On the Formation of Pore Suspensions in Green Iron-Ore Pellets
Abstract Generated abstract
This paper examines how the fine silt fraction of magnetite concentrate participates in the pore suspension formed during pelletizing of green iron-ore pellets with small additions of bentonite. Using Tagan pink bentonite and the 0 to 20 micrometer fraction of magnetite concentrate, the authors prepared suspensions at concentrations corresponding to pelletizing conditions, allowed them to settle, and compared concentrations before and after holding to estimate the amount of silt incorporated into the structured suspension. The results indicate that sufficiently concentrated bentonite suspensions form stable coagulation structures that retain nearly all of the silt fraction. An empirical linear relation is proposed for estimating silt content in the pore suspension as a function of bentonite concentration, suggesting that above low bentonite levels at least about 95 percent of the silt is included in the pore structure.
Full Text
ON THE FORMATION OF PORE SUSPENSIONS IN GREEN IRON-ORE PELLETS
V. M. Vityugin, E. N. Chulkova, N. I. Biryukova
(Submitted by the scientific seminar of the Department of General Chemical Technology)
Green iron-ore pellets are typical capillary-porous bodies with a slight degree of colloidization. The framework of these pellets is composed of relatively coarsely dispersed particles, while in the pore space there is concentrated a suspension that includes solid particles of semicolloidal size. Under production conditions, iron-ore concentrates are pelletized with small additions of bentonite (0.5–2%). The bentonite passes almost completely into the pore suspension, promoting the formation in it of a coagulation structure [1–6]. The silt fraction of the concentrate is incorporated into this structure. The amount of this fraction and its influence on the properties of the pore suspension are of great importance from both the theoretical and the practical standpoint.
For the investigation, pink bentonite from the Tagan deposit and the silt fraction of magnetite concentrate from SStOK were used. The characteristics of these materials are given in Tables 1, 2, and 3.
Table 1
Dispersion composition of the silt fraction of magnetite concentrate
| Content of fractions, %, μm | Content of fractions, %, μm | Content of fractions, %, μm | Content of fractions, %, μm | Content of fractions, %, μm | Content of fractions, %, μm | Content of fractions, %, μm | Content of fractions, %, μm | Content of fractions, %, μm |
|---|---|---|---|---|---|---|---|---|
| +30 | 30–25 | 25–20 | 20–15 | 15–10 | 10–5 | 5–1 | 1–0.5 | 0.5–0 |
| 3.70 | 3.10 | 5.10 | 4.60 | 10.10 | 18.70 | 28.90 | 5.80 | 20.00 |
Table 2
Particle-size composition of pink bentonite
| Fraction content, %, mm | Fraction content, %, mm | Fraction content, %, mm | Fraction content, %, mm | Fraction content, %, mm | Fraction content, %, mm | Fraction content, %, mm | Fraction content, %, mm |
|---|---|---|---|---|---|---|---|
| 0.5 | 1.0–0.25 | 0.25–0.10 | 0.10–0.05 | 0.05–0.01 | 0.01–0.005 | 0.005–0.001 | 0.001 |
| – | 0.1 | 0.1 | 0.2 | 1.4 | 0.9 | 8.5 | 88.9 |
Table 3
Chemical composition of pink bentonite
| Content on an absolutely dry substance basis, % | Content on an absolutely dry substance basis, % | Content on an absolutely dry substance basis, % | Content on an absolutely dry substance basis, % | Content on an absolutely dry substance basis, % | Content on an absolutely dry substance basis, % | Content on an absolutely dry substance basis, % | Content on an absolutely dry substance basis, % | Content on an absolutely dry substance basis, % | Content on an absolutely dry substance basis, % | Content on an absolutely dry substance basis, % | Content on an absolutely dry substance basis, % |
|---|---|---|---|---|---|---|---|---|---|---|---|
| SiO₂ | Al₂O₃ | TiO₂ | Fe₂O₃ | FeO | MnO | CaO | MgO | K₂O | Na₂O | SO₃ | l.o.i. |
| 58.75 | 25.03 | 0.01 | 0.00 | 0.04 | 0.91 | 3.58 | 0.00 | 1.78 | 1.78 | 1.16 | 8.41 |
Determination of the fractional participation of the silt fraction in the pore suspension was carried out by the following procedure. Bentonite suspensions were first prepared whose concentrations were close to the concentrations of bentonite in pore suspensions under pelletizing conditions. The suspension was held for 30 minutes, and then the structured mass was separated from the settled particles. Bentonite silt was added to the latter, and after thorough mixing it was likewise held for half an hour. From the difference in suspension concentration before and after 30-minute settling, the content of silt particles participating in the formation of the structured pore suspension was determined.
