Improving the Grade of Ammonium Sulfate Using Microadditives of Chromium Ion
Abstract Generated abstract
This paper examines the use of chromium ion microadditives to improve the granulometric composition and crystal habit of ammonium sulfate produced from coke-chemical saturator liquors. Laboratory crystallization experiments with pure ammonium sulfate and with liquors from the Kemerovo Coke-Chemical Plant compared chromium sulfate and dissolved metallic chromium additions under acidity and phase-ratio conditions approximating plant operation. The results indicate that chromium additions, especially about 0.05 to 0.08% calculated as chromium ion, increase the yield of the coarse fraction and transform flat plate-like crystals into thicker “rice grain” forms associated with reduced caking and better flowability. The study suggests that unused metallic chromium from the Yurga Abrasive Plant could be dissolved in acidic saturated ammonium sulfate solution and introduced into the saturator cycle, with pilot testing proposed.
Full Text
IMPROVING THE GRADE OF AMMONIUM SULFATE USING MICROADDITIVES OF CHROMIUM IONS
V. M. Vityugin, I. N. Nozhkina, L. M. Zhitkova
(Presented by the scientific seminar of the Department of General Chemical Technology)
In previously published works [1], we noted the beneficial effect of Mn, Mg, Cr ions, and others on the granulometric composition of ammonium sulfate crystallized from saturator liquors of coke-chemical production. However, the relative scarcity of chromium salts made it impossible to recommend it as an additive for production, in particular for the Kemerovo Coke-Chemical Plant.
At present, at the Yurga Abrasive Plant (Kemerovo oblast), metallic chromium is obtained as a by-product in a quantity sufficient for its use as an additive.
The metallic chromium obtained is not used at this enterprise and can be used, in the form of a dissolved sulfuric-acid salt, as an additive in the crystallization of ammonium sulfate.
Chromium belongs to the group of microelements necessary for the normal development of plants; therefore, a small content of it in the basic fertilizer \((\mathrm{NH}_4)_2\mathrm{SO}_4\) (up to 50 mg/kg) will only improve the quality of the latter.
The initial experiments were intended to determine the nature of the effect of chromium on the crystallization process of ammonium sulfate and therefore were carried out using the pure salt \((\mathrm{NH}_4)_2\mathrm{SO}_4\), without observing the temperature regime existing in production (crystallization proceeded while the suspension was cooled from \(60^\circ\mathrm{C}\) to \(24^\circ\mathrm{C}\) with stirring). The acidity of the ammonium sulfate suspension and the ratio of liquid to solid phases corresponded to factory conditions, as applied to the operating conditions of the saturator of the Kemerovo Coke-Chemical Plant (acidity—6%, S : L = 1 : 30).
Taking into account the possibility of using waste from the Yurga Abrasive Plant as a chromium additive, the chromium ion was introduced into the suspension either in the form of a solution of the salt \(\mathrm{Cr}_2(\mathrm{SO}_4)_3\) or in the form of a solution of metallic chromium in the mother liquor. The results of the studies are summarized in Table 1.
It should be noted that, in the process of crystallization of ammonium sulfate in the presence of chromium ion in the suspension, a substantial change occurs in the appearance of the ammonium sulfate crystal. Pure crystalline ammonium sulfate is characterized by flattened crystals, predominantly of tabular form; in the presence of chromium ion, the crystals become more thickened and acquire the specific form of a “rice grain.” This form of crystals ensures less caking of the product and better flowability.
