Antimony

Abstract

Antimony (Sb; CASRN 7440-36-0) is a semimetal element with chemical properties similar to lead, arsenic, and bismuth. In nature, it is found associated with sulfur as stibnite. Antimony is used in white metal, a group of alloys having relatively low melting points. White metal usually contains tin, lead, or antimony as the chief component. The emission of antimony into the human environment is overwhelmingly the result of human activity; approximately half of the antimony used in the United States is recovered from lead-based battery scrap. Most information regarding antimony toxicity has been obtained from industrial exposures. Occupational exposures usually occur through inhalation of dusts containing antimony compounds. Antimony is absorbed slowly through the oral route, and many antimony compounds are gastrointestinal irritants. The toxicity of Sb is a function of the water solubility and the oxidation state of the Sb species under consideration. The American Conference of Governmental Industrial Hygienists classifies antimony as a suspected human carcinogen.

Determination of Antimony by Atomic Absorption Spectroscopy

The antimony values encountered in most silicate rocks are below those that can readily be determined by atomic absorption spectroscopy using an aqueous solution of the rock material. Terashima,⁽⁶⁾ however describes a method in which antimony present in silicates, converted to stibine, SbH₃, introduced directly into an argon-hydrogen flame for absorption measurement at a wavelength of 217.6 nm. Satisfactory results are claimed for the range 0.06 to 4.0 ppm Sb.

Procedures based on the evolution of stibine using a flame-heated silica tube⁽⁷⁾ and absorption on a glycomethacrylate gel with bound thiol groups⁽⁸⁾ have yet to be adapted for application to rock material.

The methods described by Welsch and Chao⁽⁹⁾ and McHugh and Welsch⁽¹⁰⁾ were devised for the rapid determination of antimony in samples obtained in the course of geochemical exploration where consistency is perhaps more important than precision and accuracy. These procedures are based upon a decomposition of the antimony-containing minerals by heating with solid ammonium iodide solution in diluted hydrochloric acid and extraction of the antimony into a trioctylphosphine-methylisobutyl ketone solvent. The extract can be aspirated directly into an air-acetylene flame and the antimony absorption measured at 217.6 nm. For practical purposes the limit of determination is 0.25 ppm, representing 1 ppm Sb when a 0.5 g sample is extracted into 2 ml of TOPO-MIBK solvent.

7.1.2 Precipitation

Trace amounts of antimony are separated from an acid medium (HNO₃, H₂SO₄) as hydrated antimonic acid with MnO₂ aq. as the collector [19–22]. The latter is formed in situ by the slow reaction of a hot solution of Mn^2 + with MnO₄⁻. The MnO₂ aq. collector can also be formed by the reaction of MnO₄⁻ with ethanol [21]. Although Sb is quantitatively precipitated within the pH range 1–7, the reaction is usually carried out at pH ~1 to prevent co-precipitation of other metals such as Bi, As, Au, Fe(III), TI(III), Pb, and Cu. Tin is precipitated with Sb. Fluoride interferes in the precipitation of Sb with MnO₂ aq. The precipitate of MnO₂ aq. with Sb is dissolved in HCl (1 + l) containing some H₂O₂. The filter paper can be mineralized in conc. H₂SO₄ containing some conc. HNO₃.

Trace amounts of Sb can be co-precipitated with Fe(III) [23], A1 [22], and Zr [24,25]. In a flotation method, Fe(OH)3, surfactant, and air bubbling have been applied [26].

Traces of Sb are precipitated with H₂S from 0.5–1 M HCl or H₂SO₄ (Cu or Mo may be used as collectors). Tin does not precipitate in the presence of oxalic acid, while W and V can be masked by tartaric acid. Traces of antimony in tellurium have been co-precipitated with a small amount of tellurium as a carrier [27].

