The effects of remediation treatments application on the sediment heavy metal immobilization

Abstract

<p>Predmet izučavanja ove disertacije, osim poređenja različitih metoda procene rizika na&nbsp;osnovu karakterizacije kvaliteta sedimenta vodotokova Vojvodine, bilo je i ispitivanje&nbsp;mogućnosti imobilizacije te&scaron;kih metalau sedimentu primenom različitih remedijacionih&nbsp;tehnika kao i određivanje njihove efikasnosti (npr. solidifikacija/stabilizacija silikatnim&nbsp;materijalima, portland cementom, kalcijum-oksidom itd.) u zavisnosti od brojnih faktora.&nbsp;Osim pseudo-ukupnog sadržaja metala određene su i specifičnije frakcije metala sa posebnim<br />osvrtom na određivanje potencijalno biodostupnih frakcija.</p><p>Rezultati su ukazali da je naosnovu holandskih preporuka sediment pojedinih vodotokova&nbsp;Vojvodine (Begej, DTD-kanal,Nadela, Sava-&Scaron;abac) zagađen metalima (klasa 4) i da je&nbsp;neohodno izmuljivanje i remedijacija. Prema USEPA i kanadskim preporukama, neki uzorci&nbsp;su potencijalno toksični, ali nije zabeležena akutna toksičnost za test vrste u pornoj vodi. Za&nbsp;neke uzorke, i pored visoke pseudo-ukupne koncentracije (klasa 4), nije potvrđena&nbsp;potencijalna toksičnost na osnovu odnosa kiselog volatilnog sulfida i simultano ekstrahovanih&nbsp;metala. Dok se ne primene skuplje metode remedijacije i tretmana sedimenta, najbolje re&scaron;enje&nbsp;je izolovano skladi&scaron;tenje na specijalnim&nbsp; deponijama. Naredni koraci bi trebali da budu&nbsp;usresređeni na kontrolu i sprečavanje zagađenja kako bi se obezbedilo da revitalizacija ovih&nbsp;vodotoka ima trajni pozitivan uticaj na životnu sredinu i nesmetanu i bezbednu plovidbu, kao&nbsp;i na primenu određenih remedijacionih metoda. Poređenje rezultata koji su dobijeni različitim&nbsp;procenama kvaliteta sedimenta pokazalo je da ponekad nije dovoljan jedan pristup i da je&nbsp;potrebno je uključiti metode procene biodostupnosti, biotestove i aspekt radioaktivnosti. U&nbsp;uzorku sedimenta koji je kori&scaron;ćen za ispitivanje efikasnosti remedijacionih tretmana,&nbsp;pokazano je da cink, nikal i olovo imaju visok rizik po okolinu, jer seprocenat metala u&nbsp;izmenljivoj i karbonatnoj fazi kretao od 40.1 do 45.2%. Cr i Cd imaju umeren rizik, dok je&nbsp;bakar prisutan u ovim frakcijama u koncentraciji koja predviđa nizak rizik (5.3%). Ovo je u&nbsp;skladu i sa rezultatima analize porne vode i simultano ekstrahovanih metala i kiselog&nbsp;volatilnog sulfida.</p><p>Istraživanje prikazano u radu je dalo odgovor na pitanje da li remedijacija može uspe&scaron;no da&nbsp;ukloni zagađenje, u smislu imobilizacije metala u stanje kada oni vi&scaron;e neće biti opasnost po&nbsp;okolinu. Svi primenjeni tretmani doveli su dosmanjenja procenta kumulativno izluženih&nbsp;metala iz S/S sme&scaron;a, ali nijedna sme&scaron;a tretiranog sedimenta i ispitivanih imobilizacionih&nbsp;agenasa ne pripada grupi inertnog otpada ukoliko se kumulativne izlužene koncentracije&nbsp;metala porede sa koncentracijama koje za otpad propisuje Evropska Unija (2003/33/EC).&nbsp;Ukoliko nam je cilj dobijanje nehazardnog otpada onda moramo primeniti u tretmanu&nbsp;sedimenta kontaminiranog metalima najmanje 30% imobilizaconih agenasa (cementa,&nbsp;kalcijum-oksida). Najveća efikasnost u imobilizaciji metala postignuta je kori&scaron;ćenjem&nbsp;cementa i kalcijum-oksida u sme&scaron;i (30% cementa i 10% kalcijum-oksida) i primenom termičkog tretmana na vi&scaron;oj temperaturi (1100⁰C) sa glinom (20% gline) &scaron;to je zaključeno na osnovu koeficijenata difuzije i indeksa izlužljivosti. Dominantan mehanizam izluživanjametala iz ovih sme&scaron;a je difuzija.</p>

