A DSC study of the polymerization of 2-Vinylpyridine in dimethylformamide

The polymerization of 2-vinylpyridine (2VP) in dimethylformamide (DMF) with azobisisobutyronitrile (AIBN) as initiator was studied with a differential scanning calorimeter. By taking an appropriate amount of AIBN and after correction for its decomposition, the following values could be obtained: Heat of polymerization ΔH_p,o = ?68 ± 4 kJ/mol; overall Arrhenius activation parameters E_a = 90.0 ± 4 kJ/mol and ln A = 24 ± 1.0 (A = 2.6 × 10¹⁰ dm^3/2/mol^1/2. s).     

Ionic association equilibria of copper(II) trifluoroacetate in dimethyl sulphoxide

The molar conductivity curve and changes in the visible spectrum induced by changing concentrations have been determined for Cu(CF₃COO)₂ in dimethyl sulphoxide (DMSO) solution, at 25°C. Coupled with the spectra of the Cu(ClO₄)₂ + Bu₄N CF₃COO mixed solutions the results indicate occurence of the CuCF₃COO⁺ complex as the predominant copper(II) species in the solutions of Cu(CF₃COO)₂. The next higher complex, Cu(CF₃COO)⁰₂, is only formed at high concentrations of Cu(CF₃COO)₂ or under excess concentration of the CF₃COO^? anion. Formation of the first complex has also been studied callorimetrically, its derived thermodynamic characteristics being: K⁰₁ = 697 ± 12, ΔH⁰ = (7.85 ± 0.2) kJ/mol, and ΔS° = (80.6 ± 1.6) J/K mol, at 25°. On the other hand, K⁰₂ is only estimated as 13 ± 5. The results are compared with those previously obtained for the other divalent transition metal trifluoroacetates and the nature of the CuCF₃COO⁺ complex is discussed.     

Surface complexation modeling of soluble molybdenum adsorption by Mn3O4

BACKGROUND: Mo is a harmful element that should strictly be limited in electrolytic manganese dioxide but can readily be removed by Mn₃O₄. However, as its adsorption mechanism is not yet clear the aims of this work are to clarify the absorption phenomena and specific reaction processes of Mo onto Mn₃O₄. RESULTS: Some theoretical parameters have been obtained: the total surface site density and protonation constants (N_T = 6.84 × 10^?3 mol g^?1, , ) were obtained by non‐linear data fitting of acid‐base titrations. Distribution of soluble Mo species derived from thermodynamic calculations showed that the concentration of poly‐molybdenum acid ion was extraordinarily low and could be ignored when the concentration of soluble Mo was 1 mg L^?1. The adsorption isotherm followed the Freundlich adsorption equation. Under the conditions V = 0.15 L, W = 2 g L^?1, [Mo]_T = 1.12 mg L^?1, T = 80 °C, P = 1.013 × 10⁵ Pa, 1.0 mol L^?1 MnSO₄ and pH range 1–6.5, the non‐electrostatic model (NEM) was used to quantify Mo adsorption. CONCLUSION: The surface adsorption complexation modeling of Mo onto Mn₃O₄ can be successfully applied to predict adsorption rates of Mo onto Mn₃O₄ at different pH values, with an absolute error less than 6%. Copyright © 2009 Society of Chemical Industry     

Surface-initiated growth of copper using isonicotinic acid-functionalized aluminum oxide surfaces

Isonicotinate self-assembled monolayers (SAM) were prepared on alumina surfaces (A) using isonicotinic acid (iNA). These functionalized layers (iNA-A) were used for the seeded growth of copper films (Cu-iNA-A) by hydrazine hydrate-initiated electroless deposition. The films were characterized by scanning electron microscopy (SEM), electron-dispersive X-ray spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and advancing contact angle measurements. The films are Cu⁰ but with surface oxidation, and show a faceted morphology, which is more textured (R _q = 460 ± 90 nm) compared to the SAM (R _q = 2.8 ± 0.5 nm). In contrast, growth of copper films by SnCl₂/PdCl₂ catalyzed electroless deposition, using formaldehyde (CH₂O) as the reducing agent, shows a nodular morphology on top of a relatively smooth surface. No copper films are observed in the absence of the isonicotinate SAM. The binding of Cu²⁺ to the iNA is proposed to facilitate reduction to Cu⁰ and create the seed for subsequent growth. The films show good adhesion to the functionalized surface.     

