Increasing Stirring Speed Research Articles

Study of Strengthen Flotation Separation for Middle-Low Grade Bauxite

The ore properties and strengthen separation of bauxite were studied in this paper. The parameters in strengthen separation, such as dosage of collectors, flotation turbulence and inflation etc., were also discussed. With the increase of collector dosage, the recovery of Al2O3increased.,When the collector dosage was 900 g/t, A/S of foam was 7.06 and the recovery was 86.39%. The recovery also increased with the increase of stirring speed. When the speed of agitation mixing impeller reached 1700 r/min, the recovery was 84.56% and A/S of concentrate was 6.71. With the increase of inflation, the number of bubbles increased, the contact opportunities between bubbles and mineral particles increased, and the recovery increased. When the inflation was 0.35 m3/h, the recovery was 85.21% and A/S of foam was 6.71,. With the increase of inflation over 0.35 m3/h, the enhancement of recovery was not limited and the bubble inclusions led to the decrease of recovery of Al2O3.

Effect of stirring and temperature on synthesis yield and crystallization of hydrothermally synthesized K 2W 4O 13 nanorods

The K 2W 4O 13 was synthesized by hydrothermal treatment of crystalline WO 3·H 2O in the presence of K 2SO 4 in the stirred hydrothermal reactor operated at 120–180 °C for 1–6 h at the stirring speeds ranging from 0 rpm (static condition) to 700 rpm to investigate the significance of stirring on crystallization of the K 2W 4O 13 nanorods at different synthesis condition. The crystallization was enhanced by stirring as revealed by the increased synthesis yield with the increase of stirring speed. At 180 °C and 6 h of hydrothermal treatment, the stirring had no observable effect on phase and particle morphology. At shorter time or lower temperature, the stirring had significant effect on enhancing crystallization of the nanorods.

Some parameters describing the dissolution rate of salicylic acid at controlled pH.

Abstract Rates of dissolution of salicylic acid have been determined at constant pH in the absence of buffer salts by use of a pH-stat. The dissolution rate increased with increasing pH up to a maximum of pH 4·0. An increase in stirring speed brought about an increase in dissolution rates at each pH. Diffusion layer thickness and diffusion coefficients have been determined utilizing viscosity and density measurements.

Gastroretentive drug delivery system of acyclovir-loaded alginate mucoadhesive microspheres: Formulation and evaluation

In the present study, mucoadhesive alginate microspheres of acyclovir were prepared to prolong the gastric residence time using a simple emulsification phase separation technique. The particle size of drug-loaded formulations was measured by SEM and the particle size distribution was determined using an optical microscope and mastersizer. The release profile of acyclovir from microspheres was examined in simulated gastric fluid (SGF pH 1.2). The particles were found to be discreet and spherical with the maximum particles of an average size (70.60 ± 2.44 µm). The results indicated that the mean particle size of the microspheres increased with an increase in the concentration of polymer and decreased with increase in stirring speed. The entrapment efficiency was found to be in the range of 51.42−80.46%. The concentration of the calcium chloride (% w/v) of 10% and drug–polymer ratio of 1:4 resulted in an increase in the entrapment efficiency and the extent of drug release. The optimized alginate microspheres were found to possess good mucoadhesion (66.42 ± 1.01%). The best fit model with the highest regression coefficient values (R2) was predicted by Peppas model (0.9813). In Gamma scintigraphy analysis, the section of GIT was critically analyzed and much differentiation was present at each time point after oral administration, which revealed that the optimized formulation demonstrated gastroretention in vivo for more than 4 h, which revealed that optimized formulation could be a good choice for gastroretentive systems.

