Abstract
Dynamic experiments were carried out on the adsorption of copper (II) ions in a laboratory packed bed of activated carbon. Both pulse and step change inputs were used. Measurements were reproducible and replicate measurements furnished nearly identical parameters for a heterogeneous model of the activated carbon bed assuming Langmuir adsorption isotherm. The initial concentration of copper (II) ion was 3 ppm and the average particle size of activated carbon was 1.5 mm. The adsorption experiments in the shallow beds of activated carbon, 3 and 5 cm bed height had little effect on the parameters. Hydraulic loading, 25 and 50 ml min-1, affected dispersion and the volumetric mass transfer coefficient, but unexpectedly also changed the effective diffusivity. This apparently comes from the incorporation of errors due to instrumental noise and model approximations in the parameters. A 5 min pulse input has a low residual sum of square (RSS) with all of set of starting point while a 10 min pulse has a low RSS using some set of starting point. A step up input has a high RSS that may arise from a large number of data. These affected the Langmuir adsorption isotherm constant and diffusivity as expected from their concentration dependency. Step change and pulse simulations using the model agreed well with the experiments.
Highlights
Activated carbon has been considered for the capture and eventual recovery of metal ions in aqueous industrial discharges for many years and has enjoyed some commercial application
When the metal ion concentration in the exit reaches 5% of the inlet concentration, breakthrough is deemed to have occurred in common practice, other levels can be used in this definition
Switching in the opposite direction gives a step down input, whereas for a pulse input, the valve switches from deionised water to copper (II) ion flow; the copper (II) ion flow is maintained for a short time, either 5 or 10 min and flow switches back to deionised water
Summary
Activated carbon has been considered for the capture and eventual recovery of metal ions in aqueous industrial discharges for many years and has enjoyed some commercial application. A metal ion concentration wave moves through the carbon bed in the direction of flow When the metal ion concentration in the exit reaches 5% of the inlet concentration, breakthrough is deemed to have occurred in common practice, other levels can be used in this definition. This is the breakthrough definition used for pollution mitigation. On the other hand, when the concentration attains 95% of inlet, the adsorption capacity is deemed to be exhausted The latter breakthrough definition is used when the purpose of adsorption is metal recovery
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