The evaluation and mathematical modeling of metal ion removal from water by immobilized Sphagnum peat moss beads

A combination of experimental and modeling methods was used to evaluate the metal ion removal mechanism of immobilized Sphagnum peat moss beads. Batch equilibrium, batch kinetic and packed column experiments were performed to evaluate the beads' metal ion removal mechanism and determine parameters needed for the mathematical models. There was evidence of both precipitation and adsorption of metal ions in the batch equilibrium and batch kinetic tests. The extent of precipitation in the packed column runs was not clear. The selectivity of the beads was found to be:; Fe {dollar}>{dollar} Al {dollar}>{dollar} Cu {dollar}>{dollar} Cd {dollar}>{dollar} Zn, Ca {dollar}>{dollar} Mn {dollar}>{dollar} Mg {dollar}>{dollar} Na.; Titration tests with the beads showed that the immobilized Sphagnum peat moss has heterogeneous adsorption sites, much like those present in humic compounds. The immobilized biomass beads adsorb hydrogen ions as well as metal ions. It was found that decreasing the initial pH of the beads or the pH of the solution being treated decreased the capacity of the beads. Column run results for aluminum suggest that speciation of aluminum influences its removal by the beads.; The versatile computer models developed for the batch kinetic and column experiments include distributed mass transfer resistances as well as adsorption kinetics and the neutralization of hydrogen ions by hydroxide and carbonate species. Both models consider multicomponent adsorption, which includes hydrogen ions as one of the adsorbing species. Model results were obtained using a two-site Langmuir isotherm, with the second site primarily adsorbing hydrogen ions. These models are of value for design, scale-up and operation of actual waste water treatment systems.; Batch kinetic model results predicted aluminum removal well, but consistently underpredicted the amount of the divalent metal ions removed. It is thought that this is the result of not accounting for precipitation. The column model gave fairly good predictions of the breakthrough curves for the acid mine drainage waters, but did not predict the behavior of synthetic solutions very well. An explanation for this is the Langmuir isotherm not accurately modeling the bead's metal and hydrogen ion removal mechanism.