studies have shown that a surface-active agent is useful for qualitative analysis of complex ions in dilute aqueous solution, with the surfactant forming a particulate complex with the complex ion of concern. Experiments with a monovalent, cationic surfactant have established the prevalence of Cr₂O₇ ²⁻ (HCrO₄ ⁻) and not CrO₄ ²⁻; of [Fe(CN)₆]⁴⁻ and [Fe(CN)₅H₂O]³⁻; and of [FeFe(CN)₆]²⁻ and not [FeFe(CN)₆]⁻ or [Fe(CN)₆]³⁻. The results can be contrasted to those with ions that do not form particulate complexes with the surfactant, such as HPO₄ ²⁻ and phenolate; with the latter, no qualitative analytical information can be gained. Ion flotation appears to be a promising technique in general for the determination of ionic species present in aqueous solution; the surfactant must react with the ion of significance to form a particulate complex and the initial surfactant concentration must be controlled carefully.     

溶剂浮选法在分析化学中的应用进展

溶剂浮选法是一种集富集与分离于一体的分析方法.近些年来,因其具有选择性高、分离效果好、富集倍数大等特点越来越受到关注.综述了溶剂浮选法在分析化学中的应用,主要介绍溶剂浮选法分离痕量金属离子、有机物以及分析中草药成分方面的研究,并对其在现有的应用领域的研究进展进行了探讨.     

双水相气浮溶剂浮选-紫外分光光度法测定水中痕量氯霉素

采用双水相气浮溶剂浮选这一新型、绿色的方法分离富集水体中痕量氯霉素,用光度法检测。考察了分相盐、p H、浮选时间、氮气流速等条件,得出最佳浮选条件为:分相盐Na Cl,p H=10,浮选时间为40 min,氮气流速为25 m L/min。氯霉素浓度在1.29~25.8μg/m L浓度范围内线性关系良好,回归方程:A=0.030 3C+0.024 4,相关系数R=0.999 0。此条件下,浮选率为91.2%,用该方法分析环境水体中痕量氯霉素含量,结果令人满意。     

双水相气浮溶剂浮选-紫外分光光度法测定水中痕量氯霉素

采用双水相气浮溶剂浮选这一新型、绿色的方法分离富集水体中痕量氯霉素,用光度法检测。考察了分相盐、p H、浮选时间、氮气流速等条件,得出最佳浮选条件为:分相盐Na Cl,p H=10,浮选时间为40 min,氮气流速为25 m L/min。氯霉素浓度在1.29²5.8μg/m L浓度范围内线性关系良好,回归方程:A=0.030 3C+0.024 4,相关系数R=0.999 0。此条件下,浮选率为91.2%,用该方法分析环境水体中痕量氯霉素含量,结果令人满意。     

Potentiometric study of silver cyanide complexes

The nature of silver cyanide complexes has been studied at constant ionic strength by the potentiometric method. Measurements have been carried out in the range 1:1 to 1:20 (Ag⁺:CN⁻) and for Ag⁺ concentrations between 0·005 and 0·1 M. Two inflexions corresponding to AgCN and Ag(CN)₂⁻ have been observed at the ratios 1:1 and 1:2. The formation of Ag(CN)₄³⁻ and Ag(CN)₄²⁻ has been found to occur gradually. The existence of Ag(CN)₃³⁻ has been proved. Stability constants have been calculated from the intercept of the linear relation between the formal potential of the complex and the logarithm of CN⁻ concentration. The number of cyanide ligands has been estimated from the slope of this relation. The results indicate the possible occurrence of a mixture of the 3 and 4-coordinated complexes at high cyanide concentrations.     

The electroreduction of benzyl cyanide on iron and cobalt cathodes

An electrochemical method for preparing amines from organic cyanides using iron black and cobalt black cathodes has been studied. Benzyl cyanide underwent smooth reduction at a cobalt black cathode in an aqueous ethanolic ammonium sulphate medium to give a 74% yield of 2-phenylethylamine with a current efficiency of 50%; whereas with an iron black cathode under the same conditions, a 57% yield of 2-phenylethylamine has been obtained with a current efficiency of 33%.     

