Study On The Efficiency And Mechanism Of Adsorption Of Cu²⁺,Cd²⁺ And Ni²⁺ In Water By Athelia Rolfsii Polysaccharide

Athelia rolfsii polysaccharide（APS）is a water-soluble macromoleculeβ-glucan obtained by fermentation of Athelia rolfsii.Early laboratory research has found that APS has a good adsorption action on heavy metal ions and is a good bioadsorbent.Based on this,APS was used as the adsorbent to study its adsorption action on Cu²⁺,Cd²⁺,and Ni²⁺in water,and analyzed the influencing factors and optimal adsorption conditions for APS to adsorb heavy metal ions,and discussed its adsorption capacity and mechanism.It lays the foundation for the application of APS in the treatment of agricultural water contaminated by heavy metals.The results of this study are as follows:1.Through the study of the five influencing factors of p H,initial APS concentration,adsorption temperature,adsorption time,and coexisting ions,orthogonal experiments were used to optimize the adsorption effects of APS on Cu²⁺,Cd²⁺,and Ni²⁺.The results show that the initial concentration of APS,p H value and adsorption time have significant effects on the adsorption effect（P<0.05）.The presence of coexisting ions Na⁺,K⁺,Mg²⁺,and Ca²⁺can inhibit the adsorption of heavy metal ions by APS.The optimal process of APS to adsorb Cu²⁺was p H 4.5,the APS concentration 1.5 g/L,the adsorption temperature 40℃,the adsorption time 45min,and the adsorption rate was 88.27%;The optimal process of APS to adsorb Cd²⁺was p H 6.5,the APS concentration 1.5 g/L,the adsorption temperature 45℃,the adsorption time 60 min,and the adsorption rate was 77.81%.The optimal process of APS to adsorb Ni²⁺was p H 6.5,the APS concentration 1.5 g/L,the adsorption temperature 40℃,the adsorption time 45 min,and the adsorption rate was 82.75%.2.The stability of the compound formed by APS adsorbing Cu²⁺,Cd²⁺and Ni²⁺was greatly affected by p H.When the p H was 1,the dissolution rates of Cu²⁺,Cd²⁺and Ni²⁺can reach 81.78%,92.5%,86.18%.When the p H value was more than 3,the dissolution rate droped sharply and approached 0.The APS compound was less affected by time.At 0-24 h,the maximum dissolution rate did not exceed 5%.3.The thermodynamic analysis of APS adsorbing Cu²⁺,Cd²⁺and Ni²⁺showed that the adsorption process was accordant to the Langmuir,Freundlich and Dubinin-Radushkevich isothermal adsorption models.The maximum unit adsorption amounts of Cu²⁺,Cd²⁺and Ni²⁺were 163.93 mg/g,113.64 mg/g and 149.25 mg/g.The adsorption process involved chemical ion exchange when the E value between 8-16k J/mol.The adsorption of Cu²⁺,Cd²⁺and Ni²⁺by APS is an endothermic spontaneous process and conforms to the pseudo-second-order kinetic model.The adsorption process can be divided into three stages:fast adsorption-slow adsorption-adsorption equilibrium.4.The structures of APS before and after adsorbed Cu²⁺,Cd²⁺,and Ni²⁺were analyzed by scanning electron microscope（SEM）,X-ray energy dispersive spectrometer（EDS）,infrared spectroscopy（FTIR）,and nuclear magnetic resonance（NMR）.SEM results showed that the surface structure of APS changed after adsorbing Cu²⁺,Cd²⁺and Ni²⁺.The structure of APS is sheet or rod,and its surface became rough after adsorbing Cu²⁺,Cd²⁺and Ni²⁺,mainly rod and fragment.The EDS spectrum showed that during the adsorption process of APS,the content of Mg and Ca in APS decreased,and elemental peaks of Cu,Cd,and Ni appeared,indicating that ion exchange occurred during the adsorption process.FTIR results showed that the O-H,C-H,C-O and CCO functional groups in APS were the main groups for adsorption,resulting in electrostatic adsorption and complexation.NMR results showed that APS successfully adsorbed Cu²⁺,Cd²⁺and Ni²⁺.The adsorption mechanism included the substitution of H⁺in APS and the interaction of carbon-containing functional groups.5.The adsorption of APS in Cu²⁺,Cd²⁺and Ni²⁺mixed solution exist competitive adsorption.The competing ions can hinder the adsorption of APS to the target ion.The priorities of APS adsorption in mixed solution was:Cu²⁺>Ni²⁺>Cd²⁺.6.The desorption effect of APS was analyzed after absorbing Cu²⁺,Cd²⁺and Ni²⁺.The results showed that HCl,H₂SO₄,HNO₃and EDTA-2Na could all desorb APS 0.1mol/L HCl solution was the optimal desorbent.The maximum desorption rates of Cu²⁺,Cd²⁺,and Ni²⁺were 84.78%,90.59%,and 88.06%.The cycle of adsorption desorption can be up to 5 times.