ISSN 00201685, Inorganic Materials, 2010, Vol. 46, No. 10, pp. 1121–1125. © Pleiades Publishing, Ltd., 2010. Original Russian Text © S.V. Fomichev, I.Z. Babievskaya, N.P. Dergacheva, O.A. Noskova, V.A. Krenev, 2010, published in Neorganicheskie Materialy, 2010, Vol. 46, No. 10, pp. 1240–1245.
Evaluation and Modification of the Initial Composition of GabbroBasalt Rocks for MineralFiber Fabrication and Stone Casting S. V. Fomichev, I. Z. Babievskaya, N. P. Dergacheva, O. A. Noskova, and V. A. Krenev Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninskii pr. 31, Moscow, 119991 Russia email:
[email protected] Received February 1, 2010
Abstract—Literature data and calculation results demonstrate that it is appropriate to use the acidity coeffi cient for the initial evaluation of the properties of gabbrobasalt raw materials for fiber production and stone casting. We examine the capabilities of hydrochloric acid leaching for modifying the composition of raw materials and those of physicochemical calculations for determining the mineralogical compositions of raw materials and modification products. DOI: 10.1134/S0020168510100171
INTRODUCTION Rocks of the gabbro–basalt group are widely used to produce macadam, work stone, mineral fibers, and cast stone. Russia possesses unlimited resources of these mineral raw materials. There are a large number of deposits under development or preparation, from the Arkhangelsk oblast to Kamchatka [1]. Earlier methods for evaluating whether a raw mate rial is suitable for fiber production relied on the chem ical composition of the rock and comparison with ana logues taken as standards. These were basalts from the Berestovetskoe (Ukraine) or Marneulskoe (Georgia) locations. At present, the properties of raw materials are evaluated using the acidity coefficient Мa = (SiO2 + Al2O3)/(CaO + MgO).
(1)
This is a classic formula for assessing the acidity of raw materials for the production of mineral (slag) wool composed mainly of the above oxides (wt %). Gabbrobasalt rocks contain considerable amounts of iron oxides (up to 19 wt %) and potassium and sodium oxides (a total of 2 to 8 wt %). It is thought that the main processing properties of molten gabbro basalt rocks are determined by the total Fe content, the percentages of Fe2+ and Fe3+, and the K2O and Na2O content [1]. Therefore, it is more appropriate to evaluate the properties of gabbrobasalt rocks for min eralfiber production and stone casting using the acid ity coefficient in the form of the weight ratio of the sum of acid oxides (silica, alumina, and titania) to the sum of basic oxides (calcium, magnesium, iron, potas sium, and sodium oxides): K =
SiO 2 + TiO 2 + Al 2O 3 . CaO+MgO+FeO+Fe 2O 3 +K 2O+Na 2O
(2)
The acidity coefficient (2) characterizes not only the chemical composition of the melt but also its structure. At the same time, there is experimental evi dence that the melting behavior of gabbrobasalt rocks and the properties of their melts depend on their min eralogical composition [2]. In this paper, we describe an approach for evaluat ing gabbrobasalt rocks for mineralfiber production and stone casting using the acidity coefficient K, mod ification of raw materials by hydrochloric acid leach ing, and a procedure for physicochemical calculation of the mineralogical composition of raw materials and modification products. ACIDITY COEFFICIENT OF GABBROBASALT ROCKS FOR FIBER PRODUCTION AND STONE CASTING The standard raw materials from the Bere stovetskoe location have the following chemical com position (wt %): SiO2 48.0–51.9; Al2O3, 12.2–16.5; TiO2, 2.7–2.9; FeO, 7.5–10.2; Fe2O3, 3.9–7.6; Mn, 0.2–0.3; CaO, 8.2–12.1; MgO, 4.1–6.9; K2O, 0.3– 0.6; and Na2O, 2.3–2.6. The composition of the basalt from the Marneulskoe location is (wt %) SiO2, 47.5– 52.5; Al2O3, 14.0–18.0; TiO2, 0.2–2.0; FeO + Fe2O3, 7.0–13.5; Mn, within 0.2; CaO, 8.0–11.0; MgO, 3.5– 8.5; and K2O + Na2O, 2.5–6.0 [1]. The acidity coefficient of the raw materials from these locations lies in the range K = 2.02–2.24. Dzhigiris and Makhova [3] recommended the fol lowing starting mixture compositions for mineral fiber production (wt %): SiO2, 51.0–54.0; Al2O3, 12.0–15.0; Fe2O3, 6.0–14.0; CaO, 8.0–11.0; MgO, 5.0–10.0; and K2O + Na2O, 2.0–6.0. To improve the processing properties of starting mixtures, they pro
