Research On Copper Adsorption And Desorption For Sediments In Raohe Estuary

Sediments is both the reservoir of sink for micro-pollutants in aquatic systemsand the secondary source of pollution. Analyses were carried out by using themethods which connect scene sampling with Laboratory simulation to measure thephysical and chemical characteristics,the contents and the speciation of Cu in RaoheEstuary. The adsorption and desorption of Cu and the environmental factors had beenalso discussed in this paper.The result showed that:(1) The samples of sediment in Raohe Estuary belong to the weak oxidatedenvironment, the organic content was on the medium and low level. Most sampleswere neutral, just few of them were of light acidity.(2) The distributed range and average value of the content of Cu in the sedimentswere 2.20～398.40 mg/Kg and 121.7mg/Kg respectively, below the standard(400mg/Kg), but 7～64 times of the background due to humans activities. The evaluationresults of aggregate pollution index showed that it reached to middle or heavypollution states.(3) The research results obtained by speciation analysis showed that Cu mainlyexist in residual fraction,and the amount of effective fractions only occupied 50% ofthe total content. The relationship between the contents of Cu in different fractionswas: residue＞iron/manganese oxidex＞carbonate＞organic matter and sulfide＞soluble and exchangeable fractions, Relevant analysis taken by Spss showed that thecorrelation coefficient respectively between carbonate, organic matter and sulfidefraction, residual fraction were -0.913 and -0.800.(4) The adsorption of Cu for the sediments of Raohe Estuary was a complexdynamics process, adsorption reached equilibrium after 3 hours. In the preliminarystage of aqueous phase and solid phase for contacting, the maximum value ofadsorption rate of Cu reached 431.88 mg/Kg·h. The adsorption was greatly influencedby environmental factors. (5) The research of isothermal adsorption indicated that the Copper in thesediments in Raohe Estuary had a good correlation with the Langmuir and Freundlichequations,specially, there was a significant correlation between the latter equation andthe sediments. According to the Langmuir adsorption equation, the biggest adsorbingamount of sediment in Raohe Estuary reached 238.10 mg/Kg.(6) The desorption amount of Cu in the sediment increaseed with time, itreached equilibrium after 24 hours, and the released Cu existed mainly in effectivefraction, the process of redesorption after adsorption was very slow, and the pH, theion intensity, the water and soil ratio, etc. were important environmental factors thatinfluenced the desorption contents.