| Soil heavy metal pollution is an important ecological and environmental issue that determines food security,affects human health,and restricts agricultural development.In recent years,soil heavy metal pollution has become the focus of social attention,and is also a research hotspot in the fields of soil science and environmental science.Soil is a multi-phase system composed of minerals,organic matter and microorganisms.The complex interaction between soil components significantly affects the migration,transformation,morphological distribution and effectiveness of heavy metals in the soil.It is also the basis of soil risk assessment and pollution remediation.In this study,the typical farmland land and forestland brown soil in Linyi City,Shandong Province,as well as two typical heavy metals cadmium?Cd?and copper?Cu?were selected as objects.Through isothermal adsorption and indoor soil column experiments,the land use patterns and temperature on Cd/Cu,the effect of adsorption and migration in soil,and the fitting of the experimental results in combination with relevant models,the following main results are obtained:?1?The main minerals of farmlandsoil and forest soil in Shandong are vermiculite,illite,kaolinite and gibbsite.The Cd adsorption capacity of farmlandsoil and forestland soil was 0.296 mg g-1 and 0.401 mg g-1,respectively,and the Cu adsorption capacity was 1.138 mg g-1 and 1.198 mg g-1,respectively.The adsorption capacity of Cd/Cu in forest soil is greater than that in farmlandsoil.The adsorption capacity of two kinds of heavy metals in cinnamon soil increases with the increase of p H.The maximum adsorption capacity of Cd in forest soil under p H4 and p H6conditions is 0.388 and 0.502 mg g-1,respectively.At different temperatures,the maximum adsorption capacity of Cd/Cu by cinnamon soil were 30°C.The adsorption of Cd on farmlandsoil and forest soil was the highest.The adsorption of Cd on farmland soil was 2.28 and 1.35 times of 15°C and 45°C,respectively;The adsorption capacity of Cu was highest at 45°C,and the adsorption capacity of Cu on farmland soil was 1.30 and 1.14 times of 15°C and 30°C,respectively.Thermodynamic parameter calculations show that the adsorption of heavy metal on both soils is a spontaneous reaction with entropy increasing endotherm.?2?The migration of the two heavy metals in the farmland soil is relatively fast.The peaks of the breankthough curves?BTCs?are 0.251 and 0.273 respectively,which are higher than those offorest land,and the migration breankthough time is earlier.The Cd/Cu is 80 min and 140 min respectively.The migration ability of heavy metal Cd/Cu in Shandong cinnamon soil decreases with the increase of p H.At p H4,the migration time of heavy metal is early and the peak of the breankthough curve is higher.The effect of temperature on the migration of heavy metals Cd is:in farmland soil,the migration ability at medium temperature?30°C?is stronger than that at high temperature?45°C?and low temperature?15°C?;in forest soil,low temperature is the most likely to migrate.As for the Cu,at low temperature?15°C?,Cu has the strongest migration ability in farmlandsoil and forest soil.At 15°C,the earliest time of breakthough occurred when Cd/Cu migrated through different treatments,all of which occurred around 50 min.?3?The two site model?TSM?fits the migration behavior of Cd/Cu best?R2>0.957?,indicating that TSM can well describe the migration behavior of heavy metals in two soils.When the migration medium is forest soil and the high temperature and high p H value,the retardation factor Rd and the distribution coefficient Kdand first-order kinetic coefficient?are larger,and the migration resistance of heavy metals is large;the?value is generally small,indicating that the surface heterogeneity of the migration medium is stronger.The f-value is much less than 100,and is between0.061?0.997,the adsorption of heavy metals is greatly limited by the rate.?4?The loss of dissolved organic carbon?DOC?during Cd migration in farmland soil is greater than that in forest soil;however,there is no significant difference between the two types of soil in the DOC loss in soil column during Cu migrate.The content of DOC and heavy metals in the soil column after migration was determined,and it was found that after the migration of heavy metals,the DOC retention of farmland soil was less,while the retention of forest land was higher,and the trend of the retention of heavy metals in the soil column was the same.During the migration process,the two heavy metals may have a certain synergistic migration effect with DOC.The comparison of soil infrared spectra before and after Cd/Cu migration revealed that no new absorption peaks or absorption peak shifts were observed before and after the migration of the two heavy metals,indicating that in these two different utilization methods of cinnamon soil,during the migration process on therelatively small time scale,the main factor affecting Cd/Cu migration is physical interaction. |
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