Amitriptyline　(AMI)　is　one　of　the　most　common　tricyclic　antidepressant　personal　care　medications.　Due　to　its　environmental　persistence　and　bioaccumulation,　release　of　AMI　into　the　environment　via　wastewater　streams　in　elevated　levels　could　lead　to　significant　ecological　and　human　health　impacts.　In　this　study,　the　adsorption　of　AMI　by　montmorillonite　(SWy-2),　a　naturally　abundant　smectite　clay　with　sodium　ions　as　the　main　interlayer　cations,　was　investigated.　Maximum　AMI　adsorption　(276　mg/g)　occurred　at　pH　7-8.　After　adsorption,　examination　of　the　adsorbent＇s　X-ray　diffraction　pattern　indicated　that　interlayer　expansion　had　occurred,　where　chemical　stoichiometry　confirmed　cation　exchange　as　the　principal　adsorption　mechanism.　AMI　adsorption　reached　equilibrium　within　4　h,　with　kinetic　data　best　fitting　the　pseudo-second　order　kinetic　model　(R-2　=　0.98).　AMI　adsorption　was　unaffected　by　solution　pH　in　the　range　2-11,　where　adsorption　was　endothermic,　and　molecular　simulations　substantiated　by　Fourier　transform　infrared　spectroscopy　and　thermogravimetric　investigations　indicated　that　the　orientation　of　AMI　molecules　in　the　interlayer　was　via　an　amine　group　and　a　benzene　ring.　Overall　this　research　shows　that　SWy-2　has　significant　potential　as　a　low　cost,　effective,　and　geologically　derived　natural　material　for　AMI　removal　in　wastewater　systems.　(C)　2021　Elsevier　Inc.　All　rights　reserved.