| Nitrate nitrogen has become an important pollutant in eutrophication and nonpoint source pollution due to the excessive application and the low utilization rate of chemical fertilizers and pesticides,and the discharge of industrial and domestic wastewater.Studies have shown that the increase in nitrate nitrogen concentration cause a potential threat to human health,excessive nitrate nitrogen can also cause acute poisoning of animals and plants,pests and diseases damage and other effects.The traditional method of removing nitrate nitrogen in water is divided into biological method and physical-chemical method.Biological method is economical and environmentally friendly,but the process is slow and the treatment time is long.The physical-chemical methods include reverse osmosis,electrodialysis,ion exchange,adsorption,etc.The adsorption method is widely concerned,and one of the current research hotspots is to find a kind of high-efficiency,economical and environmentally friendly adsorbents.Biocar,also known as biomass carbon,refers to porous carbonaceous solids produced by pyrolysis of biomass raw materials(such as straw,feces,peanut shells,etc)in a limited oxygen environment at a certain temperature(commonly under 700?).Because of the high carbon content,the specific surface area is larger,the surface negative charge is higher and the charge density is higher,the stability is strong and so on,in recent years,biochar has been widely used to remove and treat pollutants in various fields.However,the nature of biochar is mainly determined by the source of raw materials and the preparation conditions,such as temperature and carrier gas.Carrier gases are mainly nitrogen and helium and other inert gases,the correlatively research for explore the CO2 as a carrier gas for the preparation of biocar is obviously lesser.At the same time,biocar applied to the water environment with the shortcoming of solid-liquid separation hard,there is the risk of secondary pollution.Magnetic biochar as a kind of energy-saving and environmentally friendly and easy to recycle adsorption material,used to deal with the nitrate nitrogen in wastewater has some researchsignificance.Therefore,in order to preferably understand the effects of CO2 and other carrier gas conditions and pyrolysis temperature on biochar,this paper investigated the effects of N2 and CO2 on the biochar of peanut shells prepared under different pyrolysis temperatures,and their effects on the adsorption performance for nitrate nitrogen in water.At the same time,the biochar prepared with N2 as carrier gas was modified by Fe3+/Fe2+ solution,and the magnetized biochars were characterized(such as electron microscopy,infrared spectroscopy,X-ray,elemental analysis and specific surface area,etc),and the adsorption performance of biochar adsorb nitrate nitrogen in waters was discussed.The result indicated that carbonization and the specific surface area of biochars were improved associated with higher charring temperature.Promotion on point of zero charge of biochars(9-20%)produced at CO2 atmosphere were a factor of 2 than that of biochars(6-10%)with N2 protection.Carbon content of biochars produced at CO2 atmosphere was reduced due to gasification of carbon when temperature was over 700?,and oxygen was imported into biomass to form new C-O bonds.After modified,the point of zero charge and specific surface area of biochars are obviously increased.The result of adsorption showed that biochars produced with N2 or CO2 protection were less efficient to adsorb nitrate nitrogen in waters,and the internal diffusion and electrostatic adsorption were acted on the adsorption process,and maximum capacity of the former predicted by Langmiur was 20%higher than that of the latter.After the modification with this method,the adsorption performance of magnetized biochars adsorb nitrate nitrogen in waters reduced considerably. |
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