Human

Accidental poisonings can result in acute toxicity, which produces vomiting and diarrhea. Most information regarding antimony toxicity has been obtained from industrial exposures. Occupational exposures usually occur through inhalation of dusts containing antimony compounds. Workers exposed to antimony trisulfide (used as a pigment and in match production) at concentrations greater than 3.0 mg m⁻³ experienced heart complications and died. In addition, a temporary skin rash, called ‘antimony spots’, can occur in persons chronically exposed to antimony in the workplace. Inhalation of antimony hydride (stibine gas) can lead to hemolytic anemia, renal failure, and hematuria. Stibine gas is produced when antimony alloys are treated with acids.

22.2.11 Antimony

Antimony is a cumulative toxic element with unknown biological function and its physico-chemical and toxic properties depend on its binding form and oxidation state (Smichowski et al., 1998; Krachler et al., 2001). The toxicity of antimony(III) ion is 10 times higher than that of antimony(V) ion, and antimony(III) has been shown to cause lung cancer (Garbooe et al., 1997). Among several industrial applications of antimony compounds, antimony trioxide is largely employed in the production of glassware and ceramics. Moreover, Sb₂O₃ is added to molten glass as a clarifying reagent and is employed as a pigment in dyes and paints as well as in the textile industry. Several antimony compounds are used as additives to metal coatings and rubber, and others are added to textiles as flame retardants (Filella et al., 2002). Therefore, there is a great risk of antimony leaching from these food packaging materials (such as plastic, enamel, and porcelain containers) into our food chain (Krachler et al., 2001).

Several atomic spectrometric techniques such as FAAS and ETAAS, AFS, ICP-OES, and ICP-MS (Smichowski et al., 1995; Guy et al., 1998; Lindemann et al., 2000; Zheng et al., 2001; Morita et al., 2007) have been proposed for the determination of antimony species in different samples. ICP-OES and ICP-MS were often used as detectors (McIntire, 1990). Recently, an Sb(V) complex, Sb(V)-citrate, was identified for the first time (Fig. 22.11) in spiked orange juice contained in poly(ethyleneterephthalate) bottles (Zheng et al., 2001).

FIGURE 22.11. Chromatographic separation of Sb(III)-citrate and Sb(V)-citrate (each 10 g L⁻¹ as Sb), PRP-X100 anion exchange column, 10 mmol L⁻¹ EDTA +1 mmol L⁻¹ phthalic acid (pH 4.5), 1.5 mL min⁻¹, Sb isotope of m/z 121 was monitored by ICP-MS.

Reproduced with permission from (McIntire, 1990).

Jiang et al. (2010) developed a method for the speciation of inorganic antimony by cloud point extraction combined with ETAAS. The method is based on the fact that formation of a hydrophobic complex of antimony(III) with ammonium pyrrolidine dithiocarbamate at pH 5.0 and subsequently the hydrophobic complex enter into surfactant-rich phase, whereas antimony(V) remained in aqueous solutions. Antimony(III) in surfactant-rich phase was analyzed by ETAAS and antimony(V) was calculated by subtracting antimony(III) from the total antimony after reducing antimony(V) to antimony(III) by l-cysteine. The proposed method was successfully applied to speciation of inorganic antimony in the leaching solutions of different food packaging materials with satisfactory results.

11.2.1 History and uses of antimony

Antimony is a fascinating element that has been used by human cultures since the Early Bronze Age. Excavations at Tello in Ancient Chaldea found fragments of an antimony base that dates back to 4000 BC. Antimony is an element present in relatively small concentrations in the earth’s crust. It is rarely found in pure form in nature, a fact recognized since antiquity. This may be the source of the name, which comes from the Greek words ‘anti’ (not) and ‘monos’ (alone). Antimony compounds are found in several types of ore and in petroleum. Although not used in large quantities, antimony is used extensively for many purposes, including being alloyed with a number of metals to improve their properties. Antimony (Sb) and its compounds are mainly used for the production of alloys, flame retardants, and in the glass industry. Antimony has been a constituent not only of printing-metal but also of lead acid batteries, pigments, an opacifier under glazes and enamels (the white oxide), and in the present day it has been used widely as a flame retardant in fabrics and in brake linings of motor cars. The most significant use of antimony is the production of antimony trioxide for flame retardation (ATSDR, 1992; Butterman and Carlin, 2004).