Study of phosphoric acid crystallization using a focused beam reflectance measurement method

AbstractA way for restoring the crystal size distributions (CSD) from measured chord length distributions (CLD) was reported in this paper. The kinetics of phosphoric acid crystallization process was investigated in cooling mode using focused beam reflectance measurement (FBRM) and digital photo technique. In order to restore the CSD from measured CLD and verify the reliability of FBRM data, digital photo technique in real time and optical microscope were applied in large crystal size and small range, respectively. Results indicated a converting constant A existed between CLD and CSD when crystal growth follows size‐independent growth (Mcabe's ΔL law) law. It was verified by Malvern particles size analysis method. The converting constant A varied with crystal morphology. The crystal growth order increased with the stirring increasing speed during phosphoric acid crystallization process. The trend was especially notable at higher speed situations. It can illustrate that the state of phosphoric acid hemihydrate crystal growth was controlled by both diffusion and surface‐integration with the increasing stirring speed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Scale-up synthesis of zinc borate from the reaction of zinc oxide and boric acid in aqueous medium

Synthesis of zinc borate was conducted in a laboratory and a pilot scale batch reactor to see the influence of process variables on the reaction parameters and the final product, 2ZnO·3B 2O 3·3.5H 2O. Effects of stirring speed, presence of baffles, amount of seed, particle size and purity of zinc oxide, and mole ratio of H 3BO 3:ZnO on the zinc borate formation reaction were examined at a constant temperature of 85 °C in a laboratory (4 L) and a pilot scale (85 L) reactor. Products obtained from the reaction in both reactors were characterized by chemical analysis, X-ray diffraction, particle size distribution analysis, thermal gravimetric analysis and scanning electron microscopy. The kinetic data for the zinc borate production reaction was fit by using the logistic model. The results revealed that the specific reaction rate, a model parameter, decreases with increase in particle size of zinc oxide and the presence of baffles, but increases with increase in stirring speed and purity of zinc oxide; however, it is unaffected with the changes in the amount of seed and reactants ratio. The reaction completion time is unaffected by scaling-up.

Application of ferric chloride both as oxidant and complexant to enhance the dissolution of metallic copper

In acidic ferric chloride solutions, Fe 3+ is oxidant and Cl − is complexant, which would accelerate the dissolution of metallic copper. Based on the thermodynamic analysis, the dissolution of metallic copper in acidic solutions containing ferric chloride was investigated in detail. The related parameters such as pH, ferric chloride concentration, excess Cl − concentration, stirring speed, solid/liquid ratio and temperature were systematically studied. The dissolution rate of copper increased significantly as the pH value decreased from 2 to 0. The presence of FeCl 3 accelerates significantly the dissolution of copper. Increasing stirring speed from 150 to 400 rpm and increasing temperature from 1 to 50 °C enhanced the dissolution rate of copper remarkably. Increasing solid/liquid ratio from 0.001 to 0.004 g/mL decreased the dissolution rate. Excess Cl − concentration, which comes from the addition of NaCl, had a slight effect on the dissolution of metallic copper. The copper dissolution rate in acidic solutions of FeCl 3 fits the following conversion-time expression: 1 − 2 3 R − ( 1 − R ) 2 3 = k t , where R is the fraction reacted of copper powder, k is the reaction rate constant, t is the dissolution time. The activation energy was found to be 24.9 kJ/mol and inward diffusion was considered to the rate-controlling step.

Transport of Hg(II) through bulk liquid membrane containing calix[4]arene thioalkyl derivative as a carrier

In this study effectiveness of 5,11,17,23 tetrakis[(propylthio)methyl]-25,26,27,28-tetrahydroxycalix[4]arene ( 1) towards Hg(II) across bulk liquid membrane has been examined. The effect of the fundamental parameters influencing the transport process, e.g. carrier concentration, type of solvent used, effect of temperature and time dependency of the process have been investigated. The mass transfer of Hg(II) was analyzed on the basis of kinetic laws of two consecutive irreversible first order reactions. Thus, the kinetic parameters ( k 1, k 2, R m max, t max, J d max, J a max) for the transport of Hg(II) were studied. The activation energy values for the extraction and re-extraction were found as 19.59 and 27.57 kJ mol − 1 , respectively. These values demonstrate that the process is diffusionally controlled by Hg(II). Observations show that the membrane entrance and exit rate constants ( k 1, k 2) increase with increasing stirring speed, carrier concentration and temperature. The effect of solvent on k 1 and k 2 was found to be in the order of CH 2Cl 2 > CHCl 3 > CCl 4. The effectiveness and reproducibility of Hg(II) transport has proved that 1 is an efficient carrier of Hg(II) in BLM process.

