Abstract: Minerals that reversibly fix ions, in particular NO3—, i.e. that can exchange one anion for another anion can be used as fertilizers and soil conditioners, as well as for the purification and treatment of water, particularly for the elimination of nitrate. The minerals used are preferably natural or synthetic mixed value metal-metal-hydroxyl salts, e.g. layered double hydroxides (LDHs) that contain exchangeable fixed anions in the intermediary layers. A method for producing anion-exchanging minerals, particularly suitable LDHs, and their use as fertilizers and soil conditioners and for the purification and treatment of water.