Study On In-situ Passivation Materials For Remediation Of Calcareous Cadmium Contaminated Soil

The pollution of heavy metal cadmium in soil seriously affects the environmental quality of soil and the food safety of human beings.In-situ passivation repair technology is one of the common methods used to control soil cadmium pollution in agricultural land.Based on the treatment of cadmium pollution in calcareous soil in the north of China,the adsorption effect and mechanism of several passivation materials were studied through aqueous adsorption experiments and soil pH experiments.After modification of the zeolite,suitable materials are preferably selected.The effects of different pH values and adsorption time on the adsorption performance of humic acid and 2mol/L NaOH modified zeolite were explored.Finally,the effects of the two materials on DTPA-Cd content,soil physical and chemical properties and water spinach under single and mixed application conditions were investigated through indoor soil experiments and field experiments,and the remediation effect was evaluated.The main findings are as follows:?1?Under the same conditions,the order of the adsorption efficiency of the material for Cd²⁺in water is as follows:Silicone fertilizer>Humic acid>Organic-inorganic composite materials>Modified mineral microcapsules>Modified aluminosilicate minerals>Modified power plant ash>Modified attapulgite>Natural zeolite.?2?The soil pH added with modified aluminosilicate minerals,silicon fertilizer,modified power plant ash and modified mineral microcapsules increased significantly with the increase of the amount of passivating agent;the pH of the soil with modified attapulgite,organic-inorganic composite and humic acid decreased,but the decrease was 0.01⁰.3 unit.?3?The adsorption capacity of thermal modified zeolite for Cd²⁺increases first and then decreases with the increase of heating temperature,and the optimal modification temperature is 300?;in chemical modification,the adsorption capacity of 2mol/L NaOH modified zeolite to Cd²⁺is the largest.?4?The adsorption capacity of the optimized 2mol/L NaOH modified zeolite and humic acid both increased with the increase of the pH of the solution,and the saturated adsorption capacity was 22.99mg/g and 28.27mg/g,the adsorption process of Cd²⁺by the two materials conforms to the second-order kinetic model,mainly chemical adsorption,and the adsorption rate is controlled by multiple steps.?5?Indoor soil experiments showed that the three treatments of single application of alkali-modified zeolite?T1?,single application of humic acid?T2?and mixed application of alkali-modified zeolite+humic acid?T3?all had a certain passivation effect on soil Cd.On the 50th day,the passivation efficiency of the three treatments on DTPA-Cd reached 33.51%,38.71%and 41.92%respectively.T1 and T3 can increase soil pH.After T2 and T3 treatment,the soil organic matter content increased by 136%and 52%,respectively.?6?Field soil experiments showed that the passivation efficiency of single application of humic acid?A?and mixed application of alkali-modified zeolite+humic acid?B?for DTPA-Cd in soil was 23.87%and 28.11%.At the same time,the treatment A and B reduced the Cd content in water spinach by 27.95%and 35.7%,the plant height increased by 22.11%and 16.8%,and the biomass increased by 56.18%and 49.39%,respectively.