Use of the quinhydrone electrode for the determination of stability constants of copper(II) complexes by continuous potentiometric measurement

The quinhydrone electrode was shown to be utilizable in automatic potentiometric determination of the stability constants of copper(II) complexes. The slow copper(II) ion-quinhydrone interaction reported by Pajdowski and Karwecka[8] did not interfere under controlled experimental conditions with the measurements. Experimental results were subjected to numerical data processing, stability constants being calculated by weighted least squares fitting. Copper(II) 2-, 3- and 4-hydroxybutyrate (a,b,c) and n-butyrate (d) complexes had the following values of logarithm of stability constants: (a) log β₁ = 2·63 ± 0·0.2, log β₂ = 4·31 ± 0·01, (b) log β₁ = 1·86 ± 0·02, log β₂ = 3·12 ± 0·01, (c) log β₁ = 1·80 ± 0·03, log β₂ = 2·63 ± 0·01, (d) log β₁ = 1·85 ± 0.·01, log β₂ = 2·49 ± 0·01.     

Enhanced removal of lead and cadmium from water by Fe3O4-cross linked-O-phenylenediamine nano-composite

A method is presented for surface encapsulation of nano-Fe₃O₄ by o-phenylenediamine via cross-linking using formaldehyde and glutaraldhyde for the formation of two newly designed magnetic nano-sorbents. These have been characterized by FT-IR, TGA, and SEM and maintained the magnetic and thermal stability characters. The metal capacity values of Pb(II) and Cd(II) have been optimized in presence of different physico-chemical parameters and confirmed the superior selectivity for Pb(II). Maximum capacity values of Pb(II) (7000-10000 ± 250-675 µmol g^?1) and Cd(II) (1500-2250 ± 30-75 µmol g^?1) at optimum conditions and excellent extraction values (94.10-100.0 ± 1.2-3.5%) from industrial wastewater have been identified.     

Reaction between Hydrosulfide and Iron/cerium (hydr)oxide: Hydrosulfide Oxidation and Iron Dissolution Kinetics

Hydrosulfide oxidation and iron dissolution kinetics were studied at normal pressure, under inert (N₂) atmosphere, in a liquid–solid mechanically-stirred slurry reactor. The kinetic variables undergoing variations were: hydrosulfide initial concentration (0.90–3.30 mmol/L), oxide initial surface area (16–143 m²/L) and pH (8.0–11.0). The hydrosulfide consumption and products (thiosulfate and polysulfide) formation were quantified by means of capillary electrophoresis, while iron dissolution was monitored through atomic absorption spectroscopy. Most of Fe(II) produced at pH = 9.5 remained associated with the oxide surface in the time-scale of the experiments. The hydrosulfide oxidation by the iron/cerium (hydr)oxide was found to be surface-controlled, with rates (R_i) of both sulfide oxidation and Fe(II) dissolution expressed in terms of an empirical rate equation: R_i = k_i[HS⁻]_t=0^−0.5[A]_t=0[H⁺]_t=0^−0.5 , where k_i represents the apparent rate constants for the oxidation of HS⁻ (k_HS) or the dissolution of Fe(II) (k_Fe), [HS⁻]_{t = 0} is the initial hydrosulfide concentration, [A]_{t = 0} is the initial Fe/Ce (hydr)oxide surface area and [H⁺]_{t = 0} is the initial proton concentration. The rate constant, k_HS, for the oxidation of hydrosulfide at pH = 9.5 was (3.4219 ± 0.65) × 10⁻⁴ mol² L⁻¹ m⁻² min⁻¹, with the rate of hydrosulfide oxidation being ca. 10 times faster than the rate of Fe(II) dissolution (assuming a 1:2 stoichiometric ratio between HS⁻ oxidized and Fe(II) produced; k_Fe = (3.9116 ± 0.41) × 10⁻⁵ mol² L⁻¹ m⁻² min⁻¹).     

