ON THE UTILIZATION OF FERRUGINOUS SLUDGE FROM THE KEMEROVO ANILINE AND DYE PLANT

A. S. BOGMA, V. M. VITYUGIN, A. G. P’YANKOV

(Presented by the scientific seminar of the Departments of PMAKhP and OKhT)

At the Kemerovo Aniline and Dye Plant, in the process of producing aniline, up to 200 tons per day of ferruginous sludge are formed. Only an insignificant part of it (up to 15%) is used in the form of Tripoli and Crocus; the remaining part is sent to a dump.

Studies have established that the sludge contains 75–80% magnetite, up to 8% free metallic iron, 2.5–3.0% free carbon, and 1.9–2.2% organic substances. The results of mineralogical investigations also indicate the magnetite nature of the sludge. An analysis of the grain-size composition, carried out by the sedimentation method, showed that the sludge is an exceptionally finely dispersed material.

The exceptionally high dispersion of the sludge, despite its high iron content, does not allow it to be used effectively in layered metallurgical processes because of its low gas permeability, in particular in the agglomeration process [1]. Such material must be pelletized.

The moisture content of the initial sludge after filtration under plant conditions is 24–25%. The maximum molecular moisture capacity of the sludge is 16.1%, the capillary moisture capacity is 29.6%, and the pelletizability index is 1.19 [2]. The optimum moisture content of the sludge before pelletizing, according to calculation [3], is about 13.5%; consequently, the sludge must be additionally dewatered.

Depending on the method of dewatering the sludge, the technological scheme for its pelletizing as a whole will be determined. Taking into account the specific features of aniline production and the composition of the sludge, as well as the need for dewatering, the pelletizing of sludge with additions of cast-iron turnings and common salt was first studied by a modified Yarkho method [4].

Experimental charges were prepared from sludge with additions of gray cast-iron turnings of 3.0–0 mm size (from 3 to 20%) and common salt (0.25–1.0%). The charge mixture was held for 90–120 min in open boxes until the maximum temperature was reached at the center of the layer. During this time the first stage of corrosion occurred in the charge; the charge mixture was thereby heated to 65–80°C. When the charge was pelletized without preliminary holding, the strength of the pellets was low. Pelletizing of the charge was carried out on a pan granulator 1 m in diameter. The green pellets, 20–30 mm in diameter, were held for hardening for several days in the laboratory room.

Studies showed that the initial moisture content of the charge has a very significant influence on the corrosion process of the turnings. The optimum moisture content in the charge is determined by the completeness of the turnings-corrosion process and depends on the amount of turnings in the charge. As the addition of turnings is increased, the optimum moisture-content index of the charge rises.

When 20% turnings are added, the optimum moisture content of the sludge, at which the corrosion process of the turnings proceeds most completely, is 17%. However, in this case, owing to the heat of the corrosion process, the moisture content of the charge mixture after one hour’s holding decreased to 9.6%, which is considerably below the optimum moisture content for nodulizing a charge of this composition (13.1%); pellets from such a charge are weak. When the deficient amount of moisture is added to the charge, the pellets obtained after hardening have a high mechanical crushing strength (41 kg per pellet after 3 days’ holding).

Reducing the addition of turnings while correspondingly reducing the moisture content of the initial sludge sharply lowers the pellet-hardening effect; with an addition of 10% turnings, the pellet-hardening effect becomes practically unacceptable.

It has been experimentally established that a practical method for reducing the addition of turnings is to prepare the charge before nodulizing in two stages. First, a charge of the following composition is prepared: 79% sludge (moisture content 17%), 20% turnings, and 1% common salt. Using the high thermal potential of this charge after one hour’s holding, the addition of turnings can be reduced to 5% of the total mass by adding the initial sludge to it. The strength of pellets from such a charge after three days’ holding becomes quite sufficient when they are processed in the electric-smelting process.

The absence of a regular supplier of cast-iron turnings for the Kemerovo Aniline and Dye Plant makes their delivery difficult. The chemical and particle-size compositions of the turnings are unstable. Taking this into account, dehydration of the sludge to the optimum moisture content by adding dry pulverulent sludge, the production of which exists at the plant, was investigated.

The studies showed that, in order to prepare the initial sludge to the optimum moisture content before nodulizing, it is necessary to add 30–32% dry pulverulent sludge at a temperature of 105–110°C. By using return material (off-grade fines) formed during the firing of pellets (10–12%) in preparing the charge, the addition of dry sludge can be reduced to 20–22%.

A technological regime for nodulizing the sludge was developed, and a technological flowsheet for nodulizing was proposed. The fired pellets obtained according to this flowsheet (diameter 20–30 mm) showed a mechanical crushing strength of 160–240 kg/pellet and withstood 28–37 drops onto a concrete slab from a height of 100 mm. The density of the fired pellets was 3.05–3.1 g/cm³.

Using the proposed nodulizing flowsheet, a batch of pellets was prepared and an experimental smelting of them was carried out in the central electric furnace laboratory of the Kuznetsk Metallurgical Combine. The results of the experimental smelting showed that it is advisable to use the fired pellets in the blast-furnace process.

Conclusions

It has been established that the agglomerability of ferruginous sludge from the Kemerovo Aniline and Dye Plant, owing to its high degree of dispersion, fully permits industrial nodulizing according to standard flowsheets used in the nodulizing of fine-grained iron-ore concentrates.

It has been shown that, when the sludge is pelletized with cast-iron filings (5% addition), it is possible to obtain ore raw material for steel production by a non-firing method.

Pelletizing ferruginous sludge without any additives requires preliminary dewatering to a moisture content of 12–14%. To prepare the sludge to the technological moisture content, it is necessary to add 25% dry sludge and 10–12% return material (off-grade fines).

Pellets made from magnetite sludge should expediently be used in the blast-furnace process.

REFERENCES

1. V. S. Abramov. Preparation of ores for smelting. In: Ferrous Metallurgy of the Capitalist Countries. Metallurgizdat, pp. 11, 3–12, Moscow, 1957.

2. V. M. Vityugin, A. S. Bogma. Proceedings of Higher Educational Institutions. Ferrous Metallurgy, No. 2, 18, Moscow, 1969.

3. V. M. Vityugin, A. S. Bogma, P. N. Dokuchaev. Proceedings of Higher Educational Institutions. Ferrous Metallurgy, No. 8, 42, Moscow, 1969.

4. N. G. Tyurenkov. Briquetting of Ores. Metallurgizdat, Moscow, 34, 1948.