1
INHIBITION OF SPONTANEOUS REACTIONS OF PROPELLANTS ON THE BASIS
OF AMMONIUM NITRATE DURING THEIR CONTACT WITH THE PYRITE
M. Marenets, M. Buller, S. Fomin, V. Shcherban, V. Banishevsky
Urgency. Experience of application of water-containing industrial propellants on the basis
of ammonium nitrate when extracting the pyrite shows, that at the certain temperature in hole a
chemical reaction between them and ore is taken place. It results in a premature detonation of
charges. Cases of spontaneous exothermal reactions are marked on the mountain enterprises of the
USA (mines in states Nevada, California, Arizona) [1, 2], Russia (Lebedinskiy, Gayskiy,
Stoylenskiy, Sokolovsko-Sarbayskiy GOK) [3, 4], Ukraine (Poltavskiy, Yuzhniy, Ingyletskiy
GOK). The analysis of the reasons of incidents has shown, that spontaneous reactions are initiated
both in drowned and in not drowned holes.
Since ammonium nitrate has the increased acidity under normal conditions, inhibitors of
decomposition of nitrate (CaCO3, MgCO3, (CH2)6N4, NH2CONH2) are entered in explosives for
neutralization of an acid. However practice of application of inhibitors shows, that they are not
always sufficiently effective means, preventing spontaneous reactions between explosive and
pyrite.
The purpose of the present research – the determination of character and conditions of
course of exothermal autocatalytic reactions of interaction of ammonium nitrate with pyrite both
directly, and at the presence of various additional components, and also search of effective
inhibitors of such interaction.
Methods of studies: derivative (derivatograph "Q-1500 D", conditions of not isothermal
dynamic heating), manometric (device "Vulcan-V", conditions of isothermal heating) and the
chemical analysis.
Objects of research: a concentrate of a natural mineral pyrite FeS2 with content of S2--ions
of 43,2 %; components of explosives: ammonium nitrate NH4NO3 (content 98,5 %), trinitrotoluene.
Investigated artificial samples – mechanical mixes pyrite with ammonium nitrate. In Ukraine pyrite
it is distributed in structure quartz- pyrite ores. This circumstance took into account at preparation
of artificial samples. Concentrate FeS2 have dried up to constant weight in a drying case and have
crushed on laboratory vibratory mill. Then FeS2 have mixed with a powder of quartz glass SiO2
(thermally inert substance). Primary, samples are prepared with mass fractions of S2--ions in weight
of pyrite: 1; 2; 3; 3,5; 4; 5; 7,5; 10; 15 %, them have mixed with ammonium nitrate in the ratio 1:1
by weight.
Experimental researches.
Results of differential-thermal researches have shown, that the temperature of started
reactions of exothermal decomposition of ammonium nitrate durring its interaction with pyrite and
intensity of process of decomposition (height of peak) depend on the quantitative content of S2--ions
(fig. 1).
To estimate the compositions of products of reaction of interaction of ammonium nitrate and
pyrite after an intensive thermal emission created substances are investigated by method of the
chemical analysis. As a result of analysis the equation of gross-reaction of interaction of ammonium
nitrate with pyrite is offered: 4NH4NO3 + FеS2 = FеSО4 + H2SО4 + 4NH3 + H2О + N2О + 2NО
Calculations of sizes of thermodynamic effects of interaction of ammonium nitrate with
pyrite have confirmed a possibility of spontaneous initiation (∆Greact.=–753,32 kJ/mole) of
exothermal reaction under standard conditions (Т=298,15 oC, Р=101,325 kPа). Reaction is
accompanied by significant allocation of heat Qreact.= 320,69 kJ/mole.
Results of manometric researches of interaction of ammonium nitrate with pyrite on
installation "Vulcan-V" are presented on diagrams of fig. 2. It is visible, that increase in
concentration of S2--ions in weight of moistened pyrite and increase of temperature in direct ratio
influence probability of development autocatalytic reactions.
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Fig. 1. Curves of the differential-thermal analysis of compositions NH4NO3–FeS2 at the
content of S2--ions in pyrite: 1 – without pyrite; 2 – 1 %; 3 – 2 %; 4 – 3 %; 5 – 4 %; 6 – 5 %; 7 – 7,5
%; 8 – 10 %; 9 – 15 %. Moistening – 5 %.
