| The in-depth development of human production practices has not only promoted social and economic development,but also brought serious environmental pollution problems.Lead and copper are two types of typical heavy metal elements,which often appear in the soil and water environment in the form of coexistence,posing a major threat to human health and ecological safety.As an efficient and environmentally friendly adsorption material,biochar can effectively fix lead and copper pollutants and reduce ecological risks.However,due to the influence of environmental factors,biochar will have an aging effect in its application,which will affect its stability and environmental remediation potential.Therefore,three common agricultural and forestry wastes（bamboo,rice husk,corncob）were used as raw materials for preparing biochar in this study,and the mechanism between aging effect and the physicochemical properties and adsorption performance of biochar was further investigated.The development mechanism on the physicochemical properties of bamboo,rice husk and corncob biochar were studied by using the fixed bed reactor of tube furnace and characterization methods,and influence mechanism of pyrolysis temperature on the physicochemical properties of biochar were analyzed.Results showed that with the increase of pyrolysis temperature,the fixed carbon content of biochar samples increased,alkalinity increased,yield decreased,polarity decreased,aromatization degree increased,and chemical stability increased.Meanwhile,Surface functional groups with hydrogen and oxygen gradually decomposed,while the porosity increased.Rice husk biochar showed better anti-aging potential because it contains more difficult-to-decompose substances.Subsequently,the chemical aging of hydrogen peroxide was used to simulate the natural aging process,and the correlation mechanism between the aging effect and the physical and chemical properties of biochar was comparatively studied.The results showed that chemical aging significantly changed the element composition of biochar,and the unstable carbon component was lost due to aging.Oxygen-containing functional groups（CO,C=O,COOH）were introduced in the aging process.In addition,it was also found that the effects of aging on the pore characteristics of biochar are quite different.After aging,the micropore volume of bamboo charcoal（500℃）is The mesoporous pore volume decreased to 36.3%and 80%of the original value,while the corncob bochar（500℃）showed new pores and the mesoporous pore volume increased significantly.High-temperature biochar has a low carbon loss rate and a stronger anti-aging ability.The carbon loss rate of rice husk biochar is significantly lower than that of bamboo biochar and corncob biochar,and may be protected by a Si-C layer inside to prevent external aging.Finally,through kinetic adsorption,isothermal adsorption and competitive adsorption experiments,the adsorption performance of biochar on lead and copper in single and binary systems was studied.At the same time,the aging effect on the adsorption of biochar in the composite heavy metal system was analyzed.The results showed that the aging effect weakens the heavy metal adsorption performance of biochar.In the Pb-Cu composite system,the adsorption effect of aging biochar on Pb2+is better than that of Cu2+,and the two were in a competitive relationship,but Cu2+showed a more obvious inhibitory effect on Pb2+adsorption.Inorganic precipitation and ion exchange were the dominant mechanisms for adsorption of biochar on Pb2+and Cu2+,and the complexation of surface functional groups contributed little.Part of the mineral components on the surface of the biochar were removed during aging process,thus the inorganic precipitation and ion exchange were weakened,Surface complexation andπbond interaction had been strengthened,but the adsorption performance of the aged biochar still showed a downward trend. |
