This study evaluated the packing density of residual biomass of cocoa bean husk as adsorbent of Hg (II) dissolved in an aqueous solution inside a continuous fixed-bed system. The effects of the height of the bed on the removal of the pollutant were evaluated. This experimental work was based on biomass preparation, adsorber design and assembly, and mathematical modelling. The variables considered in the process were initial concentration of the metal, pH, flow rate and particle size. The incident-independent variable was the packing density (mg biomass/bed volume), which translated into the height (cm) of the packing. The FTIR analyses of the husk revealed the presence of functional groups in the spectrum that favour the adsorption of the metal. The residual concentration of the solution was measured by UV/Vis spectroscopy; the maximum adsorption capacity was 99.62%, by the 10g (7.5 cm) bed. In addition, the Thomas model was the best-fitting for the experimental data. On the basis of these results, we concluded that cocoa bean husk has potential to be used as bioadsorbent of Hg (II) from aqueous solutions and that the increase in bed height in the continuous system favours the removal of the pollutant.
Bioadsorbent; cocoa shell; continuous system; molecular adsorption; mathematical modelling.