Conditions are determined on the basis of results of manometric researches, at which
interaction of ammonium nitrate with pyrite proceeds autocatalyticaly with the induction period.
Those conditions are: concentration of S2--ions in pyrite is over 3,5% at moistening a mix from
above 1% and temperature in a zone of contact is higher 60 оС.
It was of interest to investigate a role of trinitrotoluene in development of reactions as
trinitrotoluene possessing acid medium is a component of explosives. It is established (fig. 3–4),
ammonium nitrate (a prevailing component of explosives, up to 80% in composition of akvatol) at
contact with pyrite at the presence of water promotes development of a cycle of chemical reactions,
which result in thermal explosion.
Fig. 3. Thermochemical transformations of compositions with trinitrotoluene a: 1–
FeS2–ТNТ, 2 – FeS2–ТNТ–Н2О (10 %); b: FeS2–ТNТ–NH4NO3: 1 – without Н2О, 2 – 10 % Н2О
3
a
b
c
Fig. 2. Results of researches of compositions NH4NO3 – FeS2 at the presence of water on installation "Vulcan-V":
1 – absence of reactions, 2 – chemical reactions, 3 – reactions of autocatalytic type, 4 – reactions as thermal explosion. The mass fraction of water
makes: a – 5,7 %, b – 10,0 %, c – 20,6 %.
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Fig. 4. Thermochemical transformations of compositions with trinitrotoluene: 1 – FeS2–ТNТ
(10:10), 2 – FeS2–ТNТ–NH4NO3 (10:2:8) at content S2--ions in pyrite: a – 2 %, b – 3,5 %
It is known, that sulfates of metals, forming at oxidation of sulfides, including pyrite, under
action of subsoil waters and oxygen of air are satellites of sulfides. It is investigated influences of a
chemical compound of sulfates on stability of explosives on the basis of nitrate ammonium at their
contact with pyrite. It is established, that presence of sulfates of metals (sodium, calcium, cobalt,
copper, manganese, magnesium, nickel, zinc) does not result in decrease in temperature parameters
of activation of reactions and does not change character of generation of gas. Hence, it is possible to
assume, that the listed sulfates do not represent danger at application of explosives on the basis of
nitrate ammonium in iron sulphidic ores. Also it is established, that the additive of sulfate of iron
(II) 5 % catalyzes exothermal oxidation of pyrite (at 2 % S2--ions in FeS2), results to autocatalytic
development of reaction between ammonium nitrate and sulfide (on the schedule of fig. 5 it is
visible, that the period of an induction makes about 3,5 h. at temperature 80 оС) and reduces
temperature of the beginning of reaction up to 98–100 оС.
Fig. 5. Kinetic curves of compositions NH4NO3–FeS2 at the presence of sulfates 1 – in
absence of additives; 2–5 with additives of sulfates: 2 – ZnSO4⋅7H2O; 3 – CаSO4⋅2H2O; 4 –
CuSO4⋅5H2O; 5 – FeSO4⋅7H2O. The content of S2--ions in pyrite – 2 %. Temperature – 80 оС.
Moistening 10 %.
Hence, presence of sulfate of iron in ore can lead to premature operation of the charged hole.
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At the presence of sulfate of barium intensity of exothermal reactions of interaction NH4NO3
with FeS2 and with FeS (fig. 6) reduces, pressure of gas evolution decreases and the period of an
induction of the beginning of autocatalytic transformations increases.
Fig. 6. Influence of sulfates of iron (II) and barium at interaction of ammonium nitrate and
monosulfide of iron. Compositions: 1 – NH4NO3–FeS at presence FeSO4⋅7H2O (2), BaSO4 (3)
It is known, that earth water of pyrite ores frequently possesses the increased acidity.
Besides, a number of components, forming acid medium, enters also into composition of
explosives. In addition, interaction of ammonium nitrate with pyrite is accompanied by formation of
a sulfuric acid. Reaction is initiated not only by of pH level, but also by the composition of the ore.
In this connection detection of influence of concentration of hydrogen–ion, and also some ions,
presented in composition of earth water, on initiation and development of thermochemical reactions
in system "ammonium nitrate – iron ore" was of interest.
