Kinetic Modeling of Metal Biosorption by an Oscillatoria formosa ‐Dominated Mat: Suitability of the General Rate Law and Diffusion‐Based Approaches

ABSTRACT Oscillatoria formosa ‐dominated mat rapidly sorbed lead(II), copper(II), and cadmium(II) from their respective solutions. The general rate law model accurately fits the time‐course of metal sorption data, yielding r 2 values > 0.985. However, due to the variation in reaction order with changes in metal and biomass availability in solution, it is not entirely reliable for describing the actual metal biosorption kinetics. Modeling of time‐course sorption data using the intra‐particle diffusion and external mass transfer models suggested that diffusion processes were crucial in the biosorption of metal ions. The Boyd plots, however, showed a greater impact of the latter process on metal sorption kinetics than the former. The BET surface area analysis supported this view. Moreover, for variations in metal and biomass availability in the solution, no discernible trends were observed in the external mass transfer constant or the effective diffusion coefficient. This suggests a complex surface structure of the test mat biomass. The FTIR and SEM data also provided similar information. The former indicated involvement of various functional groups in metal binding, and the latter revealed an uneven, irregular, and porous surface texture of the test biomass. XRD patterns before and after metal sorption confirmed the structural integrity of the biomass framework.