Mixed valences system in cobalt iron cyanide. Microporous structure stability

Divalent transition metal hexacyanoferrates(III) have a microporous framework appropriate for separation and storage of small molecules. The nature of such porous framework is found in the existence of systematic vacancies of the building unit, the hexacyanoferrate octahedral block, [Fe(CN)₆], in the material structure. The relatively low thermal stability appears to be the main limitation of these materials for such applications. In the as-synthesized material the available free volume is occupied by water which, can be removed by moderated heating but always involving decomposition of at least a small sample fraction. For cobalt a unique behavior has been observed. The heating of cobalt(2+) hexacyanoferrate(III) leads to an inner charge transfer to form the mixed valences Co(2+)Co(III) hexacyanoferrate(II,III) system. Since this inner oxidation–reduction reaction does not modify the coordination environments for the involved metals, the porous nature of the parent compound could be preserved and at the same time with a higher thermal stability related to the formation of the most stable ferrous species. The porous structure of the obtained material was evaluated from CO₂ adsorption, X-ray diffraction, thermo-gravimetric, and infrared and Mössbauer spectroscopic data. The heat-induced charge transfer is accompanied of a progressive fracture of the material crystallites and also of a decrease for the pore volume as detected by the CO₂ adsorption. For comparative purposes, a parallel study on a porous Prussian blue (ferric hexacyanoferrate(II)) species was carried out. The porous framework of this last material is also related to systematic vacancies of the hexacyanoferrate building block but without the mentioned heat-induced charge transfer effect. In this case the sample heating has no effect on the material porous properties.     

溶剂浮选法回收湿法磷酸中碘的研究

溶剂浮选法回收湿法磷酸中的碘是一种新工艺.采用二次回归旋转实验设计方法组织实验,对实验数据处理得到的预测回归方程在实验范围内可以较好地预测各因素在不同条件下对碘回收率的影响.结果表明,影响碘回收率的最重要的因素是浮选时间、溶剂量和氧化时间.以碘回收率为指标,得出溶剂浮选法回收湿法磷酸中碘的最佳工艺条件(固定条件:湿法磷酸用量50 mL,N2流速40 mL/min):捕收剂CTMAB用量0.065 g、溶剂苯用量12 mL、氧化时间18 min、浮选时间25 min.     

The ligand-structure-selective binding of oligonucleotide by cobalt complexes

The binding of two Co(III) complexes [Co(phen)₂(DPQ)]³⁺ and [Co(phen)₂(HPIP)]Cl₃ [HPIP = 2-(2-hydroxyphenyl) imidazo [4,5-f][1,10] phenanthroline, DPQ = dipyrido[3,2-f:2′,3′-h]quinoxaline] to the normal base-paired decanucleotide d(CCTAATTAGG)₂ was studied by 2D NMR. The results indicate that the width of intercalating ligand has a large effect on the selectivity of binding site. For [Co(phen)₂(HPIP)]Cl₃, the complex binds the decanucleotide at C₂T₃:G₉A₈ and A₄A₅:T₇T₆ by intercalation from the minor groove, while [Co(phen)₂(DPQ)]³⁺ intercalates into T₃A₄:T₇A₈ region from the minor groove. The conclusion was further proved by molecular modeling.     

Ion and solvent transfers and trapping phenomena during n-doping of PEDOT films

Electrochemical quartz crystal microbalance (EQCM) measurements were made during the n-doping of PEDOT films exposed to a range of electrolytes (TEABF₄, TPABF₄ and TEATos) in CH₃CN solvent. The films were acoustically thin (“rigid”), so that the EQCM response could be interpreted gravimetrically. Correlation of the current with the time differential of the mass response allowed the determination of dopant ion and solvent fluxes as functions of applied potential during cyclic voltammetric experiments. This interpretation required the use of Faraday's law, the electroneutrality condition and the assumption (supported by variation of co-ion) that the film is permselective. The ion and solvent fluxes are in opposing directions for TEA⁺ insertion, but in the same direction for TPA⁺ insertion. As a result, the net mass change is much smaller in TEABF₄ electrolyte. In both the doping or undoping half-cycles, the ion and solvent fluxes normalise with potential scan rate, indicating that they are not subject to kinetic or transport limitations on the moderate time scale of the experiment. However, there is considerable hysteresis between the responses in the two scan directions, indicating the presence of slow polymer-based processes. When the potential limits are extended to encompass p- and n-doping regimes sequentially, additional response components on the rising edges of the two doping processes signal the participation of “trapping” phenomena. The amounts of trapped dopant charge are independent of potential scan rate for both p- and n-doping. The fraction of injected charge that is trapped is larger by an order of magnitude for cation, but the absolute amounts of trapped ion are similar for cation and anion.     

