Cobalt(III) Tetramethylenedithiocarbamate as a New Flotation Collector for Preconcentration and Separation of Lead Determinated by Zeeman ETAAS - Enimiteva et al. page 03

Results and Discussion

The values of pH, mass of Co, amount of TMDTC- and type of surfactant were optimised for procedures by using the new collector, Co(TMDTC)3. During all optimisation steps the solutions tested contained lead.

Determination of Optimal pH Value

To find an optimal pH value for Pb recovery by Co(TMDTC)3, the pH value was varied in range from 4.0 to 8.0 (Figure 1), while the cobalt mass (3.5 mg) and amount of dithiocarbamate (0.3 mmol TMDTC-) were kept constant. The percentage of recovered Pb over 95 % were obtained within pH values from 5.0 to 8.0. For further investigations by this collector pH 6.0 was chosen as appropriate, because the highest recovery of Pb (101.87 %) was reached at that pH value (Figure 1).


Determination of Optimal Co mass

The investigations for determination of optimal Co mass, as Co(HMDTC)3, were performed at a pH value optimised in the previous section (pH = 6.0). The mass of Co was changed from 2 to 4.5 mg. The flotation by this collector could not be performed by using mass of Co larger than, because of the formation of a dark-pink precipitate in the final  concentration by flotation solutions, which made the system inap­pro­priate for AAS measurement. The obtained results are presented in Figure 2. As it can be seen, the optimal lead recovery by Co(TMDTC)3 was 98.0% using 3.5 mg cobalt. Therefore, the amounts of     0.3.mmol TMDTC- and 3.5 mg Co were selected as optimal.


Determination of Optimal Amount of Dithiocarbamate

To investigate the influence of TMDTC- amount on lead separation from investigated media, two series of flotation tests were performed at pH 6.0. The first series of standard solutions contains 3.5 mg Co and the second 4.0 mg of Co. The amounts of TMDTC- were changed from 0.2 to 0.45 mmol. Data of these investigations for both collectors are presented in Figure 3. The highest recovery rate was achieved by 3.5 mg Co and 0.4 mmol TMDTC- (97.9 % of Pb recovery). Because no significant differences in recovery rates between the two different series were detected, subsequent investigations were performed by using smaller amounts of cobalt and TMDTC-  (3.5 mg Co and 0.4 mmol TMDTC-).


Selection of Surfactant

To select the most suitable surfactant for separation of lead ions, different foaming reagents were tested by flotation of a series of standard solutions under conditions previously determined as optimal. The cationic surfactant (BTC), as well as non-ionic surfactant (TX-100) foam very well, but no flotation occurred. The anionic surfactants floated with different recovery efficiencies. NaDDS and NaOL were the most successful surfactants for lead flotation with Co(TMDTC)3 (Table 2). Several anionic surfactants (NaDDS, NaOL, NaPL and NaST) and the pair of NaDDS /NaOL were also used. The detergent NaDDS shows the highest recovery rate of lead ions by flotation (98.44 %) and therefore was selected as a reagent for this method (Table 2).