Recent advances in heavy metal removal by chitosan based adsorbents

•Cross-linking can increase stability of chitosan but may decrease adsorption capacity.•Complexation is the main mechanism via which chitosan functions as an adsorbent.•Combining with magnetic particles with adsorbent can simplify regeneration process.•Desorption of metal ions from chitosan based adsorbents can be achieved via acidic treatment.•Chitosan based adsorbents can be used efficiently in packed bed columns. Chitosan, a low cost polymer, has been used in many studies for adsorption of heavy metal ions. This review covers the performance of all those adsorbents which were derived from chitosan for the adsorption of heavy metal ions in recent past. Further, the common chitosan modifications methods have been discussed in this paper among which crosslinking and grafting were found to be the most popular methods. Adsorption equilibrium and kinetics were also studied and Pseudo-second order kinetic model and Langmuir isotherm were found to be successful for modeling of most of the chitosan derivatives-metal adsorption experiments. Moreover, with focus on chitosan derivatives, effect of adsorbent structure on metal removal, adsorption mechanism, effect of co-existing ions on adsorption, adsorbent synthesis protocols and regeneration methods have been also discussed in great detail. Finally, fixed bed column design for industrial wastewater treatment was elaborated along with efficiency of chitosan based adsorbents in columns.