Modification And Activation Of Wheat Straw Charcoaland Its Adsorption Capacity For Nitrogen And Phosphorus

Wheat straw charcoal has the developed pore structure, large specific surface area, strong adsorption ability and various minerals. But straw charcoal has a little anion adsorption capacity, the main reason is electrostatic mutex because of the surface of charcoal containing a lot of negative charge. So, in order to improve the anion adsorption ability, improving the preparation process is needed. In our study, we used ferric chloride(Fe Cl3) and calcium chloride(Ca Cl2) as the agents to produce modified or activated charcoal with high adsorption properties derived from wheat straw, and finding the best preparation conditions. The preparation modified or activated charcoal were characterized and the adsorption capacity was investigated, and the aim of our study is to obtain an activated or modified charcoal that had the high adsorption capacity and its effect on nitrogen and phosphorus leaching in the soil was also investigated. Getting the main following conclusions:1. The modified charcoal and their characteristics analysis1) Charcoal were produced from wheat straw through low-temperature pyrolysis at approximately 450 C, activated with hydrochloric acid(HCl), and coated with iron(Fe Cl3·6H2O) of different amounts.Adsorption capacity was calculated based on the amount of pure nitrogen or phosphorus. The maximum adsorption capacities were 2.47 and 16.58 mg/g. The capacity difference between nitrogen adsorption and phosphorus adsorption was big, and this would have something to do with adsorption mode, modification reagent, carbonization temperature. Increasing the carbon nitrogen adsorption capacity would be by changing modification reagent and carbonization temperature2) Modified charcoal derived from wheat straw was marked as CFe-N and CFe Ca-N, CFe-P and CFe Ca-P. After Fe Cl3 modified, modified charcoals contain the iron that in the form of iron oxide. N2 adsorption, pore volume and BET specific surface area of modified charcoal CFe-N was greater than that CFe Ca-N and these properties of CFe Ca-P were larger than that of CFe-P. The surface of modified charcoal was much rough than that of the unmodified straw charcoal. The FTIR spectra showed the shapes of all carbons were simple and similar and the main difference among them is that there is a broad adsorption band around 600cm-1 in modified charcoal. This band was attributed to the stretching vibration and the bending vibration of Fe-O bonds.The nitrogen adsorption capacity of CFe-N was greater than CFe Ca-N, and the Langmuir maximum nitrogen adsorption capacity was 1.33 and 0.72mg/g respectively(for NO3-5.89 and 3.19mg/g). The phosphorus adsorption capacity of CFe Ca-P was greater than that of CFe-P, the Langmuir maximum phosphorus adsorption capacity was 22.17 and 18.59mg/g respectively.The adsorption capacity of modified charcoal decreased with solution p H increasing. With the increase of the dose of modified charcoal, nitrogen and phosphorus removal rate increased. With the adsorption time increase, the adsorption capacity of modified charcoal increased, and the adsorption equilibrium was reached over a period of time.2. The preparation of activated charcoals and their characteristics analysisActivated charcoal was named as Fe AC-N, Fe Ca AC-N, Ca AC-N, Fe AC-P, Fe Ca AC-P.1) After Fe Cl3 activation, activated charcoal had a large amount of iron oxides, and the ash content was also increase. The ash content of Ca AC-N was reduced. N2 adsorption, pore volume and BET specific surface area of these three activated charcoals were in this order: Ca AC-N > Fe AC-N > Fe Ca AC-N. N2 adsorption, pore volume and BET specific surface area of Fe AC-P were greater than that of Fe Ca AC-P. The surface of Fe AC-N, Fe Ca AC-N, Fe AC-P and Fe Ca AC-P were much rough than that of the straw charcoal, and a large number of iron or calcium compounds deposits on the surface or pore of straw charcoal. The FTIR spectra showed the shapes of all charcoals were simple and similar and the main difference is that there is a broad adsorption around 460-470 and 550-580cm-1 in activated charcoal. This band was attributed to the stretching vibration and bending vibration of Fe-O bonds.2) The nitrogen adsorption capacity of Ca AC-N was larger than that of Fe AC-N, and both were larger than that of Fe Ca AC-N, and the maximum nitrogen adsorption capacity were 21.51, 14.68 and 12.78 mg/g respectively(for NO3-95.26, 65.01 and 56.60mg/g). The phosphorus adsorption capacity of Fe AC-P was greater than that of Fe Ca AC-P, and the maximum adsorption capacity was 4.71mg/g and 2.39mg/g respectively. The adsorption capacity of the activated charcoal was decreased with the p H increased from 2 to 12. With the increase of the dose of activated charcoal, nitrogen and phosphorus removal rate was increased. With the adsorption time increase, the adsorption capacity of activated charcoal increased, and the adsorption equilibrium was reached over a period of time. Joining other ions, the adsorption capacity of activated charcoal was decreased significantly.Modified or activated wheat straw charcoal using Fe Cl3 and Ca Cl2 increased nitrate nitrogen and inorganic phosphorus adsorption capacity and maximum adsorption capacity is 95.26 and 22.17 mg/g.3. The application of wheat straw charcoal in soil1) After the application of activated charcoal or modified charcoal in soil, the nitrate and phosphate retention capacity of soil was be enhancement.2) Application of charcoal in soil can reduce the volatilization of ammonia, and the ammonia volatilization was decreased with the charcoal dose increased. The effect of activated charcoal is more than that of charcoal. Activated charcoal can extend the time of ammonia volatilization and reduce the accumulation of ammonia volatilization.3) Application of charcoal in soil can reduce the water evaporation and delay the urea decomposition, and this would inhibit the urease activity to a certain extent.