Geochemical Characteristics And Chemical Speciation Of Heavy Metals Elements In Areas Affected By Phosphogypsum

The reserves of phosphorite are huge in China, which are mainly formed as marine deposit with high content of uranium, thorium and heavy metals. In recent years, the increasing demand of phosphorus fertilizer and compound fertilizer leads to sharp augment of their by-product—phosphogypsum. Present research has revealed such a fact that a number of poisonous elements in phosphate rock transform into phosphorus gypsum. There are lots of phosphate rock and chemical enterprises in the Area of Longmen Mountain, which causes phosphorus gypsum piles up onboth sides of Tuojiang Riveror inside the river and heavily influences the local environment.And it is not quite for sure that the contents and existing form of the toxic elements inside the phosphorus gypsum zone.This paper bases on the research of Existing forms and distribution study of Uranium in phosphorus-enriched water system, which sponsored by National Natural Science Foundation, aiming to clarify the contents and existing form of heavy metals through analyzing and studying the water, soil and stream sediment that influenced by phosphogypsum in Shiting River. In addition, this paper evaluates the contamination of heavy metals in the study area by the methods of ecological accumulation index and potential ecological hazard index. Research conclusions show that:(1)Phosphorun gypsum stack is the important enrichment of heavy metals in source area. The contents of Cd and U of Hongda phosphorus gypsum piles were 9and 6 times higher than that of the local soil, and the contents of Cd and U of Jinhe phosphorus gypsum piles were 3 and 6 times higher than that of the local soil. In this situation, we suspect that the piles of phosphorus gypsum lead to the abnormal of the value of heavy metals. Heavy metals element content in phosphorus gysum may decrease with the increase of time.(2)The average contents of heavy metals such as As、Cr、Cu、Zn、Cd do not exceed the national water quality standard of level III except U, which partly exceeds the standard. It means there is no distinct pollution. Being affected by phosphorus gypsum, the contents of As、Zn、Cu、U in Shiting River become high. Generally speaking, the distribution of heavy metals gradually increases in the downstream.(3)amongtheriversedimentsofshitingriver,theaveragepollutionlevelofcdis0.34mg/kg,whichexceedsthenationalsoilqualitystandardoflevelⅡ.thevalueofcd、cr、pbanduappearsabnormalbesidethepilesofhongdaphosphorusgypsum(sd08),andthevalueofasandznappearsabnormalnexttothepilesofyingfengphosphorusgypsum.phosphorusgypsumpilemaybethemaincausesofheavymetalelementcontentincreasedinstreamsediments.(4)thecdpollutionofthesoilishighinthezoneaffectedbyphosphogypsum,andtheaveragecontentofcdis0.77mg/kg,whichexceedsthenationalsoilqualitystandardoflevelⅡ.beingaffectedbyphosphogypsum,thecontentsofheavymetalsinsoilbecomehigh,anddecreasegraduallywiththeincreaseofdistancefromthephosphorusgypsum.(5)heavymetalsinsedimentsaremainlytheresidualfraction,acidextractable,reducible,oxidationstateaccountsforasmallerproportion.themobilityofcd、cuandniisrelativelystrongerthanthemobilityofcr、u、pb、znandas.theacidextractableofheavymetalsishighestatyingfengphosphorusgypsumpilesandhongdaphosphorusgypsumpiles.(6)heavymetalsinsoilaremainlytheresidualfraction,acidextractable,reducible,oxidationstateaccountsforasmallerproportion.themobilityofcd、znandpbisrelativelystrongerthanthemobilityofcr、cu、as、niandu.beingaffectedbytheupstreamsulfuricacidplant,theoxidationstateoftheheavymetalsinthesoilincreasedsignificantly,andtheresiduestatedecreasedobviously.(7)basedontheevaluationofgeoaccumulationindex,theaselementpollutiondegreeinshitingriversedimentsisno-moderatepollution.itmeansthereisnopollutionofzn、u、cd、pb、cu、cr、nielement.basedontheevaluationofpotentialecologicalriskindex,theecologicalriskofheavymetalinthesedimentnearphosphogypsumpilesislarge,andtheecologicalharmofallotherheavymetalsbelongstoslightecologicalrisk.theecologicalriskfromhightolowis,cd>as>cu>pb>cr>zn.