Preparation Of Aloe Vera Leaf Rind Biochar And Its Adsorption Performance For Metal Ions

Nickel and cobalt are widely used in industrial production,resulting in a large amount of wastewater containing Ni²⁺and Co²⁺heavy metals,which harms the ecological environment seriously.A large number of aloe vera leaf rind will be produced after aloe vera is used as resourse in food and medicine industry,which also pollute the environment if wasted directly.In order to solve the two problems,in this thesis,the aloe vera leaf rind biochar（ABC_x）was obtained from aloe vera leaf rind,which was first prepared from carbon precursor（argillaceous biomass not completely converted to carbon）by hydrothermal method,and then activated at different temperatures.Using the same method,the N-doped biochar（UABC_x）and N,S-doped biochar（SABC_x）were prepared by adding urea as N（nitrogen）and（NH₄）₂SO₄as N（nitrogen）source and S（sulfur）source to the aloe vera leaf rind,respectively.The as-made biochar materials were characterized by SEM,BET,FTIR,XPS and ZETA potential before and after adsorption of Ni²⁺and Co²⁺.The feasibility of biochar for dealing with heavy metal ions wastewater was explored by studying the adsorption properties,such as adsorption isotherm,adsorption kinetics,effects of temperature and p H on adsorption,simulated fixed bed adsorption,competitive adsorption and regeneration adsorption for Ni²⁺and Co²⁺.The main conclusions are as follows:（1）the surface of ABC_xshows obvious irregular layer bulk accumulation structure.When the activation temperature is 800℃,the obtained ABC₈₀₀has a hierarchical porous structure.Its specific surface area is 185 m²/g with the total pore volume of 0.13 cm³/g.Frost-like attachments appear on the surface of ABC₈₀₀after adsorption of Ni²⁺and Co²⁺,and the specific surface area increases obviously.The surface of ABC₈₀₀is rich in N element（2.50%）and O element（31.36%）.The content of active groups on ABC₈₀₀surface changes obviously before and after adsorption of Ni²⁺and Co²⁺.The adsorption process is more consistent with the Langmuir isothermal adsorption model and the pseudo-second-order kinetic model,which shows that the adsorption process is dominated by chemical adsorption,and the maximum adsorption capacity for Ni²⁺and Co²⁺is 158.23 and 156.49 mg/g,respectively.The results of kinetic experiments show that the adsorption is fast and the adsorption equilibrium is reached at about 300 min.The fitting results of W-M and Boyd diffusion models show that the adsorption process is mainly controlled by liquid film diffusion and also by particle diffusion.The adsorption capacity of ABC₈₀₀for Ni²⁺and Co²⁺increases with the increase of temperature,and it has better adsorption performance for Ni²⁺and Co²⁺in a wide range of p H value（p H=2-8）.The experimental results of fixed bed,competitive adsorption and regeneration show that ABC_xhas the potential to be applied to tackle wastewater containing heavy metals.（2）the surface of UABC_xshows obvious irregular layer bulk accumulation structure.The specific surface area and the total pore volume of UABC₈₀₀pyrolyzed at 800℃are 32 m²/g and 0.04 cm³/g,respectively.The proportion of non-micropores for UABC₈₀₀is as high as 0.75,showing a hierarchical porous structure.Frost-like attachments are found on the surface of UABC₈₀₀after adsorption of Ni²⁺and Co²⁺,and the specific surface area increases obviously.The surface of UABC₈₀₀is rich in N（3.85%）and O（46.06%）,and the content of active groups on UABC₈₀₀surface changes obviously before and after adsorption of Ni²⁺and Co²⁺.The adsorption process of UABC_xfor Ni²⁺and Co²⁺is more consistent with the Langmuir isothermal adsorption model and the pseudo-second-order kinetic model,which shows that the adsorption process is dominated by chemical adsorption,and the maximum adsorption capacity of Ni²⁺and Co²⁺is 175.44 and 228.31 mg/g,respectively.The results of kinetic experiments show that the adsorption is fast and the adsorption equilibrium is reached at about 300 min.The fitting results of W-M and Boyd diffusion models show that the adsorption process is mainly controlled by liquid film diffusion and also controlled by particle diffusion.N doping can effectively improve the adsorption properties of UABC_x,especially for Co²⁺.The adsorption capacity of UABC₈₀₀for Ni²⁺and Co²⁺increases with the increase of temperature,and it has better adsorption performance for Ni²⁺and Co²⁺in a wide range of p H value（p H=2-8）.The experimental results of fixed bed,competitive adsorption and regeneration show that UABC_xhas the potential to be applied to tackle wastewater containing heavy metals.（3）the surface of SABC_xshows obvious irregular lamellar stacking structure.When the pyrolysis temperature is 800℃,the specific surface area and the total pore volume of as-made SABC₈₀₀is 149 m²/g and 0.13 cm³/g,respectively.The proportion of non-micropores for SABC₈₀₀is 0.31,showing a hierarchical porous structure.Frost-like attachments appear on the surface of SABC₈₀₀after adsorption of Ni²⁺and Co²⁺,and the specific surface area increases obviously.The surface of SABC₈₀₀is rich in N（4.79%）,O（29.94%）and S（6.21%）elements.The content of active functional groups composed of N,O and S on SABC₈₀₀surface changes significantly before and after adsorption of Ni²⁺and Co²⁺.The adsorption process of SABC_xfor Ni²⁺and Co²⁺is more consistent with Langmuir isothermal adsorption model and pseudo-second-order kinetic model,which shows that the adsorption process is dominated by chemical adsorption,and the maximum adsorption capacity of Ni²⁺and Co²⁺is 245.10 and 223.71 mg/g,respectively.The results of kinetic experiments show that the adsorption is fast and the adsorption equilibrium is reached at about 100 min.The fitting results of W-M and Boyd diffusion models show that the adsorption process is mainly controlled by liquid film diffusion and also controlled by particle diffusion.N and S co-doping can effectively improve the adsorption properties of SABC_x,especially for Ni²⁺.The adsorption capacity of SABC₈₀₀for Ni²⁺and Co²⁺increases with the increase of temperature,and it has better adsorption performance for Ni²⁺and Co²⁺in a wide range of p H value（p H=2-8）.The experimental results of fixed bed,competitive adsorption and regeneration show that SABC_xhas the potential to be applied to tackle wastewater containing heavy metals.