Preparation Of Carbonized Adsorbent From Sludge And Corncob And Its Adsorption Characteristics For Pb²⁺

In this paper,the carbonized adsorbent was prepared from dewatered sludge of municipal sewage treatment plant and corncob in the surrounding countryside of Xi'an by ZnCl₂ chemical activation and mixed co carbonization.By means of orthogonal experiment and single factor influence experiment,the preferred preparation conditions of carbonized adsorbent were determined,the adsorption law of Pb²⁺and the treatment of actual wastewater were explored.And the adsorption mechanism of Pb²⁺was studied by adsorption kinetic model fitting,adsorption isotherm model fitting and the analysis of BET,SEM and FT-IR,providing reference and guidance for the resource utilization of dewatered sludge and corncob and for the treatment of actual wastewater containing Pb²⁺.The order of factors affecting the preparation of carbonized adsorbent from sludge and corncob is:raw material ratio>carbonation time>carbonization temperature>impregnation ratio.The preferred preparation conditions of carbonized adsorbent from sludge and corncob are as follows:3 mol/L ZnCl₂ as the activator,the ratio of dewatered sludge and corncob is 1:3,the ratio of impregnation is 1:3,the carbonization temperature is 450?and the carbonization time is 0.5 hour.And the iodine adsorption value and yield of the preferred carbonized adsorbent prepared from sludge and corncob are 968.6 mg/g and 18.7%,respectively.What's more,the preferred carbonized adsorbent prepared from sludge and corncob has a rich pore structure,with a specific surface area of 991.20 m²/g,mainly mesopores,whose N₂ adsorption-desorption isotherm is type II adsorption isotherm.The preferred conditions of Pb²⁺adsorption are as follows:initial pH is 5.0-5.5,adsorption temperature is 25?and adsorption time is 4.0 h,respectively.Under the preferred conditions,the adsorbent has a better adsorption effect on the simulated wastewater with an initial Pb²⁺concentration of 10 mg/L,and the optimal adsorbent dosage is 6 g/L.And under this condition,the removal rate of Pb²⁺is 90.10%,and the adsorption capacity is 1.50 mg/g.Coexisting metal ions(Cu²⁺,Cd²⁺and Ni²⁺)compete for the adsorption of Pb²⁺,and the selective adsorption order of metal ions on the carbonized adsorbent from sludge and corncob is Cu²⁺>Pb²⁺>Ni²⁺>Cd²⁺.The carbonized adsorbent prepared from sludge and corncob has good desorption performance and strong recyclability.At the sixth adsorption-desorption cycle,the Pb²⁺removal rate was still as high as 92.97%,and the desorption rate was as high as 93.92%.The treatment result of the actual wastewater was:when the adsorbent dosage was 32g/L,Cu²⁺was almost completely adsorbed,and the Pb²⁺removal rate reached 96.10%,which both reached the maximum allowable discharge concentration limit of pollutants in the Comprehensive Wastewater Discharge Standard?GB 8978-1996?after treatment.The adsorption of Pb²⁺by the carbonized adsorbent prepared from sludge and corncob is more in line with the quasi-second-order kinetic model?R² is 0.9971-0.9995?and the Freundlich isothermal model?R² is 0.9920-0.9966?,which indicates that the adsorption type is non-uniform chemical adsorption,easy to spontaneously proceed.After the adsorption of Pb²⁺,the pores on the surface of the carbonized adsorbent prepared from sludge and corncob were blocked and significantly reduced,and a lot of bright strips were loaded.It is speculated that these bright strips were heavy metal compounds formed after Pb²⁺adsorption.In the process of Pb²⁺adsorption,the hydroxyl and carboxyl groups on the adsorbent play a major role.