| With the modernization of agriculture, the crop yield increased and at the same time the amount of agricultural waste also showed a rising trend. However, at present the utilization rate is very low. The unreasonable way to deal with agricultural waste resulted in the pollution of water, air, soil and other aspect. As a large agricultural country, China has become the largest agricultural waste output country in the world. Therefore the recycling and free-pollution disposal of agricultural waste is especially important to our country. Biomass-derived charcoal, also named biochar, refers to the highly aromatic substance remaining after pyrolysis of biomass under complete or partial exclusion of oxyen. As a kind of comprehensive utilization of agricultural wastes, biochar derived from agricultural can solve the management of them. Due to its characteristics of high stability against decay and high capability of adsorption, biochar plays a significant role in global climate change, carbon cycle in biogeochemical process and environmental system. In this thesis, biochar were produced from the pyrolysis of different feedstock at350℃-500℃. The characteristics of three biochars were investigated to find out the mechanisms of effects of biochar on soil improvement and explore the potential value of the three biochar as a kind of soil conditioner to improve soil fertility and other aspects. The adsorpents of Cd2+and Pb2+in aqueous solution by three biochars were also investigated and the mechanisms were revealed by combined the characteristics of biocar. Furthermore, the potential value of biochar as adsorbent material for treatment of heavy metal contaminated water was discussed. The main results of this thesis are as following:1.Biochars were produced fromthe pyrolysis of wheat straw, corn straw and peanut shellrespectively. Basic physical and chemical properties, surface characteristics and nutrient of three biochars were determined. The variability in biochar characteristics depends on the material used to produce it (feedstock). The pH of three biochars is higher and the fill density of them is lower. The electrical conductivity and water-soluble salt of biochar derived from peanut shell are much more than biochar derived from wheat straw and corn straw. It proved that biochar derived from peanut shell has an greater advantage than the other two in improving soil physical and chemical properities soil fertility. Biochar derived from corn straw has a good adsorption characteristics than wheat staw and peanut shell because of its higher levels in CEC and surface oxygenic functional groups.Biochar derived from corn straw contains large amounts of C/N, total K, available K, available P and available N, so it can privde more available nutrients to plant than the other biochars.2.The adsorpents of Cd2+and Pb2+in aqueous solution by three biochars were investigated. The effect of pH, contract time, initial solution concention, adsorbent particle size and adsorbent dose on the adsorption of Cd2+and Pb2+on biochars were also estimated. The results indicated that adsorption equilibrium of Cd2+and Pb2+on biochars almost reached in10minutes. The equilibrium adsorption data fitted well to the Langmiur and Freundlich equation. The maximum adsorption capacities of Cd2+and Pb2+by three biochars is equal to or more than clay mineral and the maximum adsorption capacities of Cd2+and Pb2+on biochar derived from corn straw was much larger than wheat straw and peanut shell.When150mg (6g-L-1) biochar were used, adsorption capacity of Cd2+on three biochars was90%, and Pb2+on biochar from corn straw was90.30%while52%and47%on biochar devired from wheat straw and peanut shell respectively. It suggested that biochar derived from corn straw was expected to be good adsorbents for heavy metals removal from contaminated water. A combination of chemical adsorption and physical adsorption may be three biochars adsorption mechanism of Cd2+and Pb2+. |
PDF Full Text Request