Multistage Mixer Research Articles

Optimization of Re solvent extraction from molybdenite roasting dust leaching solution and the performance evaluation of extraction in a multi-stage mixer–settler

Separation of Re from roasting dust leaching solution of molybdenite using a multi-stage mixer–settler extractor was studied. Systematic solvent extraction tests were performed using TBP as an extractant diluted in kerosene. The optimum extraction conditions were as follows: pH=0, temperature 25°C, 500rpm agitation rate, 6min contact time and 40% v/v TBP. The results showed that the extraction reaction is exothermic. A flow sheet was developed for the process. Three different extraction ways were studied in a laboratory size mixer–settler: Namely, counter-current, cross-current and co-current. The results showed that counter-current was the best. In addition, it was found that 2h of continuous operation was necessary to reach a steady state condition for the process. Extraction as high as 95.43% was obtained.

Noise performance of phase-insensitive frequency multicasting in parametric mixer with finite dispersion

Noise performance of dual-pump, multi-sideband parametric mixer operated in phase-insensitive mode is investigated theoretically and experimentally. It is shown that, in case when a large number of multicasting idlers are generated, the noise performance is strictly dictated by the dispersion characteristics of the mixer. We find that the sideband noise performance is significantly degraded in anomalous dispersion region permitting nonlinear noise amplification. In contrast, in normal dispersion region, the noise performance converges to the level of four-sideband parametric process, rather than deteriorates with increased sideband creation. Low noise generation mandates precise dispersion-induced phase mismatch among pump and sideband waves in order to control the noise coupling. We measure the noise performance improvement for a many-sideband, multi-stage mixer by incorporating new design technique.

Broadband parametric multicasting via four-mode phase-sensitive interaction

Optical frequency multicasting with significantly enhanced signal-to-noise-ratio (SNR) is demonstrated over wide wavelength range. High-fidelity multicasting relies on a four-mode phase-sensitive (PS) parametric process. Four-mode seeding was used to drive dual-pump, multistage mixer and achieve high-efficiency frequency comb generation and signal replication assisted by field interference. New PS mixer was measured to possess near 12-dB of spectrally uniform optical SNR advantage over conventional, phase-insensitive (PI) parametric multicaster. In signal attenuation regime, PS operation was measured with better than 10dB over the entire mixer band, indicating highly controllable PS interference. The role of the new PS mixer in near-noiseless signal replication is elaborated.

Spectral linewidth preservation in parametric frequency combs seeded by dual pumps

We demonstrate new technique for generation of programmable-pitch, wideband frequency combs with low phase noise. The comb generation was achieved using cavity-less, multistage mixer driven by two tunable continuous-wave pump seeds. The approach relies on phase-correlated continuous-wave pumps in order to cancel spectral linewidth broadening inherent to parametric comb generation. Parametric combs with over 200-nm bandwidth were obtained and characterized with respect to phase noise scaling to demonstrate linewidth preservation over 100 generated tones.

Generation of wideband frequency combs by continuous-wave seeding of multistage mixers with synthesized dispersion

We numerically and experimentally demonstrate efficient generation of an equalized optical comb with 150-nm bandwidth. The comb was generated by low-power, continuous-wave seeds, eliminating the need for pulsed laser sources. The new architecture relies on efficient creation of higher-order mixing tones in phase-matched nonlinear fiber stages separated by a linear compressor. Wideband generation was enabled by precise dispersion engineering of multiple-stage parametric mixers.

Recovery of nitric acid from waste etching solution using solvent extraction

A process was developed to recover nitric acid from the waste stream of wafer industry using solvent extraction technique. Tributyl phosphate (TBP) was selected among several extractants because of its better selectivity towards HNO 3, overall superiority in operation, favorable physical properties and economics. The waste solution containing 260 g/L CH 3COOH, 460 g/L HNO 3, 113 g/L HF and 19.6 g/L Si was used as feed solution for process optimization. In the pre-treatment stage >99% silicon and hydrofluoric acid was precipitated out as Na 2SiF 6. Equilibrium conditions for HNO 3 recovery were optimized from the batch test results as: four stages of extraction at an organic:aqueous (O:A) ratio of 3, four stages of scrubbing at O:A ratio of 5 and five stages of stripping at an O:A ratio of 1.5. The extraction of HNO 3 was suppressed by the presence of acetic acid (HAc) in the feed solution. To examine the feasibility of the extraction system a continuous operation was carried out for 200 h using a multistage mixer–settler. The concentration of pure HNO 3 recovered was 235 g/L with a purity of 99.8%.

