Cementation of Lead From Lead Sulfate Slurries. III. Kinetics and Reaction Mechanisms With Iron Precipitant

1988 ◽  
Vol 41 (12) ◽  
pp. 1897 ◽  
Author(s):  
IJ Bear ◽  
RCA Flann ◽  
R Woods ◽  
JR Gardner
Keyword(s):  
Particle Size ◽  
Surface Area ◽  
Sulfate Solution ◽  
Lead Sulfate ◽  
Initial Reaction ◽  
Kinetic Regime ◽  
Fast Reaction ◽  
Steady Rate ◽  
Effective Particle ◽  
Percentage Yield

The cementation of lead from lead sulfate powders with iron metal precipitant has been studied in stirred aqueous slurries. The kinetics followed two alternative regimes analogous to those observed previously for the lead sulfate/zinc system. Kinetic regime No. 1 was characterized by an initial fast reaction and a subsequent period of stagnation or even apparent reversal. For this regime, the percentage yield for constant reaction period increased with decrease in the initial partial pulp density (IPPD) of lead sulfate. With regime No. 2, the initial reaction was slower but the reaction continued to completion at a steady rate. Also, the percentage yield for constant reaction period increased with increase in IPPD of lead sulfate. Two mechanisms (Mech. 1 and Mech. 2) corresponding to the two kinetic regimes are proposed to explain the observed kinetics and these mechanisms operate in the same way as they do for the lead sulfate/zinc system. However, the particle size/surface area of the iron was found to be the important parameter in determining which mechanism controlled the reaction, whereas it was the effective particle size/surface area of the lead sulfate when zinc was the precipitant. For the same iron powder, control of the reaction can be transferred from Mech. 1 to Mech. 2 by commencing the slurry cementation in ferrous sulfate solution rather than water. Comment is made concerning the use of iron precipitant in a commercial operation.

scholarly journals Development of nitazoxanide-loaded colon-targeted formulation for intestinal parasitic infections: centre composite design-based optimization and characterization

2020 ◽  
Vol 6 (1) ◽  
Author(s):  
Charu Bharti ◽  
Upendra Nagaich ◽  
Jaya Pandey ◽  
Suman Jain ◽  
Neha Jain
Keyword(s):  
Particle Size ◽  
Desirability Function ◽  
In Vitro Release ◽  
Entrapment Efficiency ◽  
In Vitro Drug Release ◽  
Release Studies ◽  
Percentage Yield ◽  
Vitro Release ◽  
Selection Of

Abstract Background The current investigation is focused on the development and characterization of Eudragit S100 coated nitazoxanide-loaded microbeads as colon-targeted system utilizing central composite design (CCD) and desirability function. The study initiated with the selection of a BCS class II drug nitazoxanide and its preformulation screening with excipients, selection of polymer and identification of concentration for CCD, selection of optimized formulation based on desirability function, and in vitro release studies in simulated gastric and colonic media and stability studies. A two-factor, three-level CCD was employed with two independent variables, i.e. X1 (chitosan % w/v) and X2 (sodium tripolyphosphate % w/v), and three dependent variables, i.e. Y1 (particle size in micrometres), Y2 (percentage yield) and Y3 (percent entrapment efficiency), were chosen. Additionally, surface morphology, mucoadhesion and in vitro drug release studies were also conducted. Result Chitosan concentration showing maximum entrapment and optimum particle size was selected to formulate chitosan beads. The polynomial equation and model graphs obtained from the Design-Expert were utilized to examine the effect of independent variables on responses. The effect of formulation composition was found to be significant (p ˂ 0.05). Based on the desirability function, the optimized formulation was found to have 910.14 μm ± 1.03 particle size, 91.84% ± 0.64 percentage yield and 84.75% ± 0.38 entrapment efficiency with a desirability of 0.961. Furthermore, the formulations were characterized for in vitro drug release in simulated colonic media (2% rat caecal content) and have shown a sustained release of ∼ 92% up to 24 h as compared to in vitro release in simulated gastric fluid. Conclusion The possibility of formulation in enhancing percentage yield and entrapment efficiency of nitazoxanide and the utilization of CCD helps to effectively integrate nitazoxanide microbeads into a potential pharmaceutical dosage form for sustained release.

Controlled Release Behaviors of Ketoprofen from Matrix Polymer of Chitosan and poly(ethylene glycol)

2013 ◽  
Vol 813 ◽  
pp. 399-402
Author(s):  
Chimsook Thitipha ◽  
Thitiphan Chimsook
Keyword(s):  
Particle Size ◽  
Controlled Release ◽  
Drug Release ◽  
Ethylene Glycol ◽  
Diffusion Method ◽  
Poly Ethylene Glycol ◽  
Matrix Polymer ◽  
Percentage Yield ◽  
Poly Ethylene ◽  
Composition Ratios

The aim of present work was to prepare floating microsphere of ketoprofen using matrix polymer of chitosan and poly (ethylene glycol) by solvent diffusion method. The floating microsphere of ketoprofen was prepared from matrix polymer of chitosan and poly (ethylene glycol) with various composition ratios and evaluated such as particle size, drug compatibility and drug release of microspheres. The scanning electron microscopy of microspheres confirmed their hollow structures with smooth surface. Formulation CPK 4 to CPK 6 exhibited the best controlled release pattern in ketoprofen. The concentration and size of poly (ethylene-glycol) affected the particle size, percentage yield and drug release of microspheres.

