Mass transfer and deodorization efficiency in a countercurrent spray tower for low superficial gas velocities

The aim of this study was to characterize mass transfer and deodorization efficiency in a countercurrent spray tower for low superficial gas velocities. The influence of operating parameters (U_G = 0.005 to 0.025 m s^?1, U_L = 6.1 × 10^?5 to 2.4 × 10^?4 m s^?1) on the liquid retention (ε_L), the drop diameter (d_g), the interfacial area (a) and the overall liquid and gas phase mass transfer coefficients (K_La, K_Ga) were estimated. The spray efficiency of some malodorous compounds was also estimated. A negative influence of the superficial gas velocity was demonstrated, during the spraying of water or chemical neutralizing scrubbing solutions. There was also an increase with the liquid flow rate. Abatements obtained were very good with respect to ammonia (>90%), and acceptable for the other compounds.     

Treatment of settled piggery waste by a down‐flow anaerobic fixed bed reactor

A study of the effect of organic volumetric loading rate (B_V) on the performance of a down‐flow anaerobic fixed bed reactor (DFAFBR) treating settled piggery waste was carried out at a range of between 1.1 and 6.8 g COD dm^?3 d^?1. The reactor operated at good removal efficiencies and stability under the operational conditions studied. Logarithmic empirical equations described adequately the removal efficiency for different parameters studied (COD, SCOD, BOD, TS, VS, TSS, VSS and phosphorous). Although process stability was affected by the increase of B_V, process failure was not observed. A logarithmic relationship was found to describe the influence of B_V on the TVFA/alkalinity ratio (p). A linear correlation was found between the effluent substrate concentration and the values of p and between p and the CO₂/CH₄ ratio in the biogas. The effect of the hydraulic volumetric loading rate (H_V) on the flow pattern of the reactor was evaluated. Dispersion number (D_n) was in the range of 0.17–0.37 for the maximum and minimum values of H_V studied, respectively. The ratio between the real and theoretical HRT increased as the H_V decreased. These results demonstrate that axial dispersion increased as the H_V and the Reynolds number decreased. Due to the hydraulic behaviour of the reactor, the kinetic model developed by Lawrence and McCarty was used for describing the experimental results obtained. Maximum specific substrate removal rate (K), specific organic loading rate constant (K_L), microbial decay coefficient (K_d), microbial yield coefficient (Y), maximum microbial growth rate (U_M) and saturation constant (K_S) were found to be: 3.1 (g COD g VSS^?1 d^?1), 3.0 (g COD g VSS^?1 d^?1), 0.062 (d^?1), 0.15 (g VSS g COD removed^?1), 0.39 (d^?1) and 2.6 (g SCOD dm^?3), respectively. Copyright © 2004 Society of Chemical Industry     

Electrodeposition from a fluidized bed electrolyte. II. Effects of bed porosity and particle size

Mass transfer from a fluidized bed electrolyte containing inert particles has been found to depend on bed porosity and particle size. The optimum porosity was found to vary from 0.52 – 0.57 with decreasing particle size but mass transport increased with particle size.A mass transfer entry length effect was observed on the cylindrical cathode but its position within the bulk of the bed was found not to be critical, thus indicating that the hydrodynamic entry length was small. The limiting current density was found to vary as (d _e/L _e)^0.15 whered _e is the annular equivalent diameter andL _e the electrode length.List of symbols Re_I modified Reynolds No. =U _o d _p /v(1–) - Re_II particle Reynolds No. =U _o d _p /v - Re_O sedimentation Reynolds No. =U _i d _p v (constant value) - Re_t terminal particle Reynolds No. =U _t d _p /v - Sc Schmidt No. =v/D - St_I modified Stanton No. =k _L /U _o - C _b bulk concentration, M cm^–3 - D diffusion coefficient, cm² s^–1 - d _t tube diameter, mm - d _e electrode equivalent diameter, mm - d _p particle diameter, mm - bed porosity - zF Faradaic equivalence - cd current density - i _L limiting current density, mA cm^–2 - i _LO limiting current density in the absence of particles - k _L mass transfer coefficient, cm s_–1 - L _e electrode length, mm - m, n constants or indices - v kinematic viscosity, cm² s^–1 - U _o superficial velocity, cm s^–1 - U _i sedimentation velocity, cm s^–1     

