Preparation Of Dewatered Sludge-walnut Shell Adsorbent And Its Adsorption Characteristics For Cu²⁺

In this paper,the orthogonal experimental design,chemical activation method and single factor experiment method were used to to determine optimum conditions for preparation of dewatered sludge-walnut shell adsorbent.The adsorption performance of dewatered sludge-walnut shell adsorbent on Cu²⁺was clarified,and its adsorption mechanism was speculated by modern characterization methods.In order to explore the ways of resource utilization of sludge and agricultural and forestry waste,and provide a certain data basis for the treatment of heavy metal wastewater by adsorption.The water content and pH of the dewatered sludge in Xi'an Municipal Wastewater Treatment Plant are 79.94-84.64%and 6.01-6.46,respectively.The existence of Pb,Cr,Cu,Zn and Ni in dewatered sludge is mainly in the stable state,and the Cd in the dewatered sludge of some sewage plants is mainly unstable.Adsorbent was prepared under the conditions of raw material ratio?dry mass ratio of dehydrated sludge and walnut shell?,carbonization temperature,carbonization time and solid-liquid ratio of 2:1 to 1:2,500-650?,0.5-2h and 1:1-1:4,respectively.Through range and variance analysis,it was found that the main order of factors affecting the average iodine adsorption value of dewatered sludge-walnut shell adsorbent was carbonization time and solid-liquid ratio?g:mL?,raw material ratio,carbonization temperature;the preferred conditions for the preparation of dewatered sludge-walnut shell adsorbent are:3 mol/L ZnCl₂ activator,carbonization time,solid-liquid ratio,raw material ratio of dewatered sludge and walnut shell,carbonization temperature They were 1 h,1:2,1:1,and 500°C,respectively,and the adsorption iodine value was 807.04 mg/g.When the initial concentration of Cu²⁺in simulated wastewater was 20 mg/L,the removal rate of Cu²⁺by dewatered sludge and walnut shell adsorbent reached 93.07%under the optimal adsorption conditions of pH,water temperature,adsorbent dosage and adsorption time of 3.0,35?,16 g/L and 3 h,respectively.The adsorption process of dewatered sludge and walnut shell adsorbent on Cu²⁺was in better accordance with Lagergren quasi-second order kinetic model.When the initial concentration of Cu²⁺increased from 20 mg/L to 80 mg/L,the equilibrium adsorption capacity of the adsorbent on Cu²⁺increased from 1.25 mg/g to 4.71 mg/g,and the adsorption kinetic rate decreased from 0.0621 min^-1 to 0.0084 min^-1.The Freundlich adsorption isothermal model can better describe the adsorption isothermal law of Cu²⁺by dewatered sludge and walnut shell adsorbent.Under the condition of water temperature of 30-45°C,the adsorption capacity and 1/n are 1.2-1.87[(mg·g^-1)(L·mg^-1)ⁿ]and 0.40-0.47,indicating that the adsorption process is easy to occur,which belongs to multi-layer adsorption.The preferred dewatered sludge-walnut shell adsorbent has a pore size of mesopores?2-50 nm?and macropores?50-61.5 nm?,and their adsorption isotherms for N₂ belong to type II adsorption isotherms.The main functional groups for adsorbing Cu²⁺by the adsorbent are groups such as O-H?acid?,Si-O-and-COOH.In the XRD pattern of adsorbent adsorbed by Cu²⁺,the characteristic diffraction peaks of SiO₂ at 26.52°,20.86°and 50.26°were enhanced,indicating that the dewatered sludge-walnut shell adsorbent combined with Cu²⁺formed a compound with crystal structure.The inorganic microprecipitation mechanism may play an important role in the adsorption of Cu²⁺by the SEM image of the adsorbent before and after adsorption.