Filtterionen

Filtterionen is a term used in filtration science to describe ions whose movement through a porous filter or membrane is significantly influenced by the characteristics of the filter medium. The concept is employed to analyze and predict selectivity in membrane-based processes such as nanofiltration, ultrafiltration, and electrodialysis. In this context, filtterionen are not defined by chemical identity alone but by how their size, charge, hydration shell, and interactions with the filter surface govern their permeation or retention.

The transport of filtterionen is governed by a combination of mechanisms. Size exclusion or steric hindrance limits the passage of larger ions relative to pore size. Electrostatic interactions between charged filter surfaces and ions contribute through Donnan effects and charge screening, often leading to preferential rejection or passage of ions with certain valences. Hydration shells and ion pairing can modify the effective size and mobility of filtterionen, influencing filtration performance, especially at higher ionic strength.

Applications of the concept include water treatment and desalination, where the selective removal of specific ions such as hardness ions (for example Ca2+ and Mg2+), nitrate, or certain heavy metals is desired. In pharmaceutical purification and analytical chemistry, controlling filt terionen movement helps adjust ionic strength and impurity profiles in processed streams.

Measurement and modeling approaches combine permeation experiments with analytical techniques (ion chromatography, conductivity) and transport equations that account for diffusion, convection, and electrostatic effects. Design considerations focus on membrane charge, pore structure, and operating conditions to optimize the selective filtration of target ion groups. See also: ion filtration, nanofiltration, electrodialysis, Donnan exclusion.