Use of three types of magnetic biochar in the removal of copper(II) ions from wastewaters

Three types of magnetic biochars (MBC1, MBC2, and MBC3) were synthesized from biochar using NaBH₄ as a reducing agent of Fe(II) to Fe(0) to remove copper(II) ions from different wastewaters. Based on the research it was found that removal of copper(II) ions by MBC1 occurs with a yield of 99.8% for the concentration 50 mg/dm³ and decreases to 71.7% at 200 mg/dm³. The maximum pH sorption was found at pH 5. The highest correlation coefficient values (65.55 mg/g) were obtained for the Langmuir isotherm model. Application of 0.5 mol/dm³ HNO₃ as a desorbing agent gives the highest desorption percentage 98.92%.     

Effect of LiClO4 on radical polymerization of methyl methacrylate

The effect of LiClO₄ on the polymerization of methyl methacrylate (MMA) with dimethyl 2,2′-azobisisobutyrate (MAIB) was investigated at 50°C in methyl ethyl ketone. The polymerization proceeded homogeneously even at [LiClO₄] as high as 3.00 mol/L. The polymerization rate (R_p) and the molecular weight of the resulting polymer profoundly increased with increasing [LiClO₄]. R_p at 3.00 mol/L [LiClO₄] was 12 times that in the absence of LiClO₄. The rate equation depended on the presence or absence of LiClO₄: R_p = k′[MAIB]^0.5 [MMA]^1.5 in the presence of 3.00 mol/L [LiClO₄] and R_p = k[MAIB]^0.5 [MMA]^1.0 in the absence of LiClO₄. The overall activation energies of polymerization were 38.5 kJ/mol in the presence of 3.00 mol/L [LiClO₄] and 77.4 kJ/mol in the absence of LiClO₄, respectively. The tacticities of resulting poly(MMA) were insensitive to the presence of LiClO₄. In the copolymerization of MMA and styrene, Q and e values of MMA increased with increasing [LiClO₄], leading to enhanced alternating copolymerizability. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1361–1368, 1997     

Adsorption of chlorophyll-a from acetone solution on natural and activated bentonite

The adsorption of chlorophyll-a on bentonite desiccated at 110°C, untreated and acid-treated with H₂SO₄ solutions over a concentration range between 0·25 and 2·50 mol dm^?3, from acetone solution at 25°C has been studied. The adsorption isotherms may be classified as using Giles' classification, as type S (untreated sample and 0·25 mol dm^?3 H₂SO₄-treated sample), type H (0·50 mol dm^?3 H₂SO₄-treated sample) and type L (1·00 and 2·50 mol dm^?3 H₂SO₄-treated samples). This fact suggests that the bentonite surfaces (low, high and medium affinity, respectively) behave in differently relation to the adsorption of the chlorophyll-a molecules. The experimental data points have been fitted to the Freundlich equation in order to calculate the adsorption capacities (K_f) of the samples; K_f values range from 0·43 mg kg^?1 for the untreated bentonite up to 108·89 mg kg^?1 for the 0·50 M H₂SO₄-treated bentonite. The removal efficiencies (R) have also been calculated and range from 5·71% for the untreated bentonite up to 85·18% for the 0·50 M H₂SO₄-treated bentonite.     