Kinetic data and substrate specificity of a keratinase from Chryseobacterium sp. strain kr6

BACKGROUND: Keratinases are important enzymes for biotechnological processes involving keratin hydrolysis. In this work substrate specificity and kinetic properties of a keratinase from Chryseobaterium sp. were investigated. RESULTS: The optimal conditions for activity of purified keratinase with respect to pH, temperature and sodium chloride concentration were established using factorial design and surface response techniques. The optimum conditions for keratinase activity were pH from 7.4 to 9.2, temperature from 35 °C to 50 °C and NaCl concentration from 50 to 340 mmol L^?1, having azocasein as substrate. Subsequently, the kinetic parameters for this substrate were determined to be K_m = 0.75 mg mL^?1 and V_max = 59.5 U min^?1. The K_i value for 1,10‐phenanthroline was estimated at 0.78 mmol L^?1. The enzyme specificity was evaluated over different synthetic and insoluble substrates. The protease exhibited specificity with selectivity for hydrophobic and positively charged residues. In relation to the insoluble substrates, the enzyme hydrolyzed preferably chicken nails. CONCLUSIONS: This enzyme effectively hydrolyzes insoluble keratin substrates. The knowledge of keratinase properties is an essential step in the development of biotechnological processes involving keratin hydrolysis. Copyright © 2008 Society of Chemical Industry     

Enhanced mass transfer at the rotating cylinder electrode: III. Pilot and production plant experience

Enhanced mass transfer at a rotating cylinder electrode, due to the development of surface roughness of a metal deposit, has been studied in a range of commercial and pilot scale reactors known as ECO-CELLS. The data obtained for relatively restricted ranges of process parameters show reasonable agreement with the more definitive data obtained under laboratory conditions. With scale-up factors of approximately six times in terms of the rotating cylinder diameter, enhanced mass transfer factors of up to 30 times are reported (in comparison with hydrodynamically smooth electrodes) due to the development of roughened deposits during the process of metal extraction from aqueous solution.Nomenclature a, b, c constants in Equation 15 - A active area of rotating cylinder (cm²) - C (bulk) concentration of metal (mol cm^–3 or mg dm–3) - c concentration change over reactor (mol cm^–3 or mg dm^–3) - C _IN,C _OUT,C _CELL inlet, outlet and reactor concentrations of metal (mol cm^–3 or mgdm^–3) - d diameter of rotating cylinder (cm) - D diffusion coefficient (cm₂ s_–1) - f _R fractional conversion - F Faraday constant=96 500 A s (mo1^–1) - I current (A) - I _L limiting current (A) - I _o useful current (A) - j _D ^' mass transport factor (=St Sc ^c) - K constant in Equation 27 - K _L mass transport coefficient (cm s^–1) - m slope of Fig. 8 (s^–1) - M molar mass of copper = 63.54 g mol^–1 - n number of elements in the cascade - N volumetric flow rate (cm^{3 –1}) - P Reynolds number exponent for powder formation (Equation 28) - R total cell resistance (Q) - t time (s) - U peripheral velocity of cylinder (cm s^–1) - V _cell cell voltage (V) - V _R,V _T effective cell, reservoir volume (cm³) - W electrolytic power consumption (W) - x velocity index in Equation 27 - z number of electrons - Re Reynolds number=Ud/v - Sc Schmidt number=v/D - St Stanton number=K _L/U - gu kinematic viscosity (cm² s^–1) - cathode current efficiency - rotational speed (revolutions min^–1) - peak to valley roughness (cm)     

Reverse osmosis separations for some alcohols and phenols in aqueous solutions using aromatic polyamide membranes

