Lanthanum-calcium bimetallic-modified attapulgite- chitosan hydrogel beads for efficient phosphate removal from water: Performance evaluation, mechanistic and life cycle assessment.

Phosphorus is a critical factor in the control of eutrophication. We developed a three-dimensional porous, bimetallic-modified adsorbent La-Ca-CS/ATP to remove excess phosphate from water. Langmuir model showed that the theoretical adsorption capacity of La-Ca-CS/ATP was up to 123 mg P/g. The amount of La and Ca leached by La-Ca-CS/ATP was small, and the adsorption of 36.08 mg P/g was maintained during the five cycles of La-Ca-CS/ATP. The La-Ca-CS/ATP adsorption mechanism mainly involved surface precipitation, ligand exchange, electrostatic attraction, and inner-sphere complexation. Molecular dynamics demonstrated that La and Ca had complementary effects on binding sites and energy barriers within the range of 0.5-0.7 nm and 1.2-2 nm, enhancing the adsorption effect of La-Ca-CS/ATP. The life cycle assessment results showed that adding calcium could help reduce the environmental impact of lanthanum and chitosan. The production of La-Ca-CS/ATP adsorbed 73.88 P mg/g and emitted 24.73 kg CO eq, which was less than other adsorbents.