sorption -
the process in which one substance takes up or holds another (by either absorption or adsorption)
natural action,
natural process,
activity,
action a process existing in or produced by nature (rather than by the intent of human beings); "the action of natural forces"; "volcanic activity"
soaking up,
absorption (chemistry) a process in which one substance permeates another; a fluid permeates or is dissolved by a liquid or solid