Results of manometrical researches are presented in fig. 7. Influence of acidity of the
medium, created by various acids, on character of thermochemical reactions is shown.
Fig. 7. Influence of рН medium on development of thermochemical reactions, where levels:
1 – absence of reactions; 2 – chemical reactions; 3 – reactions of autocatalytic type; 4 – reactions as
thermal explosion.
From the schedule of fig. 7 it is visible, that hydrogen–ions really initiate autocatalytic
reactions between ammonium nitrate and pyrite.
From the differential-thermal analysis it is established, that the additive of sulfate of iron (II)
in system "ammonium nitrate – pyrite", stabilized under conditions of the increased acidity of the
medium, created by a sulfuric acid, reduces temperature of the beginning of exothermal reactions
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up to 78,0 оС (table). That is earth water (the acid medium, presence of FeSO4) catalyzes
development of chemical reactions between ammonium nitrate and pyrite, that results in thermal
explosions.
Derivatografic researches are carried out for an estimation of an possibility of prevention of
development of the exothermic reactions, beginning at sufficiently low temperatures, under
conditions of an aggressive environment (presence of ions of iron (II), significant acidity of the
water medium). Results of researches of influence of inhibitors are shown in the table under
conditions of an aggressive medium. Compositions "ammonium nitrate–pyrite–inhibitors" under
conditions of the simulated aggressive medium (the acid medium, presence of FeSO4) are
investigated. CaO, MgO, ZnO, CaCO3, MgCO3, BaSO4, CaSO4, CuSO4, MgSO4, ZnSO4,
NH2CONH2 and (CH2)6N4 are investigated as inhibitors.
Influence of inhibitors on parameters of reactions of interaction of pyrite with ammonium nitrate
Тmах, оС Тfin, оС
Heat effect, kJ/mole
Loss of
Additive
Mass,
Тst, оС
mg
is absent
(Р=0,90 n=3)
mass, %
78,0
107,5
118,0
208,2±12,4
16,8
СаО
10,0
115,0
175,0
176,0
more than 818,2
31,0
ZnO
10,0
162,5
193,0
207,5
272,0±6,2
12,4
MgO
10,0
115,0*
137,5*
147,5*
465,8 ** ±16,5
11,8*
NH2CONH2
10,0
122,5
215,0
216,0
785,2±10,3
36,4
NH4Cl
11,6
125,0
181,0
183,0
more than 805,8
41,5
СаСО3
3,0
102,5
138,0
147,5
560,6±2,1
29,8
10,0
145,0
163,0
173,0
272,0±10,3
10,5
3,0
147,0
168,0
172,5
366,8±14,4
12,2
10,0
145,0
162,5
170,0
241,1±12,4
9,0
ВаSO4
The note. * – parameters of the first exothermic peak on a curve of the differential-thermal analysis
(DТА); ** – a total thermal emission at the two first peaks of curve DТА.
Results of the table show, that ZnO, CaCO3 and BaSO4 are effective inhibitors for
development of exothermic reactions in system "ammonium nitrate –iron ore".
Conclusions. Character and conditions of course of exothermic autocatalytic reactions of
interaction of ammonium nitrate, making a basis of industrial explosives, with pyrite are
established.
Search of inhibitors of the given reactions under conditions of the simulated aggressive
medium (the acid medium, presence of FeSO4) is carried out.
It is shown, that as the most effective inhibitor of spontaneous autocatalytic reactions of
explosives on the basis of NH4NO3 at their practical application under real conditions for extraction
FeS2 can act BaSO4.
THE LITERATURE
1. Blasting hazards of gold mining in sulfide-bearing ore bodies / Miron Yael // Inf. Circ. / Bur.
Mines. US Dep. Inter. – 1992. – No. 9335. – Р. 1 – 10.
2. Baron V.L., Cantor V.H. Technique and technology of blasting operations in USA. – M.:
Nedra, 1989 (in Russian).
3. Galkin V.V., Vetluzhskih V.P., Pavlyutenkov V.M. Reasons of decomposition and failure of
aquatol charges.// Industrial safety. – 1988. – No. 10. – P. 47 – 49 (in Russian).
4. Dubnov L.V., Baharevich N.S., Romanov A.I. Industrial explosives. – M.: Nedra, 1988. – 358
p. (in Russian).