The results of the study are given in Table 4.
Table 4
Change in the concentrations of bentonite suspensions and suspensions of bentonite with silt after holding
| Initial bentonite concentration, \(C_1'\), % | Bentonite concentration after holding, \(C_1''\), % | Average concentration of bentonite + silt, \(C_2'\), % | Concentration of bentonite or silt after holding, \(C_2''\), % | \(\Delta C = \dfrac{C_2' - C''}{C_2'}\) |
|---|---|---|---|---|
| 4 | 2.45 | 9.90 | 9.53 | 3.74 |
| 8 | 7.52 | 20.50 | 19.90 | 2.85 |
| 12 | 11.32 | 29.90 | 29.40 | 1.67 |
| 16 | 15.44 | 37.60 | 37.20 | 1.06 |
| 20 | 20.00 | 47.20 | 47.20 | 0.00 |
As can be seen from the data in Table 4, in bentonite suspensions at concentrations of 4–16%, within half an hour an insignificant portion of the bentonite settles out; a 20% suspension forms a stable homogeneous coagulation structure. Thus, the smaller the amount of bentonite, the more difficult it is to achieve homogeneity and, consequently, increased plasticity of the pelletized mass. Bentonite suspensions at concentrations above 20% retain the silt fraction. Based on the results of the investigations, a dependence was obtained for the silt content in the pore suspension on the bentonite concentration, expressed by the equation
\[ y = 95.25 + 0.25x. \]
The first coefficient in the equation of the straight line is equal to 95.25, i.e., at bentonite concentrations greater than 4%, no less than 95% of the silt is structured in the pore suspension.
Conclusions
-
In the formation of pellets from iron-ore concentrates, the silt fraction of the latter (0–20 μm) passes practically completely into the pore suspension and participates in the creation of a coagulation structure.
-
An equation has been obtained that makes it possible, to a first approximation, to calculate the content of the silt fraction in the pore suspension for different amounts of bentonite in the pelletized charge.
References
-
P. A. Rebinder. Collection dedicated to the memory of P. P. Lazarev. Publishing House of the Academy of Sciences of the USSR, pp. 113–131, 1959.
-
A. M. Vasiliev. Fundamentals of the Modern Methodology and Technique of Laboratory Determinations of the Physical Properties of Soils. Moscow, 1953.
-
A. F. Lebedev. Soil and Ground Waters. Publishing House of the Academy of Sciences of the USSR, 1936.
-
H. J. Illig. Probleme der Herstellung, Trocknung und Schmelze von Glasgemengegranulaten. “Silikattechnik,” 1971, 22, No. 7, 7–12.
-
S. Kirchhof. Granulieren des Glasgemenges. “Silikattechnik,” No. 9, 1962, 325–329.
-
V. M. Vityugin, I. N. Lantsman, S. I. Belgorodskaya. Investigation of the rheological properties of bentonites from the Tagan deposit. Proceedings of the 3rd Regional Conference of the D. I. Mendeleev “Znanie” Society, dedicated to the 75th anniversary of the Chemical-Technological Faculty of TPI, published by TPU, 1971.