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Research On Hydroxyapatite Complex Technology To Immobilize Heavy Metals In Contaminated Sediment

Posted on:2015-06-30Degree:MasterType:Thesis
Country:ChinaCandidate:M WangFull Text:PDF
GTID:2181330467958553Subject:Municipal engineering
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In recent years, with the rapid development of industry, a large number of industrial wastewater and sewage which was untreated or could not reach the standard below into water bodies with a lot of the heavy metal pollutants that enriched in the sediment at last. When the external environment condition changes, the heavy metals in sediment may release back into the overlying water and lead to the deterioration of the overlying water quality. At present, the use of agents for immobilization of heavy metals in sediment which is in order to reduce the impact on the environment has become a great application prospect of environmental remediation technology.In the experiment, diatomite, calcium dihydrogen phosphate, calcium carbonate, nano hydroxyapatite (nHAP) and hydroxyapatite (HAP) were selected as agents to immobilize heavy metals in sediment. The hydroxyapatite was selected as the best agent, and the best dosing quantity was10%. CaO and MgO was mixed with HAP in different proportion respectively, two new agents, HC (HAP+CaO) and HM (HAP+MgO), were obtained. Then the HC an HW were used to immobilize heavy metals in sediment. For the immobilization, BCR extraction test, toxicity characteristic leaching procedure (TCLP) and simulated release test of pollutants were used as the evaluated method.BCR extraction test and toxicity characteristic leaching procedure (TCLP) were used to evaluate the effect of immobilization. All the five agents, especially HAP and nHAP, had obvious effect on immobilizing heavy metals. Considering the cost of nHAP, HAP was selected as the agent to immobilize heavy metals in sediment. According to the test,10%was the best proportion for HAP to immobilize heavy metals. When the dosage of HAP was10%, the BCR result showed that the stable (oxides and residual) of Zn, Mn, Pb and Cd were increased7.97%,7.61%,13.61%and4.17%; the TCLP result showed that the leaching amounts of Zn, Mn, Pb and Cd were reduced75.95%、28.13%、78.47%and79.09%, respectively. From the spectrum of SEM and FTIR, it could be seen that HAP had its own unique structure and composition, and the mechanism of HAP in immobilizing heavy metals mainly include:induction of heavy metal adsorption, reaction with heavy metals or mineral precipitation, surface adsorption of heavy metals directly.CaO and MgO was mixed with HAP in different proportion respectively, two new agents, HC (HAP+CaO) and HM (HAP+MgO), were obtained. Then the HC an HW were used to immobilize heavy metals in sediment. For the immobilization, BCR extraction test and toxicity characteristic leaching procedure (TCLP) were used as the evaluated method. The results showed that in the sediment with composite additives, more than63%Zn,55%Mn,72%Pb and67%Cd were immobilized in the oxidizable and the residual fractions. Comparing to the raw sediment, the Zn, Mn, Pb and Cd in residual fraction of sediments with composite additives increased more than10%,. The TCLP results showed that nearly85%Zn, Pb, Cd and50%Mn were reduced in the leaching solutions when the dosage of oxides was10%in the composite additives.The pollutants release experiment demonstrated that the cumulative release amounts of heavy metals in the immobilized sediments were all less than that in raw sediment, and in the24day, the test reached to the equilibrium. When the dosage of oxides was10%, comparing to the raw sediment, the decrease amount of Zn, Mn, Pb and Cd in the sediment which was immobilized by HC was58.23%,60.71%,47.31%and55.88%, respectively. The decrease amount of Zn, Mn, Pb and Cd in the sediment which was immobilized by HM was68.19%,29.55%,44.09%and50.91%, respectively. The using of composite additives was highly efficient in reducing the TP releasing from the sediments while that adding HAP can increase the TP concentration in the beginning of the test. When the dosage of Cao was10%, the sediment with HC could decrease the release of the TP, even little than the raw sediment release.
Keywords/Search Tags:sediment, heavy metals, immobilization, hydroxyapatite, complex
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