Particle size, leaf pubescence and condition of humidity at leaf surfaces are key factors determining the retention of volcanic ash on crop foliage.

2021 ◽  
Author(s):  
Noa Ligot ◽  
Benoît Pereira ◽  
Patrick Bogaert ◽  
Guillaume Lobet ◽  
Pierre Delmelle
Keyword(s):  
Particle Size ◽  
Surface Area ◽  
Leaf Surface ◽  
Volcanic Risk ◽  
Chilli Pepper ◽  
Leaf Pubescence ◽  
Leaf Surfaces ◽  
Plant Foliage ◽  
Leaf Surface Area ◽  
Ash Deposit

<p>Volcanic ashfall negatively affects crops, causing major economic losses and jeopardising the livelihood of farmers in developing countries where agriculture is at volcanic risk. Ash on plant foliage reduces the amount of incident light, thereby limiting photosynthesis and plant yield. An excessive ash load may also result in mechanical plant damages, such as defoliation and breakage of the stem and twigs. Characterising crop vulnerability to ashfall is critical to conduct a comprehensive volcanic risk analysis. This is normally done by describing the relationship between the ash deposit thickness and the corresponding reduction in crop yield, i.e. a fragility function. However, ash depth measured on the ground surface is a crude proxy of ash retention on plant foliage as this metrics neglects other factors, such as ash particle size, leaf pubescence and condition of humidity at leaf surfaces, which are likely to influence the amount of ash that stays on leaves.</p><p>Here we report the results of greenhouse experiments in which we measured the percentage of leaf surface area covered by ash particles for one hairy leaf plant (tomato, Solanum lycopersicum L.) and one hairless leaf plant (chilli pepper, Capsicum annuum L.) exposed to simulated ashfalls. We tested six particle size ranges (≤ 90, 90-125, 125-250, 250-500, 500-1000, 1000-2000 µm) and two conditions of humidity at leaf surfaces, i.e. dry and wet. Each treatment consisted of 15 replicates. The tomato and chilli pepper plants exposed to ash were at the seven- and eight-leaf stage, respectively. An ash load of ~570 g m<sup>-2 </sup>was applied to each plant using a homemade ashfall simulator. We estimated the leaf surface area covered by ash from pictures taken before and immediately after the simulated ashfall. The ImageJ software was used for image processing and analysis.</p><p>Our results show that leaf coverage by ash increases with decreasing particle size. Exposure of tomato and chilli pepper to ash ≤ 90 μm always led to ~90% coverage of the leaf surface area. For coarser particles sizes (i.e. between 125 and 500 µm) and dry condition at leaf surfaces, a significantly higher percentage (on average 29 and 16%) of the leaf surface area was covered by ash in the case of tomato compared to chilli pepper, highlighting the influence of leaf pubescence on ash retention. In addition, for particle sizes between 90 and 500 µm, wetting of the leaf surfaces prior to ashfall enhanced the ash cover by 19 ± 5% and 34 ± 11% for tomato and chilli pepper, respectively.</p><p>These findings highlight that ash deposit thickness alone cannot describe the hazard intensity accurately. A thin deposit of fine ash (≤ 90 µm) will likely cover the entire leaf surface area, thereby eliciting a disproportionate effect on plant foliage compared to a thicker but coarser deposit. Similarly, for a same ash depth, leaf pubescence and humid conditions at the leaf surfaces will enhance ash retention, thereby increasing the likelihood of damage. Our study will contribute to improve the reliability of crop fragility functions used in volcanic risk assessment.</p>

Physical Properties Variability of Zinc Powders Obtained by Electrochemical Method

2021 ◽  
Vol 316 ◽  
pp. 689-693
Author(s):  
K.D. Naumov ◽  
V.G. Lobanov
Keyword(s):  
Particle Size ◽  
Specific Surface ◽  
Bulk Density ◽  
Surface Area ◽  
Specific Surface Area ◽  
Current Density ◽  
Zinc Concentration ◽  
Regulatory Change ◽  
Average Particle ◽  
Zinc Powders

