A comprehensive review on zinc(II) sequestration from wastewater using various natural/modified low-cost agro-waste sorbents

Release of hazardous heavy metals into the environment by industries is one of the major problems affecting human health. Researchers worldwide are working on the preservation of the quality of water and the prevention of environmental contamination. Removal of heavy metals from wastewater by various methods has been widely researched. Heavy metal sequestration/remediation is considered expensive due to the use of non-regenerable metals and the high cost involved when conventional methods are used. Scientists are involved in the adsorption process and various materials, with various materials being used for this purpose. Adsorption is an efficient purification technique due to benefits like stabilization, utility, low cost, installation convenience, and efficiency. Adsorption reduces heavy metal levels to very low concentration through the use of low-cost agro-waste adsorbent materials such as agricultural/non-agricultural biomass, algal/food biomass, activated carbon/biochar, and zeolite/clay minerals. Adsorption of metal on an adsorbent is a complex problem, specifically agro-waste, as it is regulated by different variables. Complexation, chemisorption, surface adsorption, pore complexity, micro-precipitation, and ion-exchange are part of this process. In adsorption, the functional components of biological material such as sulphydryl, amido, hydroxyl, and carboxyl groups are attached to metal ions and are separated from wastewater. This review discusses how low-cost biosorbents like sawdust, leaves, fruit peels, and crop waste-like husk, shell, hull, fiber, residue, and biofertilizers can be used as adsorbent material for the removal of zinc(II) metal ions from wastewater.