Effects Of Sulfhydryl Modified Rice Husk Biochar On Adsorption Characteristics Of Cadmium And Activity Of Cadmium In Soil

The treatment of heavy metal pollution has been a hot topic worldwide.Cadmium,as one of the representative heavy metal pollutants,it will seriously affect the nervous system,digestive system,hematopoietic system and blood circulation system when the human body’s intake reaches a certain level,and may even cause death of humans or animals.Since heavy metal pollutants will not be converted and disappeared,various methods need to be used to fix them,and the mercapto group can form a stable metal complex with heavy metals.The rice husk introduced in this article is a natural agricultural and forestry waste,which is often pyrolyzed into biochar for better resource utilization.Rice husk biochar has many excellent characteristics such as large specific surface area,high porosity,rich functional groups on the surface and high stability,which can be used to improve soil physical and chemical properties and remove heavy metals in wastewater.Therefore it is an important adsorption and passivation material.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 thiolmodified 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,Grafting mercapto groups on rice husk biochar prepared by pyrolysis at 350℃ and 550℃,respectively,and thioglycolic acid and 3-mercaptopropyl trimethoxysilane（MPTMS）are used as sulfhydryl group donors to modify rice husk biochar.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 at 350℃ 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℃,pH=5,solid-liquid ratio 1 g-L^-1,and reaction time 240 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^-1 increased 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 pH,and increase soil cation exchange capacity(3.15～3.65 ccomKg^-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.