A novel Araucaria gum/carrageenan/Mg–Fe LDH nanocomposite for advanced batch and fixed-bed adsorption of mercuric ions from aqueous medium

In the present work, several meticulously planned batch and fixed-bed adsorption experiments were performed to compare the adsorption capacities of the synthesized magnesium-ferric layered double hydroxide (Mg-Fe LDH, MFL), carrageenan/Mg-Fe LDH nanocomposite (MFC), and Araucaria gum/carrageenan/Mg-Fe LDH nanocomposite (MFAC) for mercuric ion removal from aqueous medium. Various physicochemical approaches were conducted to characterize the fabricated adsorbents, proving the successful incorporation of potassium κ-carrageenan and Araucaria gum on the LDH surface. The relatively greater particle size (130 nm), irregular pore distribution, average pore radius (3.2086 nm), and pH_PZC (6.25) of MFAC were mainly responsible for its superior Hg²⁺ adsorption. Through a series of batch adsorption tests, Hg²⁺ adsorption on the MFAC nanocomposite exhibited a maximum adsorption capacity of 505.74 mg g^-1 at 20 °C, pH 6, and a solid dosage of 2 g L^-1 after 30 min. Several kinetics and isotherms were well-fitted for the adsorption process. Fixed-bed column tests proved that MFAC achieved 550.50 mg g^-1 at a bed height of 1 cm, a Hg²⁺ solution concentration of 80 mg L^-1, and a flow rate of 30 mL min^-1 at 20 °C and pH 6 over 300 min. Thus, MFAC can be efficiently applied in wastewater treatment, offering major support for further research into practical applications.