Activated carbon adsorption of cyanide complexes and thiocyanate ion from petrochemical wastewaters

Experimental isotherms indicate that thiocyanate and nickel cyanide complex (tetracyanonicklate (II)) adsorb to an equal extent from synthetic and actual waste solutions at loadings below 10 mg/g carbon. Loading of nickel hexammine complex is an order of magnitude less. Adsorption of the divalent nickel cation is strongly pH dependent and is believed to be a chemisorption by precipitation or reaction on the carbon surface. In pure solution, ferrocyanide (hexacyanoferrate (II)) adsorption was comparable to that of thiocyanate or nickelocyanide, but adsorption from the waste liquor tested was negligible. This difference may be due to solvation of ferrocyanide with methanol in the wastewater to form a species with entirely different adsorption characteristics. Chemical oxygen demand (COD) values were obtained for several of the pure materials (SCN^?, 1.1; Fe(CN)₆^?4, 0.5; Ni(CN)₄^?2, 0.4 mg $\text{COD}\text{mg}$ ion) and the wastewater to monitor adsorption of organic background materials.     

Ion—solvent interactions in acetonitrile + water mixtures

Standard Gibbs energies of transfer, ΔG°_t of alkali metal chlorides (M = Li, Na, K, Rb and Cs) and potassium bromide and iodide from water to the aqueous mixtures of 20, 40, 60 and 80 mass per cents of acetonitrile (ACN) have been determined at 25°C from emf measurements performed on the double cell comprising AgAg X and M (Hg) electrodes. The individual ionic contributions to ΔG°_t have also been evaluated using the reference electrolyte (RE = Ph₄AsBPh₄) method, the required ΔG°_t's of the RE being obtained from the measured solubilities of salts viz. Ph₄AsPic, KBPh₄ and KPic (Pic = picrate and Ph = phenyl). The observed increasing ΔG°_t values of the halide ions X^? and their order Cl^? ? Br^? ? I^? furnish the thermodynamic evvidence for the effect of the well known decreased H-bonding and the anion destabilizing propensities of dipolar aprotic cosolvent ACN. But the observed shallow minima in ΔG°_t-composition profiles for M⁺ and H⁺ are indicative of the result of the oppositg effects of water structure breaking propensities and the protophobic character of ACN and their relative order is the combined effects of acid—base, Born-type and soft—soft interactions. Moreover, while the distinctly pronounced stabilization of large tetraphenyl ionshas been ascribed as the combined effects of dispersion and cavity-forming interactions, the less pronounced solvation of Pic^? has been attributed to the combined effects of increased dispersion interactions of benzene nucleus and of decreased H-bonding interactions of O-atoms of the substituents. These contentions have been further substantiated by comparing ΔG°_t(i) values of some selected ions in ethylene glycol—water mixtures.     

离子液体溶剂浮选法分离富集盐湖卤水中的锂

首次将疏水性离子液体(IL)1-辛基-3-甲基咪唑六氟磷酸盐应用于溶剂浮选,对盐湖卤水中的锂进行富集分离,用火焰原子吸收光谱法对锂进行测定。考察了磷酸三丁酯(TBP)用量、相比V(O):V(A)、浮选时间、气体流速、浮选温度、共存离子、溶液的pH值对浮选率的影响。结果表明,最佳浮选条件为:浮选温度40℃,V(TBP):V(IL)=8:1,相比V(O):V(A)=5,气体流速为50 mL/min,溶液pH=2.5时浮选15 min,此时Li+的浮选率达到85%。离子液体作为浮选剂用来浮选Li+也适用于痕量锂的分析检测。     

Ion, solvent and polymer dynamics in polyaniline conducting polymer films

We describe the application of a new model for the visualization of mobile species (ion and solvent) transfers accompanying redox switching of electroactive films. The system studied was polyaniline, for which the mobile species population changes were determined from redox-driven film mass changes using a thickness shear mode acoustic wave resonator. Acoustic admittance data were used to establish conditions under which the resonator frequency response could be interpreted gravimetrically. Charge and frequency changes accompanying the first redox transition of polyaniline films exposed to aqueous perchloric acid were then used to determine the film's ion and solvent populations. The data are best described by a mechanism in which the early stages of film oxidation are associated with proton transfer (exit) and the latter stages with perchlorate transfer (entry) to satisfy electroneutrality; solvent enters throughout film oxidation and exits throughout film reduction. The alternative of a single ion satisfying electroneutrality throughout would require the rather less likely situation of a non-monotonic solvent flux. Application of the model's diagnostic criteria indicates that the film solvent population is in equilibrium on the timescale of slow scan voltammetry, but shows thermodynamic non-idealities. Hysteresis in the film ion population signals failure of the redox state to maintain equilibrium with the applied potential.     