Scaling-up experience of actinides partitioning from intermediate level high salted alkaline waste streams of Purex process using Versatic-10 extractant

Partitioning of minor alpha-emitting actinides, especially U, Pu and Am from medium active alkaline waste is possible from intermediate level liquid wastes (ILLW) produced during spent fuel reprocessing following Purex process. This paper deals with the efficient removal of alpha-activity from ILLW by solvent extraction process. Counter current batch extraction with O/A ratio 2:1 as well as multistage mixer settler has demonstrated that most of the alpha-activity was removed from the alkaline effluents using 20% Versatic-10 (V-10) in dodecane after giving 3 to 4 contacts, thus converting alkaline waste as non-alpha waste. Under the optimum conditions (pH 9.0-9.5 and VA-10), both Pu(IV) and Am(III) are highly extractable whereas U(VI) is relatively poorly extracted. To assess the applicability of this process for regular treatment of the waste, a feasibility study on pilot plant scale using six stage mixer settler was operated to treat the ILLW. The results indicated that almost >99.90% alpha-emitting actinides are removed. Dilute nitric acid (0.5M HNO3) served as the most efficient strippant for all these actinides. This facilitate an easy regeneration of the extractant which can be recycled. This method is useful in obtaining alpha-free wastes and had positive impact on ease and safety aspects during subsequent waste treatment and long term storage.

Flooding, holdup, and drop size measurements in a multistage column extractor

AbstractThe hydrodynamics of a pilot plant multistage mixer column extractor was studied for the toluene/water physically equilibrated system. The effects of rotational speed, and continuous and dispersed phase flow rates were investigated under a variety of operating conditions. Dispersed phase axial holdup profiles, determined by a noninvasive ultrasonic method, showed a strong nonuniformity. Depending on the operating conditons, holdup profiles can change from a concave shape to a sigmoidal form with a maximum in the bottom of the column. Sauter mean diameter and drop size distribution profiles are strongly affected by rotational speed. Significant, but weaker, are the effects of continuous and dispersed phase flow rates. Continuous monitoring of the holdup profile in the proximity of flooding leads to the formulation of proper criteria for the prediction of flooding. These criteria are appropriate for models allowing for axial variation of the holdup along the contactor.

Interfacial effects in a multistage mixer–settler operation

AbstractA pilot‐scale mixer–settler with twenty‐one stages was used to investigate the interfacial tension change during extraction cycle for the complicated system: NdCl3–SmCl3–EuCl3–GdCl3–TbCl3–DyCl3–HCl– 1 M D2EHPA–kerosene. Interfacial tension, total rate earth (TRE) concentrations in both phases, aqueous acidities, and organic entrainment in the raffinate, etc., were measured for each stage. Murphree stage efficiencies based on organic phase were calculated and related to the interfacial tension profiles. In general, the lower the interfacial tension, the higher the stage efficiency observed. For the extraction section, the stage efficiency ranged from 80%–100%, but for stripping (including scrubbing) section, it varied from 100%–15%. For high acidic stripping agent, 5 M HCl, the relatively lower stage efficiency might be due to the protonation of the acidic extractant, therefore the interfacial resistance increased significantly. From the information of stage efficiency, mass transfer direction, and interfacial tension versus solute concentration etc., the Marangoni effect could be used to explain the interfacial phenomena of this complicated extraction system. The results of real stream tests in this investigation will be useful in future plant design.

Backmixing in multistage mixer columns—III. Slightly viscoelastic liquids

Hydrodynamique des colonnes Mixco avec des solutions legerement viscoelastiques de polyacrylamide. Le degre de retromelangeage est notablement plus faible que dans le cas de fluides newtoniens, ce qui est attribue au comportement elastique des solutions

Backmixing in multistage mixer columns—II Additional results

A previous investigation showing the influence of the viscosity of Newtonian liquids and flow rate of the feed on backmixing in baffled Mixing-Columns is extended here in order to take into account different geometrical arrangements and different rheologic behaviour of the fluids. In particular, both the influence of one of the most significant parameters which define the geometrical configuration of the apparatus (i.e. the diameter of the opening of the interstage baffle) and the backmixing characteristics of such systems when the fluid exhibits non-Newtonian pseudoplastic behaviour are considered. With reference to the first point, results, which agree well with less extensive results available in literature, are correlated in terms of dimensionless backflow rate, rotational and flow Reynolds numbers and a shape factor. With reference to the second point, a suitable “apparent” viscosity is defined and the possibility of using the general correlation introduced for Newtonian fluids even for pseudoplastic fluids is shown.

Multistage mixer columns—a contribution to fluid-dynamic studies

An experimental investigation was carried out in order to test the suitability of fluid-dynamic models for the interpretation of data for multistage mixer columns of the RDC and Mixco types. Mean local concentration values in the inside of the compartments were measured and experimental impulse response curves were systematically compared with the theoretical curves corresponding to the models. Furthermore the results of static and dynamic methods of measurement of model parameters were compared. In order to bring out possible causes of error due to buoyancy phenomena, feed was introduced either into the bottom stage (ascending flow) or the top stage (descending flow). Local inspection and comparison of experimental and theoretical dynamic curves as well as results of different methods for measuring the amount of backmixing confirm the great reliability of the model of a cascade of ideal tanks with backmixing for the systems considered.

Heat transfer in multistage mixer columns

The problem of heat transfer and temperature distribution in a multistage mixer column is examined. Temperature profiles are predicted by a fluid-dynamic model consisting of a cascade of mixed vessels with backmixing between stages. For the purpose of verifying the validity of the model in practical situations, heat transfer coefficients and backmixing factors were determined in two different six-stage columns under varying operating conditions. The experimental investigations, carried out at typical operating conditions, gave good agreement with the temperature profile predictions of the model.