Effects of ammonium fluoride on the decomposition of geochemical samples as fluorinating agent and its analytical application.
In this work, the effects of ammonium fluoride on the decomposition of geochemical samples were investigated by analyzing some certified reference materials (CRM). The major and minor elements were detected by inductively coupled plasma optical emission spectrometry (ICP-OES), while trace and ultra-trace elements were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Decomposition time, temperature and the amount of ammonium fluoride were studied in detail. In the process of sample decomposition, on one hand, ammonium fluoride was used as the fluorinating agent because ammonium fluoride can be dissociated under acid medium to yield fluoride ions to attack silicon compound effectively. On the other hand, ammonium fluoride was used as a latent solvent since ammonium salt may dissolve insoluble fluorine compounds. The removal of insoluble fluorine compounds decreased the memory effect on digestion vessels caused by fluoride coprecipitation. By testing CRMs and many real samples, it was found that trace and ultra-trace elements could be digested using ammonium fluoride instead of hydrofluoric acid and the dissolution ratios of major and minor elements, for example Al, Ca, Mg, Fe, Na and K, improved noticeably. Moreover, the use of ammonium fluoride instead of hydrofluoric acid contributes to a greener environment and safer for operators.
Hydrofluoride decomposition of natural materials including zirconium-containing minerals
Recently, interest in ammonium hydrogen difluoride (NH4HF2) as a versatile fluorinating agent for the decomposition of natural materials resumed. It is considered to be a new and more efficient than hydrofluoric acid (HF) reagent in analytical chemistry. Thermodynamically possible fluorination reactions with NH4HF2 are exothermic and proceed even at room temperature with the entropy reserve. The fluorination products are of high symmetry phases (tetragonal or cubic) with partial substitution of fluoride ion for oxide (or hydroxide). The fluorination of refractory silicate zircon (ZrSiO4) is kinetically hindered, and its complete decomposition requires the use of a Teflon autoclave at 200oC. The fluorination products are cubic (NH4)3Zr(OH)xF7-x (x ≤ 0.3) and tetragonal double salt (NH4)3SiF7, which can be separated due to incongruent sublimation of (NH4)2SiF6. The mechanism of the latter process is proposed.
Medical management of hydrofluoric acid exposure.
Hydrofluoric acid burns are usually due to accidental exposure. Deep tissue injury may result, damaging nerves, blood vessels, tendons, and bone. Concentrated hydrofluoric acid may cause immediate pain; dilute solutions may result in a delay of symptoms for many hours. Symptoms are usually out of proportion to the observed injury. Appropriate first aid and medical management can dramatically affect the prognosis. Local treatment consists of copious water lavage and the application of topical neutralization agents. For more severe exposures, calcium gluconate injection or intraarterial infusion of calcium gluconate may be indicated as well. Life-threatening alterations of electrolytes can occur, with ensuing arrhythmias. Inhalation, ingestion, and ocular exposures require specialized treatment and referral.