Kinetic Study of an Effective Pb(II) Transport through a Bulk Liquid Membrane Containing Calix[6]arene Hexaester Derivative as a Carrier

The article describes transport of Pb(II) through bulk liquid membrane (BLM) containing calix[6]arene hexaester derivative (1) as a carrier. The effect of various parameters such as temperature, carrier concentration, stirring speed and type of solvent on the Pb(II) transport efficiency of the carrier through BLM was evaluated. The activation energy values for the extraction and re-extraction were found as 56.33 kJ mol−1 and 14.79 kJ mol−1, respectively. These values demonstrate that the process is diffusionally controlled by Pb(II). Observations indicate that the membrane entrance and exit rate constants (k1, k2) increase with increasing stirring speed as well as carrier concentration and decrease with increasing temperature. The effect of solvent on k1 and k2 was found to be in the order of CH2Cl2 > CHCl3 > CCl4.

Leaching of magnesium from desiliconization slag of nickel laterite ores by carbonation process

The leaching of magnesium from desiliconization slag of nickel laterite ores by carbonation process was studied. The influence of various parameters was investigated to optimize the conditions and determine the kinetics of the reaction. The results show that with increasing stirring speed, liquid-to-solid ratio and reaction time, and decreasing temperature, the leaching rate of magnesium enhances. The leaching process of the desiliconization slag in the range of 288–298 K is controlled by the surface chemical reaction model. The apparent activation energy is −20.45 kJ/mol, and the kinetics model is obtained.

Mass Transfer Enhancement of Propane Absorption into Dodecane-Water Emulsions

A one-dimensional unsteady heterogeneous parallel mass transfer (ODUHPMT) model was developed for the absorption enhancement of volatile organic compounds (VOC) by the dispersed droplets. An analytical solution for enhancement factor was obtained based on surface renewal theory and the Laplace domain transformation. The absorption rate of propane into water at different stirring speeds with the added micro dodecane droplets was investigated experimentally in a thermostatic stirred tank. The mass transfer flux across the gas-liquid interface and the enhancement factor were measured. The results showed that the dodecane has an obvious enhancement effect on propane absorption into water, the maximum enhancement factor reached 11. The enhancement factor increased with increasing dodecane volume fraction and decreased with increasing stirring speed. The experiment data agreed well with the model predictions and showed high prediction accuracy of ODUHPMT model.

Desiliconization kinetics of nickeliferous laterite ores in molten sodium hydroxide system

A novel process was proposed for treating nickeliferous laterite ores with molten sodium hydroxide. The effect on silicon extraction caused by the factors, such as stirring speed, reaction temperature, particle size and NaOH-to-ore mass ratio, was investigated. The results show that increasing stirring speed, reaction temperature and NaOH-to-ore mass ratio while decreasing particle size increases silicon extraction rate. The desiliconization kinetics of nickeliferous laterite ores in molten sodium hydroxide system was described successfully by chemical reaction control model. The activation energy of the desiliconization process was found to be 44.01 kJ/mol, and the reaction rate based on a chemical reaction-controlled process can be expressed as: 1–(1–α) 1/3= 27.67exp[−44 010/( RT)] t.

Preparation and characterization of twisted periodic mesoporous ethenylene-silica nanorods

Twisted periodic mesoporous ethenylene-silica nanorods were prepared using cetyltrimethylammonium bromide in concentrated aqueous ammonia solutions at the stirring rate of 600 rpm. The pore channels run along the long axis of the nanorod. The helical pitches are about 1.2 micrometers. Small-angle X-ray diffraction pattern was indexed to the p6 mm hexagonal symmetry. The morphologies of the ethenylene-silicas are sensitive to stirring conditions. For example, twisted nanorods and spiral nanofibers combined with nanospheres were obtained under static condition. With increasing stirring speed, both the length and helical pitch of the nanorod increased slightly. With decreasing the concentration of ammonia, the particle lengths decreased, while the particle diameters increased. Chiral mesostructures were obtained when the ammonia concentration was ≥ 20 wt%. The formation of the twisted mesoporous ethenylene-silica nanorods was studied by taking TEM images after different reaction time.

