Study On Soil Remediation And Navel Orange Planting In Gannan Rare Earth Tailings

The ionic rare earth mines in southern Jiangxi suffer a lot of mining.Due to their special mining processes,they were extremely damaged to the environment,especially the pool leaching and heap leaching processes.Thus,it is urgently necessary to rehabilitate the ecology of abandoned rare earth mining areas.Herein,the abandoned rare earth mining area in Yangmei village,Dingnan County,Gannan was used as the research object to explore the impact of heap leaching mining process on the mine soil and analyze the degradation characteristics of the abandoned mine soil.According to the obstacle factors faced by the soil in the abandoned mining area,three kinds of organic fertilizers combined with biochar and fly ash were selected as soil amendments,planting the local economic crops Gannan navel orange and two kinds of understory grasses(clover,paspalum)as a field experiment conducted in the abandoned mining area of Yangmei Village.It explores the improvement effect of different restoration measures on the soil of the abandoned mining area and its impact on the safe planting of navel oranges.The main research results are as follows:(1)The main obstacles to soil in abandoned rare earth mines are:poor soil physical structure,significant increase in soil bulk weight to 1.43 g/cm~3,significant decrease in total porosity,high soil sand content,low clay grain content and obvious sanding;low soil fertility,serious lack of soil organic matter,available nitrogen,available phosphorus,total nitrogen and total phosphorus,comprehensive fertility is only 0.64,which is at the low level of class III;the soil acidification is serious,and the soil p H(4.34)in the abandoned mining area has dropped by 0.59 units in the control area,which is a strongly acidic soil;there is a potential risk of rare earth elements,besides,the total amount of rare earth elements in the abandoned mining area and the total amount of bioavailable state are 4.16times and 1.78 times of the background value of the total amount of rare earth in the soil of Jiangxi Province,respectively,which is a certain risk;the total soil Pb content is higher than the agricultural land soil pollution risk screening value,and the ratio of the effective state content to the total amount is 23.73%,which has certain toxicity.(2)The improvement effects of different remediation measures on the soil(0-60 cm)in the abandoned mining area are:the soil physical properties were improved,compared with CK,the soil bulk density was significantly reduced,the total soil porosity,field water holding capacity and maximum water holding capacity were significantly increased;soil acidification was improved,and p H increased by 2.14-2.73 units,the soil changed from strongly acidic soil to weakly acidic-neutral soil;soil nutrients were greatly improved,and soil total nitrogen,total phosphorus,total potassium,organic matter,available nitrogen,available phosphorus and rapidly available potassium were significantly higher than CK,the comprehensive score of soil fertility has been greatly improved;The number and diversity of bacteria in the surface soil increased,and the number of bacterial OTU,species richness,Chao1 index,ACE index,and Shannon index all increased significantly;the content of rare earth elements in the effective state decreased,compared with CK,regarding the decrease of 32.33%-50.20%,but the total effective state was still higher than the total rare earth in Jiangxi Province The background value;the available content of non-rare earth heavy metals is higher than that of CK due to the input of organic fertilizer,among which the content of available Pb is higher;planting clover and paspalum wetsfeteini under forest can increase the vegetation coverage in the mining area,but it will compete with navel oranges for nutrients and reduce the comprehensive soil fertility,especially paspalum wetsfeteini.(3)The impact of distinct remediation measures on the food safety of navel oranges are:all restoration measures can reduce the total amount of rare earths in the leaves,peels and pulps of navel oranges,with a reduction of 15.48%-43.16%in leaves,27.34%-46.87%in peels and 6.35%-42.43%in pulps;the contents of rare earth elements and non-rare earth heavy metals Cr,Ni,Cu,Zn,As,Cd and Pb in the pulp of all restoration measures are far lower below the contaminant limits in food and could be consumed with confidence;the roots of clover and paspalum wetsfeteini planted in the forest were easily enriched in rare earth elements,and the content of rare earth elements in the soil could be reduced by recycling the roots.From the comprehensive analysis of soil properties,navel orange fruit safety,and green coverage in the mining area,clover+biochar+fly ash+navel orange planting organic fertilizer(grass 1ABD)was the best treatment.