Study On Useing Biochar Prepared By Marine Waste To Adsorb Oil From Seawater

In recent years,a series of oil leakage accidents has been occured frequently in offshore oil exploitation and transportation.Oil spills on the sea surface caused serious harm to the growth and reproduction of marine organisms.The adsorption method has the advantages of high efficiency and no secondary pollution.However,the traditional oil absorption materials are expensive and difficult to recycle.Therefore,it is particularly important to develop a new type of environment-friendly and inexpensive adsorption materials for marine oil spill.Biochar(BC)is a carbon-rich particle prepared by oxygen-limited pyrolysis of biomass materials.Due to its excellent characteristics such as large specific surface area and rich pores,biochar has strong adsorption capacity to oil.Biomass materials are widely available and cheap.Biochar prepared from marine waste(such as shrimp shells,crab shells,etc.)is expected to be used in the treatment of large-scale marine oil spills.To facilitate the recovery of biochar after oil absorption,transition metals(Fe,Co,Ni,etc.)or their oxides are introduced into the biochar matrix to form magnetic biochar(MBC),which can be rapidly separated by an external magnetic field.In this paper,the wastes of three kinds of marine organisms were selected as biomass raw material,and the effects of biomass materials and three preparation conditions including pyrolysis temperature,heating rate and pyrolysis time on the oil absorption capacity of biochar were systematically studied.Four kinds of biochar were optimized and screened out.Combined with the characterization methods of elemental analysis,specific surface area analysis and functional group analysis,the effects of different pyrolysis temperatures on the elemental composition and structural properties of the optimized screened biochar were studied.The adsorption mechanism was analyzed by adsorption kinetics,isotherm models and thermodynamics.Biochar was magnetized by co-precipitation method.The effect of Fe loading on the structure and properties of biochar was studied,and the adsorption mechanism of magnetic biochar was analyzed.The recoverability of magnetic biochar was verifyed by test and its recycling performance was studied.The main conclusions of this study were as follows:(1)36 kinds of biochar were prepared from shrimp shells,crab shells and clam shells,respectively.Compared with the heating rate and pyrolysis time,it was found that the pyrolysis temperature had a greater effect on the oil absorption performance of biochar.By comparing the oil adsorption capacity of different biochar,four kinds of biochar were screened out:shrimp shell biochar at 350?(SS350),shrimp shell biochar at 450?(SS450),crab shell biochar at 650?(CS650)and crab shell biochar at 750?(CS750).(2)Pyrolysis temperature had a significant effect on the physicochemical properties of biochar,and the specific surface area,aromaticity and hydrophobicity of biochar changed with the increase of temperature.It was obvious that SS450 and CS650 had the highest specific surface area,the best aromatics and hydrophobicity,and the best oil absorption capacity during the study.Besides,biochar contained a large number of oxygen-containing functional groups which were conducive for adsorption.(3)The adsorption process of SS450 and CS650 conformed to the pseudo-second-order kinetic model.Besides,its adsorption rate was controlled by the diffusion rate within the particle and the diffusion rate in the liquid film.Within the study temperature range,the adsorption to oil in seawater of SS450 and CS650 was more consistent with Freundlich model,and the adsorption process of biochar was favorable.(4)To further explore the adsorption mechanism of biochar to oil,SS450 was taken as an example.It was found that the abundant pore structure and graphitization structure may be the key factors affecting the adsorption rate and adsorption performance of biochar.The adsorption of SS450 to oil maybe affected by the combined action of surface adsorption and pore interception,which mainly including?-?interaction and hydrogen bond.(5)The MSS450 loaded with Fe₃O₄particles was prepared by doping solutions including Fe Cl₃·6H₂O and Fe SO₄·7H₂O with SS450.Through kinetic and thermodynamic studies,MSS450 can also be described by pseudo-second-order kinetic equations and conformed to Freundlich model.The adsorption process of MSS450 can occur spontaneously at the studied temperature(15?25?).MSS450 can also be successfully separated from seawater by an external magnetic field.The adsorption-desorption experiments on MSS450 showed that MSS450 can be recycled.