Formulation and in vitro evaluation of buoyant controlled release lercanidipine lipospheres

The aim of this study was to prepare and evaluate buoyant lipospheres containing lercanidipine hydrochloride. The lipospheres were prepared by modified melt dispersion technique using hydrophobic matrix of cetostearyl alcohol (CSA). The influence of formulation factors (stirring speed, lipid:drug ratio, lipid:surfactant polymer composition) on particle size, encapsulation efficiency and in-vitro release characteristics of lipospheres were investigated. The yields of all prepared formulation and encapsulation efficiencies were high for formulations which contain high lipid amount. The mean particle size significantly decreased (p < 0.001) by increasing the lipid:surfactant polymer and stirring speed (p < 0.001) of the system. Reduction in encapsulation efficiency (p < 0.001) and drug content (p < 0.001) was observed with increasing stirring speed and percentage of poloxamer 407 in formulation. Although lercanidipine hydrochloride release from Cetostearyl alcohol lipospheres were very slow and incomplete for all formulations f1–f6 (∼65% drug released in 12 h) and was increased (∼85% drug released in 12 h) in lipospheres formulations f7–f12, containing Poloxamer 407. Percentage of buoyant lercanidipine lipospheres of CSA (96–100% buoyancy up to 12 h) decreases (p < 0.001) with increasing percentage of poloxamer 407 and achieved the release profile suitable for peroral administration.

Microcalorimetric Studies on Chemical Oscillation of Microgels

By use of isothermal titration calorimetry (ITC) and ultrasensitive differential scanning calorimetry (US-DSC), we have investigated the energy change in the periodic swelling-to-deswelling of thermally sensitive poly(N-isopropylacrylamide) (PNIPAM) microgels containing ruthenium(II) tris(2,2'-bipyridine) (Ru(bpy)3) which is a catalyst for Belousov-Zhabotinsky (BZ) reaction. As temperature increases, the induction period and oscillation period of BZ reaction decrease because the reaction rate increases. However, the oscillation disappears at a temperature above the lower critical solution temperature (LCST) of the microgels since Ru(bpy)3 is trapped in the microgels and cannot react with BZ substrates. As microgel size increases or the cross-linking density decreases, the restriction of polymer networks on Ru(bpy)3 decreases, so that Ru(bpy)3 can readily contact with BZ substrates, leading the oscillation amplitude to increase. In addition, the so-called transient chaos occurs at a low stirring speed, and it wanes with the increasing stirring speed. All the facts indicate that the contact between Ru(bpy)3 and BZ substrates determines the oscillation of the microgels.

A Study on Nucleation for Protein Crystallization in Mixed Vessels

This study investigated mechanisms of secondary nucleation for the crystallization of the protein hen egg white lysozyme. A parametric study of the secondary nucleation of lysozyme in a stirred tank crystallizer was performed, testing the influence of stirrer speed, the size and volume of added seed crystals, solution temperature, supersaturation, and sodium chloride concentration on measured nucleation rates. The measured rates were highly variable, which made assessment of the influence of experimental parameters difficult. Only stirrer speed exhibited significant influence over experimental variability (10-fold increase in nucleation rates with a 50% increase in stirring speed). These results were interpreted by comparison with parameter influence that is commonly observed with secondary nucleation of nonproteins. A novel tubular crystallizer was used to assess the influence on secondary nucleation of fluid shear forces acting on lysozyme crystals. It was observed that fluid shear forces acting on mounted lysozyme crystals do not notably influence secondary nucleation. Overall, the results suggest that attrition is an important source of secondary nuclei in lysozyme crystallization and that secondary nucleation caused solely by fluid shear forces is not.

