Drainless Technology for Processing High-Moisture Iron-Containing Sludge and Dust

1. Literature review

In world practice, technologies for the production of iron-containing briquettes are known, but they differ from the technology we offer, using expensive and complex technologies (thermal, vacuum) of preliminary dehydration and multi-stage agglomeration technologies, which are energy-intensive and expensive technologies. [1,2,3,4]. The closest to the proposed technology is the production technology of metallurgical self-healing briquettes of the Russian company EcoMashGIO. In contrast to the proposed technology, iron-containing sludge with a moisture content of 15-20% is used; it is applicable for stale sludge taken from the sludge storage. In essence, the proposed technological scheme of “EcoMashGIO” does not exclude the transportation of iron-containing pulp along a multi-kilometer sludge pipeline and storage in sludge reservoirs. In addition, cement is used as a binder and strengthening material in the EcoMashGIO technology, which increases the cost of a metallurgical briquette. [5,6].

The prerequisites for the development of this project were the new patterns established by the authors in the processing of high-moisture iron-containing sludge and calcium- and magnesium-containing materials (lime, dolomite dust) for chemical dehydration of sludge, hardening of the mixture, by the type of mixing cement with water, with the production of stone-like material in the form of fine sand . When high-moisture sludge is mixed with dehydrating materials due to the exothermic reaction of active calcium and magnesium oxides with sludge moisture, the temperature of the system rises to 95-110 0 C, and part of the moisture evaporates and is removed in the form of steam [7,8,9,10].

This version of the technology was introduced at JSC “ArcelorMittal Temirtau” in the water supply workshop for dehydration of oily scale using powdered lime and dolomite waste to produce lime scale for sintering production [9].

2. Research methodology

To study the processes of combining the operations of dehydration, hardening and agglomeration of iron-containing sludge, a laboratory installation was developed (Figure 1) and experiments were carried out to study the conditions that ensure the production of iron-containing briquettes suitable for steelmaking [11,12].

In the process of mixing and subsequent exposure, the temperature of the mass, the rate of dehydration, and the chemical composition were measured.

The shaping process was carried out on a laboratory hydraulic press with a force of 125, 180 and 280 kN. Cylindrical briquettes with a diameter of 50 mm and a height of 60 mm, produced under laboratory conditions, had a strength of 94, 265, and 505 kN/cm², respectively, and a density of 2.7 kg/cm³. The amount of fines less than 5 mm when dropped onto a steel plate from a height of 2 m was 0.6%.

3. Research results

Research has established new patterns that have made it possible to develop a non-firing method for producing iron-containing material and self-healing briquettes. The essence of the method, which is one of the main provisions of scientific novelty, is to combine the processes of dehydration, self-hardening of the mixture with the process of shaping by applying external pressure to the hardening mixture in molds to obtain agglomerated material in the form of briquettes. The proposed technology does not require drying and firing, and a set of strength properties occurs in air as the material cools during the day. Innovative patents of the Republic of Kazakhstan have been obtained for the proposed technical solution [13,14].

As a result of additional research, a new efficient resource-and-energy-saving technological scheme for the production of agglomerated iron-carbon-containing material for metallurgical production technologies has been developed.

The developed innovative technologies for the preparation of wet sludge for processing were presented in the Catalog of the Exhibition of Achievements of the Domestic Industry “Development of the Mining, Metallurgical and Coal Industry”[15], and reflected in the materials of the All-Russian Conference “Research in the field of processing and disposal of industrial waste and from the school of young scientists [16].

4. Discussion of research results

Slurry pulp from wet gas cleaning technology or systems is pumped directly to the proposed plant (Figure 2), where the slurry condenses in pressure hydroclones to a moisture content of 40-50%, and the thickened sludge is sent to the conveyor, where pulverized lime and / or pulverized dolomite, as well as screenings of coke breeze or pulverized coal. From the conveyor, the materials are fed into the screw mixer-activator, where the process of chemical dehydration is carried out. From the mixer, the dehydrated heated slurry-lime mixture enters a roller or vibrating press, where agglomerated material with a residual moisture content of 5-9% is formed. Briquettes are stored on pallets for cooling and holding pressure at ambient temperature. The clarified water from the hydrocyclone is pumped and returned to the process.

The proposed technology, in essence, makes it possible to create a closed water supply system not through a clarification pond (sludge accumulator), but through the proposed installation (separation), which significantly reduces water consumption, labor and energy costs for transporting pulp through a multi-kilometer sludge pipeline to the sludge storage and clarified water back for the technology, as well as the cost of maintaining slurry pumps, slurry pipelines and slurry tanks.

Thus, iron ore sludge in the form of agglomerated composite material can be used as a substitute for iron ore concentrate in the through technology of steel and cast iron smelting. Eliminates the allocation of land for a sludge storage for sludge storage and provides a more complete disposal of man-made production waste.

The proposed project is the basis for the creation of resource-saving, low-waste, closed and environmentally friendly wasteless processes that solve not only the problems of raw materials, the maximum involvement of waste in economic circulation, but also environmental problems of production.

The competitiveness of the proposed technology in comparison with similar foreign analogues is as follows:

- exclusion of transportation and storage of sludge in the sludge storage and processing of sludge in the immediate vicinity of the source of formation;

- reduction of labor and energy costs for transportation and storage of sludge, maintenance of sludge pumps, sludge pipeline and sludge collector;

- there is no need to dry the sludge before the production of iron ore briquettes:

- a one-stage process of dehydration, self-hardening and shaping to obtain complex iron-carbon-containing agglomerated material in one production cycle;

- use of waste calcium- and magnesium-containing dusts (pulverized waste) as a dehydrating and binding material, and as a reducer of screenings of coke or coal of own production;

As a result of the project implementation, products will be produced in the form of secondary iron-carbon-containing material and iron-carbon alloy as a substitute for iron ore raw materials and scrap for the production of steel and iron and alloys.

5. Conclusion

The proposed project and technology will allow organizing production for the processing of high-moisture iron-containing sludge and obtaining a complex iron-containing material as a secondary metal-containing raw material for metallurgical plants for the production of steel and rolled metal. (limestone and dolomite dust of dry gas cleaning plants) as dehydrating and binding materials, as well as screenings of coke and coal as a reducing agent.

The proposed technology also solves the problems of environmental pollution and land acquisition for storage of production waste.

The proposed project and technology will make it possible to exclude the storage of iron-containing sludge in ash and sludge collectors and sludge fields, obtain new marketable products and reduce the consumption of natural iron ore and fluxing materials and solve not only technological but also environmental problems of metallurgical production. The proposed processing scheme will reduce environmental charges for waste storage, reduce the amount of off-balance water and groundwater pollution.