A Review on the Removal of Cu²⁺ and Ni²⁺ Ions from Water Using Biodegradable Organic Materials

Abstract

Water contamination by copper (Cu²⁺) and nickel (Ni²⁺) ions remains an important environmental and public health concern because these metals persist in aquatic systems, accumulate in living organisms and may cause toxic effects at elevated concentrations. Conventional removal methods, including chemical precipitation, membrane filtration, ion exchange and electrochemical treatment, are useful but may be restricted by cost, energy demand, sludge generation and limited selectivity under some treatment conditions. This review examines biodegradable and naturally sourced organic materials for the removal of Cu²⁺ and Ni²⁺ from aqueous media, with emphasis on agricultural waste-derived adsorbents, biopolymer-based materials, bio-derived nanocomposites and vegetable-oil-based green extractants. The discussion considers material classification, adsorption and extraction mechanisms, kinetic and thermodynamic behaviour, and operational factors such as pH, contact time, adsorbent dosage, initial metal concentration and temperature. Reported studies indicate that many modified agricultural residues, chitosan- and cellulose-based materials, nanocomposites and fatty-acid-rich oils can achieve high removal efficiencies under laboratory conditions. However, comparison across studies remains difficult because experimental designs, wastewater matrices and regeneration assessments vary considerably. The review identifies key research gaps, including limited evidence from real industrial wastewater, insufficient reuse data, selectivity challenges in multi-metal systems and uncertainty about spent adsorbent management. Future work should prioritise scalable, selective and environmentally responsible treatment systems.