| In the process of municipal solid waste treatment,concentrated liquid will be produced.The concentrated liquid contains various metal ions,such as direct discharge,the heavy metal will cause obvious harm to the environment and human health,and the cost of treating the concentrated liquid is relatively high.How to remove heavy metals in concentrates have become one of the hot spots of interest.In this study,sodium alginate was selected as carrier,combined with environmentally friendly polyethyleneimine and Fe(Ⅲ).SA,SA-PEI,SA-PEI-Fe(Ⅲ)gel ball gel were successfully prepared by sol-gel method,homogeneous loading method and embedding method.Based on the heavy metal species in the concentrate,Cu(Ⅱ)and Cr(Ⅵ)were selected as the treatment targets.The adsorption performance of Cu(Ⅱ)and Cr(Ⅵ)was investigated by static adsorption experiments and the adsorbent was regenerated.Characterization to explore the adsorption mechanism of the adsorbent in depth,the main conclusions are as follows:(1)FTIR results show that PEI and Fe(Ⅲ)are successfully loaded to sodium alginate.The adsorption of Cu(Ⅱ)by three gel spheres mainly depends on carboxyl,hydroxyl and amine functional groups,amine and Fe(Ⅲ)is active sites of Cr(Ⅵ).The surface of the three gel spheres was observed by SEM and both had pore structure.XRD confirmed that Fe(Ⅲ)was successfully introduced and not oxidized.(2)Static adsorption experiments showed that the adsorption of Cu(Ⅱ)and Cr(Ⅵ)by three gel spheres was greatly affected by pH,and the optimum pH for adsorption of Cu(Ⅱ)and Cr(Ⅵ)was 5.5 and 2,SA gel ball has no adsorption effect on Cr(Ⅵ),and is not affected by pH;elevated temperature is beneficial to the adsorption of Cu(Ⅱ)and Cr(Ⅵ),the maximum adsorption capacities of SA gel beads,SA-PEI gel spheres and SA-PEI-Fe(Ⅲ)gel spheres for Cu(Ⅱ)were 156.52 mg/g,260.5 mg/g and 211.31 mg/g,respectively,and the maximum adsorption capacity for Cr(Ⅵ)was 0.6.mg/g,163.5mg/g and 164.87mg/g;adsorption of Cu(Ⅱ)by SA gel sphere is mainly monolayer adsorption,equilibrium time is9.5h,SA-PEI gel sphere is Cu(Ⅱ)and Cr(Ⅵ)adsorption equilibrium time is 36 h and 13 h,for Cu(Ⅱ)multi-layer adsorption for Cr(Ⅵ)single layer adsorption,SA-PEI-Fe(Ⅲ)gel sphere for Cu(Ⅱ)and Cr(Ⅵ)are multi-layer adsorption,equilibrium time is 45 h and 30h;SA-PEI andSA-PEI-Fe(Ⅲ)gel spheres have obvious synergistic effect on Cu(Ⅱ)and Cr(Ⅵ)mixed metals due to ion bridge and electrostatic shielding;inorganic anions will promote the adsorption of Cu(Ⅱ)and cations promote the adsorption of Cr(Ⅵ);regeneration and recycling SA-PEI demonstrated and SA-PEI-Fe(Ⅲ)gel beads with good re-use properties.(3)Comparison of adsorption performance and mechanism of three gel spheres: It was found that PEI was introduced into SA to make the distribution of functional groups on the adsorption interface with Cu(Ⅱ)uneven,which induced multi-layer adsorption and continued to introduce Fe(Ⅲ),the distribution of active sites of adsorbed Cr(Ⅵ)is uneven;the introduction of PEI enhances the adsorption performance of Cu(Ⅱ)and Cr(Ⅵ),and improves the disadvantage of SA gel spheres not adsorbing Cr(Ⅵ).However,the adsorption of Cr(Ⅵ)at low concentration is poor,and the continued introduction of Fe(Ⅲ)further enhances the adsorption of Cr(Ⅵ),so that the SA-PEI-Fe(Ⅲ)gel sphere is suitable for any concentration of Cu(Ⅱ)and Cr(Ⅵ)have good adsorption effects and are more suitable for treating actual wastewater.(4)There are many kinds of metal ions and inorganic ions in the concentrated solution.The SA-PEI-Fe(Ⅲ)gel ball still has good adsorption effect on heavy metal Cu(Ⅱ)and Cr(Ⅵ)in the presence of many kinds of heavy metal ions and inorganic ions;the experiment was carried out with the actual concentrate to confirm that the SA-PEI-Fe(Ⅲ)gel sphere still has good adsorption effect on heavy metals in the actual concentrate.It provides the basis for the study of removing heavy metals from the concentrated solution. |
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