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

Abstract

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 CO2 eq, which was less than other adsorbents.