Adsorption Of Heavy Metals From Aqueous Solution By Iron (Hydrogen) Oxide-Chitosan Modified Aluminum Sludge

Increased industrialization and urbanization processes continue to intensify heavy metal pollution.Water metal contamination is one of the most serious environmental pollutions in the world.The high toxicity and bioaccumulation of heavy metals pose a serious threat to the ecological environment and human health.In this paper,the removal of heavy metal ions from water by adsorption method with simple operation and universality..The new composite adsorbent AlS-Fe-CS was obtained from the aluminum sludge of the water purification plant,which was loaded with iron?hydrogen?oxide and chitosan.It provides a new modification method for the utilization of aluminum sludge as an adsorbent,and solves the problems of poor mechanical stability and poor site utilization of iron?hydrogen?oxide and chitosan.A series of static adsorption experiments have been conducted to study the adsorption characteristics and mechanism of Cr⁶⁺,Ni²⁺and Cu²⁺on AlS-Fe-CS in single,binary and ternary systems.In addition,the interaction of heavy metals in the adsorption process of binary and ternary systems and the selective adsorption of AlS-Fe-CS were discussed.Main conclusions are as follows:?1?Preparation of AlS-Fe-CS:the dosage of aluminum sludge was 3g,and the dosages of modifier chitosan and FeCl₃?6H₂O were determined by orthogonal experiments to be 3g and8.11g,respectively.Comparing the results of material characterization before and after modification,chitosan and iron?hydrogen?oxide were successfully compounded into aluminum sludge,and AlS-Fe-CS was more fluffy and rough than aluminum sludge.?2?In the single system,solute pH,reaction time,initial concentration,and temperature have significant effects on the adsorption of heavy metals.The adsorption amount of Cr⁶⁺decreased with the increase of pH,while the adsorption amount of Ni²⁺and Cu²⁺increased with the increase of pH.When pH?6,the precipitation reaction may be the main reason for the rapid increase of Ni²⁺and Cu²⁺adsorption.The reaction time of three heavy metal ions showed a two-stage mode in which the initial adsorption amount increased rapidly and then the growth rate slowed to equilibrium.Increasing the temperature and the initial concentration can effectively increase the equilibrium adsorption capacity of Ni²⁺and Cu²⁺,but the temperature rise is not conducive to the adsorption amount of Cr⁶⁺.?3?In the multi-system,Ni²⁺and Cu²⁺showed strong competitive adsorption,while Cr⁶⁺and Cu²⁺coexisting on AlS-Fe-CS showed synergistic effect.Under the combined action of various factors,the adsorption order of Cr⁶⁺,Ni²⁺and Cu²⁺by AlS-Fe-CS is:Cr⁶⁺>Cu²⁺>Ni²⁺,and the binding ability of Cr⁶⁺,Cu²⁺with AlS-Fe-CS is much stronger than that of Ni²⁺.With the prolonged adsorption time,Cu²⁺would gradually replace the adsorbed Ni²⁺,but Ni²⁺can dominate the competition with Cu²⁺by increasing the concentration of Ni²⁺.?4?Adsorption mechanism:the adsorption of Cr⁶⁺on AlS-Fe-CS is uneven multilayer adsorption,the adsorption process is mainly electrostatic and adsorption-reduction process;the adsorption of Cu²⁺and Ni²⁺mainly forms a metal complex with the nitrogen and oxygen atoms on the surface of the adsorbent—OH and—NH₂.The difference in electronegativity and first-order hydrolysis constant of Cu²⁺and Ni²⁺may be the main reasons for their different affinity with AlS-Fe-CS.The positive charge of AlS-Fe-CS under experimental pH conditions may be the main reason for Cr⁶⁺to maintain dominant adsorption in multi-systems.In addition,the synergistic adsorption of Cr⁶⁺by Cu²⁺and the competitive adsorption between Cu²⁺and Ni²⁺are also important reasons for the adsorption of Cr⁶⁺in ternary system is greater than that of Cu²⁺and Ni²⁺.