Heavy Metal Removal Using Plant Origin Biomass and Agricultural Waste-Derived Biomass from Aqueous Media: a Review

The effectiveness of natural low-cost plant-based biomass and agricultural waste in order to remove the iron, aluminum, copper, and other heavy metals is presented in this review paper along with the experimental, equilibrium conditions and their ability as a low-cost bioadsorbent and analytical techniques used for the bioadsorption. The recent research focuses on the usage of various parts of the plants like leaves, seeds, peels, roots, etc., and other bioadsorbents in the form of husks, shells, and fibers in their natural, pre-treated, and modified states. This review has taken into account the use of adsorption isotherm and kinetics models as well as the influence of experimental parameters made by researchers like initial concentration, contact time, bioadsorbent mass, speed of agitation, temperature, and pH on heavy metal elimination. The review of the pertinent literature shows that the maximum removal efficacies of copper, aluminum, and iron using the various natural low-cost adsorbents vary between 50 and 100% with optimal pH from 4-9 for copper, 2-8 for iron and aluminum, and contact time varying from 20 min-24 h for copper, 90-240 min for aluminum, and 15 min-24 h for iron. However, optimal value adsorbent dose is in the range of 0.1 to 10 g/l for copper and iron, 1.5-10 g/l for aluminum. Additionally, the pseudo-second-order kinetics and Langmuir isotherm are the ascendent models that superlatively defined the copper, aluminum, and iron equilibrium data. The thermodynamic factors indicate that the biosorption of copper, aluminum, and iron on the bioadsorbents was spontaneous and endothermic at temperatures ranging from 25 to 60 degrees C for copper, from 25 to 50 degrees C for aluminum, and from 30 to 70 degrees C for iron. The carboxyl, hydroxyl, esters, alkynes, ether or phenol, and amine groups are the primary functional groups associated in the removal of metal ions by the majority of the studied bioadsorbents, regardless of their sources. Plant origin biomass and agricultural waste-derived biomass have been discovered to be viable replacements for commercial activated carbons in the treatment of metal-contaminated water. However, gaps in applicability, regeneration, reuse, and safe disposal of laden adsorbents, as well as optimization and commercialization of appropriate adsorbents, have been identified. Finally, the prospects for future research on heavy metal ions biosorption are outlined.