On Clinker Formation Processes in Mixtures Based on Nepheline Sludge
Abstract Generated abstract
This study examines clinker formation in cement raw mixes using nepheline sludge from the Uzhur deposit as the clay component. Limestone and sludge mixtures with saturation coefficients from 0.64 to 0.95 were fired with two-hour holds, and the products were analyzed for loss on ignition, free calcium oxide, and calcium oxide assimilation, with phase behavior evaluated using the CaO, SiO2, Al2O3 system. Carbonate decomposition occurred mainly between 500 and 900 °C and was little affected by sludge content, while active clinker compound formation began after 900 °C, especially at 1000 to 1100 °C, with slower calcium oxide assimilation above 1100 °C. The results indicate that nepheline sludge can serve as a raw-mix clay component over a broad dosage range, yielding belite clinkers at lower saturation and alite clinkers at higher saturation.
Full Text
ON CLINKER FORMATION PROCESSES IN MIXTURES BASED ON NEPHELINE SLUDGE
V. A. BUTKEVICH, N. S. DUBOVSKAYA
(Presented at the scientific seminar of the Department of Silicate Technology)
For the comprehensive utilization—including cement production—of the nepheline rocks of the Uzhur deposit, located in Krasnoyarsk Krai, studies are needed of clinker formation processes in raw mixes containing nepheline sludge. The content in the latter of alkaline oxides and of certain clinker minerals in hydrated form affects the clinker formation processes in these mixes.
The present work is devoted to the study of processes in raw mixes prepared using nepheline sludge as the clay component.
Preliminary studies of nepheline sludge showed that the investigated samples contain no alkali-metal oxides, while calcium oxide is present as hydrated calcium silicates. In this case the nature of the aluminosilicate component of the raw mix differs from that of natural clay raw material. The authors considered it justified to assume that the processes of decomposition of the carbonate component and the formation of clinker minerals would have a specific character, and they investigated clinker formation processes in raw mixes over a wide range of values of the saturation coefficient.
The chemical compositions of the limestone and sludge used, and of the calculated raw mixes, are given in Table 1. The percentage content of the components in the mixes is given in Table 2.
From limestone and nepheline sludge, taken in the indicated weight ratios, a series of raw meals was prepared. The raw meals were fired in a silite furnace with a two-hour holding period.
In the firing products, the loss on ignition and free calcium oxide were determined by chemical methods, and calcium oxide was calculated
Table 1
Chemical composition of materials
| Name of materials | SC | SiO₂ | Al₂O₃ | Fe₂O₃ | CaO | MgO | l.o.i. |
|---|---|---|---|---|---|---|---|
| Limestone | — | 1,41 | 1,49 | 0,6 | 53,21 | 0,41 | 42,88 |
| Nephel. sludge | — | 24,82 | 7,06 | 4,02 | 46,74 | 2,12 | 15,24 |
| Mix No. 1 | 0,64 | 20,84 | 6,11 | 3,44 | 47,84 | 1,83 | 19,94 |
| » 2 | 0,80 | 17,44 | 5,31 | 2,94 | 48,78 | 1,58 | 23,95 |
| » 3 | 0,90 | 15,94 | 4,94 | 2,73 | 49,19 | 1,49 | 25,71 |
| » 4 | 0,95 | 15,27 | 4,79 | 2,62 | 49,38 | 1,42 | 26,52 |
Table 2
Component composition of the mixtures
| limestone | nepheline sludge | $n$ | $p$ | KH |
|---|---|---|---|---|
| 17.0 | 83.0 | 2.19 | 1.77 | 0.64 |
| 31.5 | 68.5 | 2.10 | 1.80 | 0.80 |
| 37.9 | 62.1 | 2.08 | 1.80 | 0.90 |
| 40.8 | 59.2 | 2.06 | 1.82 | 0.95 |
calcium that entered into interaction during firing. In the calculation, the calcium oxide bound in the compounds of nepheline sludge was taken into account [1].
The results of the determinations and calculations are presented in Figs. 1, 2, 3. The processes of decomposition of the carbonate component of the mixture proceed mainly in the temperature range 500–900°. Moreover, the composition of the raw mix, i.e., its content of nepheline sludge, does not play a significant role. The rate of decarbonization remains practically constant.
Fig. 1. Losses on ignition of fired products
Fig. 2. Content of free calcium oxide in fired products
This can be judged from the change in loss on ignition and in the content of free calcium oxide in the fired products in the indicated temperature range.
After 900°, calcium oxide begins to be assimilated by acidic oxides with the formation of clinker compounds. From 900° the curve of the content of free calcium oxide turns sharply downward. At the same time, the calculated amount of assimilated calcium oxide (Fig. 3) increases for three of the investigated charges.
Active formation of clinker compounds takes place at 1000–1100°. Above 1100° assimilation of calcium oxide continues, but much more slowly; at 1200° a small amount of free calcium oxide remains.
Fig. 3. Rate of calcium oxide assimilation during firing of mixtures
(vertical axis: CaO assimilation, %; horizontal axis: temperature, °C; 1 — KH = 0.64; 2 — KH = 0.80; 3 — KH = 0.90; 4 — KH = 0.95)
amount: 1–3%. Experimental specimens from raw mixes 1 and 2 at this temperature are strongly fused and, in the cooled state, contain a large amount of clinker glass, readily detectable with the naked eye.
Using the phase diagram of the CaO—SiO₂—Al₂O₃ system, we calculated the fusibility curves of the investigated raw-mix compositions and established the phase composition of the cooling products [2].
On the basis of raw mixes 1 and 2 it is possible to obtain belite clinkers, and on the basis of raw mixes 3 and 4—alite clinkers with tricalcium silicate contents of 12–34% and 57–67%, respectively.
Thus, nepheline sludge can be used in the raw mix as the clay component over a wide range of dosages.
REFERENCES
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Yu. V. Nikiforov, R. A. Zozulya, Zh. M. Orner. On clinker-formation processes in raw mixes based on magnesian blast-furnace slags. Proceedings of Giprocement, issue XXXIII, Stroiizdat, Moscow–Leningrad, 1967.
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G. V. Kukolev. Chemistry of Silicon and Physical Chemistry of Silicates. Vysshaya shkola, Moscow, 1966.