Investigation of copper adsorption to peat using the simple metal sorption model

Abstract

The Simple Metal Sorption (SiMS) equilibrium model was used to simulate the proton/cation exchange behavior of peat with dissolved copper. The SiMS model represents proton binding and metal binding as cation exchange for heterogeneous sorbents as a function of pH, salt concentration, total metal concentration and total ligand concentration. The SiMS model uses fewer parameters than other cation exchange models for multidimensional datasets and can be executed on a standard spreadsheet. The cation exchange selectivity coefficient, K(Me,app), is represented as K(Me,app) = KMe[H+](alpha)(LT/MeT)(beta) I(psi). The model is similar to standard surface complexation approaches, with an intrinsic relationship described by mass action laws (KMe = metal equilibrium constant) and variable terms that are expressed as simple power functions of proton concentration, ligand to metal ratio (LT/MeT), and ionic strength (I). The model successfully simulated the proton exchange behavior of acid-washed, Sphagnum peats over a range of 4 to 8 pH units with ionic strength differing by three orders of magnitude (I = 0.001 to 0.1). Simulation of copper binding on five peat data sets and the dried biomass of Potamogeton lucens was also successful (0.94 < r2 < 0.99). However, there was no apparent relationship between model parameters and peat characteristics. Incorporation of the SiMS model into a framework for predicting metals removals in wetlands will require more work.