Ion and solvent transfers at homoionic junctions between concentrated electrolyte solutions

A unified treatment of liquid junction potentials and membrane potentials which accounts for both ionic and solvent transfers at homoionic junctions between ultra concentrated electrolyte solutions, also in terms of the primary hydration parameters and the Stokes-Robinson hydration theory, is described. Application to the determination of cation transference numbers, ₊, water transference numbers, _w, and primary hydration numbers,h, is described as a rational scheme for characterization of concentrated electrolytes as possible new salt bridges for the minimization of liquid junction potentials in electroanalysis. Examples of application of this scheme are presented based on multiple regression analysis of electromotive force measurements of such homoionic concentration cell as Ir | Cl₂ | HCl (m ₂) HCl (m ₁) | Cl₂ | Ir and Hg | Hg₂SO₄ | Li₂SO₄ (m ₂) Li₂SO₄ (m ₁) | Hg₂SO₄ | Hg, with fixedm ₁ molality and variedm ₂ molality. Based on the electromotive force of analogous homoionic transference cells but with interposed membranes, application of the present procedure can be extended to the determination of ion and solvent transport parameters, notably the degree of permselectivity, of membranes for use either as selective sensors in electroanalysis or selective separators in industrial electrochemistry.     

Voltammetric study of the cyanide complexes of osmium—II. The behaviour of lower oxidation state cyanide complexes of osmium on a platinum rde

It was found that the product of the reduction of the cyanide complex of hexavalent osmium, OsO₂(OH)₂(CN)^2?₂ is the Os(OH)₄(CN)^3?₄ complex and the product of the reduction of the OsO₂(CN)^2?₄ complex is the Os(OH)₂(CN)^2?₂ complex. Further reduction of the Os(OH)₄(CN)^3?₄ complex of trivalent osmium is complicated by a follow-up chemical reaction and the stable reduction product is a complex of divalent osmium, Os(OH)₂(CN)^4?₄ which forms a reversible redox system with the Os(OH)₂(CN)^3?₂ complex with a formal redox protential (1 M KOH, 0.1 M KCN) of ?760 mV/sce. The Os(OH)₄(CN)^3?₂ and Os(OH)₂(CN)^4?₄ complexes are stable only in solutions with at least a ten-fold excess of OH^? ions over the concentration of CN^t- ions. At greater cyanide concentrations, the chemical reactioins, Os(OH)₄(CN)^3?₂ → Os(OH)₂(CN)^3?₄ and Os(OH)₂(CN)^4?₄ → Os(CN)^4?₆, occur. The reaction rate for the latter reaction was found to be ?₄ = 1.87 × 10^t-4 l mol^?1 s^?1 in solutions with pH = 11.8. The characteristics of the individual forms of the cyanide complexes of osmium are also discussed.     

Magnetostructural study of tetracoordinate cobalt(II) complexes

Five tetracoordinate cobalt(II) complexes of the formula [CoX₂L₂] have been investigated by SQUID magnetometry; X is the (pseudo)halide ligand and L is the N- or P-donor ligand. The complexes exhibit a moderate magnetic anisotropy expressed by the zero-field splitting parameter D. Its value ranges as D/hc = −13 to + 5 cm 21 −1. The value of the D-parameter increases with the angular deformation δ that measures a deviation of the X–Co–X and L–Co–L angles with respect to the ideal tetrahedron.     

Stability constants of cobalt(II) chloride complexes

Cobalt-60 has been used as a tracer in an investigation of solutions containing cobalt(II) chloride complexes. By a cation-exchange method values have been obtained for the stability constants β_j = [CoCl_j^(2−j)+]/[Co²⁺][Cl⁻]^j, valid for 20° and ionic strength 0·691 M maintained with perchloric acid.