The influence of Na+ and Ca2 + on the migration of colloids or/and ammonia nitrogen in an unsaturated zone medium

• The influences of ion valence on the migration of colloids and ammonia nitrogen were investigated.
• The order of the migration blocking effect is bivalent ions > monovalent ions.
• Colloids may block the migration of ammonia nitrogen.
• The presence of ions enhanced the colloid-blocking effect on NH4+ migration.
• Higher ion valence may increase both the particle size and its Zeta potential.

This experiment was conducted with an indoor sand-column device, the migration of colloids with the presence of Na+ and Ca2 + and the migration of ammonia nitrogen with the presence of Na+, Ca2 + or/and colloids was studied. The results showed that the migration of colloids was influenced by the ion valence state, different ions with different valence could block the migration of colloids. In addition, the blocking effect of bivalent ions was more obvious than that of monovalent ions. In the presence of Na+ and Ca2 +, the Rd value of the ammonia-nitrogen migration process were 1.01 and 1.41, respectively, which indicated that bivalent ions have a greater blocking effect on ammonia-nitrogen migration than monovalent ions. Colloids could also block the ammonia-nitrogen migration, and Rd value in the ammonia-nitrogen migration process was 1.17. Moreover, the presence of Na+/colloids and Ca2 +/colloids could enhance the blocking effect on the ammonia-nitrogen migration, and resulting the Rd values at 1.20 and 1.52, respectively. The cohesion of colloids caused by the compaction of its electric double layer with those ions added maybe the key causes of those blocking.

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