Cobalt(III) Tetramethylenedithiocarbamate as a New Flotation Collector for Preconcentration and Separation of Lead Determinated by Zeeman ETAAS - Enimiteva et al. page 02

Materials and Methods

Apparatus

The flotation was performed in a flotation cell, consisting of a glass cylinder (4 x 105 cm) with a sintered glass disk (porosity No.4) (Stafilov et al., 2001). The pH measurements of the solutions during the coprecipitation were carried out with a digital Iskra pH-meter MA 5705 using a combined glass electrode (Iskra M 0101). The atomic absorption spectrometric (AAS) measurements were performed with a Zeeman atomic absorption spectrophotometer Varian SpectrAA 640Z. A lead hollow cathode lamp was used as a primary source. Optimal instrumental parameters for ETAAS determina­tion are given in Table 1.
table_01

Reagents and Standards

Stock solution of Co(II) (1 mg/mL) was prepared by dissolving an appropriate amount of Co(NO3)2x6H2O in redistilled water. Stock solution of Pb(II) was delivered by Solution Plus Inc. (USA) with the concentration of 1.mg mL-1. From these solutions other diluted solutions were prepared. Ammonium tetramethylenedithio­carbamate, NH4-TMDTC, was prepared as 0.1 mol/L solutions in redistilled water.




Foaming reagents tested for the procedure were: sodium dodecylsulfate (NaDDS), sodium oleate (NaOL), so­di­um palmitate (NaPL), sodium stearate (NaST), benzethonium chloride (BTC) and triton X-100 (TX-100). They were prepared as 0.5 % solutions in appropriate solvents as follows: TX-100 in water, NaDDS and NaOL in 95 % ethanol, NaPL and NaST in 99.7 % propan-2-ol. The pH of media was regulated by a HNO3 solution (0.1 mol/L) and solutions of KOH (1.25 %, 2.5 % and 10 %). A saturated solution of KNO3 was used to adjust the ionic strength of the system. To transfer the content of the beaker into the flotation cell a 0.1 mol/L solution of NH4NO3 was used.

Flotation Procedure

The first step of the recommended procedures is the coprecipitation of lead traces present in 0.5 L acidified water sample in the solid precipitate of cobalt(III) tetramethylene­di­thio­carbamate solid precipitation. The second step is the flotation separation of the solid phase of Co(III) dithiocarbamate salt from the aqueous system. The coprecipitation was performed in a beaker, while the flotation separation in a flotation cell:
Coprecipitation: After adding 3 mL of saturated KNO3 solution into 0.5 L of the water sample analysed, 3 mg of Co(II) [3 mL of 1 mg/mL Co(NO3)2 stock solution] was added.. For this procedure the medium pH was adjusted to 6.0 by KOH solution. Then 0.3 mmol TMDTC¯ (3 mL of 0.1 mol/L solution of NH4-TMDTC) was introduced. Co(II) oxidized to Co(III) and a green precipitate of Co(TMDTC)3 was formed (Pavlovska et al., 2001; Bundalevska et al., 2005; Zajkova Paneva et al., 2005). After 15 min of stirring, 1 ml of NaDDS solution was added and the content of the beaker was transferred into the flotation cell by using a small amount of the electrolyte solution (0.1 mol/L solution of NH4NO3) to avoid dissolution and change the ionic strength of the system.
Flotation: When the investigated system was placed in the flotation cell a stream of fine air bubbles (which effluxes from the bottom of the cell at a rate of 50 mL/min) was passed through the solution for 1 min.  The foamy layer was formed at the surface of the liquid phase and the processed solution in the cell was cleared up. The liquid phase was vacuum extracted through pipette immersed into the cell. The solid phase left in the cell was dissolved by 4.mL hot 65 % HNO3. The cell and the pipette-tube were washed by 3 mL of 4 mol/L HNO3 and 2 mL hot 65 % HNO3. The solution created was sucked off through the bottom of the cell and collected in a 25 mL volumetric flask. The flask was filled up to the mark with redistilled water and the sample was ready for ETAAS measurements.