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Browsing by Subject "nanofibrilloitu selluloosa"

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  • Heinonen, Reija (2020)
    Mining of sulfide minerals produces acidic effluents rich in soluble metals and sulfate. The effluents pose a risk to the environment and must therefore be treated prior to their release. Conventionally, effluents are neutralized, and remaining metals are precipitated as hydroxides by means of alkaline minerals or industrial chemicals. The process leads to a formation of large amounts of disposable sludge containing valuable metals. Efforts are needed for more sustainable and resource efficient water treatment in the spirit of circular economy. Nanofibrillated cellulose (NFC) adsorbents are a promising and sustainable alternative to conventional treatments as cellulose is the most abundant natural polymer. In addition, NFC can be prepared from industrial byproducts and its surface properties can easily be modified to adsorb pollutants with different chemical properties. Understanding the adsorption mechanisms is essential for the rational development and use of NFC in water treatment and environmental protection in the future. Based on previous studies, anionic NFC retains metal cations and sulfate anions simultaneously from aqueous solutions. However, the adsorption mechanisms in conditions comparable to e.g. authentic mining water with high metal salt concentrations are poorly understood. In this Master’s Thesis work, adsorption experiments with pure metal salt solutions of increasing metal concentrations (0-800 mM) were carried out to investigate the adsorption mechanisms of metal cations and anions. Based on previous studies five cations with different chemical properties were chosen: Na⁺, Mg²⁺, Mn²⁺, Al³⁺ ja Fe³⁺. The adsorption was examined in both metal chloride and sulfate solutions to also elucidate the co-adsorption of counter ions and their possible effects on metal adsorption on NFC. The Freundlich adsorption isotherm model was utilized to analyze the adsorption of metals. In addition, removal percentages were calculated for both metal cations and their counter anions. NFC was observed to retain all metal cations equally regardless of their different properties and pH-values of the metal salt solutions. The removal percentage of both cations and anions ranged mainly between 14–20 % and the removal capacity of NFC decreased only slightly with increasing initial concentrations. No remarkable differences were observed in the adsorption isotherms of different metals and the adsorption was almost linear in the whole concentration range. Despite the relatively low removal percentages, the amounts of metals adsorbed by NFC (mmol/g dry weight) were tenfold compared to those previously obtained in many studies. According to the results, NFC adsorbed cations non-specifically with weak interactions and the dominating adsorption mechanism resembles physical rather than chemical adsorption. Upon the adsorption of cations, an equal amount of negative charge was co-adsorbed and hence the adsorption of anions was deemed electrostatic in nature.