Effect Of Organic Matter And Attapulgite On Bioavalibility Of Cd In Soil

The non-contaminated soil, sand, attapulgite and organic fertilizer from Gansu Shuangtai Aotu Science and Technology were taken as the experiment materials. As research materials, attapulgite and organic fertilizer were added to the mixture samples of sand and soil in different proportions respectively?except CK? to conduct the immobilization experiment. In the immobilization process, four types of leaching extraction of heavy metal content of DTPA, EDTA, hydrochloric acid and deionized water at different time points?day 3, 6, 12, 24, 48? and different samples were determinated to analyse changes of the heavy metals concentrations and bioavailability, and to study change of heavy metals along time and different treatment. The physical and chemical properties of the passivated soil samples and form distribution of heavy metals in BCR extraction were combined to analyze the correlation between heavy metal extraction in soil with attapulgite and organic fertilizer adding and other factors.Experimental results showed that:1. In the immobilization process with different proportions adding of attapulgite and organic fertilizer, compared to CK, the change trend of extraction concentration was basically the same, and extractable concentrations of CK were higher than other treatments. The EDTA, DTPA extraction and water soluble state of heavy metal concentration showed a decreasing trend along the passivation time, hydrochloric acid extraction heavy metal concentrations remained unchanged or slightly reduced with the passivation time. So adding of attapulgite and organic fertilizer is effective in reducing the bioavailability of heavy metal.2. The effect of attapulgite and organic fertilizer on the extraction of Cd in the soil was that: the heavy metal extraction concentrations in the different treatments with the addition of attapulgite showed extremely significant differences?P<0.001?, along the time, especially the difference is very obvious between CK group and other treatments. So the adding of attapulgite had great influence on the heavy metal extraction concentrations. In the addition of organic fertilizer, with the passivation time, DTPA, EDTA and HCl extraction concentration has significant difference?P<0.001?, water soluble extraction showed different changes between different metals concentration.3. The correlation between leaching state and properties showed that: For the six treatments with the addition of attapulgite, the DTPA, EDTA, and hydrochloric acid extraction had significant negative correlation with the pH?P<0.01?; the four types extraction showed significant positive correlation with the EC?P<0.01?; the four types extraction showed inconsistent positive correlation with the NO₃^--N; the correlation between the four types extraction and the NH₄⁺-N did not reach significant level?P >0.05?. For the six treatments with the addition of organic fertilizer, the DTPA, EDTA, and hydrochloric acid extraction had significant negative correlation with the pH?P<0.01?; the DTPA, EDTA, and hydrochloric acid extraction had significant positive correlation with the EC?P<0.05?; the DTPA, EDTA, and hydrochloric acid extraction had significant positive correlation with the NH₄⁺-N?P<0.05?; the correlation between NO₃^--N and the four types extraction did not reach a significant level?P > 0.05?.4. The correlation between leaching state and chemical forms showed that: With the addition of attapulgite, there was significant positive correlation between DTPA and hydrochloric acid extraction with the reduction state and acid-soluble?P<0.01?; the EDTA extraction had significant positive correlation with the acid-soluble?P<0.001? showed significantly positive correlation with the reduction state?P<0.01?; the water soluble extraction reflected inconsistent correlation with the four chemical forms of acid-soluble, reduction state, oxidation state and residual. With the addition of organic fertilizer, the DTPA, EDTA, hydrochloric acid extraction showed significant positive correlation with the acid-soluble and reduction state?P<0.01?. The correlation between DTPA extraction and oxidation state reflected inconsistent. The EDTA extraction showed positive correlation with the oxidation state. There was significant positive correlation between hydrochloric acid extraction and oxidation state?P<0.05?. The water soluble extraction showed a significant positive correlation with the acid-soluble and oxidation state?P<0.05?. The four types extraction showed negative correlation with the residual.