Effect Of Acid Mine Drainage Irrigation And Its Remediation On Fractions Of Nutrient Elements In Soils

The sulfide in metal tailings could be oxidized by the air,rainwater and microorganisms and form acid mine drainage（AMD）with strong acidity and high content of heavy metals.The AMD could be transported into farmland through surface runoff and agricultural irrigation,resulting in soil acidification,heavy metal pollution,and the decline of soil quality.Previous studies focused mainly on the risk assessment and remediation of soil pollution.The analyses of nutrients in AMD polluted soils during these remediations,however,were limited.Therefore,we collected acid mine drainage and uncontaminated farmland soils from a pyrite tailings at Tongling City,Anhui Province,constructed experiments of AMD irrigation on soils,and studied the effects of sewage irrigation on soil nitrogen,phosphorus and potassium fractions.Meanwhile,we collected farmland soils polluted by acid mine drainage（AMD）near the tailing area,constructed experiments of soil remediation by using rice husk biochar（B）,lime（L）and phosphate rock（P）,and studied the impacts of these remediations on soil phosphorus fractions.The main results were as follows:Decreased p H and increased electrical conductivity in the irrigated soils were observed due to the acid mine drainage inputs.During the nine weeks irrigation period,the iron/aluminum-bound phosphorus（Na OH-P）in soils increased significantly and correlated significantly with the AMD（r=0.38,P<0.05）;the decreased residual phosphorus（Res-P）,stable Na HCO₃-P and calcium-bound phosphorus（HCl-P）indicated that AMD irrigations promoted the dissolution of Res-P and formation of Na OH-P.The increased ammonia nitrogen（NH₄⁺-N）and nitrate nitrogen（NO₃^--N）,decreased organic matter and stable total nitrogen in those irrigated soils indicated that the inputs of AMD promoted the mineralization of soil organic nitrogen.The bioavailable potassium in contaminated soils was stable during the irrigations.This study indicated that the discharge of acid mine drainage from mine tailing has a significant effect on the fractions of nitrogen and phosphorus of nearby farmland soils.Addition of rice husk biochar（B）and lime（L）alone increased the soil p H significant;whereras addition of rice husk biochar（B）and phosphate rock（P）alone increased the soil electrical conductivity significant.During the period of 120 days’remediation,addition of rice husk biochar（B）and phosphate rock（P）alone increased various phosphorus fractions in the soils;whereas the addition of lime（L）increased the bioavailable phosphorus,calcium-bound phosphorus and residual phosphorus,and decreased the iron/aluminum-bound phosphorus.In addition,decreased iron/aluminum-bound phosphorus and increased calcium-bound phosphorus were observed during the addition of rice husk biochar and lime.These results indicated that addition of rice husk biochar and phosphate rock increase phosphorus in soils by releasing phosphate,while the addition of lime and rice huck biochar alone promotes the dissolution of iron/aluminum-bound phosphorus and transform partially into calcium-bound phosphorus.The combined addition of rice husk biochar,lime and phosphate rock increased soil p H and electrical conductivity.During the period of remediation,addition of three modifiers increased the bioavailable phosphorus,calcium-bound phosphorus and residual phosphorus in soils,with a higher increase than that of the single modifier addition.In addition to the application of rice husk biochar+lime（BL）,the combined remidiation of the other three treatments increased the iron/aluminum-bound phosphorus in soils significant.These results indicated that the combined of modifier promotes the release of phosphate.The iron/aluminum-bound phosphorus could be dissolved partly by lime,and increased by rice husk biochar,resulting in no significant changes during the remediation of rice husk biochar+lime（BL）.The variation trends of iron/aluminum-bound phosphorus,calcium-bound phosphorus and residual phosphorus are similar during the combined addition of modifiers and single modifier.Soil improvement experiments showed that the single and combined addition of rice husk biochar,lime and phosphate rock had significant effects on soil phosphorus fractions.