Alkaline hydrolysis of homopolymers and copolymers of 2-hydroxypropyl methacrylate

Homopolymers of 2-hydroxypropyl methacrylate (HPMA) and copolymers with acrylic acid (AA) were prepared in 1,4-dioxane. The reactivity ratios were determined to be r_AA = 0.27 ± 0.04 and r_HPMA = 2.2 ± 0.2. The alkaline hydrolysis by sodium hydroxide of the HPMA monomer and polymers showed that while the HPMA monomer hydrolyzed readily as expected for a low-molecular-weight carboxylic ester the HPMA homopolymer and water-soluble sodium acrylate (NaA) copolymers were extremely resistant to alkaline hydrolysis. The saponification reaction followed a second-order rate equation, being first order with respect to both HPMA and hydroxide ion concentration. The Arrhenius parameters, activation energy E and frequency factor A, for the alkaline hydrolysis of HPMA monomer in water were found to be E = 10.3 Kcal/mol and A = 1.5 × 10⁸ L/mol min, and those for the NaA–HPMA copolymers in water were found to be E = 24 kcal/mol and A = 4 × 10¹² L/mol min. The NaA–HPMA copolymers had a limiting extent of hydrolysis, ranging from 9–90% ester conversion. A sharp rate decrease at low conversion was noted during the HPMA homopolymer hydrolysis in 58/42 dimethyl sulfoxide/water, allowing the calculation of two distinct reaction rates. © 1992 John Wiley & Sons, Inc.     

The diffusion coefficient of copper sulphate in aqueous solution

The diffusion coefficient, D, of CuSO₄ in aqueous solution was determined at 298.1 K by chronopotentiometry and also with a rotating disc electrode using the mixed control Levich equation. For 0 < [CuSO₄] < 0.05 mol dm^?3, D = {7.35 ± 0.18 ? (5.3 ± 1.4) [CuSO₄]^{$\text{1}\text{2}$}} × 10^?10 m² s^?1, at a constant ionic strength of 1.58 mol dm^?3 maintained with either H₂SO₄ or Na₂SO₄ (pH = 2). It was shown that substantial variations in the concentration of the supporting electrolyte had negligible effect on the above values of D. It was found that literature values of D vary over a three-fold range, even when corrected to the same temperature and CuSO₄ concentration. Much of this variation probably arises from rotating disc determinations carried out at disc potentials where activation control is significant. This problem is overcome if the mixed control Levich equation is used to treat the data instead of the commonly used simple (diffusion only) Levich equation.     

EXPERIMENTAL STUDIES AND PARAMETER OPTIMIZATION OF SEPARATION OF COPPER USING HOLLOW FIBER–SUPPORTED LIQUID MEMBRANE

The separation of copper from a leach liquor bearing 204.59 mol/m³ Cu, 40.83 mol/m³ Zn, 33.94 mol/m³ Co, 255.58 mol/m³ Ni, and 75.72 mol/m³ (NH₄)₂SO₄ has been carried out with a hollow fiber membrane using LIX 84-I as the mobile carrier. Central composite inscribed (CCI) design was used to design the experiments. The factors considered for the CCI design were pH, LIX 84-I concentration in the membrane phase, flow rate, and acid concentration in the strip solution. A reduced quadratic model was found to fit the experimental data. Detailed analysis of the effect of different factors as well as their interaction on the extraction of copper has been done. The optimized condition for maximum copper flux was found to be pH 4.5, 39.88% LIX 84-I, 360 mL/min flow rate, and 7% H₂SO₄ in strip solution. The highest copper flux of 7.46 × 10^?5 mol/m² · s was obtained experimentally at the above conditions, which is in good agreement with the predicted value of 7.57 × 10^?5 mol/m² · s.     

