Low-Cost Adsorbents for Heavy Metal Removal from Aqueous Solutions

The contamination of water by heavy metals poses severe environmental and public health challenges worldwide. Conventional treatment methods often rely on costly and energy-intensive materials such as commercial ion-exchange resins and activated alumina. In response, researchers have turned to low-cost, readily available adsorbents derived from agricultural and industrial by-products—tea residues, spent coffee grounds, fruit peels, biochars and other waste biomasses. These materials offer abundant surface functional groups (carboxyl, hydroxyl, amino) that facilitate metal binding through ion exchange, complexation and electrostatic attraction. Optimisation of pH, contact time, adsorbent dose and temperature has yielded adsorption capacities on a par with conventional sorbents. Activation strategies, including chemical treatments and composite formation, further enhance porosity and surface chemistry. Attention to regeneration and reuse supports circular-economy principles, while bench- and pilot-scale studies affirm the global applicability of these adsorbents in cost-sensitive water-treatment scenarios.

Research from Nature Portfolio

Recent studies have demonstrated the potential of untreated brewed tea waste for rapid removal of lead, cadmium, nickel and zinc. Optimal adsorption occurred at mildly acidic pH, achieving equilibrium within minutes and maximum capacities up to 2.5 mg g⁻¹. The adsorption behaviour conformed to Langmuir isotherm models, indicating monolayer coverage, while kinetic analyses pointed to chemisorption mechanisms. In a foundational work, spent coffee powder functionalised with polyethylenimine and iron ions enabled successive removal of arsenate, copper and phosphate. This composite achieved high adsorption capacities (up to 200 mg g⁻¹ for copper), with distinct rate-limiting steps identified via kinetic modelling and column experiments, underscoring its applicability in continuous-flow systems.

Low-Cost Adsorbents for Heavy Metal Removal from Aqueous Solutions publication trend

The graph below shows the total number of articles in low-cost adsorbents for heavy metal removal from aqueous solutions across all publications each year (not limited to Nature Index journals).

Technical terms

Adsorption isotherm: A curve describing the relationship between the amount of adsorbate bound per unit mass of adsorbent and its concentration at equilibrium, under constant temperature.

Pseudo-second-order kinetic model: A model that describes adsorption kinetics assuming the rate-limiting step involves chemisorption through electron sharing or exchange.

Biochar: A carbon-rich material produced by pyrolysis of biomass under limited oxygen, characterised by high porosity and surface area for adsorption.

Activated carbon: A highly porous carbonaceous material produced via chemical or thermal activation, widely used for adsorption of contaminants due to its large surface area and functional groups.

References

1. Adsorption capability of brewed tea waste in waters containing toxic lead(II), cadmium (II), nickel (II), and zinc(II) heavy metal ions. Scientific Reports (2020).
2. Successive extraction of As(V), Cu(II) and P(V) ions from water using spent coffee powder as renewable bioadsorbents. Scientific Reports (2017).
3. Waste tea as a novel adsorbent: a review. Applied Water Science (2018).
4. Adsorption of Cadmium, Manganese and Lead Ions from Aqueous Solutions Using Spent Coffee Grounds and Biochar Produced by Its Pyrolysis in the Fluidized Bed Reactor. Materials (2020).
5. Removal of Copper from Water by Adsorption with Calcium-Alginate/Spent-Coffee-Grounds Composite Beads. Materials (2019).