On the issue of determining the electric charge of particles in granulated charges
Abstract Generated abstract
This paper examines the use of the suspension effect to determine the sign of electric charge on particles in moist granulated charge materials for fluxed iron ore pellet production. The authors measured pH differences between suspensions and their filtrates for iron ore concentrate, limestone, bentonite, and a production charge mixture, using different waters, holding times, and solid to liquid ratios. The results indicate that the method can estimate particle charge sign, but that outcomes are sensitive to dispersion medium, aging, moisture conditions, and the ratio of solid phase to liquid. The study concludes that reliable application requires close laboratory modeling of production conditions, particularly moisture distribution and the relation between free and bound water.
Full Text
ON THE ISSUE OF DETERMINING THE ELECTRIC CHARGE OF PARTICLES IN GRANULATED CHARGE MATERIALS
V. M. Vityugin, E. N. Chulkova, N. V. Morozova
(Presented by the scientific seminar of the Department of General Chemical Technology)
Knowledge of the sign of the charge of particles in moist granulated charge materials is of considerable interest for the rational selection of charge components. Increasing the mechanical strength of green granules is possible through additions of finely dispersed materials with a charge opposite in sign to the charge of the particles of the main component. In this case, obviously, the optimum amount of additive will be determined by the transition of the moist charge into the isoelectric state.
The simplest and most accurate method for estimating the charge of particles is based on the use of the suspension effect [1, 2]. The readily experimentally determined value $\mathrm{pH}_c$ of a suspension, as a rule, differs from the value $\mathrm{pH}_f$ of the filtrate from this suspension. The sign of the suspension effect, calculated from the difference $\Delta \mathrm{pH} = \mathrm{pH}_c - \mathrm{pH}_f$, corresponds to the sign of the charge of the disperse particles in the suspension. With a negative charge of the particles $\mathrm{pH}_f > \mathrm{pH}_c$; with a positive charge $\mathrm{pH}_f < \mathrm{pH}_c$; and in the absence of excess charge on the particles $\mathrm{pH}_f = \mathrm{pH}_c$.
In the present work, the results are given of an experimental verification of this method for estimating the sign of charge as applied to a charge mixture and charge components for the production of fluxed iron-ore pellets. Samples of the materials studied were taken from the production streams of the pelletizing plant of the Sokolovsko-Sarbaisky Mining and Processing Combine. The composition of the pelletized charge was:
iron-ore concentrate — 91%
limestone — 8%
bentonite (Makharadze) — 1%
All materials were preliminarily screened through a sieve with openings of 100 $\mu$ and soaked in water (distilled water—$\mathrm{pH} = 6.0$, or tap water—$\mathrm{pH} = 7.15$). The pH values of the suspension and filtrate were measured both immediately after soaking and after the suspension had been kept for one day. For the measurements a pH meter of the LPU-01 type was used. The measurement results are summarized in Table 1.
To check the influence of the quantitative ratio of the disperse phase and the dispersion medium on the values of $\mathrm{pH}_c$ and $\mathrm{pH}_f$, special experiments were carried out with different solid-to-liquid ratios, T:Zh, at a constant amount of disperse phase. These experiments were performed on suspensions of iron-ore concentrate in distilled water. The holding time of the suspension in all experiments was 1 day. The ratio T:Zh was varied in the range from 3:2 to 1:4. The results of the study are shown in Table 2.
Evaluating the results of the series of experiments carried out, one may conclude that the method is suitable for determining the charge of particles. However, in doing so it is obviously necessary to observe strictly the modeling of the state of the charge material under laboratory and production conditions.
Table 1
Influence of holding time and the character of the dispersion medium on the sign of the charge of the dispersed phase
| No. | Material | Water | Fresh suspension, pH\(_c\) | Fresh suspension, pH\(_\phi\) | Fresh suspension, \(\Delta\)pH | Suspension after one-day holding, pH\(_c\) | Suspension after one-day holding, pH\(_\phi\) | Suspension after one-day holding, \(\Delta\)pH |
|---|---|---|---|---|---|---|---|---|
| 1 | Iron-ore concentrate | dist. | 7,60 | 7,81 | −0,21 | 7,66 | 7,64 | +0,02 |
| 2 | Limestone | ” | 8,06 | 7,89 | +0,17 | 7,93 | 7,92 | +0,01 |
| 3 | Bentonite | ” | 9,62 | 8,27 | +1,35 | 9,15 | 7,92 | +1,23 |
| 4 | Charge material | ” | 6,82 | 7,76 | −0,94 | 7,35 | 7,55 | −0,20 |
| 5 | Iron-ore concentrate | tech. | 7,22 | 7,85 | −0,63 | 7,49 | 7,94 | −0,45 |
| 6 | Limestone | ” | 7,13 | 7,99 | −0,86 | 7,93 | 7,92 | +0,01 |
| 7 | Bentonite | ” | 8,30 | 8,12 | +0,18 | 9,15 | 7,90 | +1,25 |
| 8 | Charge material | ” | 7,28 | 7,36 | −0,08 | 7,74 | 7,77 | −0,03 |
Maintaining the holding time of the charge material, the ionic composition, and the pH value of the water presents no difficulty. As for keeping the amount of moisture constant, this question proves to be more difficult to solve.
Table 2
Influence of the S:L ratio of aqueous suspensions of iron-ore concentrate on the values of pH\(_c\) and pH\(_\phi\)
| No. | S:L ratio | pH\(_c\) | pH\(_\phi\) | \(\Delta\)pH = pH\(_c\) − pH\(_\phi\) |
|---|---|---|---|---|
| 1 | 3 : 2 | 7,65 | 7,76 | −0,11 |
| 2 | 1 : 1 | 7,80 | 7,89 | −0,09 |
| 3 | 1 : 2 | 7,89 | 7,92 | −0,03 |
| 4 | 1 : 3 | 8,07 | 8,07 | ±0 |
| 5 | 1 : 4 | 8,08 | 8,08 | ±0 |
Iron-ore charge material suitable for pelletizing, as a rule, has a moisture content of 8.5–9%. Measuring the pH of such a system is difficult when ordinary equipment is used. And in order to measure pH\(_\phi\), the water must be squeezed out of the charge material at rather high pressures. In addition, one cannot fail to take into account the fact that, during pelletizing, as a result of compaction of the pellets, redistribution of moisture occurs. This cannot but affect the value of pH\(_c\). Finally, it must not be forgotten that the suspension effect depends to a substantial degree on the ratio of free to bound water in the disperse system.
LITERATURE
- Yu. M. Chernoberezhskii. Vestnik LGU, No. 4, p. 84, 1959.
- Yu. M. Chernoberezhskii, S. N. Zubkova, S. O. Usanova, L. V. Afanas’eva. Kolloidnyi zhurnal, vol. 27, p. 780, 1965.