Characteristics Of Soil Quality Degradation And Restoration Of An Ion-type Rare Earth Mine In Southern Jiangxi

Due to the special mining technology of ion-absorbed rare earth mine,the ecological environment was seriously destroyed,such as soil erosion,low soil fertility,soil pollution serious,etc.Xinfeng country,based on the exploitation of heap leaching process for study with middle Y and rich Eu-type rare earth mine,Regional research methods to collect soil samples,testing in laboratory.The effects of different modifiers on soil remediation were studied by soil culture experiment.The results show:（1）The soil texture of the leaching area changed from middle loam to tight sand,and the soil pH was extremely acidic.The soil texture in the mining area changed from middle loam to pine soil,and the value of soil pH was only 4.5,which was obviously acidified.With the increase of the depth of the soil,the soil texture gradually changed from tight sand to sandy loam and light loam.In addation,the value of soil pH gradually increased.However,the soil pH of the whole profile did not changed which was still extremely acidic.（2）The regional soil fertility showed: CK > SR > LM > MM.According to the soil comprehensive fertility grade,the soil comprehensive fertility of CK was in gradeⅡ（general）,the soil comprehensive fertility of the mining area was in grade Ⅲ（poor）.The soil nutrient was seriously degraded in the study area.With the increase of the depth of the soil,the soil comprehensive fertility gradually increased,but the whole comprehensive fertility of the whole profile was still in grade Ⅲ（poor）.（3）The value of soil NH₄⁺/AN was 88.86% in the leaching area,which proved that residue of ammonium sulfate in soil was still high.With the increase of the depth of the profile,the content of ammonium ions increased gradually,the value of NH₄⁺/AN was from 89% to 95%,Available nitrogen predominantly existed with ammonium form.（4）The rare earth elements in the whole study area has a certain enrichment in the mining area,which is 6.31 times of the background value of soil rare earth in Jiangxi province.The rare earth residual in the leaching area is still higher than that in the control area after leaching,which is 1.82 times of the soil background value in Jiangxi province.With the increase of the depth of the profile,the residual of rare earth elements in the soil decreased gradually.（5）Only the concentration of heavy metal As in the soil of the leaching area exceeded that of the three levels of soil environmental standards,reaching the serious pollution level,while Pollution levels of other heavy metals were lighter comparatively.Soil combined pollution was mainly about the residual of rare earth elements pollution,Y element of the leaching area was in the moderate pollution level,Ce element was in the pollution-free level,other elements were all in the free pollution-moderate pollution level;Only Ce element of the mining area was in the free pollution-moderate pollution level,Other elements were all in moderate and severe pollution level.In general,the heavy metal pollution in the leaching area is not the main factor that hinders the growth of vegetation.（6）The addition of modifier has improved the soil texture to some extent.When cultured for 40 days,the soil texture of the treatment of single application of bio-carbon has changed from tight sand to light loam;the soil texture has changed from tight sand to sandy loam by adding fly ash;the soil texture has changed from tight sand to medium loam when lime is added.（7）At the end of the culture,the value of soil pH was significantly increased,and the soil pH was increased as follows: single lime > biochar + lime > biochar + fly ash > biochar > fly ash.（8）In the 40 th day of adding modifiers,the index of soil comprehensive fertility has been obviously improved by the treatment of biochar,fly ash,and also biochar + fly ash.According to the result of processing,most treatment could reach GradeⅠ（good）,and the cooperation of biomedical carbon and fly ash worked best,while the other two modifiers still showed no significant influence on the 40 th day.Their effects of treatment were divided into Grade II（general）.（9）After adding modifier in the soil,the bio-availability contents of Y,La,Nd and Ce in soil were decreased obviously,and the content of refractory was significantly increased,which could significantly reduce the harmful toxicity of rare earth heavy metals.（10）When adding the modifier for 40 days,the four chemical forms of soil rare earth Y,La and Nd elements were related to the soil p H,while soil organic matter did not show significant correlation with the four chemical forms.Both the value of soil pH and the content of organic matter were related to the reduction state and residual state of Ce element in soil.There was no significant correlation between soil CEC and four chemical forms of Ce element.On the contrary,the exchangeable state and reduction state of Y,La and Nd elements showed significant correlation with soil CEC.