Antimony trioxide (+ 3 antimony), a white powder, is the single most important economic form, used primarily as a fire retardant. It is a stable substance that is not volatile and dissolves in water slightly. According to Butterman and Carlin (2004), ‘More than one-half of the primary antimony consumed goes into flame retardants. The remainder is used principally in glass for television picture tubes and computer monitors, and in ammunition, cable covering, friction bearings, lead-acid (LA) batteries, and solders. It is used in the same applications worldwide, but its distribution among applications differs from country to country.’ Antimony trioxide is also used in the manufacturing of ceramics and in glassware to remove bubbles and stabilize colour (ATSDR, 1992). The oxychloride (Sb₆O₆C₁₄) has wide applications as a flame retardant in which the reaction with Hd and OHd radicals reduces the rate of flame propagation so that the treated material will smoulder rather than burst into flames. Other uses are in semiconductors, pewter, Babbitt metal, and as pigments in paints and lacquers, glass and pottery. Modern use of antimony chloride as a flame retardant means that antimony may be present in domestic and other fabrics in the home, and in conveyor belting in workplaces. Antimony compounds are used as fire-retardants, in an attempt to meet the requirements of legislation designed to reduce the fire risk of furniture and furnishings. Antimony compounds added to fabrics have the property of restraining the spread of fire so that they smoulder and do not burst into flames.

20.11.1 Antimony trifluoride

Antimony trifluoride and antimony pentafluoride are the only two antimony compounds of commercial significance. Although antimony forms stable mixed halides such as SbCl₄F, SbCl₃F₂, SbCl₂F₃, SbClF₄, Sb₂F₁₁ and polymer (SbCl₄F)₄, these forms have remained a laboratory curiosity. In the early stage of chlorofluoro- carbons and fluorocarbons production, antimony trifluoride was used on a very large scale in a process known as Swarts reaction [88]. The effectiveness of SbF₃ as a fluorinating agent is increased substantially by addition of Cl₂, Br₂, or SbCl₅ to the reaction mixture [89]. However, the modern hydrocarbon or fluorocarbon industry does not use such large quantities of SbF₃. The major use of SbF₃ is in the manufacturing of SbF₅. Small quantities of SbF₃ are also being used in selective fluorination processes and recently it is being used in the manufacturing of fluoride glass, fluoride glass optical fiber preform [96], and transparent conductive films (97). The total worldwide consumption of SbF₃ is about 15 tons/year.

Low Antimony Alloys

Low antimony alloys containing 1–2.7% antimony are used primarily as grid alloys for automobile batteries. The low antimony content reduces transfer of antimony to the negative grid and reduces water loss, particularly when combined with a Pb–Ca negative grid. These alloys contain only a small amount of eutectic (<1–15%) as seen in Figure 5. Sufficient antimony is present to recover from deep discharge. A large freezing range presents casting problems of cracks, holes, trapped air, and so on unless nucleant levels are closely controlled. Selenium is the preferred nucleant used in these alloys.

Figure 5. The grain structure of a lead–antimony alloy (1.6% Sb) shows small amount of eutectic and rounded structure due to selenium nucleant. Magnification 160×.

Because low antimony alloys contain small amounts of second-phase material, and are relatively fluid, they have also been used for long-spined tubular battery grids and can be continuously cast into grids. Modified alloys can be continuously cast into strip that is subsequently expanded or punched to form grids. Rolled lead–antimony alloys have such low mechanical properties due to breakup of the cast-in second-phase particles that this material is not used in continuous grid production.

