The Study On Cadmium Adsorption In Soils Of Chengdu Suburban Area Under Acid Rain Condition

The dangers and impacts of acid rain has became utmost concern, Soil as acid rainfinally receptors， has close relationship with it.Acid rain may not only impact on plantgrowth, but also change the soil of physicochemical property, Leading to the changes ofbioavailability of heavy metal. This will do harm to healthy, when heavy metal cameinto food chain. It maybe also harm to underwater through the leaching downward ofheavy metals. Since2004, Chengdu has been plot as a nation acid controlling area.According to recent survey, The pollution of acid rain of Chengdu has alleviate, Butstill meet the serious challenge. What’s more, cadmium content is on high side inChengdu agriculture soils, the values even beyond the level3standard, In terms ofnational soil environmental quality. The people did a lot of research to cadmium in soil,but under the condition of acid rain in Chengdu city agricultural soils, they studied lesson the part of cadmium chemical behavior and the effects of acid rain. To deal with theproblems mentioned above, we carried on research.We focused on cadmium, a heavy metal in three major agriculture soils（paddysoil、yellow soil and purple soil）in suburban area of Chengdu city. According to theprecipitation feature in Chengdu, acid rain were simulated through consideringvarious pH and concentrations of positive and negative ions in order to take the staticadsorption experiment.The results of the experiment show five point. 1.The adsorption values brought down with the pH reducing in the three type ofsoil. The heavy metal adsorption values in the three type of Chengdu city behaved asyellow soil＞paddy soil＞purple soil. when the concentrations of cadmium is low,the Slope of adsorption line is greater, it is shows that the adsorption values increasingas concentrations of cadmium raise. on the contrary, when the concentrations ofcadmium is high, the adsorption values growth slowed.2.The adsorption characteristics of cadmium in the three type of soils weredescribed by Frendlich and Henry pattern, Temkin model not fit the adsorptioncharacteristic. When the acid rain pH reached2, the Henry pattern better thanFrendlich.3. The adsorption values reduced with the SO₄^2-increasing in the three type ofsoil. The purple soil cause the adsorption quantity changed tiny. The paddy soil causethe adsorption quantity change is largest among three soils. The adsorption valuesreduced with the NO₃^-increasing in the three type of soil.4.The adsorption values reduced with SO₄^2-and NO₃^-increasing in the three typeof soil, under the same cation condition.5.The adsorption values reduced with Ca²⁺and NH₄⁺increasing in the three typeof soil, under the same condition.This research also shows that, in the acid rain conditions, different concentrationsof cadmium have great influence on the adsorption capacity. Different types of soil onthe effect of adsorption capacity are different, even if they are the same type of soil,which adsorption capacity is also different. It is not only involved with the physicaland chemical characteristics of soil, but also the utilization ways of soil.