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Table 1. Dissolution of the components of basalt upon leaching with hydrochloric acid of different concentrations (5–32 wt %) at 20, 70, and 100°C Degree of leaching, % 20°C
70°C
100°C
Component wt % HCl
Si Al Ti Fe(II, III) Ca Mg Na K Mn Cr V
5
10
18
32
5
10
18
32
5
10
18
32
1.6 6.0 1.2 32.0 23.8 37.1 3.1 1.9 36.0 8.8 5.3
1.7 6.7 3.3 34 7 24.7 43.3 3.5 2.2 39.3 12.0 9.1
1.8 7.7 7.0 39.8 27.9 53.3 4.2 2.6 44.8 21.0 25.1
1.2 6.8 4.1 38.4 27.0 48.8 3.2 2.0 37.6 26.3 11.3
2.3 14.5 10.5 41.5 37.0 46.0 12.2 7.7 44.1 10.2 23.0
2.2 14.7 10.0 44.6 34.1 50.6 11.4 7.2 47.6 16.9 25.6
0.4 15.5 11.0 46.3 37.2 55.5 11.2 7.1 43.5 70.8 66.9
0.4 11.0 7.4 45.0 34.3 51.3 7.2 4.5 44.5 25.0 31.0
2.7 19.5 15.5 47.5 42.0 52.3 18.5 11.7 50.0 10.9 34.3
2.1 22.0 16.8 49.5 42.5 55.0 19.1 12.0 52.1 12.4 38.9
0.6 23.8 10.6 51.6 44.1 58.7 19.2 12.1 49.5 11.8 48.4
0.4 21.2 10.2 51.4 43.2 59.0 17.3 10.9 49.5 11.2 44.7
posed the composition (wt %) SiO2, 57.0–59.0; Al2O3, 9.0–11.0; Fe2O3, 8.0–10.0; CaO, 8.5–10.5; MgO, 3.5–5.5; and K2O + Na2O, 5.0–7.0. The K value of these compositions lies in the range 2.13–2.30. Starting mixture compositions for stone casting using rocks of the gabbro–basalt group were presented by Lipovskii and Dorofeev [4]. Mixtures for chemi cally stable and wearresistant articles should contain (wt %) SiO2, 45.0–49.0; Al2O3, 12.0–18.0; FeO + Fe2O3, 10.0–15.0; CaO, 9.0–14.0; MgO, 6.0–11.0; and K2O + Na2O, 2.0–5.0. The average K is 1.72. Basalt–hornblendite mixtures should have the follow ing chemical composition (wt %): SiO2, 48.0–49.0; Al2O3, 14.0–15.0; FeO + Fe2O3, 15.0–17.0; CaO, 11.0–12.0; MgO, 6.0–7.0; and K2O + Na2O, 2.0–4.0. The average K is 1.70. The chemical composition of hornblendite raw materials is (wt %) SiO2, 49.0–52.0; Al2O3, 12.0–15.0; FeO + Fe2O3, 12.5–15.0; CaO, 10.0–12.0; MgO, 8.0–11.0; and K2O + Na2O, 1.5– 2.0, with an average K of 1.78. According to Lipovskii and Dorofeev [4], the best casting properties are offered by melts with K = 1.5–1.8, and the optimal K is 1.7–1.9. Thus, it is reasonable to use gabbrobasalt raw materials with acidity coefficients K = 2.0–2.35 for mineralfiber production and those with K = 1.50– 1.90 for stone casting. COMPOSITION MODIFICATION OF GABBROBASALT RAW MATERIALS FOR FIBER PRODUCTION AND STONE CASTING The properties of articles from gabbrobasalt rocks are determined primarily by their chemical composi tion, which varies widely between different Russian
locations. For this reason, rock from a particular loca tion cannot always be processed into materials with tailored properties without composition modification. Of the 52 locations (whose compositions are presented in [1]), the acidity coefficient lies in the range recom mended for fiber production (2.00–2.35) only in 17 loca tions and in the range 1.50–1.90 (stone casting) only in 9 locations. Raw materials from the other locations require composition modification. To this end, dolomite, lime, or silica is commonly added to raw materials (admixture process). The mod ifying addition content ranges from 10 to 30 wt %. This step requires additional effort and power. Carbonate rocks must be ground in order to reduce the time needed for the heating and decarbonization of dolo mites and limestones and the time needed for calcium and magnesium oxides to react with other oxides in the melt during the