The following dissertation contains a study of the removal of heavy metals from river sediments
and the determination of their contents. The removal of lead, zinc, and cadmium from the sampled river sediments was done by washing the sediments with selected reagents, namely: EDTA, citric acid, and DL-malic acid. Two sediments were sampled along the Drava River, sediment S (old) in year 2007 and sediment N (new) in year 2021. Total metal content of lead, zinc, and cadmium was determined by acid digestion of the sediment with nitric(V) acid (1+1). The approximate values are 350 ppm for lead, 1200 ppm for zinc, and 8 ppm for cadmium. Analyses of sediment washing efficiency were performed using selected reagents: EDTA at different pH values; citric, DL-malic, and L-tartaric acids at different concentrations; citrate and tartrate salts; a solution of combination of EDTA and citric acid at different concentrations; a solution of a combination of EDTA and DL-malic acid at different concentrations. For the selected reagents, the following optimal operating conditions were determined: the expected time or duration of washing, the concentration of a particular reagent/ligand, the temperature at which washing is performed, the ratio between the volume of washing solution and the mass of sediment (R/S), and in the case of EDTA, the pH. Quantitative determination of lead, zinc, and cadmium content was performed by inductively coupled plasma atomic emission spectroscopy (ICP-AES), also called inductively coupled plasma optical emission spectroscopy (ICP-OES).
All reagents were able to remove lead, zinc, and cadmium from the sediment to some extent, however the most effective combinations were EDTA and citric acid (70%, 35%, and 60% removal efficiency for Pb, Zn and Cd, respectively) and EDTA and DL malic acid (70%, 30%, and 60% removal efficiency for Pb, Zn and Cd, respectively) and also L-tartaric acid (Pb 50%, Zn 50%, Cd 60%). The optimum conditions for the selected reagents are as follows: EDTA (0.01 M) + citric acid (0.1 M), 1 h ultrasonic bath (without heating), R/S = 10/1; EDTA (0.01 M) + DL -malic acid (0.1 M), 1 h ultrasonic bath (without heating), R/S = 10/1; L-tartaric acid (0.3 M), 1 h ultrasonic bath (without heating), R/S = 10/1.
The washing of sediment with selected reagents proved to be an effective method for removing
lead, zinc, and cadmium from river sediments on a laboratory scale. Further research should include regeneration or the possibility of processing used reagents in rinsed solutions, as these contain high concentrations of heavy metals. Metals can be removed using extraction with various substances, such as adsorbents, absorbents, and ion exchange resins. Other reagents can also be used for sediment washing, such as phytic acid or phytates, which would require an optimization of experimental conditions (e.g. pH etc.).
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