Studies of the crystallization process of ammonium sulfate in the presence of chromium showed that the “rice-grain” form is retained only—
Table 1
Effect of chromium ions on the sieve composition of ammonium sulfate
| Type of additive | Amount, % | Yield of the +0.25 mm class, % | +1.5 mm | +1.0–1.5 mm | −1.0 +0.5 mm | −0.5 +0.25 mm | −0.25 mm | Crystal form |
|---|---|---|---|---|---|---|---|---|
| No additive | — | 84.1 | 21.0 | 33.4 | 30.1 | 18.5 | 15.9 | plate-like |
| Cr₂(SO₄)₃ salt | 0.2 | 85.8 | 6.0 | 20.4 | 39.2 | 30.2 | 14.2 | “rice grains” |
| Solution of metallic Cr | 0.16 | 89.0 | 3.0 | 6.3 | 43.7 | 36.0 | 11.0 | “rice grains” |
| Solution of metallic Cr | 0.08 | 89.0 | 8.5 | 33.2 | 25.2 | 22.0 | 11.0 | “rice grains” |
| Solution of metallic Cr | 0.065 | 93.3 | — | 44.5 | 32.3 | 16.5 | 6.2 | “rice grains” |
| Solution of metallic Cr | 0.043 | 94.9 | — | 26.0 | 37.4 | 31.6 | 5.1 | single plates |
| Solution of metallic Cr | 0.035 | 97.1 | 4.4 | 41.4 | 33.2 | 18.1 | 2.9 | single plates |
| Cr₂(SO₄)₃ salt | 0.025 | 84.5 | 4.2 | 45.7 | 27.8 | 17.0 | 5.5 | single plates |
| Cr₂(SO₄)₃ salt | 0.016 | 92.6 | 3.0 | 53.5 | 33.0 | 23.2 | 7.4 | single plates |
| Solution of metallic Cr | 0.013 | 91.4 | 3.0 | 32.0 | 35.4 | 21.0 | 8.6 | 3/4 plate-like |
| Cr₂(SO₄)₃ salt | 0.004 | 86.0 | 2.6 | 23.1 | 33.1 | 27.2 | 14.0 | single crystals in the form of “rice grains” |
... when a certain amount of additive is introduced. Thus, when an additive amounting to less than 0.04% of the total ammonium sulfate (calculated as chromium ion) is introduced into the suspension being crystallized, flat, tablet-shaped crystals appear in the crystalline product, which leads to some increase in the yield of the +1.5 mm class. At low chromium concentrations (0.013%), the crystalline product consists by 3/4 of flat, tablet-shaped crystals.
Analysis of the data obtained gives grounds to assume that, under the operating conditions of the saturator: \(t^\circ C = 60\), \(T : L = 1 : 30\), acid 6%, a chromium additive in an amount from 0.08 to 0.05% will contribute to a qualitative improvement of the crystalline product.
These assumptions were confirmed by the results of studies obtained in the crystallization of ammonium sulfate from the Kemerovo Coke-Chemical Plant.
The crystallization process proceeded under conditions close to plant conditions. As the results of the study showed (Table 2), with the introduction of the additive
Table 2
Effect of chromium ions on the granulometric composition of ammonium sulfate
from the Kemerovo Coke-Chemical Plant
| Amount of additive, % | Fraction yield +0.25 mm, % | +1.0 mm | +0.5–1.0 mm | +0.25–0.5 mm | −0.25 mm | Crystal form |
|---|---|---|---|---|---|---|
| No additive | 73.8 | 2.8 | 35.2 | 35.8 | 26.2 | plate-like |
| 0.2 | 83.2 | 36.2 | 28.4 | 18.6 | 16.8 | “rice grains” |
| 0.1 | 86.3 | 26.3 | 30.0 | 30.0 | 13.7 | “rice grains” |
| 0.065 | 90.6 | 13.0 | 37.0 | 40.6 | 9.4 | “rice grains” |
| 0.043 | 84.3 | 22.0 | 31.5 | 30.6 | 18.7 | “rice grains” |
| 0.021 | 75.0 | 8.5 | 25.5 | 40.9 | 25.0 | single plate-like crystals |
of chromium, the yield of the coarse class (+0.25 mm) in the crystalline product increases to 90%, and all the ammonium sulfate consists of crystals resembling “rice grains.”
The optimal concentration of chromium in a saturated ammonium sulfate solution, with its optimal additions to the suspension (0.08—0.05%), is 0.0005 g/ml.
Such a chromium content can be achieved by dissolving metallic chromium in a saturated ammonium sulfate solution at an acidity of 6%, at a temperature of 60°C, for 30–60 minutes.
Under industrial conditions, this can be carried out by introducing metallic chromium, ground to 10 mm, into the pan of the return flows of the saturator cycle.
A pilot-plant test of the process of crystallization of ammonium sulfate in the presence of chromium ions is planned to be carried out at the Kemerovo Coke-Chemical Plant.
LITERATURE
- V. M. Vityugin, I. N. Nozhkina. Purification and crystallization of ammonium sulfate. In: Proceedings of the 5th All-Union Conference on the Technology of Inorganic Substances. Kiev, 1966.