The aim of this paper is to establish a regulatory change of zinc powders key physicochemical properties with varying electroextraction conditions. It was studied influence zinc concentration, alkali concentration and current density. Quantitative dependencies of zinc powders particle size and specific surface area from mentioned electroextraction parameters are shown. At increasing of zinc concentration, decreasing of NaOH concentration and decreasing of current density of powders particle size growth, correspondingly specific surface area is declined. It is indicated, that electrolytic zinc powders bulk density varies from 0.61 g/cm3 to 0.75 g/cm3 with a decrease of average particle size from 121 μm to 68 μm. In comparison, spherical powders bulk density used in various industries is currently 2.45-2.6 g/cm3. In all experiments, metal zinc content varied in the range of 91.1-92.5%, the rest - ZnO. To a greater extent, this indicator depends on powder washing quality from alkali and storage conditions.

scholarly journals Surface and Catalytic Properties of NiO and Co3O4 Solids Doped with Cobalt and Nickel Ions

2002 ◽  
Vol 20 (5) ◽  
pp. 467-484
Author(s):  
G.A. El-Shobaky ◽  
A.M. Turky ◽  
A.M. Ghozza
Keyword(s):  
Particle Size ◽  
Thermal Treatment ◽  
Surface Area ◽  
Catalytic Properties ◽  
Excess Oxygen ◽  
Average Particle ◽  
Surface Excess ◽  
Nickel Ions ◽  
Nickel Species ◽  
Cobalt And Nickel

The effects of doping NiO and Co3O4 solids with cobalt and nickel species on their surface and catalytic properties were investigated. The amounts of dopant, in the form of the corresponding nitrate, were varied between 0.5–6.0 mol% cobalt ions and 2.0–6.0 mol% nickel ions. Pure and variously doped solids were subjected to thermal treatment at 300–700°C. The techniques employed were XRD, nitrogen adsorption at −196°C, decomposition of H2O2 at 30–50°C and estimation of the amount of surface excess oxygen on the variously prepared solids as determined by the hydrazine method. The results obtained revealed that the pure and variously doped NiO samples precalcined at 300°C consisted of a finely divided NiO phase having an average particle size of ca. 40 Å. Pure and variously doped Co3O4 specimens preheated at 500°C and 700°C were composed of a Co3O4 phase with a much bigger particle size (230 Å and 350 Å, respectively, for the solids precalcined at 500°C and 700°C). Doping of NiO followed by thermal treatment at 300°C and 500°C resulted in a measurable decrease in its BET surface area (19–23%), while doping of Co3O4 with nickel species followed by heating at 500°C and 700°C brought about a significant increase in its specific surface area (56–60%). Doping each of the NiO and Co3O4 solids with cobalt and nickel species greatly increased the amount of surface excess oxygen and effected a considerable increase in their catalytic activities. This increase was, however, much more pronounced in the case of NiO which attained a value of ca. 100-fold. Doping of NiO with cobalt species followed by thermal treatment at 300°C and 500°C decreased the activation energy (DE) of the catalyzed reaction to an extent proportional to the amount of dopant added. On the other hand, doping of Co3O4 with nickel species followed by thermal treatment at 500°C and 700°C did not change the value of DE. These results suggest that doping of Co3O4 with nickel species did not modify the mechanism of the catalyzed reaction but increased the concentration of catalytically active sites without changing their energetic nature.

scholarly journals FORMULATION AND EVALUATION OF PERINDOPRIL MICROENCAPSULES BY USING DIFFERENT POLYMER

2017 ◽  
Vol 10 (2) ◽  
pp. 153
Author(s):  
Leena Jacob ◽  
Abhilash Tv ◽  
Shajan Abraham
Keyword(s):  
Drug Delivery ◽  
Particle Size ◽  
Release Rate ◽  
Oral Drug Delivery ◽  
Entrapment Efficiency ◽  
Water Soluble ◽  
Oral Drug ◽  
Percentage Yield ◽  
Drug Entrapment Efficiency

Objective: The study was carried out with an objective to achieve a potential sustained release oral drug delivery system of an antihypertensive drug, Perindopril which is a ACE inhibitor having half life of 2 hours. Perindopril is water soluble drug, so we can control or delay the release rate of drug by using release retarding polymers. This may also decrease the toxic side effects by preventing the high initial concentration in the blood.Method: Microcapsules were prepared by solvent evaporation technique using Eudragit L100 and Ethyl cellulose as a retarding agent to control the release rate and magnesium stearate as an inert dispersing carrier to decrease the interfacial tension between lipophilic and hydrophilic phase. Results: Prepared microcapsules were evaluated for the particle size, percentage yield, drug entrapment efficiency, flow property and in vitro drug release for 12 h. Results indicated that the percentage yield, mean particle size, drug entrapment efficiency and the micrometric properties of the microcapsules was influenced by various drug: polymer ratio. The release rate of microcapsules could be controlled as desired by adjusting the combination ratio of dispersing agents to retarding agents.Conclusion:Perindopril microcapsules can be successfully designed to develop sustained drug delivery, that reduces the dosing frequency and their by one can increase the patient compliance.

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