Study On Contaminated Characteristics Of Heavy Metals And Chemical Controlling Of Polluted Cd In The Coastal Soil Of Weihe River (xi’an)

More and more attention was paid to the heavy metal pollution in soil sinceindustrial and argricultural development and urbanization. The heavy metal pollution insoil along the coastal areas of Weihe River as the city “moat” of Xi’an has an importantimpact on economic development and the level of people’s living. So study on theheavy mental in those areas was mean. Chemical controlling method, which is used toremediate contaminated soil, has the advantage of economy and convenience.The papernot only studied distribution characteristics of heavy metals on the coastal soil of WeiheRiver in Xi’an, but also evaluated the degree of pollution. Further, researched thechemical regulation when control agent on the contaminated soil with pollution heavymetals and pollution section. After clearing the effects on all kinds of control agent ofleaching-out toxicity on cadmium soil, I selected two typical control agents and theircomposite stabilizer to study the effective state Cd and dynamic changes of Cdspeciation on contaminated soil. The main results obtained as follows:(1) The average concentrations of the first three heavy metals which were Pb、Cr、Cd、As、Ni、Cu and Mn in Weihe coast of Xi’an were all higher than the backgroundlevel of heavy metals in Shanxi Province. Obviously, the average content of Cdexceeded its background level4.2times as more.The biggest mean single pollutionindex for all heavy metals was Cd within3~6,which belongs the state of severepollution, followed by Pb and Cr. The rest metals kept light pollution which less then1of the single pollution index. Cd was also the biggest which stayed “serious” pollution, when evaluated using mean single potential ecological risk index (126.73), theremaining metals less the40stayed “ligth”pollution. It stayed “moderate”pollution oneach sampling section when using total pollution index or total potential ecological riskindex, especially on the section of Gengzhen07#bridge and followed by Tianjianrendu05#and Xinfen08#bridge and Xianyang02#bridge. Cd in the soil of07#wouldmigration and transformation with exchangeable speciation almost52%~62%, strongerpotential migration ability and bioavailability, and then indirectlythreat human health.(2) Add all kinds of single control agent to07#soil，sample of Gengzhen Section,the best passivation effects were potassium dihydrogen phosphate、peat and chitosan, thehighest passivation rate reached to70.37%、40.74%and12.96%respectively. The regulation effectwith diatomaceous earth and calcium carbonate is more wors（t-22.22%and-72.22%）, which nopassivation effect showed, and even increasee amount of Cd leaching. By complex formulationstudy, peat grouping respectively made with potassium dihydrogen phosphate and chitosan indifferent mass combination, was higher rate of passivation compared with single control agent peatwhich with the rate40.74%under the same dose. The best passivation effects to the contaminatedCd soil were the composite stabilizer which made with potassium dihydrogen phosphate and peatby mass combination1:1, the highest rate of their passivation to79.94%,which judged fromsystem of single potassium dihydrogen phosphate and all composite stabilizer.And while best to58.76%, from single chitosan and composite stabilizer which made with chitomsn and peat by masscombination1:2, which was still almost a little good compared to the groups of peat and potassiumdihydrogen phosphate overall.(3) Add peat or potassium dihydrogen phosphate or their composite stabilizer to Cdsoil of07#, the effective state Cd content in the soil with control agent were significantlyreduced than none agent which with content of1.08mg/kg after3days of culture in thetraining period. There was a fluctuantions of the effective state Cd which was increasedin the14days compared to7days ago with peat. During the period of28-day culture,the effective state Cd content with potassium dihydrogen phosphate was decreasedsteadily, which was always lower than adding peat in different does. The bestpassivation effect was potassium dihydrogen phosphate which was in the3days, thehighest rate of passivation to0.097mg/kg. It was3days that steadily reduced theeffective state Cd content with the composite stabilizer of peat and potassium dihydrogen phosphate by mass combination2:1or1:2which while the excellentpassitivation effect relatively with high does after7days.(4) It was showed that increasing dosage of peat was beneficial to decrease thecontent of soil effective state Cd, the percentage of exchangeable speciation decreasedfrom54.85%to the range of15%to20%. While it decreased from54.85%to the rangeof9.84%to10.41%adding potassium dihydrogen phosphate, which was better effect ofpassivation than adding peat. Composite stabilizer mixed peat and potassiumdihydrogen phosphate in different proportions also decreased the percentage of F1from54.85%to the range of10.01%to11.49%, which would less exchangeable speciation,more combination state and residue state compared with that before culture.