Cobalt(III) Tetramethylenedithiocarbamate as a New Flotation Collector for Preconcentration and Separation of Lead Determinated by Zeeman ETAAS

 

Vangelica Enimiteva, Trajče Stafilov* and Katarina Čundeva
Institute of Chemistry, Faculty of Science, Sts. Cyril and Methodius University, P.O. Box 162, MK-1000, Skopje, Macedonia; *e-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Abstract

A fast method for the preconcentration of lead in fresh water samples using colloidal precipitate flotation is described. Co(III) tetramethylenedithiocarbamate, Co(TMDTC)3, was used as a flotation collector formed of Co(II) and TMDTC– anion. During the reaction, Co(II) oxidizes in Co(III) and as a product of the reaction green amorphous precipitate of Co(TMDTC)3 is obtained, which coprecipitates lead traces from the water matrix. A successful separation of lead was attained at the correct optimized pH of the system, mass of Co, amount of TMDTC–, type of tenside and other important experimental parameters. After flotation separation from the liquor, the solid sublate containing traces of lead was dissolved by nitric acid and the determination was performed by using Zeeman electrothermal atomic absorption spectrometry (ZETAAS). The results of the ZETAAS analysis are validated with the method of standard additions and by the application of the method to the water reference material.

Key words: Lead, fresh water, flotation, cobalt(III) tetramethylenedithiocarbamate, ZETAAS

Introduction

Lead has no biological role and is very toxic to humans and other organisms (Klassen et al., 1996; Hayes A.W. (ed.), 2001; WHO, 2003). This heavy metal affects the gut, central nervous system and causes anaemia. It can damage nervous connections (especially in young children) and cause blood and brain disorders. Long term exposure to lead or its salts (especially soluble salts or the strong oxidant PbO2) can cause nephropathy and colic-like abdominal pains. Lead has many anthropogenic sources. It was once commonly used in automobile fuels, paint and plumbing. Although these uses have decreased, lead is still used in batteries and alloys, and it is found in sewage wastes and in fossil fuel combustion products. Therefore this highly toxic element is an important chemical of concern in the environment and it is very important to follow its concentration in fresh water (drinking, river or lake).
The most used method for lead determination in water matrices is atomic absorption spectrometry (AAS). However, if the level of lead in water samples is very low, their direct determination is impossible without any previous step of preconcentration (Mizuike & Hiraide, 1982; Mizuike, 1983; Zolotov & Kuzmin, 1990; Caballero et al., 1999). Recently, significant attention has been paid to flotation techniques as enrichment methods for heavy metals before their AAS. Among several flotation techniques colloid precipitate flotation, so called coflotation, is the most useful.



Coflotation has the advantages in relation to the other conventional carrier precipitation techniques, as coprecipitation, liquid-liquid extraction, ion-exchange etc. (Mizuike & Hiraide, 1982; Mizuike, 1983; Zolotov & Kuzmin, 1990; Caballero et al., 1999). Many factors influence the performance of a proper flotation. During the performance of the most frequently used precipitate flotation, the primary condition is the selection of the suitable collector. The bulky hydrated metal oxides, as hydrated iron(III) oxide, hydrated aluminium(III) oxide etc., were the first reagents used for those purposes. Our experience has shown that the addition of dithiocarbamate anions to water systems containing metal cations, yield metal dithiocarbamate salts, which could play a role of precipitate collector with very high flotation effectiveness (Čundeva & Stafilov, 1997; Čundeva et al., 2000; Pavlovska et al., 2001; Stafilov et al., 2001; Pavlovska et al., 2000; Bundalevska et al., 2005; Zajkova  Paneva et al., 2005; Paneva et al., 2007; Čundeva et al., 2007; Bakreska Kormušoska et al., 2009). During the precipitation of these dithiocarbamate salts metal traces present in the aqueous solution incorporate in their structure forming hydrophobic solid phase surface that is the most important criterion for the successful flotation by air bubbles. The aim of this work is to present cobalt(III) tetramethylenedithiocarbamate, Co(TMDTC)3, as a new flotation collector of lead traces. Establishing previously the experimental conditions of separation procedure, this work gives a clear insight into the degree of lead recoveries by Co(TMDTC)3.