Effect Of Phosphorus On The Transformation Of Iron Mineral And Arsenic Near Dabaoshan Mining Area

Due to human activities and weathering process,acid mine wastewater often causes serious heavy metal pollution in soil and water during mining of metal sulfide mines.In particular,Dabaoshan in Guangdong Province is a typical polymetallic sulphide mine.Heavy metal pollution caused by acid mine wastewater is one of the most serious environmental problems in this area.On the other hand,because abundant amorphous iron minerals in the local soil,the available content of phosphorus in the soil is low,which is called chemical phosphorous deficiency.Thus,a large amount of phosphorus fertilizer is needed during crop cultivation.However,when much phosphorus entering the soil environment,it will lead to the release of arsenic from soil particles,causing food safety problems.In this study,by field sampling and circular flow experiments?0,1,5,10,50,100mg/L?,the interaction,migration and transformation of phosphorus,arsenic and iron minerals in three farmland soils?S6,S8 and TR?along Hengshi River affected by acid mine wastewater was studied.The results showed that the release of arsenic could be induced by the change of pH?3⁷?and high phosphate concentration in the solution.The arsenic release in upstream field is higher than in downstream.Moreover,As?V?is the main form affected by phosphate in soil solution.The concentration of arsenic in solution reached the maximum after about 7 days when the application rate of phosphorus was P₁₀?200 mg/kg?.The highest concentration of arsenic in soil solution of S6,S8 and TR reached 2298.4,829.9and 153.9 ug/L,respectively.The As?V?status accounted for 93%,97%and 18%of arsenic.On the other hand,it was confirmed by results of XRD and SEM that most of the minerals produced in the process are amorphous iron or aluminum?hydr?oxides.With the mineral generation,the concentration of arsenic in soil solution decreased to 314.2,98.1 and 34.1?g/L.With the increase of phosphorus application,mineral particles become finer?<100nm?.The analysis of XPS and SEM-mapping confirmed that the distribution of arsenic is related to iron minerals.In addition,with the increase of soil depth,the combination of amorphous iron mineral and phosphorus reduced the availability of phosphorus and increased the availability of arsenic.In order to further study the possible arsenic release process in soil,the effects of phosphate?0,1,5 and 10 mM?on the transformation of arsenic-containing jarosite and arsenic release process were studied through batch experiments.The results showed that the arsenic-containing jarosite in the soil had phase transition in the presence of ferrous in soil.The low content of phosphate?1 mM?can promote mineral transformation,and the particle size gradually decreased and migration increased.However,the effect on the activity of arsenic was limited.Conversely,high content of phosphorus?10 mM?inhibits the conversion of jarosite,but arsenic can be displaced into the solution,resulting in the release of arsenic.In this study,the trend and distribution of phosphorus,arsenic and iron in the mining area were discussed from the macro-environment and micro-mineral scales,which provided a basis for fertilizer application in the mining area.