『Abstract
　The rate at which iron- and aluminium-natural organic matter (NOM) complexes dissociate plays a critical role in the transport of these elements given the readiness with which they hydrolyse and precipitate. Despite this, there have only been a few reliable studies on the dissociation kinetics of these complexes suggesting half-times of some hours for the dissociation of Fe(III) and Al(III) from a strongly binding component of NOM. First-order dissociation rate constants re-evaluated here at pH 6.0 and 8.0 and 25℃ using both cation exchange resin and competing ligand methods for Fe(III) and a cation exchange resin method only for Al(III) complexes. Both methods provide similar results at a particular pH with a two-ligand model accounting satisfactorily for the dissociation kinetics results obtained. For Fe(III), half-times on the order of 6-7 h were obtained for dissociation of the strong component and 4-5 min for dissociation of the weak component. For aluminium, the half-times were on the order of 1.5 h and 1-2 min for the strong and weak components, respectively. Overall, Fe(III) complexes with NOM are more stable than analogous complexes with Al(III), implying Fe(III) may be transported further from its source upon dilution and dispersion.』

1. Introduction
2. Materials and methods
　2.1. Isolation and characterisation of NOM
　2.2. Preparation of Fe(III)- and Al(III)-organic ligand complexes
　　2.2.1. Concentration of SRFA and NOM required for prevention of Fe(III) or Al(III) precipitation
　　2.2.2. Determination of Fe(III)-SRFA and Al(III)-SRFA formation rate constants
　2.3. Dissociation of Fe(III)-SRFA and Fe(III)-NOM using a cation exchange resin
　　2.3.1. Experimental set-up for the cation exchange resin experiments
　　2.3.2. Rate of Fe(III) adsorption to the resin
　　2.3.3. Rate of dissociation of Fe(III)-SRFA and Fe(III)-NOM complexes
　2.4. Dissociation of Fe(III)-SRFA and Fe(III)-NOM using the competing ligand method
　2.5. Dissociation of Al(III)-organic ligand complexes
　　2.5.1. Rate of Al(III) adsorption to the resin
　　2.5.2. Dissociation rate of Al(III)-organic ligand complexes
　2.6. Modelling of data to determine the dissociation rate constants
　　2.6.1. Rate of metal adsorption to the resin
　　2.6.2. Dissociation rate of Fe(III)- or Al(III)-organic ligand complexes
3. Results and discussion
　3.1. SRFA concentration required to prevent precipitation of Fe(III) and Al(III)
　3.2. Formation rate of Fe(III)-SRFA
　3.3. Formation rate of Al(III)-SRFA
　3.4. Dissociation of Fe(III)-SRFA and Fe(III)-NOM - cation exchange resin method
　　3.4.1. The molar resin concentration
　　3.4.2. Rate of ⁵⁵Fe(III) adsorption to the resin
　　3.4.3. Dissociation rate of Fe(III)-SRFA and Fe(III)-NOM complexes using the resin
　3.5. Dissociation of Fe(III)-SRFA and Fe(III)-NOM using the competing ligand method
　　3.5.1. EDTA as a complexing ligand
　　3.5.2. Comparison of the resin and competing ligand methods
　3.6. Dissociation of Al(III)-organic complexes
　　3.6.1. Rate of Al(III) adsorption to the resin
　　3.6.2. Dissociation rate of Al(III)-organic complexes
4. Conclusions
Appendix A. Supplementary data
References