formation of silicates and alumi nosilicates [1]. As an alternative to the admixture approach, we proposed hydrochloric acid leaching of gabbrobasalt rocks (the process was described in detail in [5] and was patented [6]). It follows from the data in Table 1 that the highest degrees of leaching correspond to components con taining iron, calcium, and magnesium, whose concen trations appear in the denominator in (2). The sum con tent of these components in gabbrobasalt rocks always exceeds the sum content of aluminum and titanium, which appears in the numerator in (2). The silica content of the gabbrobasalt rocks in Russia is 38–59 wt % and has an insignificant effect on K when the degree of SiO2 leaching with hydrochloric acid is ≤2.7 wt %. Thus, leaching with hydrochloric acid increases the acidity coefficient, and this approach can be applied to gab INORGANIC MATERIALS
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EVALUATION AND MODIFICATION OF THE INITIAL COMPOSITION
brobasalt raw materials with K < 1.50–1.90 in stone casting and K < 2.00–2.35 in mineral fiber production. Consider specific examples of raw materials from Russian locations, whose chemical compositions are taken from [1] (Table 2). The acidity coefficient of the Bulatovskoe basalt (Arkhangelsk oblast) is 1.50. It can be used in stone casting without chemical modification. For mineral fiber production, its K should be raised. This can be achieved by leaching the basalt with 5% HCl at 100°C [5] instead of the admixture method. The acidity coef ficient of the rock recovered from the leaching solu tion is K = 2.00 (Table 2), and the rock is suitable for basalt fiber production. The acidity coefficient of the Pervouralskoe horn blendite (Sverdlovsk oblast) is 1.32. Without composi tion modification, this material cannot be used in mineral fiber production or stone casting. After leach ing with 5% HCl at 20°C, the acidity coefficient of the product is 1.84 (Table 2), and it can be used as a raw material for stone casting. After leaching with 10% HCl at 70°C, the acidity coefficient is 2.15 (Table 2), and the leached rock can be used in mineral fiber pro duction. The compositions recommended for fiber produc tion in different regions of Russia are presented in [1]. In particular, it is recommended to add 20 wt % lime stone to the Bugotakskoe diabase (Novosibirsk oblast, K = 1.73). The mixture thus prepared will have K = 1.20 (Table 2), that is, it will be unsuitable for fiber production or stone casting. At the same, after leach ing the Bugotakskoe diabase with 5% HCl at 20°C, the mixture will have K = 2.31 (Table 2), which is suitable for mineral fiber production. DISCUSSION The main criteria for evaluating raw materials for fiber production or stone casting are their chemical and mineralogical compositions, which must ensure the desired processing properties of the melt (temper ature range of melting and manufacture, viscosity, crystallization behavior, shrinkage, and others). Some of these properties are governed by the acidity coeffi cient. The rise in K with increasing silica and alumina content in the mixture hinders its melting and increases the melt viscosity. The best casting properties are offered by melts with K = 1.5–1.8 [4]. Khan et al. [2] present data on the variation in the shrinkage of silicate melts when K decreases from 1.5 to 1.2. The shrinkage of he melt increases from 0 to 7%; the solidification shrinkage, from 3 to 15%; and the shrinkage of the solid material, from 0.08 to 1.15%. With decreasing K, the degree of crystallinity increases, leading to olivine precipitation. An increase in K is accompanied by an increase in residual glass content [4]. The optimal value of K is 1.7–1.9. As mentioned above, the content of iron oxides in the Russian gabbrobasalt rocks ranges from 5.76 to INORGANIC MATERIALS
