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 (6.25) of MFAC were mainly responsible for its superior Hg adsorption. Through a series of batch adsorption tests, Hg adsorption on the MFAC nanocomposite exhibited a maximum adsorption capacity of 505.74 mg g at 20 °C, pH 6, and a solid dosage of 2 g L 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 at a bed height of 1 cm, a Hg solution concentration of 80 mg L, and a flow rate of 30 mL min 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.