Clay Minerals Flashcards
The high net negative charge is permanent in
2:1 clays - it doesn’t change, even if the soil solution changes.
Clay minerals have a
High net negative charge.
Isomorphous substitution:
Ions of similar size and shape are swapped between soil solution and clay sheets.
Isomorphous substitution: 2:1 clays have a
More open structure, therefore the clay lattice is more exposed to IS.
pH dependant charge: arises from
Chemical interactions with edges of clays (& humus) reacting with the soil solution.
Clay edges contain hydroxyl (-OH) groups, bonded to
Either Al3+ or Si4+ cations.
pH dependant charge: at lower pH values, hydroxyl clays may
Become positively charged.
pH dependant charge: a strong / negative charge occurs depending on
The soil pH.
The pH value at which hydroxyl groups dissociate depends on
Environmental conditions, such as temperature, and the type of clay.
pH dependant charge: Greater on clays with a less regular structure, such as
2:1 clays, 1:1 clays have fewer broken, exposed edges.
pH dependant charge: a positive charge may be generated at various pH through the
Absorption of protons from solution.
pH < 7 - geothite.
pH < 9 - gibbsite.
