3D-Printing of Zeolitic Permeable Reactive Barrier (PRB) and its Adsorptive Performance in Heavy Metal Removal

Abstract

Zeolite has been proven to be an effective material for heavy metal adsorption from wastewater, commonly utilized in granular form packed in fixed column beds. Other studies have suggested that compact monolithic structures in column adsorbent and catalyst applications exhibit superior adsorption kinetics and lower pressure drops, resulting in reduced maintenance requirements and enhanced performance. This study aims to investigate the feasibility of incorporating zeolite into 3D-printed monoliths for flowthrough adsorption of iron (II) from synthetic single-component acid mine drainage solutions. 3D-printed permeable reactive barrier (PRB) structures were produced through direct-ink writing using an Eazao Bio 3D ceramic printer with the following printing parameters: 1.2 mm nozzle diameter, 11 mm/s printing speed, and 0.4 MPa extrusion pressure. A 2² factorial design was employed to assess the effects of zeolite:binder ratio and printing layer on the compressive strength of the printed PRB. The optimal PRB formulation was further investigated by assessing the effects of zeolite:binder ratio and solution flow rate on the Fe removal efficiency of the PRB after column adsorption. A maximum strength of 1.24 MPa was achieved at a 0.5 mm layer height. Leaching of iron was prominent during column adsorption, resulting in only 7.25% Fe removal, possibly due to the acidity of the solution causing the displacement and release of Fe ions in the effluent. Further studies are recommended to explore ways to minimize Fe leaching and enhance the economic potential and performance of the 3D-printed PRB.