Preparation Of Biochar By KMnO₄/MnSO₄ Assisted Hydrothermal Carbonization Of Some Biomass And Its Adsorption Capacities For The Pb（Ⅱ）

Due to the potential excellent physical and chemical performances as well as application prospect, biochar is drawing more and more attention nowadays. Besides, biochar material can be adopted as a management of waste. As an important method to produce biochar, hydrothermal carbonization（HTC） characterizes relatively lower reaction temperature, simplified reaction conditions and a wide range of raw materials. In this paper, hydrothermal coal and modified hydrothermal coal were prepared adopting hydrothermal carbonization method considering its easy-to-control characterization under conventional medium conditions and medium KMnO₄/MnSO₄, respectively. After that, the preparation process, organization, structures and other properties were characterized, the thermodynamic and dynamic properties of adsorption of Pb（Ⅱ） were compared. The research includes mainly the following three aspects:1. Research on absorbability property of synthetic hydrothermal coal produced from ashtree through KMnO₄/MnO₂ assisted hydrothermal method.Adopt ash wood chips as raw material ashtree coals were prepared under temperature of 220 Celsius degree in the media of pure water, MnSO₄ solution and KMnO₄ solution which were marked as HC, M2 HC and M7 HC, respectively. Then the modification effect of MnSO₄ and KMnO₄ for ash wood chips hydrothermal carbonization was primarily investigated by measuring the p H value, volume of gas and productivity of hydrothermal coal. The chemical elements and ash content of obtained ashtree coal were analyzed and characterized with XRD, FTIR, SEM, XPS and other instruments to study the absorbability of Pb（Ⅱ） in detail. The results indicate that（1） hydrothermal carbonization of ash wood chips reacted in media of MnSO₄ solution, water and KMnO₄ solution all obtained decreased p H value with acid products, while volumes of gas increased successively and the productivity of ashtree coal decreased successively which means that KMnO₄ encourages the carbonization of organic materials;（2） the inorganic ash content of M7 HC was 11.6% apparently increased than HC and M2 HC, the contents of C and H in M7 HC were increased VI while decreased in M2 HC comparing with HC which indicates that KMnO4 reduced the quantity of polar functional groups and lowered the polarity of hydrothermal coal;（3） the three types of ashtree coal were all graphite-like coal with pretty low crystallization, M7 HC contained microcrystal of Mn3O4 and Mn CO3 mainly distributed on the surface of large coal particles with irregular shapes, the particle size of M7 HC was between HC and M2 HC, the p H value of M7 HC is around 7 while the value is 4 for HC and M2 HC on the isoelectric points;（4） Pb2+ was 100% absorbed by M7 HC between wider range of p H（3-7） which is apparently superior to HC and M2 HC, the absorbability shows M7HC>HC>M2HC,（5） the Pb2+ absorbability of HC, M2 HC and M7 HC follows the Langmuir isotherm adsorption equation, the maximum absorptions under the conditions of p H=5.5 and 25 Celsius degree were 24.28, 21.52 and 95.05 mg/g, respectively, topped by M7 HC which was 3.9 times of HC and 4.4 times of M2 HC,（6） the absorption of Pb（Ⅱ） on HC, M2 HC and M7 HC follows pseudo-second order kinetic equation, the absorption rate of M7 HC is faster then M2 HC and HC.2. Effect of KMnO₄ concentration on preparation of hydrothermal coal from waste of cattle through hydrothermal method and Pb（Ⅱ） absorbability Select waste of cattle as representative of manure organic raw material and take Pb（Ⅱ） as typical heavy metal pollutant to investigate the composition, structure and adsorption of heavy metal ions of KMnO₄ modified hydrothermal coal. The obtained original and modified hydrothermal coal were marked as DMHC and Mn-DMHC. The results indicate:（1） although both of the ash contents of DMHC and Mn-DMHC are high, the latter is 3% higher than the former. The content of C, H and N for Mn-DMHC is lower than DMHC, while the content of O is higher. KMnO₄ increased the oxidation level of organic waste of cattle, strengthened its polarity and reduced the aromatization of the surface;（2） The hydrothermal coal of cattle waste are irregular large particles constituted by micro particles. The size of Mn-DMHC is smaller than DMHC. Accounting for the modification of KMnO₄ the surface area of hydrothermal coal was increased from 15.87 to 52.94 m2/g, the volume of holes was increased from 0.056 to 0.145 cm3/g, the organization and structure were strikingly improved at the meantime;（3） The most appropriate p H value was selected as 5.5, and the optimum dosage of Mn-DMHC was determined as 1g/L through correlative tests;（4） The absorption of Pb（Ⅱ） for DMHC and Mn-DMHC follows pseudo-second order kinetic equation, the absorption constant is between 0.042 and 0.89 g/（mg·h）;（5） The absorption of Pb（Ⅱ） on DMHC follows the Freundlich isothermal adsorption model, and Langmuir isothermal adsorption model on Mn-DMHC. The absorption of Pb（Ⅱ） on Mn-DMHC peeks with a p H value of 5.5 under the temperature of 25 Celsius degree with a maximum quantity of 82.25 mg/g.3. Effect of KMnO₄ concentration on hydrothermal coal produced from peanut shells through hydrothermal method and adsorption performance of Pb（Ⅱ） Take peanut shells as organic raw material, adopt hydrothermal method to prepare hydrothermal coals in water（PSC） and KMnO₄ modified solutions（5%PSC, 10%PSC and 15%PSC）. Then characterize and analyze the obtained hydrothermal coal to study the absorption performance of Pb（Ⅱ）. The results indicate that:（1） the modification of Mn notably increased the ash content of hydrothermal coal from peanut shells, the obtained hydrothermal coal（PSC and x% PSC） were either semi-amorphous carbon or completely amorphous carbon, besides disperse Mn CO3 were produced between the structure and in the holes with reduced surface area rate, volume and aperture;（2） for the three types of modified hydrothermal coals and original one, the absorption shows: 15%PSC>10%PSC>5%PSC>PSC, the modification of Mn apparently increased the absorption of hydrothermal coal produced from peanut shells;（3） the absorption of PSC and 5% PSC follow Freundlich isothermal adsorption model, while 10% PSC and 15% PSC follow Langmuir isothermal adsorption model with maximum absorption quantity of 56.53mg/g and 75.47mg/g;（4） the absorption of Pb（Ⅱ） for PSC and Mn modified hydrothermal coal all follow pseudo-second order kinetic equation, and the absorption processes are all controlled by chemical absorption mechanism with a absorption contant between 0.214 and 8.804 g/（mg·h）.