The performance of aromatic polyamide membranes for reverse osmosis separations of eight alcohol and four phenol solutes in dilute aqueous solutions has been studied. The Taft polar parameter σ^* for the solutes studied were in the range of ?0.3 to 1.388. Positive solute separations were obtained for each one of the solutes. In the σ^* value range of ?0.3 to 0, data on PR/PWP ratio scattered close to 1, and solute separation decreased with increase in σ^*. For the phenol solutes, PR/PWP ratio decreased and solute separation increased with increase in σ^*. The results are interpreted on the following basis. The aromatic polyamides are more nonpolar than cellulose acetates. In the σ^* range of ?0.115 to ?0.3, solute separation is governed primarily by polar interactions; in this range, solute transport parameter D_AM/Kδ is well correlated by the expression D_AM/Kδ = C^* exp (ρ^*σ^*). The solute separation for ethyl and methyl alcohol solutes (σ^* = ?0.1 and 0, respectively) is reduced by the nonpolar character of the membrane material. Positive solute separation for each of the phenolic solutes is due to preferential sorption of solute at the membrane-solution interface caused by both the nonpolar character of the membrane material and acidity of the solutes.     

Application of the Stover–Kincannon kinetic model to nitrogen removal by Chlorella vulgaris in a continuously operated immobilized photobioreactor system

BACKGROUND: The aim of this study was to evaluate the ammonium nitrogen removal performance of algae culture Chlorella vulgaris in a novel immobilized photobioreactor system under different operating conditions and to determine the biokinetic coefficients using the Stover–Kincannon model. RESULTS: The photobioreactor was continuously operated at different initial ammonium nitrogen concentrations (NH₄‐N₀ = 10–48 mg L⁻¹), hydraulic retention times (HRT = 1.7–5.5 days) and nitrogen/phosphorus ratios (N/P = 4/1–13/1). Effluent NH₄‐N concentrations varied between 2.1 ± 0.5 mg L⁻¹ and 26 ± 1.2 mg L⁻¹ with increasing initial NH₄‐N concentrations from 10 ± 0.6 mg L⁻¹ to 48 ± 1.8 mg L⁻¹ at θ_H = 2.7 days. The maximum removal efficiency was obtained as 79 ± 4.5% at 10 mg L⁻¹ NH₄‐N concentration. Operating the system for longer HRT improved the effluent quality, and the percentage removal increased from 35 ± 2.4% to 93 ± 0.2% for 20 mg L⁻¹ initial NH₄‐N concentration. The N/P ratio had a substantial effect on removal and the optimum ratio was determined as N/P = 8/1. Saturation value constant, and maximum substrate utilization rate constant of the Stover–Kincannon model for ammonium nitrogen removal by C. vulgaris were determined as K_B = 10.3 mg L⁻¹ d⁻¹, U_max = 13.0 mg L⁻¹ day⁻¹, respectively. CONCLUSION: Results indicated that the algae‐immobilized photobioreactor system had an effective nitrogen removal capacity when the operating conditions were optimized. The optimal conditions for the immobilized photobioreactor system used in this study can be summarized as HRT = 5.5 days, N/P = 8 and NH₄‐N₀ = 20 mg L⁻¹ initial nitrogen concentration to obtain removal efficiency greater than 90%. Copyright © 2008 Society of Chemical Industry     

基于ETS活性的有机物降解与硝化过程中微生物动力学

通过考察有机物生物降解和氨氮生物硝化过程中活性污泥电子传递体系（ETS）活性的变化规律,研究了ETS活性表征污泥生物活性的可行性,结合米门公式分析了有机物生物降解和硝化反应过程生物活性动力学。试验结果表明,活性污泥的ETS活性可以有效地揭示出有机物生物降解和氨氮生物硝化反应的进程,同时对系统受到的有机物和氨氮冲击负荷及硝化过程中碱度的变化有着灵敏的反映,这说明用ETS活性表征污泥的生物活性是可行的;有机物生物降解过程生物活性米氏常数K_s^T=368.9 mg·L^-1,U_m^T=90.9 mg TF·（g TSS·h）^-1,K_s^I=88.42 mg·L^-1,U_m^I=277.8 mg INTF·（g TSS·h）^-1;氨氮硝化过程生物活性米氏常数K_s^T=16.89 mg·L^-1,U_m^T=34.6 mg TF·（g TSS·h）^-1, K_s^I=6.0 mg·L^-1,U_m^I=196.08 mg INTF·（g TSS·h）^-1;生物活性动力学分析进一步验证了进行有机物生物降解的异养菌生长速率高于进行硝化反应的自养型硝化菌。     

