Researchers from engineering institutions in Bengaluru and Warangal, India, have demonstrated that 3D printed geopolymer monoliths fabricated using Direct Ink Writing (DIW) can remove cadmium from contaminated water while offering significantly improved durability compared with conventional bead-based adsorbents. Published in Scientific Reports, the study evaluates the performance of structured geopolymer adsorption beds under both batch and continuous-flow conditions, highlighting their potential for industrial wastewater treatment applications.
The work was carried out by Shabnam Siddiqui, Chikkanayakanahalli Ramaiah Ramakrishnaiah, Srinath Suranani, and Yalachigere Kempaiah Suneetha, researchers based at engineering institutions in Bengaluru and Warangal, India. The team focused on metakaolin-based geopolymers, a class of aluminosilicate materials known for their low cost, chemical stability, and ion-exchange capability.
From powdered adsorbents to 3D printed structures
Cadmium contamination remains a persistent environmental and public health issue due to the metal’s toxicity, mobility, and tendency to bioaccumulate. While adsorption is widely used for cadmium removal, many existing systems rely on powdered adsorbents, which can be difficult to handle, recover, and regenerate at scale.
To address these limitations, the researchers used DIW to fabricate self-supporting geopolymer monoliths with controlled lattice geometry and internal porosity. Hydrogen peroxide was incorporated into the geopolymer ink as a foaming agent, enabling the formation of interconnected pores while maintaining printability and mechanical integrity. Crucially, compositionally identical geopolymer beads were also produced via a line injection method, allowing a direct and fair comparison between conventional packed beds and 3D printed structures.
Batch adsorption performance
Initial batch experiments using powdered geopolymer established optimal adsorption conditions. Cadmium uptake was strongest at pH 5, balancing electrostatic attraction, ion exchange, and surface complexation while avoiding cadmium hydroxide precipitation.
Equilibrium data closely followed the Langmuir isotherm model, indicating monolayer adsorption, with a maximum capacity of 87.1 mg/g for the powdered material. Adsorption kinetics were best described by a pseudo-second-order model, suggesting that chemisorption was the dominant process.
Continuous-flow column testing
To evaluate industrial relevance, the team performed dynamic column experiments using both bead-packed beds and stacks of 3D printed monoliths under identical conditions. While bead beds achieved a slightly higher maximum dynamic adsorption capacity (37.5 mg/g) compared with monoliths (35.9 mg/g), the 3D printed structures exhibited significantly shorter mass transfer zones and more uniform flow behavior. This indicates improved mass transfer and reduced channeling, both critical factors for predictable and scalable fixed-bed adsorption systems.
Breakthrough data were well described by the Thomas model, a standard approach for predicting adsorption performance in continuous-flow systems. Across all tests, monoliths maintained removal efficiencies comparable to beads while offering superior flow control.
Regeneration and durability advantages
A key finding emerged during regeneration testing. Geopolymer beads began to crack after just three adsorption–desorption cycles. In contrast, the 3D printed monoliths retained their structural integrity and adsorption efficiency over eight consecutive cycles, the highest reusability demonstrated among comparable bulk adsorbents in the study’s comparative analysis.The researchers attribute this durability to the engineered porosity and cohesive monolithic architecture enabled by additive manufacturing, which reduces mechanical stress and simplifies handling during regeneration.
Implications for scalable water treatment
While some reported adsorbents achieve higher cadmium adsorption capacities, they often rely on expensive precursors, complex fabrication methods, or lack proven long-term reusability. This study argues that 3D printed geopolymer monoliths strike a practical balance between performance, durability, and scalability.
By enabling one-step fabrication of structured adsorption beds with controlled geometry, DIW offers a route to robust, regenerable adsorbents suitable for continuous-flow systems. The work positions additive manufacturing as a process-level enabler for environmental applications, where reliability, ease of handling, and lifetime cost are paramount.
Geopolymers and additive manufacturing
Interest in 3D printed geopolymers has been growing as researchers and industry explore low-carbon alternatives to conventional cement-based materials and functional ceramics. In 2024, the GLAMS project demonstrated the feasibility of using 3D printing to process geopolymer binders derived from simulated lunar soils, highlighting their potential for in situ construction in extraterrestrial environments.
Elsewhere, Nano Dimension-backed research showed how additively manufactured geopolymer structures could enhance nuclear waste immobilization by improving chemical stability and containment performance. More recently, Northumbria University secured EU funding to advance sustainable 3D printed construction materials, with geopolymer systems identified as a promising route to reduce embodied carbon while maintaining structural performance. Together, these efforts underline how geopolymers are increasingly being investigated not only for construction, but also for environmental and infrastructure applications enabled by additive manufacturing.
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Featured image shows the experimental setup used for fixed-bed column adsorption tests with geopolymer beads and 3D printed monoliths. Image via Siddiqui et al., Scientific Reports.
