LİTYUM(I) ADSORPSİYONU İÇİN Pichia stipitis MAYASI İLE YENİ BİR HİBRİT ADSORBENT GELİŞTİRİLMESİ

Abstract

In this thesis study, the adsorption of lithium(I) ions, which is a rare element found at low concentrations in nature and widely used at various industries as raw material, from aqueous solutions by using live, dry and pretreated Pichia stipitis yeast cells and by hybrid adsorbents prepared with the treatment of yeast cells with activated carbon in the presence of iron(III) ions. In the first part of the study, it was aimed to enhance lithium(I) adsorption capacities of live and dry yeast cells due to their low lithium(I) adsorption capacities by applying various pretreatments (treating with hot water at 80oC, autoclaving, treating with betaine monohydrate) to both of the biosorbents. As pretreatment did not indicate a noticeable increase in lithium(I) adsorption capacities of yeast cells, the studies were focused on hybrid adsorbent production from live and dry yeast cells with the treatment of activated carbon in the presence of iron(III) ions. For this purpose, the effects of initial pH value before treatment, dry cell/activated carbon ratio (w/w) at constant activated carbon and iron(III) concentrations, activated carbon/iron(III) ratio (w/w) at constant dry cell concentration, activated carbon type, agitation rate and use of pretreated cells were investigated at 25oC to examine the production of hybrid adsorbent at optimum conditions and its capability for lithium(I) adsorption. Finally, optimum hybrid adsorbent production conditions were determined by mixing 2 g/L dry yeast cell+0.3 g/L commercial activated carbon+0.072 g/L iron(III) at 85 pm in aqueous medium whose pH value adjusted to 9.5 and the hybrid adsorbent produced at these conditions were used in all adsorption studies. In this part of thesis studies, the effects of initial pH, initial lithium(I) concentration, adsorbent concentration and mixing rate on the lithium adsorption capacities of live and dry P. stipitis yeast cells and hybrid adsorbent were investigated at 25oC. For all the adsorbents it was observed that the maximum lithium(I) adsorption capacity was obtained at pH 10.0, increasing initial lithium concentration to 50.0 mg/L enhanced the lithium(I) adsorption capacity, increasing adsorbent concentration to 10 g/L reduced the lithium(I) adsorption capacity and agitation rate did not affect the adsorption capacity. At the initial pH value of 10.0, 50 mg/L initial lithium(I) concentration and 2-2.3 g/L adsorbent concentration, the maximum lithium(I) adsorption capacities of live and dry yeast cells and hybrid adsorbent were determined as 1.06 mg/g (134.1 µmol/g), 1.24 mg/g (178.1 µmol/g) and 1.70 mg/g (245.3 µmol/g), respectively. Langmuir and Freundlich equilibrium models were used to define the adsorption equilibrium mathematically and it was seen that the experimental data for all adsorbents fitted to Langmuir model more accurately. It was shown that lithium(I) ions adsorbed by dry yeast cells and hybrid adsorbent were desorbed at 100% efficiency and these adsorbents could be used at least five times consecutively. At the last part of the experimental studies, structural and surface properties of dry yeast cells, activated carbon and hybrid adsorbents, used as adsorbents for lithium(I) adsorption, were investigated by optical microscope, SEM/EDS, BET surface area and porosity, zeta potential, point of zero charge and FTIR analyses and lithium(I) adsorption mechanisms were tried to be explained.