Neue photoreaktive Polymere mit seitenständigen Dimethylmaleinimid-Gruppen. I. Radikalische homo-und copolymerisation von N-(5-methyl-3-oxa-4-oxo-hexen-5-yl)-dimethylmaleinimid

The homopolymerisation of N-(5-methyl-3-oxo-4-oxo-hexen-5-yl)-dimethylmaleimide (DMI-MA) leads to linear poly(methylmethyacrylates) with pendant lightsensitive dimethylmaleimide groups. Due to steric hindrance of the methyl substitutents, the carbon-double bond is not involved in the reaction, even at conversions of over 90%. The reaction velocity constant for the homopolymerisation is k_p/k = 2,0 – 2,2.10^?2 (65°C, toluene, AIBN) and the activation energy E_a = 62,36 ± 2 KJ/mol^?1. Measurement of the copolymerisation reactivity ratios for the monomer pairs DMI-MA/methacrylic acid (MAS), DMI-MA/methylmethacrylate (MMA) and DMI-MA/ethylacrylate (EA) gave the following values: DMI-MA (r₁): MAS (r₂) = 1,36 ±0,06 : 0,77: ± 0,06; DMI-MA (r₁) : MMA (r₂) = 1,16 ± 0,17:0,475 ± 0,17 and DMI-MA (r₁): EA(r₂) = 1,60 ± 0,15: 0,44 ± 0,15.     

Heavy Metal Removal and Neutralization of Acid Mine Waste Water ‐ Kinetic Study

The influence of the apatite on the efficiency of neutralization and on heavy metal removal of acid mine waste water has been studied. The analysis of the treated waste water samples with apatite has shown an advanced purification, the concentration of the heavy metals after the treatment of the waste water with apatite being 25 to 1000 times less than the Maximum Concentration Limits admitted by European Norms (NTPA 001/2005). In order to establish the macro‐kinetic mechanism in the neutralization process, the activation energy, Ea, and the kinetic parameters, rate coefficient of reaction, k_r, and k_t were determined from the experimental results obtained in “ceramic ball‐mill” reactor. The obtained values of the activation energy Ea >> 42 kJ mol^?1 (e.g. Ea = 115.50 ± 7.50 kJ mol^?1 for a conversion of sulphuric acid η_H2SO4 = 0.05, Ea = 60.90 ± 9.50 kJ mol^?1 for η ^H2SO4 = 0.10 and Ea = 55.75 ± 10.45 kJ mol^‐1 for η ^H2SO4 = 0.15) suggest that up to a conversion of H2SO4 equal 0.15 the global process is controlled by the transformation process, adsorption followed by reaction, which means surface‐controlled reactions. At a conversion of sulphuric acid η ^H2SO4 > 0.15, the obtained values of activation energy Ea < 42 kJ mol^‐1 (e.g. Ea = 37.55 ± 4.05 kJ mol^‐1 for η ^H2SO4 = 0.2, Ea = 37.54 ± 2.54 kJ mol^‐1 for η ^H2SO4 = 0.3 and Ea = 37.44 ± 2.90 kJ mol^‐1 for η ^H2SO4 = 0.4) indicate diffusion‐controlled processes. This means a combined process model, which involves the transfer in the liquid phase followed by the chemical reaction at the surface of the solid. Kinetic parameters as rate coefficient of reaction, kr with values ranging from (5.02 ± 1.62) 10‐4 to (8.00 ± 1.55) 10‐4 (s^‐1) and transfer coefficient, kt, ranging from (8.40 ± 0.50) 10‐5 to (10.42 ± 0.65) 10‐5 (m s^‐1) were determined.     

Extraction of Actinide(III,IV, V,VI) Ions and TcO4 − by N,N,N′,N′‐Tetraisobutyl‐3‐Oxa‐Glutaramide

