Sewage sludge generated in wastewater treatment plants accumulates varied contaminations of inorganic as well as organic character. Among them, heavy metals constitute a group of chemical substances which are highly dangerous for natural environment, because of the possibility of their mobilization and migration in environment as a result of changes in surrounding system. Moreover, they are pollutants toxic for humans, non-biodegradable and accumulate in living organisms. In recent years, there has been a great interest in the removal of heavy metals from sewage sludge with different chemical compounds solution and especially metal chelating agents. The goal of this work was to determine the optimal time for extraction of selected metals (Zn, Cu, Cd, Ni, Pb) from contaminated industrial and municipal sewage sludge by using 0.1 M solutions of EDTA (disodium salt of ethylenediaminetetraacetic acid), as well as citric acid. The analyzed wastewater sludge was collected from metallurgic industry treatment plant and from municipal wastewater treatment plant. In sewage sludge samples, the principal parameters were determined and after mineralization with mixture of concentrated mineral acids: HNO3 and HCl (1 : 3) the total content of analyzed heavy metals was detected using atomic absorption spectrophotometry. Chemical extraction of metals from sewage sludge 5 g samples was carried out with 50 c3 portions of 0.1M EDTA and citric acids solution for different periods of time, i.e. from 0.5 to 24 hours. After given time of shaking, the liquids were decanted, filtered through a filter paper, and finally the extracts were analyzed for heavy metals content with AAS method. It was observed that both applied solutions effectively washed metals from studied sewage sludge samples. For the period of time from 0.5 up to 5.0 hours, the concentration of almost all metals increased linearly and in the 6th hour of extraction the process was limited and finally for the period of time from 8.0 up to 24 hours, the detected metal contents in extracts were practically the same. The analysis of dependences of metal concentration versus time of extraction yielded in the optimal time of process, what value was determined as equal to 6 hours. The efficiencies of the metals removal from the studied sewage sludge by mans of the analyzed solutions of extractants were compared. Copper and lead reached higher concentration in liquids after EDTA extraction. It indicated that EDTA solution was a more effective extractant for the afore-mentioned metals. The concentration of zinc was higher in citric acid solution and citric acid was determined as more effective compound for zinc removal. For nickel and cadmium, the concentrations of metals were similar in both type of washing solution, which indicated that the efficiencies of both solutions were comparable.
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Praca przedstawia wyniki badań zawartości szkła w krzemionkowych popiołach lotnych z wykorzystaniem metody ekstrakcji chemicznej w 1% roztworze kwasu fluorowodorowego oraz metody Rietvelda. Analiza fazowa metodą Rietvelda wskazuje na dominację szkła na poziomie 71-85%. Udział szkła oznaczony metodą ekstrakcji waha się w granicach 41-73%. Pod wpływem działania HF szkło w popiołach lotnych nie rozpuszcza się całkowicie. Ekstrakcja 1% roztworem HF prowadzi do rozpuszczenia w popiołach również fazy krystaliczne - kwarc i mullit. Wyekstrahowane popioły o uziarnieniu 0-16 μm charakteryzują się mniejszym udziałem kwarcu β w stosunku do próbek wyjściowych, co wiąże się z obecnością w tych popiołach głównie amorficznej formy krzemionki. Wzrost udział mullitu w ługowanych popiołach tłumaczy się mniejszą rozpuszczalnością tego składnika w 1% roztworze HF w porównaniu z krystalicznym kwarcem i szkłem. Wyniki badań wskazują na zmienną budowę i właściwości szkła występującego w popiołach, co jest zgodne z wcześniejszymi wynikami badań.
EN
In this paper, a glass content in siliceous fly ashes was investigated by chemical treatment with the 1% HF solution, and the Rietvield quantitative analysis. The glass content in fly ashes determined with the Rietvield analysis was 71-85%, whereas the chemical method indicated 41-73%. The HF solution dissolves glass partially from fly ashes. Treatment with the 1% HF solution removes also the crystalline phases such as mullite and β-quartz. After chemical treatment, the 0-16 μm fly ashes indicated lower amount of β-quartz in comparison to the initial samples. It is attributed to the presence mainly of amorphous silicon dioxide in these fly ashes. The increase of mullite content in the fly ash samples after treatment with the 1% HF solution is connected with the smallest solubility of mullite in comparison to crystalline quartz and glass. The results confirm variable structure and properties of glass included within the fly ashes, agreeing with the early investigations.
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