[Transport of hydroxyapatite nanoparticles in saturated packed column: effects of humic acid, pH and ionic strengths].

Quartz sand was selected as collector and saturated packed column was constructed to explore the effects of environmental factors (humic acid, pH and ionic strengths of the bulk solution) on the transport and fate of hydroxyapatite nanoparticles (Nano-HAP) through measuring zeta potentials and representative c(i)/c(0) of Nano-HAP. It was suggested that zeta potentials of Nano-HAP colloids became more negative with increasing humic acid concentration and the change in solution composition from 0 to 10 mg/L humic acid yielded an increase in the zeta potentials of Nano-HAP colloids from -15 mV to -55 mV and a sharp decrease in a (attachment efficiency) from 1.0 to 0.012, meanwhile, the increase in bulk solution pH yielded a slight decrease in a which enhancing its transportation in saturated packed column. However, zeta potentials of Nano-HAP colloids became less negative as the ionic strength of bulk solution increased due to the compression of diffuse double layer and yielded an increase in a which greatly impeded its mobility during the pore-water solution, meanwhile, divalent cations have significantly stronger influence on the transport of Nano-HAP than monovalent cations of the bulk solution. The increase in the concentration of monovalent cation (Na+) from 1 to 100 mmol/L yielded an increase in a from 0.030 to 0.13, and divalent cations (Ca2+) from 0.2 to 10 mmol/L yielded a greatly increase in alpha from 0.030 to 1.0. It is important to note that the results could considerably contribute to gain insights in the transport and fate of Nano-HAP in natured and engineered porous media.