Abstract

The extraction behavior of U(VI), Np(V), Pu(IV), Am(III), and TcO₄ ^? with N,N,N′,N′‐tetraisobutyl‐3‐oxa‐glutaramide (TiBOGA) were investigated. An organic phase of 0.2 mol/L TiBOGA in 40/60% (V/V) 1‐octanol/kerosene showed good extractability for actinides (III, IV, V VI) and TcO₄ ^? from aqueous solutions of HNO₃ (0.1 to 4 mol/L). At 25°C, the distribution ratio of the actinide ions (D _An) generally increased as the concentration of HNO₃ in the aqueous phase was increased from 0.1 to 4 mol/L, while the D _Tc at first increased, then decreased, with a maximum of 3.0 at 2 mol/L HNO₃. Based on the slope analysis of the dependence of D _M (M=An or Tc) on the concentrations of reagents, the formula of extracted complexes were assumed to be UO₂L₂(NO₃)₂, NpO₂L₂(NO₃), PuL(NO₃)₄, AmL₃(NO₃)₃, and HL₂(TcO₄) where L=TiBOGA. The enthalpy and entropy of the corresponding extraction reactions, Δ_r H and Δ_r S, were calculated from the dependence of D on temperature in the range of 15–55°C. For U(VI), Np(V), Am(III) and TcO₄ ^?, the extraction reactions are enthalpy driven and disfavored by entropy (Δ_r H<0 and Δ_r S<0). In contrast, the extraction reaction of Pu(IV) is entropy driven and disfavored by enthalpy (Δ_r H>0 and Δ_r S>0). A test run with 0.2 mol/L TiBOGA in 40/60% 1‐octanol/kerosene was performed to separate actinides and TcO₄ ^? from a simulated acidic high‐level liquid waste (HLLW), using tracer amounts of ²³⁸U(VI), ²³⁷Np(V), ²³⁹Pu(IV), ²⁴¹Am(III) and ⁹⁹TcO₄ ^?. The distribution ratios of U(VI), Np(V), Pu(IV), Am(III) and TcO₄ ^? were 12.4, 3.9, 87, >1000 and 1.5, respectively, confirming that TiBOGA is a promising extractant for the separation of all actinides and TcO₄ ^? from acidic HLLW. It is noteworthy that the extractability of TiBOGA for Np(V) from acidic HLLW (D _Np(V)=3.9) is much higher than that of many other extractants that have been studied for the separation of actinides from HLLW.     

Synthesis,Characterization, and Applications of a New Chelating Resin Containing 4-2-(Thiazolylazo) Resorcinol (TAR)

A new phenol–formaldehyde based chelating resin containing 4-(2-thiazolylazo) resorcinol (TAR) functional groups has been synthesized and characterized by Fourier transform infrared spectroscopy and elemental analysis. Its adsorption behavior for Cu(II), Pb(II), Ni(II), Co(II), Cd(II), and Mn(II) has been investigated by batch and column experiments. The chelating resin is highly selective for Cu(II) in the pH range 2 ～ 3, whereas alkali metal and alkaline earth metal ions such as Na(I), Mg(II), and Ca(II) are not adsorbed even at pH 6. Quantitative recovery of most metal ions studied in this work except Co(II) is achieved by elution with 2M HNO₃ at a flow rate of 0.2 mL min^?1. A similar trend is observed for distribution coefficient values. The quantitative separations achieved on a mini-column of chelating resin include Cd(II) – Cu(II), Mn(II) – Pb(II), Co(II) – Cu(II), Mn(II) – Ni(II), and Mn(II) – Co(II) – Cu(II). The recovery of copper(II) is quantitative (98.0–99.0%) from test solutions (10–50 mg/L) by 1 mol/L HNO₃-0.01 mol/L EDTA. The chelating resin is stable in acidic solutions below 2.5 M HNO₃ or HCl as well as in alkaline solution below pH 11. The adsorption behavior of the resin towards Cu(II) was found to follow Langmuir isotherm and second order rate.     