<p>This work is concerned with the comparison of the different methods of metal risk assessment&nbsp;in sediments based on examination of the qualityof water courses in Vojvodina. Besides, it&nbsp;deals with the possibility of applying remediation treatments of contaminated sediment and&nbsp;with the efficiency of the different methods, that is the techniques, for immobilization of&nbsp;sediment heavy metals by applying S/S and thermal treatments. A dominant mechanism is&nbsp;proposed for the process of leaching ofthe metals from treated mixtures.</p><p>Comparison of the results obtained by the different methods of sediment quality assessment&nbsp;showed that in some cases one approach to solving this problem is not &nbsp;sufficient. Metal&nbsp;concentrations in particular sediment samples (the Begej, the DTD Canal, the Nadela, the&nbsp;Sava at &Scaron;abac) indicate the presence of contamination, the analyzed samples being of Class 4.&nbsp;According to the Dutch regulations, a sedimentof &nbsp;Class 4 is of unacceptable quality and&nbsp;requires urgent intervention in the sense of sediment dredging, disposal into special depots,&nbsp;and, if possible, remediation. For some samples, despite a high pseudo-total concentration&nbsp;(Class 4), no potential toxicity was confirmed onthe basis of the ratioof the acidic volatile&nbsp;sulfide and simultaneously extracted metals. The results showed that, apart from chemical&nbsp;analyses, biological tests are also necessary, but also sequential extraction analysis, which can&nbsp;more clearly define the way of metal binding to the particular sediment fractions, to allow a&nbsp;more reliable prediction of metal mobility, potential toxicity and bioavailability. In the&nbsp;analysis of sediment quality it is also necessary toinclude the aspect of radioactivity, as it has&nbsp;been shown that the results of this analysis can, not only confirm some of the results of the&nbsp;other analyses, but also indicate the sediment age, origin of contamination and potential&nbsp;toxicity.The subsequent steps should be directed to the control and prevention of&nbsp;contamination, in order to ensure that the water course reviatalization has a lasting positive&nbsp;effect on the environment, an unimpared and safe navigation and application of remediation&nbsp;methods.</p><p>In the sediment sample (Class 4) that was usedfor the examination of the efficiency of it&nbsp;appeared that zinc, nickel and lead exhibit a high risk, as the percentages of these metals in&nbsp;the exchangeable and carbonate phases were in the range from 40.1 &nbsp;to 45.2%. On the other&nbsp;hand, chromium and cadmium exhibited a moderaterisk, whereas copperin these fractions&nbsp;was present at the levels corresponding to a low risk (5.3%). This is alsoin agreement with&nbsp;the results of pore water analysis and simultaneously extracted metals and acid volatile&nbsp;sulphide examinations.</p><p>The investigations presented in this work provided an answer to the question whetehr the&nbsp;remediation can successfully remove the contamination in the sense of the immobilization of&nbsp;metals in a state that will not be harmful tothe environment. All the treatments applied&nbsp;yielded a decrease of the percentage of cumulatively leached metals from the S/S mixtures,&nbsp;but none of the mixtures of treated sediments with the tested immobilization agents belongs to&nbsp;the group of inert materials if the cumulative leached concentrations are compared with the&nbsp;concntrations for the wastes given by the EU legislation (2003/33/EC). Ifthe goal is to obtain a non-hazardous material it is necessary to treat the contaminatedsediment with at least 30% of the immobilizing agent (cement or calcium oxide). Based on the diffusion coefficients and leachability index, the highest immobilization efficiency was achieved using a mixture of cement and calcium oxide (30% of cement and 10% of CaO) and by applying thermal treatment at a higher temperature (1100⁰C) with clay (20%). A dominant mechanism of leaching metals from these mixtures is diffusion.</p>