engleski

Effect of impeller size on the kinetics of copper exchange onto zeolite NaX

Effect of hydrodynamics on ion exchange kinetics in a batch reactor is still not properly studied despite the fact that proper mixing parameters may considerably improve the process of solid suspension and influence the hydrodynamic layer thickness responsible for the mass rate transfer. For this reason the aim of this work was to analyse the influence of hydrodynamic conditions generated by different impeller diameters on the maximum amount of copper exchange onto zeolite NaX and exchange kinetics as well. Investigations were carried out in a 2.1 dm3 baffled batch reactor at the state of complete suspension. Mixing was conducted using straight blade turbine (4-SBT) which impeller to tank diameter ratio (D/T) were varied in the range from 0.46 to 0.68. Solution containing Cu2+ was prepared by dissolving the appropriate weight of Cu(NO3)2∙3H2O. The initial concentration (7 mmol/L) was checked by Perkin Elmer Lambda 25 UV/VIS spectrophotometer. Zeolite NaX was crushed and sieved to obtain particles in the range from 0.071 – 0.09 mm. In the first part of the examination just suspended impeller speed, NJS, was determine for different impeller diameters and mass of zeolite (10.5, 13.125, 15.75 and 18.345 g) according to the Zwietering criterion. For all examined conditions power consumption was determined as well. In the second part of examination the influence of hydrodynamic on the kinetics of copper exchange on zeolite were analysed. Kinetics experiments were carried out at just suspended impeller speed (NJS) for all impellers and solid/liquid ratios used, while solution temperature was kept constant. Obtained experimental kinetics data were fitted using Elovich and Blanchard model [1-2]. The obtained results showed that just suspended impeller speed decreases as impeller diameter increases. The increase in zeolite mass causing the slight increase of NJS which is more pronounced in the systems with smaller impeller. Power consumption, at the state at complete suspension, generally decreases as impeller diameter increases. Kinetics results indicated that amount of copper ion sorbed increases sharply with the time in the initial stage and then gradually until the equilibrium is reached for all hydrodynamics conditions examined. Considering the relationship between amount of copper exchanged and power consumption at the state of complete suspension it is possible to suggest more viable (D/T) ratio for the examined process.

impeller size ; mass of zeolite ; ion exchange kinetics

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