Study On Adsorption Properties Of CMCC/SA-PPy Composite Gel Beads Based On Sodium Carboxymethyl Cellulose For Cr(Ⅵ) And Ni(Ⅱ)

In China,heavy metal pollution is a significant ecological and environmental problem that poses a threat to both national sustainable development and human health.This paper aims to investigate an efficient method for treating heavy metal ions in water.The selected method is the adsorption method,which is highly effective and convenient to operate.The matrix used in this study is non-toxic,harm Less,and low-cost sodium carboxymethyl cellulose（CMCC）,which is mixed with sodium alginate（SA）in a 1:1 volume ratio.Polymerized polypyrrole（PPy）is used as a modifier and crosslinked with glutaraldehyde（GA）to prepare CMCC/SA-PPy gel spheres.The target pollutants selected for this study are the heavy metals Cr（Ⅵ）and Ni（Ⅱ）with different ion types.Static adsorption studies are conducted to determine the optimal adsorption conditions under single-factor conditions,such as dosage,p H,temperature,adsorption time,initial concentration,and coexisting ions.The adsorption properties of CMCC/SA-PPy gel beads for the two heavy metal ions are studied in detail,and the adsorption mechanism is discussed.Dynamic adsorption behavior is also studied by changing the adsorbent height,initial concentration,and flow rate.The main conclusions of this study are as follows:（1）The orthogonal test results show that the optimum ratio of CMCC/SA-PPy material is 0.024 g/m L CMCC and 0.032 g/m L SA mixed at a volume of 1:1.The amount of pyrrole is0.02m L,the amount of glutaraldehyde is 0.01 m L,and CMCC/SA-PPy composite gel beads are polymerized under the oxidation of Fe Cl₃.SEM and XRD characterization show that CMCC/SA-PPy gel spheres are more disordered,rough,and amorphous than CMCC/SA gel.EDS and FTIR show that CMCC/SA and PPy are successfully crosslinked by Schifft-base reaction and acetal reaction through glutaraldehyde.（2）Static adsorption experiments show that the adsorption effect of CMCC/SA-PPy composite gel beads on Cr（Ⅵ）is better than that of Ni（Ⅱ）.Cr（Ⅵ）reaches adsorption equilibrium at about 11 hours,and the equilibrium adsorption capacity is 108.92 mg/L;Ni（Ⅱ）reaches adsorption equilibrium at about 7 hours,and the equilibrium adsorption capacity is96.20 mg/L.Under the influence of single-factor conditions,the adsorption capacity of Cr（Ⅵ）decreases with an increase in p H,while the adsorption capacity of Ni（Ⅱ）increases with an increase in p H,which is due to the different forms of the two heavy metals in water.The selectivity of CMCC/SA-PPy gel beads to Cr（Ⅵ）and Ni（Ⅱ）increases with an increase in dosage,and the optimal dosage is 0.085 g.Both Cr（Ⅵ）and Ni（Ⅱ）are spontaneous endothermic processes dominated by chemical reactions.After four desorption tests,the adsorption capacity of Cr（Ⅵ）and Ni（Ⅱ）on the gel beads can still be maintained at about95.36 mg/L and 78.15 mg/L,respectively.The regeneration and recycling performance is good,and the coexisting ions have little effect on the adsorption process.（3）The competition and binary experiments demonstrated that CO₃^2-had the most significant effect on the adsorption of Cr（Ⅵ）,resulting in a 23.5%inhibition rate.On the other hand,Cl-had little impact on the adsorption of Cr（Ⅵ）by CMCC/SA-PPy gel beads.The adsorption process of Ni（Ⅱ）by Fe³⁺was significantly inhibited,resulting in a 21.35%inhibition rate.Binary experiments also showed that the presence of Cr（Ⅵ）promoted the adsorption of Ni（Ⅱ）when both ions were present.（4）The dynamic adsorption test revealed that the dynamic adsorption capacity of Cr（Ⅵ）and Ni（Ⅱ）was inversely proportional to the influent concentration and flow rate.However,the dynamic adsorption capacity was directly proportional to the packing height.This is due to the fact that as the influent concentration and flow rate increase,the adsorption sites on the surface of the gel ball become occupied quickly,leading to a shift from surface adsorption to intraparticle diffusion.As a result,the internal mass transfer resistance of the gel ball increases,and the dynamic adsorption capacity decreases.Conversely,increasing the adsorbent height allows for greater contact between the water flow and the CMCC/SA-PPy gel ball,increasing the penetration time and the dynamic adsorption capacity.（5）Adsorption mechanism:The BDST and Yoon-Nelson models accurately predicted the running time of the dynamic adsorption process for Cr（Ⅵ）and Ni（Ⅱ）.The adsorption mechanism of CMCC/SA-PPy gel beads for Cr（Ⅵ）and Ni（Ⅱ）mainly involves surface physical adsorption,electrostatic adsorption,coordination,and ion exchange.In an acidic environment,the protonation of CMCC/SA-PPy gel spheres due to the presence of-NH2 and-COOH and the solution environment results in electrostatic adsorption being the primary means of Cr（Ⅵ）adsorption.Conversely,in an alkaline environment,ion exchange and the coordination of-OH and-NH2 are the primary means of Ni（Ⅱ）adsorption.