A COMPREHENSIVE APPROACH FOR MODELING SORPTION OF LEAD AND COBALT IONS THROUGH FISH SCALES AS AN ADSORBENT

ABSTRACT Removal of lead and cobalt cations from both industrial and municipal water is of extreme importance for waste water disposal standards. Using fish scales as an adsorbent, 95% of the lead cations and 70% of the cobalt ions can be removed. The processes related to the removal of the cations include adsorption and precipitation. The effect of precipitation of the cations in a neutral medium (pH 7) is studied and is found to be insignificant. Although the effect of precipitation is negligible in the studied experimental runs, it may assume significance in a highly nonporous medium. As sorption dictates the interactions between the bulk and adsorbed phases, it is the most important factor influencing the transport of the chemical species through the medium. Mobility of the cations has extreme importance to overall sorption characteristics because of high adsorption coefficients of the fish scales. It can be further concluded that even at cation concentration levels of 1000 ppm, sorption behavior is insensitive to change. To investigate the nature of the sorption mechanism, a series of experimental runs was conducted using fish scales of the Gadus Morhua (Atlantic cod) and Lethrinus nebulosus (spangled emperor or shouairi) species as substrates. A simulation model based on the theory of surface excess with mechanical entrapment is developed in this study. Numerical simulation results demonstrate reasonable agreements with the experimental results. This study illustrates that variations of flow rates of the cations did have a considerable effect on breakthrough time intervals. An increase in flow rate led to earlier contaminant breakthrough. However, variance of the cation concentrations did not have a dominant effect on the corresponding breakthrough values. The effect of porosity of the adsorbents is observed, and it is determined it has a profound impact on adsorption phenomena. The dispersion parameter is found to be a function of porosity, and its effect was studied in relation to the flow rate of the bulk phase. A decrease in porosity of the adsorbent results in an increase of the retardation factor of the contaminant in bulk phase and an equivalent delay in the breakthrough interval. In order to study the adsorption characteristics by surface excess model, the pH parameter was maintained at a constant pH value of 7 for all the experimental runs. The adsorption coefficient (K) was coupled into the numerical model as a parameter independent of the pH values. The numerical simulations did fit reasonably well with the experimental data. The surface excess theory has been tested in the past only for anionic solutions. The significance of this research is that this model has been applied for the first time with respect to a bio-adsorbent in relation to heavy metal cations. It is found to be suitable for describing adsorption behavior of metallic contaminants at neutral pH. For studying adsorption with respect to the pH variable, a different adsorption model based on, the Langmuir isotherm is proposed.

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