Fermentation and oxygen transfer characteristics in serine alkaline protease production by recombinant Bacillus subtilis in molasses‐based complex medium

Serine alkaline protease (SAP) production in a complex medium based on physically pretreated molasses by recombinant Bacillus subtilis carrying pHV1431::subC gene is described. The effects of oxygen transfer were investigated in 3.5 dm³ bioreactor systems with controls for agitation rate, dissolved oxygen, pH, temperature, and foam formation under two different agitation rates, ie N = 500 and 750 min^?1, and four different air flow rates, ie Q/V_R = 0.2, 0.5, 0.7, and 1.0 vvm, at a molasses concentration equivalent to initial sucrose concentration (C_So) of 20 kg m^?3. The yield values (Y_X/S, Y_X/O, Y_S/O) and maintenance coefficient of oxygen (m_O), were calculated. m_O decreased with the increase in the air‐inlet rate. Increase in oxygen transfer rate increased the rate of growth and SAP activity, and affected the cultivation time to achieve maximum expression of SAP activity. At Q/V_R = 0.5 vvm and N = 750 min^?1, SAP activity reached 2250 U cm^?3 at t = 36 h. The oxygen transfer coefficient (K_La) and oxygen uptake rate (?r_O) were measured throughout the fermentations and their variation with the oxygen transfer conditions determined. New correlations for the calculation of K_La and ?r_O are proposed. Copyright © 2004 Society of Chemical Industry     

A TBP/BTBP-based GANEX Separation Process. Part 1: Feasibility

Abstract

A GANEX (Group ActiNide EXtraction) separation system for transmutation has been developed. In this separation process the actinides should be extracted as a group from the lanthanides and the fission and corrosion/activation products. This can be achieved by combining BTBP (bis-triazine-bipyridine) with TBP (tri-butyl phosphate) in cyclohexanone. From 4M nitric acid this organic system extracts the actinides (log(D_Am) = 2.19, log(D_Pu) = 2.31, log(D_U) = 1.03, log(D_Np) = 0.53) and also separates them from the lanthanides (log(D_La) = ?2.0, log(D_Ce) = ?1.72, log(D_Nd) = ?1.05, log(D_Sm) = ?0.18, log(D_Eu) = ?0.02). One problem encountered is that some of the fission and corrosion products are also extracted. The new system however still looks feasible.     

Enantiomeric Separation of Tryptophan by Ultrafiltration Using the BSA Solution System

Abstract

The optical resolution of racemic tryptophan was performed by ultrafiltration using the BSA solution system. The pH of the feed solution had a strong influence on the complexation constants between BSA and tryptophan, especially for L-tryptophan. The complexation constant for L-tryptophan reached a maximum value at pH 9 (K _L = 110,000), varying by 2 orders of magnitude in the range from pH 6 (K _L = 1000) to pH 11 (K _L = 21,000). Smaller variations of the complexation constant of D-tryptophan were observed. Based on these data, the recovery and the purity of the permeate were optimized by a proper control of the physicochemical parameters of the feed solution (essentially pH and initial concentrations). In one stage, 91% purity with a 89% recovery of D-tryptophan has been easily obtained with a high permeation rate (6.3 × 10^?4 mol·m^?2s^?1 at 1.5 bar).     

Oxygen transfer into newtonian and non-newtonian fluids in mechanically agitated vessels

Oxygen transfer into Newtonian and non-Newtonian fluids was studied in stirred tank vessels of 0.0018, 0.006 and 0.036 m³ operating volumes. Emphasis was given to the rheological effects of the pseudoplastic medium on the volumetric oxygen transfer coefficient, K_La. Results indicate that K_La is a strong function of gassed power input per unit volume (P_g/V) for the Newtonian fluid, but a weak function of P_g/V for the non-Newtonian fluid, and a strong function of superficial gas velocity (V_s) for both fluids for paddle-type impellers. K_La is found to decrease rapidly with an increase in apparent viscosity for values of μ_a greater than 2.0 Pa · s. In addition to various correlations, a dimen-sionless correlation including the impeller Reynolds number, impeller Weber number, and the aeration number is presented for the prediction of K_La in a gas-liquid non-Newtonian system.     

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.     

