ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2006, Vol. 51, No. 5, pp. 712–716. © Pleiades Publishing, Inc., 2006.
Original Russian Text © D.P. Nesterov, D.V. Makarov, V.T. Kalinnikov, 2006, published in Zhurnal Neorganicheskoi Khimii, 2006, Vol. 51, No. 5, pp. 780–784.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
Reaction of Magnesium Oxide and Magnesium Silicates
with Ammonium Hydrodifluoride
D. P. Nesterov, D. V. Makarov, and V. T. Kalinnikov
Tananaev Institute of Rare Element and Mineral Chemistry and Technology, Kola Research Center,
Russian Academy of Sciences, ul. Fersmana 14, Apatity, Murmansk oblast, 184200 Russia
Received August 2, 2005
Abstract—The reactions of magnesium oxide and magnesium silicates (forsterite and serpentines) with ammo-
nium hydrodifluoride is studied using DTA, X-ray powder diffraction, and IR spectroscopy. The conditions for
the formation of intermediate phases are determined. The structure of the silicate mineral does not significantly
affect the fluorination.
DOI: 10.1134/S0036023606050044
Ammonium hydrodifluoride is a solid product of rahedral layers in serpentines can be stacked in several
utilization of fluorine-containing industrial gases; it is modes. The most distinctive mode is when a complex
highly reactive and can be regenerated from either solu- sheet is bent with the tetrahedral structural element on
tion or gas. Reactions with ammonium hydrodifluoride the inner side of the bend. The antigorite unit cell
yield, apart from simple fluorides, coordination com- includes one complex sheet, which is folded in such a
pounds with various ammonium and fluorine contents, way that the polarity at each bend line inverts.
as well as nonvolatile oxyfluorides; the extent to which
Serpophite is a serpentine variety characterized by
fine-crystalline and cryptocrystalline ophitic aggre-
gates. Serpophites tend to structure disorder.
the latter are understood determines whether NH HF is
4
2
used successfully in fluoride metallurgy [1].
According to Rakov [2], NH HF , approaching
4
2
hydrogen fluoride in reactivity, has several strengths: it
is readily dehydrated, and fluorination reactions do not
require complicated equipment.
EXPERIMENTAL
The starting materials used were reagent grade mag-
nesium oxide; native monomineral samples of magne-
sium silicates: forsterite Mg SiO and serpentines (ser-
Systematic investigations of the reactions of
NH HF with minerals and concentrates are now under-
2
4
4
2
pophite and antigorite) Mg (OH) [Si O ]; and doubly
6
8
4
10
way in the Far East of Russia [1, 3–7]. However, the flu-
orination of minerals contained in raw material is not
fully described in the literature.
crystallized analytical grade ammonium hydrodifluo-
ride NH HF .
4
2
The starting materials, taken in stoichiometric pro-
portions, were carefully ground, placed into a platinum
crucible (sample sizes were 200–400 mg), and heated
at 2.5 K/min in a Q-1500 derivatograph.
The X-ray powder diffraction analysis of reaction
products was carried out on a DRON-2 diffractometer
using CuK radiation.
Here, we report on the reaction of NH HF with
4
2
magnesium oxide and with two varieties of magnesium
silicates, namely forsterite (an island silicate, i.e., a
mineral with isolated tetrahedra; its simplified formula
is Mg SiO ) and serpentines (serpophite and antigorite;
2
4
sheet minerals with the simplified formula
α
Mg (OH) [Si O ]).
6
8
4
10
IR-spectroscopic investigations were performed on
The forsterite structure is built of MgO octahedra a UR 20 instrument.
6
that share their edges to form zigzag chains and are
linked through SiO tetrahedra. Each oxygen atom is at
4
RESULTS AND DISCUSSION
the same time a corner of three octahedra and one tetra-
hedron.
Reaction of Magnesium Oxide
with Ammonium Hydrodifluoride
Serpentines are built of two-layer sheets: one (tetra-
hedral) layer is built of silicon–oxygen tetrahedra and
Rakov indicated in his review [2] that magnesium
the other (octahedral, brucite) layer contains magne- with ammonium hydrodifluoride forms the following
sium cations in octahedral voids that are formed by compounds: (NH ) MgF · 2H O, (NH ) MgF , and
4
2
4
2
4 2
4
oxygen ions and hydroxide groups. Octahedral and tet- NH MgF . The dihydrate is dehydrated at 110°C.
4
3
7
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