Study On The Pyrolysis Stabilization Of Cadmium-loaded Phytolacca Acinosa Roxb Biomass And The Photocatalytic Performance Of Biochar

In recent years,with the rapid development of industry,the situation of heavy metal pollution in water body is serious.There are many methods to deal with heavy metal pollution in water bodies.Among them,the adsorption method has been widely studied and applied because of its advantages of easy operation,high efficiency,and low cost.Biomass has a wide range of raw materials and has a certain enrichment capacity for heavy metal ions.It is a good adsorption material for treating heavy metal wastewater.However,there are still few studies on the safe disposal and reuse of polluted biomass loaded with heavy metals.In this study,the cadmium loading process of Phytolacca acinosa Roxb biomass(PB)was studied using Phytolacca acinosa Roxb as raw material,and the influence of pH value,material dosage and initial concentration of the solution on the cadmium loading process of PB was analyzed.At the same time with the help of adsorption kinetics and adsorption models such as isotherms and thermodynamics are fitted and analyzed for experimental data;Then the cadmium-loaded biomass(PB-Cd)was pyrolyzed and stabilized.The content,existence form and stability of cadmium in PBC-Cd were studied at different pyrolysis product,in view of the pyrolysis product,PBC-Cd;Furthmore,tetracycline was taken as the target pollutant to study the photocatalytic performance of PBC-Cd.The effects of pH value,dosage and initial concentration of tetracycline on the photocatalytic process were investigated.The photocatalytic degradation process of tetracycline by PBC-Cd was analyzed by combining free radical capture experiment and characterization technology.The following are the foremost findings:(1)The Cd2+removal efficiency of PB increased with the increase of pH(3-7).With the increase of material dosage,it increased rapidly first and then gradually stabilized.With the increase of the initial concentration of the solution gradually deceased.The optimum conditions for the cadmium loading process of Phytolacca acinosa Roxb biomass are as follows:pH=7,solid-liquid ratio is 5g/L,and the initial concentration of Cd2+is 25mg/L;The kinetic and isotherm experimental data were consistent with the aquasi-second-order model and Freundlich model respectively,which indicated that cadmium loading process of PB was a multi-layer adsorption model based on chemical reaction,and chemical adsorption was the main adsorption process.The thermodynamic results show that the process of cadmium loading in PB is endothermic reaction.(2)Pyrolysis stabilization of PB-Cd showed that the mass and volume of PB-Cd could be significantly reduced by pyrolysis,and the concentration of Cd in PBC-Cd would increase compared with PB-Cd;The cadmium in the original PB-Cd mainly exists in the acid soluble and reducible state is converted into the oxidation state and residue state;The results of leaching experiments showed that the leaching toxicity of cadmium was significantly reduced.The study found that the PBC-Cd500 obtained at 500℃ has a higher cadmium concentration and lower cadmium leaching toxicity than the cadmium-loaded Phytolacca acinosa Roxb biomass carbon obtained at other temperatures.(3)The characterization of biochar by SEM,BET,XPS,UV-vis and PL showed that PBC-Cd500 had a larger SBET and PV than PBC-Cd300 and PBC-Cd400.PBC-Cd500 and PBC500 had similar response and utilization efficiency to visible light.(4)The photocatalytic degradation mechanism of tetracycline in water by PBC-Cd shows these conclusions.The degradation rate of tetracycline hydrochloride solution(volume 200 mL,pH 4,initial concentration 10mg/L)was photocatalyzed by 30 mg of PBC-Cd500,and the degradation rate reached 78%within 180 minutes.After the reaction,the dissolution concentration of Cd in the solution was 0.0208 mg/L,which was lower than the identification standard of solid hazardous waste(GB-5085.3-2007).(5)The first-order reaction kinetic equation better explained the photocatalytic process.Experimental results of ESR and free radical capture showed that superoxide radicals(·O2-)and photogenerated holes(h+)played an important role in the degradation of tetracycline hydrochloride.