Despite the benefits of antimony as an alloying element for battery grids, modern vehicle requirements have led to significant reductions in the use of lead–antimony alloys for starting, lighting, and ignition batteries. Antimony added for mechanical properties increases the electrical resistance of the alloys and subsequently the grids produced from them. Thin grids require alloys of the highest conductivity for optimum performance. Lead–antimony alloys are 3–10% less conductive than comparable calcium or tin alloys, and reduce battery performance.

During battery operations, the positive grid is oxidized. In positive grids containing lead–antimony, some of the antimony is released from the corrosion product of the grid, dissolved in the electrolyte, and transferred to the negative plate. There it modifies the plate potential during charging to promote the breakdown of the water in the electrolyte and the generation of hydrogen. This gassing phenomenon causes a general water loss in the batteries. The effects are accelerated at elevated temperatures. Batteries using lead–antimony alloy grids generally must have periodic water additions. Thus, sealed and maintenance-free batteries do not use lead–antimony alloys.

3.6 Electroanalytical applications of nanoparticle modified electrodes: detection of antimony

Antimony is a toxic heavy metal, and its prevalence is due to industrial applications (Toghill and Compton, 2011). At high dosages, symptoms are similar to those observed for arsenic poisoning, and it has been linked to autism and sudden infant death syndrome (SIDS). The trivalent species is reported to be more toxic than the pentavalent species, though the total antimony concentration is required to be monitored. Consequently, the maximum acceptable level of antimony in drinking water is reported to be 5 μg L^− 1 in the EU (Council of the European Union, 1998) and 20 μg L^− 1 in other continents (WHO, 2003). In recent years, antimony has also become a focus of concern and research in relation to the toxic gas hypothesis (i.e. SbH₃ production by fungi) for SIDS (Thompson and Faull, 1995; Department of Health, 1998; Craig et al., 2001).

An authoritative review by Toghill and Compton (2011) provides a thorough overview of the electroanalytical methods used for the sensing of antimony, showing that mercury, gold and carbon are viable electrode materials. However, it is highly surprising to note that there are very limited reports of nanoparticle modified electrodes (Dominguez-Renedo and Arcos-Martinez, 2007a, 2007b; Toghill and Compton, 2011). Gold (Dominguez-Renedo and Arcos-Martinez, 2007a), and silver (Dominguez-Renedo and Arcos-Martinez, 2007b) nanoparticle modified screen printed sensors have been reported by Dominguez-Renedo and Arcos-Martinez for the sensing of antimony (III), providing detection limits of 0.08 and 0.11 μg L^− 1 at the gold and silver surfaces, respectively.

In addition, sensing of antimony (V) using electrochemical techniques is an under-explored area. Existing studies in the literature show that antimony (V) sensing is achievable using mercury, gold and various modified electrodes; Lu et al. (2012) give a thorough overview. Surprisingly, it has only been shown that the sensing of antimony (V) is a viable approach using unmodified edge plane pyrolytic graphite electrodes exhibiting a detection limit of 0.71 μg L^− 1 (Lu et al., 2012). Clearly, this analyte is ripe for exploration using nanoparticle modified electrodes.

10.3.1.4 Antimony oxide

Combinations of antimony oxide and halogenated flame retardants are classic in the flame-retardancy field and were used as early as in the 1950s. There is no need to go over the mechanism and applications of these synergistic systems.^22,23 On the other hand, the use of antimony oxide in nonhalogen systems is less reviewed, and is summarized here.

There are a few intriguing instances in which antimony oxide has been shown to work in a nonhalogen system. It was shown to have a flame-retardant effect in epoxy resins, with the action attributed to the white reflective layer forming.²⁴ It is also claimed that combinations of antimony oxide with melamine cyanurate and a pentaerythritol worked in polyamide or styrenic systems without halogen.²⁵ Antimony oxide appears to be superior to a number of other metal oxides and hyroxides in this combination. A synergistic additive combination of antimony oxide, polyphenylene oxide or a novolac, and zinc borate or wollastonite in a halogen-free flame-retardant nylon formulation was shown to be effective.²⁶