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University of Belgrade , Belgrade , Serbia
University of Belgrade , Belgrade , Serbia
University of Belgrade , Belgrade , Serbia
University of Belgrade , Belgrade , Serbia
Mining and Metallurgy Institute Bor
In this paper, the results of changes in pH and conductivity values of the solutions during the rinsing of the adsorbent, as well as during the adsorption of copper ions were presented. Prior to the adsorption experiments, the sunflower heads were rinsed with 200 cm3 of distilled water in ten equal portions (20 cm3 each). After each water volume passes through the layer of the adsorbent, the pH and conductivity value of filtrate was measured.After the rinsing, the same adsorbent was then used for the adsorption experiments.As an aqueous phase, synthetic solutions of Cu2+ ions were used, with an initial concentration of 0.2 g dm-3. The obtained results show that from the beginning of rinsing the adsorbent, the pH value of rinsed water increases, reaching a constant value after passing 100 cm3 of water, and remains constant with further rinsing. It is assumed that an increase in pH value, during rinsing, occurs due to a transfer of H+ ions from the aqueous phase to the molecular structure of adsorbent to be exchanged there with alkali and alkaline earth metal ions.As for conductivity change during the rinsing of the adsorbent, it can be seen thata sudden increase in the aqueous phase conductivity occurs just after the first two portions of water passed through a bed of the adsorbent, reaching the peak around the volume of 0.05 dm3 , it drops down rapidly. After V > 0.05 dm3 the conductivity of leachate continues to decrease but now more and more slowly, tending to achieve the initial conductivity of distilled water used for rinsing.Thisincrease in the conductivity of the rinsed solution occurs most likely due to increasing in the concentration of alkali and alkalineearth metal ions in the solution, which are being transferred from the structure of the adsorbent into the solution during the rinsing. With further rinsing, the conductivity decreases, as a result of the decrease in the concentration of alkali and alkaline earth metal ions in the solution due to the dilution of the solution. During the adsorption of copper ions, quite a different behavior in changing of the pH and conductivity value in relation to the pH and conductivity change when rinsing the adsorbent with distilled waterwas noticed. The pH value rapidly drops downat the very beginning of the process, reaching a constant value in the next 30 minutes, and remains unchangeable with further process time.A very quick decrease in the initial pH occurs due to the releasing of H+ ions in the aqueous phase as a result of the deprotonation of functional groups existing in the molecular structure of adsorbent, where they are exchanged with copper ions.As for change of the conductivity of the solution, during the adsorption of copper ions, it can be seen that conductivity increasesat the very beginning of the process, reaching a constant value after 30 minutes. This increase can be attributed to the increase in the concentration of alkali and alkalineearth metal ions in the solution, which are exchanged with copper ions during the adsorption process.
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