Dissolution rate of limestone for wet flue gas desulfurization in the presence of sulfite

Limestone dissolution rate was measured by a pH-stat method with CO 2 sparging and dissolved sulfite. The dissolution rate of limestone under these conditions was found to be controlled by mass transfer and surface kinetics. As can be seen from the results, in the presence of sulfite, limestone dissolution rate increases with increasing stirring speed, reaction temperature and CO 2 partial pressure. The crystallinity of limestone has a great impact on the dissolution rate: The lower the value of the crystallinity of limestone is, the higher the dissolution rate is. The presence of sulfite promotes the dissolution rate when pH value is below 5.5 but inhibits it when pH value is above 5.5.

Optimisation of porosity of 7075 Al alloy 10% SiC composite produced by stir casting process through Taguchi method

In this paper an attempt has been made to achieve a set of values of stir casting process variables that may yield optimum porosity to the 7075 Al alloy with 10% SiC composite. The effect of selected process variables on the porosity of 7075 Al alloy 10% SiC composite and subsequent optimal settings of the variables have been obtained using Taguchi method. The results indicate that the holding time, holding temperature and stirring speed are the significant variables. Stirring time is insignificant variable. As the holding time, holding temperature and stirring time increases the porosity decreases. When the stirring speed increases, porosity increases. The predicted optimal value of porosity is 4.71%.

Equilibrium studies on hydrolysis of urea in a semi-batch reactor for production of ammonia to reduce hazardous pollutants from flue gases

The increasing environmental awareness and the mandate of the pollution control agencies in various part of country for lowering emission of air pollutants such as CO 2, NO x, SO 2 and fly ash emissions, has increased the urgency for reviewing options and alternatives to accomplish the above objective. The addition of ammonia into the flue gas stream as a conditioning agent is found to be used in recent years for the reduction of air pollutants. Flue gas conditioning requires in situ generation of ammonia as the transportation and storage of anhydrous ammonia is hazardous in nature. The equilibrium study on hydrolysis of urea was done in a semi-batch glass reactor to investigate the effect of reaction temperature, initial feed concentration and stirring speed on ammonia production. Few experiments were carried out in a semi-batch reactor at atmospheric pressure by using different concentration of urea solution from 10 to 40 wt% of urea to water and equilibrium study has been done. The study reveals that conversion increases exponentially with an increase in temperature but the conversion decreases with increase in the inlet feed concentration of urea solution. Furthermore, the effect of stirring speed on conversion has also been studied and it found that conversion increases with increase in stirring speed.

An empirical model for kinetics of boron removal from boroncontaining wastewaters by the electrocoagulation method in a batch reactor

Boron removal from boron containing wastewaters prepared synthetically via the electrocoagulation method was studied. The experiments in which aluminum plate electrode was used were carried out in a batch reactor. The solution pH, initial boron concentration, current density, type of supporting electrolyte, temperature of solution and stirring speed were selected as experimental parameters. The obtained experimental results showed that efficiency of boron removal increased with increasing current density and decreased with increasing boron concentration in the solution. Supporting electrolyte had not significant effects on the percent of total boron removal. pH was very important parameter effecting boron removal and optimum pH was determined to be 8.0. This pH value reached an agreement with activity-pH diagrams for Al +3 species in equilibrium with Al(OH) 3 and boron species in aqueous media. As a result of increasing interaction between boron ions and dissolved aluminum ions in solution, the increasing solution temperature increased boron removal efficiency. Increasing stirring speed decreased boron removal efficiency where the increasing stirring speed decreased the capability of floc formation of aluminum ions. As a result, it was seen that about 99% of boron in the wastewater could be removed at optimum conditions. In addition, the process kinetics was predicted by using heterogeneous fluid–solid reaction models. It was seen statistically that the kinetics of this process agreed with the pseudo-second-order model as follows: X B /(l− X B ) = 18,241 ⁎[OH] ⁎[C] −3.45⁎[CD] 7.79⁎[t] 1.41⁎[S] −3.65⁎exp[−30,668/ R ⁎T ].