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18.72 wt %, and that of potassium and sodium oxides, from 2.09 to 7.94 wt %. These oxides lower the melting point and ensure high quality of mineral fibers owing to the low melt viscosity at the melting and processing temperatures. The total Fe content and Fe2+ : Fe3+ ratio are among the key parameters of basalt raw mate rials for stone casting and basalt fiber production. An increased Fe2+ content is needed in the former case, and an increased Fe3+ content, in the latter [3, 4]. In an oxidizing atmosphere, the forming Fe3+ acts as a modifier of silicate melts. In a reducing atmosphere, Fe2+ cations break up silicon–oxygen complexes, reducing the viscosity of the melt, increasing its crys tallization capability, and extending its casting range. The last factor is of particular importance in the fabri cation of continuous fibers. Varying the process atmo sphere, one can control magnetite and olivine precip itation from the melt. In an oxidizing atmosphere, some of the Fe2+ ions convert to Fe3+, leading to mag netite crystallization. An oxidizing atmosphere favors olivine crystallization because the melt then contains a sufficient amount of Fe2+. Zemtsov and Ogarysheva [7] analyzed the compo sitions of gabbrobasalt rocks from three Russian and two foreign manufacturers in relation to the acidity coefficient K, “successfully used to evaluate raw mate rials in stone casting using rocks of the gabbro–basalt group” [7, p. 35]. The range K = 1.50–1.90 was found to included only the compositions of Paroc (Finland) and Rockwool (Denmark) fibers, with K = 1.82 and 1.70, respectively. According to Zemtsov and Ogary sheva [7], their data on the role of iron, sodium, and potassium cations in the formation and properties of basalt melts strongly suggest that one must take into account the contents of these components in prelimi nary evaluation of gabbrobasalt rocks as raw materials for fiber production and stone casting. Therefore, one should do away with property evaluation based on the acidity coefficient. As mentioned above, the properties of molten gab brobasalt rocks depend in many respects on their mineralogical composition. Unfortunately, data on mineralogical compositions are missing even for most of the mined locations. The existing procedures for petrochemical conversion of chemical analysis data for rocks to quantitative relationships between their components require rather much effort and have a number of drawbacks. We proposed a method for evaluating the mineral ogical composition of magmatic rocks based on chem ical analysis through physicochemical calculations [8]. The mineralogical compositions calculated by this method for the locations under consideration are pre sented in Table 2. Fibers produced from gabbrobasalt raw materials have a glassy structure and remain Xray amorphous at annealing temperatures of up to 700°C. A literature search revealed no data on the effect of the mineralogical composition of gabbrobasalt rocks on the properties of the mineral fibers produced from
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45.95
After leaching with 5% HCl, 100°C
Starting mixture: 37.48 12.22 80% unmodified rock + 20% lime stone
45.52 14.25
After leaching with 5% HCl, 20°C
37.92 13.75
After leaching with 10% HCl, 70°C 46.26 15.16
38.16 15.16
After leaching with 5% HCl, 20°C
Initial
38.77 16.13
Initial
–
–
–
0.21
0.22
0.23
0.25
0.30
47.24 11.41
Initial 9.19
TiO2
SiO2
Al2O3
Composition
3.47
2.94
4.32
4.06
4.98
7.34
2.79
5.32
FeO
6.08
5.17
7.60
5.12
6.29
9.24
3.52
6.69
Fe2O3 15.9
MgO
24.90
13.65
17.92
6.93
8.01
3.44
2.52
4.02
6.40
8.15
10.52 12.96
9.60 10.49
9.8
CaO
0.17
0.20
0.21
0.28
0.29
0.30
0.36
0.41
K2O
0.15
1.40
1.44
1.27
1.39
1.43
1.00
1.23
Na2O
37.0
–
–
42.0
50.0
46.0
31.0
33.0
Pl
7.0
–
–
31.0
37.0
18.0
52.0
57.0
Py
5.0
–
–
5.0
6.0
23.0
3.0
