Effects Of Modified Biochar And Its Aging On The Passivation Effect Of Soil Heavy Metal Cadmium

In recent years,the overall soil environment in China has been stable and improved,but the problem of heavy metal pollution in soil cannot be ignored.The heavy metal cadmium is one of the main pollutants causing heavy metal pollution in China’s soil.At present,biochar has shown great potential in the field of soil heavy metal pollution remediation due to its wide source of raw materials,low production cost,environmental friendliness,no pollution,and good long-term stability.In this thesis,corn straw biochar was selected as raw material and modified to obtain KMn O₄-KHCO₃modified biochar with high adsorption and passivation ability to Cd（II）.The properties of corn stover biochar before and after modification and its adsorption mechanism for Cd（II）were explored through relevant characterization analysis and adsorption experiments.Finally,the optimum environmental conditions and remediation effect of KMn O₄-KHCO₃modified biochar for soil cadmium passivation were explored through constant temperature soil stabilization experiments,and its long-term stability was also discussed.The main research results are as follows:（1）Using potassium permanganate and potassium bicarbonate as modifiers,the corn stover biochar was modified at the corresponding heat treatment time and heat treatment temperature,and the optimal improvement of its adsorption of Cd（II）was explored.The performance conditions were as follows:the mass concentration of potassium permanganate solution was 0.5%,the immersion time of potassium permanganate solution was 8 h,the mass ratio of corn straw biochar to potassium bicarbonate was 1:2.5,the heat treatment temperature was 500℃,and the heat treatment time was 1.5 h.Compared with before modification,the KMn O₄-KHCO₃modified biochar prepared under this condition has a rougher surface and more micropores;the specific surface area and average pore volume are significantly increased;the main functional groups are C=O,C-OH,and the successful Load Mn Ox.（2）The adsorption of Cd（II）on corn stover biochar before and after modification followed the law of pseudo-second-order kinetic equation,mainly chemical adsorption;and conformed to the Langmuir isotherm adsorption model,that is,monolayer adsorption,and the adsorption process was spontaneous Endothermic reaction,the system disorder increases during the reaction.KMn O₄-KHCO₃modified biochar participated in the adsorption of Cd（II）through surface complexation,cation-πinteraction,surface precipitation and physical adsorption.At 298 K,the saturated adsorption capacity of KMn O₄-KHCO₃modified biochar was 18.98 mg/g,which was 2.4 times higher than that before modification.（3）The optimum environmental conditions for KMn O₄-KHCO₃modified biochar to remediate heavy metal cadmium-contaminated soil are:ambient temperature 35℃;soil moisture content 25%～35%;soil p H value 5～8.With the increase of KMn O₄-KHCO₃modified biochar dosage,soil p H,organic matter content,cation exchange capacity,soil available phosphorus content and soil available potassium content were increased to varying degrees.The addition of KMn O₄-KHCO₃modified biochar can change the distribution ratio of soil cadmium occurrence forms,and promote the conversion of weak acid extractable cadmium,which is easily absorbed and utilized by organisms,into more stable reducible,oxidizable and residual cadmium.At the same time,the aged KMn O₄-KHCO₃modified biochar had a better passivation effect on soil heavy metal cadmium than the fresh KMn O₄-KHCO₃modified biochar.