Adsorption Behavior Of Heavy Metal (Zinc) On Silane Modified Biochar

Environmental problems are more and more paid attention to,among which heavy metal pollution is more severe,because heavy metals can be left in the environment by changing their morphology,and are not easily degraded by the environment.With the increase of accumulated quantity,once the environment is beyond the scope of environmental tolerance,it will not only cause adverse impact on the environment,but also enter the food chain Human body,produce toxic effect.Zinc is one of the heavy metal pollutants.Although zinc is one of the trace elements needed for the growth of animals and plants,once it exceeds the normal range,it will cause harm to animals,plants and human body.The adsorption method has always been a common method for the treatment of heavy metal pollution.Biochar is the preferred material for the adsorption of heavy metals because of its excellent pore structure,rich surface functional groups and cheap raw materials.China is a large agricultural country,which will inevitably produce a large number of agricultural wastes.Therefore,using rice husk carbon as biochar raw material can reduce the waste of resources.However,the ability of biochar to adsorb heavy metals is limited.It is necessary to study how to improve the passivation ability of biochar to heavy metals through modified methods.In this paper,the rice husk biochar is modified by sulfhydryl,preparation of four thiol-modified rice husk biochar under two different pyrolysis temperatures and two different sulfhydryl modification methods,analytical and detection methods are used to compare and analyze the physical and chemical properties of thiol-modified biochar to determine the best thiol-modified material.The adsorption characteristics of sulfhydryl modified rice husk biochar to cadmium are explored through batch adsorption experiments,and the effects of thiol-modified rice husk biochar on soil basic properties and cadmium metal morphology are studied through soil cultivation experiments in the laboratory.The treatment of heavy metal pollution in soil and water provides a practical basis.The test results are obtained as follows:First of all,Graftingmercapto groups on rice huskbiochar prepared by pyrolysis at350℃and550℃,respectively,andthioglycolicacidand3-mercaptopropyltrimethoxysilane（MPTMS）are used as sulfhydryl group donors to modify rice huskbiochar.Characterization is performed by specific surface area and pore size analysis,scanning electron microscopy with energy spectroscopy,fourier infrared spectroscopy,and X-ray diffraction.The results show that rice husk biochar prepared at350℃pyrolysis temperature is modified with MPTMS as a modifier.The sulfhydryl-modified rice husk biochar obtained by the preparation:the surface is clearer and smoother,the sulfur ratio is relatively larger,and the specific surface area is relatively increased before modification,and the thiol content is the largest.Then,rice husk biochar prepared at 350℃pyrolysis temperature was selected to study the adsorption effect of sulfhydryl modified rice husk carbon on cadmium.Through batch tests:reaction temperature 45℃,p H=5,solid-liquid ratio 1g·L^-1,and reaction time240 min^-1,the adsorption model is more in line with the langmuir isothermal adsorption model,and the maximum adsorption amount obtained by fitting is from before modification 12.80 mg·g^-1increased to 21.05 mg·g^-1;the adsorption kinetics show that it is more in line with the quasi-secondary kinetics,with a correlation coefficient R²>0.9992;the adsorption desorption experiments show that thiol-modified rice husk biochar had better affinity for heavy metal cadmium adsorption and stability.The whole adsorption process is mainly based on the spontaneous and uniform monolayer’s rapid endothermic chemisorption.Finally,rice husk carbon before and after thiol modification is added to the soil,its influence on the basic properties of the soil as follows:it can improve soil p H,and increase soil cation exchange capacity(3.15～3.65 ccom Kg^-1),in simulated soil contaminated with heavy metal cadmium,the organic binding state and residue state of cadmium increase with the increase of the proportion of rice husk biochar added.The soil with thiol modified rice husk biochar has the lowest desorption rate after absorbing heavy metal cadmium,and the desorption rate in the third month is in the range of 0.01%to 2.62%.The modification of sulfhydryl group will not affect the original characteristics of rice husk biochar,and can improve the basic properties of the soil and the passivation ability of rice husk biochar to the heavy metal cadmium in the soil.