Transport behavior of humic acid-modified nano-hydroxyapatite in saturated packed column: Effects of Cu, ionic strength, and ionic composition

► Divalent cations have a strong effect on the deposition of humic acid-modified nano-hydroxyapatite (nHAP). ► Divalent Ca2+ cation bridges the humic acid-modified nHAP and causes greater deposition than monovalent Na+ cation. ► Cu2+ cation has a greater effect on the deposition of humic acid-modified nHAP than Ca2+ cation due to their strong exchange with Ca2+ of nHAP and its surface complexation with nHAP.