Effect of isolated NOM and its fractions on colloidal stability in water

The effect of different NOM on colloidal stability in water was conducted by electrophoresis experiments with a model particle Al(OH)₃ and the characteristic transformation of the isolated NOM after adsorption on the particle was discussed. The pH value, Ca²⁺ and characteristics of isolated NOM were evaluated as the main factors. The results indicated that the pH_iep of Al(OH)₃ was 5-6, and the adsorbed organic matter is the principal factor that decrease Zeta potential. It is the free Ca²⁺ in solution that reduces the electrostatic repulsion between adsorbed NOM molecules and make the particle surface less negatively charged; The 'Cation Bridge' effect of complexed Ca²⁺ promoted the adsorption of isolated NOM although contributed little to particle stability. As polyanions, the adsorption of isolated NOM onto metal hydroxide did not follow the Langmuir adsorption model. The fraction with higher molecular weight and carboxylic acidity in different NOM was mainly removed by adsorption and the larger molecular weight and aromaticity fraction in NOM contributed to the increase of particle stability.