KLa measurement in two‐phase partitioning bioreactors: new insights on potential errors at low power input

BACKGROUND: Two‐phase partitioning bioreactors (TPPBs) are based on the addition of a non‐aqueous phase (NAP) to a biological process in order to overcome a limited delivery of gaseous substrates to the microorganisms in the case of compounds with low affinity for water. However, the high power input (P_g/V) required to disperse the NAP is often the major limitation for TPPB applications at full scale. Therefore, the accurate determination of the overall mass transfer coefficient (K_La) at low P_g/V values is a critical issue as these operational conditions are more attractive from a scale‐up point of view. RESULTS: NAP addition altered the typical shape of the dissolved oxygen curves used for K_La determination at the lowest P_g/V values tested (70–80 W m^?3). Below a threshold P_g/V value of 600 W m^?3, the presence of the NAP increased the error in K_La measurements up to 115% relative to controls deprived of NAP. CONCLUSIONS: The error in K_La measurements at low P_g/V values might be related to failures in the fundamental assumption regarding liquid phase homogeneity in the mass transfer model used. Copyright © 2010 Society of Chemical Industry     

Nonsymmetrical Separations in Thermal Diffusion Columns

Abstract

The influence of the feed composition upon the actual degrees of separation attained at the top and bottom sections of a thermogravitational column is discussed using the classical phenomenological theory of Furry, Jones, and Onsager. It is shown that, except for a feed composition of C ₀ = 0.5 (mass fraction), the separation profile is nonsymmetric, i.e., the separations in the top and bottom sections of the column are nonsymmetric with respect to the feed composition, the asymmetry increasing as the feed composition moves away from C ₀ = 0.5. An equation for the determination of the optimum feed location as a function of the feed composition is derived.     

Mass transfer characteristics of low H/D bubble columns

The mass transfer characteristics of 0.2, 0.6 and 1.0 m diameter bubble columns having a low height to diameter ratio (0.6 < H/D < 4) and operated at low superficial gas velocities (0.01 < V_G < 0.08 m/s) were investigated. Different types of spargers were used to study their effect on the column performance. The values of effective interfacial area, a , and volumetric mass transfer coefficient, k_L a , were measured by using chemical methods. The values of a and k_L a were found to vary from 40 to 420 m²/m³ of clear liquid volume and from 0.01 to 0.16 s^?1, respectively, in the range of V_G, and V_L covered in this investigation. The value of the liquid-side mass transfer coefficient, k_L, was found to vary from 3 × 10^?4 to 7 × 10⁴ m/s. The effect of the physical properties of the system on the values of a was also investigated. The height to diameter ratio and the column diameter did not have significant effect on the values of gas holdup, a and k_L a . It was found that the sparger design is not of critical importance, provided multipoint/multiorifice gas spargers are used. The comparative performance of bubble columns having low H/D with horizontal sparged contactors and tall bubble columns has been considered.     

Study on Volumetric Oxygen Transfer Coefficient of the Simulated Plant Cell Two‐Phase Culture System

The effects of the volumetric percentage of simulated plant cells, organic solvents, agitation speeds and aeration rates on the volumetric oxygen transfer coefficient, K_La, were studied in the simulated plant cell two‐phase culture system. The experimental results showed that K_La increased as the volumetric percentage of organic solvents, H, increased, but this effect became less significant at high values of H. When the volumetric percentage of simulated plant cells, E, was higher than 30%, the effects of H on K_La became less appreciable. In comparison with a one‐phase culture system, K_La was higher in the two‐phase culture system and can be regulated more easily to suit the cell growth and the production of secondary metabolites. Combining with the rheological properties of the system, it was found that the effects of E on K_La were very similar to that of E on the flow behavior index, n, in the system. An experiential correlation of K_La of the system (with oleic acid as organic solvent) was obtained as K_La = 0.21N^0.91Q^0.90exp(4.1H–4.3E) (herein N is the stirring speed and Q, the aeration rate), which may be useful for the design of the two‐phase culture system.     