Modeling of the Extraction Equilibrium of Copper from Sulfate Solutions with Acorga M5640

The extraction equilibrium of copper from sulfate media with the aldoxime Acorga M5640 in ShellSol D70 has been investigated. The distribution results were interpreted by taking into account the nonideality of the aqueous phase. The activity of copper and hydrogen ions in the target systems CuSO₄/H₂SO₄/Na₂SO₄ and CuSO₄/H₂SO₄/Fe₂(SO₄)₃/ZnSO₄ were calculated through the speciation of the aqueous solutions and by applying the Pitzer model. The experimental pH values were found in good agreement with the predicted pH values. A model considering the dimerization of the aldoxime extractant was proposed to predict the distribution ratio and the copper loading isotherms. The extraction constant at infinite dilution and the apparent dimerization constant were evaluated from the experimental data and were found to be 10^{3.06 ± 0.07} and 51 ± 9 M^?1, respectively, at 25°C.     

Effect of the addition of fluoride on the conditional solubility of alumina in LiCl-KCl eutectic melt

Owing to its well-known high complexing power toward Al³⁺ ion, fluoride ion is able to increase the solubility of alumina in alkali chloride melts. To determine the extent of this effect, the formation of aluminium(III) fluoro-complexes was studied potentiometrically in LiCl-KCl eutectic at 470°. But the sodium fluoride addition appeared to produce not only the complexation effect but also a mineralization effect on alumina. So, the thermodynamical stability of alumina formed in this melt by precipitation from aluminium chloride with carbonate ion (oxide anion donor) depends on the fluoride ion concentration. These two effects explain the solubility variation of alumina in the LiCl-KCl eutectic + NaF mixtures. A pF^? - pO^2? diagram, which represents the stability area of the various aluminium (III) species is established, and leads to some conclusions concerning the electrowinning of aluminium from molten chloride melts.The cumulative formation constants of the aluminium(lII) fluoro-complexes (AlF^3?i_i) have been obtained, whose values are the following: 2.5 ± 0.4, 4.7 ± 0.6, 5.7 ± 0.5, 7.5 ± 0.4, 8.0 ± 0.5, 9.0 ± 0.6, respectively for i = 1, 2, 3, 4, 5 and 6. It has been shown that oxyfluoride species such as AlOF^1?j_i does not exist. The solubility products of gamma and alpha-alumina have been determined and are equal to 10^?42.9 and 10^?44.0 respectively (all the constants are given in the molality scale). They differ widely from the solubility product of the alumina obtained in the absence of fluoride ion, ie 10^?27.4.     

Oxidation of Esculetin,a Model Pollutant Present in Cork Processing Wastewaters,by Chemical Methods

The ozonation of esculetin (6,7-dihydroxycoumarin), a major pollutant present in the wastewater generated in the cork industry, was accelerated at high pH, with apparent second-order rate constants in the range from 3.3 × 10⁴ L/(mol·s) at pH=2 to 8.4 × 10⁷ L/(mol·s) at pH=9. The acid-base equilibrium of esculetin was studied, resulting in a pK_a value of 7.37. Taking into account this pK_a, the rate constants for the reaction between ozone and the un dissociated and dissociated forms of esculetin were 3.0 × 10⁴ and L/(mol·s) 6.67 × 10⁸ L/(mol·s), respectively. Apparent first-order rate constants for the photolysis by UV irradiation were also evaluated, with values between 0.12 × 10^?2 min^?1 at pH=2 and 1.15 × 10^?2 min^?1 at pH=9, while the quantum yields for this photo-degradation reaction varied from 0.99 × 10^?2 mol/Eins to 11.1 × 10^?2 mol/Eins at these pHs. The Fenton's reagent system was used for the generation of hydroxyl radicals, and the rate constant for the reaction between esculetin and these radicals was determined to be 1.06 × 10¹⁰ L/(mol·s). Finally, several chemical oxidation systems were used in the degradation of this pollutant: single oxidants (ozone, UV irradiation) and advanced oxidation processes (Fenton's reagent, UV/H₂O₂, O₃/H₂O₂, O₃/UV, O₃/H₂O₂ /UV, and photo-Fenton system). The results revealed that the most efficient methods in terms of esculetin removal were ozonation among the single oxidants, and the photo-Fenton system among the combined processes.