CFD Modeling of a Bubble Column Reactor Carrying out a Consecutive A → B → C Reaction

In this paper, we develop a CFD model for describing a bubble column reactor for carrying out a consecutive first‐order reaction sequence A → B → C. Three reactor configurations, all operating in the homogeneous bubbly regime, were investigated: (I) column diameter D_T = 0.1 m, column height H_T = 1.1 m, (II) D_T = 0.1 m, H_T = 2 m, and (III) D_T = 1 m, H_T = 5 m. Eulerian simulations were carried out for superficial gas velocities U_G in the range of 0.005–0.04 m/s, assuming cylindrical axisymmetry. Additionally, for configurations I and III fully three‐dimensional transient simulations were carried out for checking the assumption of cylindrical axisymmetry. For the 0.1 m diameter column (configuration I), 2‐D axisymmetric and 3‐D transient simulations yield nearly the same results for gas holdup ?_G, centerline liquid velocity V_L(0), conversion of A, χ_A, and selectivity to B, S_B. In sharp contrast, for the 1 m diameter column (configuration III), there are significant differences in the CFD predictions of ?_G, V_L(0), χ_A, and S_B using 2‐D and 3‐D simulations; the 2‐D strategies tend to exaggerate V_L(0), and underpredict ?_G, χ_A, and S_B. The transient 3‐D simulation results appear to be more realistic. The CFD simulation results for χ_A and S_B are also compared with a simple analytic model, often employed in practice, in which the gas phase is assumed to be in plug flow and the liquid phase is well mixed. For the smaller diameter columns (configurations I and II) the CFD simulation results for χ_A are in excellent agreement with the analytic model, but for the larger diameter column the analytic model is somewhat optimistic. There are two reasons for this deviation. Firstly, the gas phase is not in perfect plug flow and secondly, the liquid phase is not perfectly mixed. The computational results obtained in this paper demonstrate the power of CFD for predicting the performance of bubble column reactors. Of particular use is the ability of CFD to describe scale effects.     

Gas-liquid mass transfer in “dead-end” autoclave reactors

Gas-liquid volumetric mass transfer coefficients, (k_La), have been obtained for “dead-end” autoclave reactors operated in two different modes: (a) gas introduced into the gas phase, and (b) gas introduced through a dip-tube in the liquid. Three different methods of k_La determination have been compared. Effects of agitation speed, impeller diameter, gas to liquid volume ratio (V_g/V_L), position of the impeller and reactor size on k_La have been investigated. The k_La data were found to be correlated as: k_La = 1.48 × 10^?3 (N)^2.18 (V_g/V_L)^1.88 (d_I/d_T)^2.16 (h₁/h₂)^1.16 The critical speed of surface breakage, at which transition from the surface convection to the surface entrainment regime occurs, was also determined for different impeller positions, impeller diameters and gas to liquid volume ratios.     

High Molecular Weight Pyridine Amines as Solvents for Uranium(VI) and Its Separation from Thorium

Abstract

Three high-molecular-weight pyridine amines, 5-(4-pyridyl)nonane, 2-hexylpyridine, and diphenyl-2-pyridylmethane, have been studied as components of solvent extraction systems. Results are presented to show the dependence of the uranium extraction coefficient (D _a ^o = [U_org]/[U_aq]) on equilibrium concentrations of hydrochloric, nitric, and sulfuric acid solutions with and without thiocyanate ions. The optimal conditions for the extraction have been carefully selected from an extensive and critical investigation of the various factors involved; e.g., the effects of diluents, concentration of the mineral acids, thiocyanate ions, salting and complexing agents, and the concentration of the solvents. The extraction mechanism and composition of the extracted complexes of uranium have been studied from partition and slope-analysis data. The results obtained give an orderly picture of the mechanism of extraction of uranium thiocyanate complexes (partly in relation to the hydration and solvation of the compounds extracted). Anomalous extraction behavior was observed at solvent concentrations greater than 0.05 M. The results have been interpreted on the basis of the formation of micelles of the salt molecules of the solvents. It has been shown that these pyridines will extract the metal efficiently and reversibly from dilute acid chloride, nitrate, and sulfate solutions containing thiocyanate. Common salts have no depressing effect on extraction. Distribution coefficients and separation factors of several metal ions, with respect to uranium(VI), are reported for the three mineral acid systems, and a method for the separation of thorium-234 from uranium is also described.