RU2279492C1 - Zinc cake pirometallurgical processing method - Google Patents

Abstract

FIELD: non-ferrous metal metallurgy, namely processing of zinc cakes in rotary kiln.

SUBSTANCE: method comprises steps of filtering pulp of zinc cake in press filters; mixing filtered cake having humidity 19 - 23% with coke fines, fluxing additives, circulating dust or with other dust-like zinc-containing products suitable for rotary-kiln processing in apparatus providing turbulent motion of materials; then subjecting prepared charge to rotary-kiln processing.

EFFECT: improved efficiency of rotary kiln due to lowered yield of reverse dust, enhanced quality of rotary-kiln processed oxide due to increased concentration of zinc and lead and lowered content of non-sublimated components in it.

2 cl, 1 tbl

Description

The invention relates to the metallurgy of non-ferrous metals and can be used for the processing of zinc-containing materials, for example, by-products of zinc electrolyte production - zinc-containing cakes by Weltzing.

A known method of processing zinc cakes by Weltzing, including filtering the pulp of zinc cake on disk vacuum filters, followed by drying and granulation in drying drums heated with fuel oil or gas (A.P. Snurnikov. Zinc hydrometallurgy. - M .: Metallurgy. - 1981. - p. 326-327.). The disadvantages of the method is the high final humidity of the filtered cake, which requires the use of thermal drying of the material for its granulation with significant fuel consumption, inevitable dust formation and removal of part of the dust with exhaust gases into the atmosphere.

Also known is a method of pyrometallurgical processing of zinc cakes, including mixing, rolling and drying zinc cakes with a solid carbon reducing agent and Waelz rolled material (AS USSR No. 876761, class C 22 V 19/38, publ. B. B., pr . from 02/12/1980).

The disadvantage of this method is the need for energy-intensive heat drying of materials in the process of mixing and granulation of the charge. As a result of vacuum filtration of the pulp, zinc cake with a moisture content of 28-35% is obtained, the preparation of granules of which without drying, only by mixing with other components of the Waelz mixture, while maintaining their necessary ratios, is not possible (the material remains in the form of a viscous mass).

The closest in technical essence and the achieved result is a method of processing zinc cakes by Weltzing, including filtering cakes on a press filter (humidity of the obtained product is not higher than 23%) and loading cakes for Weltzing without drying stage in drying drums, while coke is fed into the furnace trifles, fluxes and circulating dusts (see V.V. Geikhman, L. A. Kazanbaev, P. A. Kozlov and others. Studies of filtration of zinc cake under pressure. - Color metals, 2000, No. 5. - p.30 -32).

The disadvantage of this method is the lack of preparation of filtered zinc cakes for processing by Weltzing: mixing filtered zinc cakes with other components of the mixture, the formation of sufficiently strong granules. Zinc cake, filtered under pressure, despite a residual moisture content of 19-23%, is mechanically unstable and easily crumbles during transportation. The supply of such material to the Waelz kiln is accompanied by intense dust formation in the drying zone and the transfer of fine fractions of the charge into dust chambers and then into Waelz oxide.

The technical result of this invention is the reduction of dust during the loading of the charge and its drying in the Waelz kiln, the ingress of non-combustible components of the charge (iron, copper, cobalt, nickel, silica and others) in the marketed product - Waelz oxide (for example, the iron content in oxide reduced from 3-4 to 0.5-1% compared with the method of the prototype), the reduction of dust formation.

This result is achieved by the fact that in the method of pyrometallurgical processing of zinc cakes, including dehydration of cake on press filters and Waelz with a dosage of coke breeze, fluxes, circulating dusts, dosage of the charge components to zinc cakes is carried out in a mixer in a turbulent mode of motion with particle collision at a speed of particles rotation of the blades of the mixing device from 6 to 10 rpm Another difference is that dusty zinc-containing materials are additionally added to zinc cakes, which are recommended for processing by Weltz in chemical composition.

In contrast to the known mixing and granulation technologies, the proposed method allows the process to be carried out without heat drying, which allows reducing about 40-50 nm ^{3 of} natural gas and preventing the emission of up to 0.5 kg of dust into the atmosphere per 1 ton of charge.

The method is as follows.

After hydrometallurgical treatment (dissolution of zinc in sulfuric acid, preliminary washing from sulphates) in the form of thick pulp, zinc cake is filtered under pressure in a press filter (for example, on a horizontal press filter of the Finnish company Larox), where it is sold direct filtration, mechanical (diaphragm) dehydration at elevated pressure (up to 16 bar), drying by passing compressed air through a layer of cake. It turns out a filtered cake with a moisture content of 19-23% in the form of flat plates that are quite easily destroyed by falling and other mechanical influences.

Zinc cake after filtration, coke breeze (lump sizes less than 10 mm), fluxing additives (mainly limestone with lump sizes less than 10 mm), recycled dust, and if not enough, other dusty ones (particle size of 80% of the material should not exceed 1 mm) zinc-containing materials suitable for processing by Weltzemia in chemical composition are loaded into the mixing device using dispensers. The ratio of the listed components of the Waelz mixture is determined by their chemical composition in order to ensure efficient extraction of zinc and lead with high Waelz kiln productivity. The consumption of coke breeze is established based on the requirements of the process efficiency and minimization of losses with clinker (in the form of a carbon-containing part).

Mixing and granulation of the components of the charge is carried out in a mixer that provides a turbulent mode of motion with particle collisions, for example, in a rotary or turbo-blast one. The necessary effect of plasticization of wet zinc cake with thorough mixing with other components of the mixture and the formation of granules is steadily achieved when the rotation speed of the blades in the range from 6 to 10 r / s.

In the optimal operating modes of the mixer in terms of speed of rotation of the blades and in productivity, a granulated welts mixture is obtained with a predominance (above 80-85%) of granules from 3 to 10 mm in size. The moisture content of the final product is from 12-13 to 17-18%.

The mixture prepared according to the proposed method is loaded into a Waelz furnace for pyrometallurgical processing (distillation of zinc, lead, cadmium, indium and other valuable components with their conversion to an enriched product - Waelz oxide).

The proposed method is tested in an industrial environment.

Tests have shown that the cake obtained by filtering the pulp in a press filter (Larox type) has a moisture content of 21-22%. When loaded into a turbopaste mixer, it is well plasticized and mixed with coke breeze, fluxes, circulating dusts, dusty zinc-containing materials. In this case, granules with a predominant size of 3 to 10 mm and a moisture content of 16-17% are obtained. Part of the granules is large particles of coke, "coated" with cake with dust particles included in it, the rest is a homogeneous mixture of dust particles and cake.

In the process of testing, mixing modes are optimized: it is shown that the process proceeds efficiently and with the formation of granules at a speed of the mixing device (blades) in the range of 6-10 r / s.

At lower mixing speeds, the particle collision forces are not enough for effective destruction and plasticization - the mixture remains loose, coke breeze (especially large particles larger than 5 mm) is not smeared with cake, and when welded, the coke use efficiency decreases, which is manifested by an increase in the carbon content in clinker . At rotational speeds of more than 10 r / s, plasticization of the cake occurs very quickly, the resulting viscous mass is not granulated and, not having time to unload, "wraps" the working bodies of the mixer.

The loading of the granulated charge into the Waelz kiln for 14 days showed positive results of the application of the proposed method — the yield of recycled material in the furnace decreased from 6-7 to 2-3% —the resulting turnover was not sufficient to reduce the moisture content of the mixture when mixing, therefore, dusty ones were added Zinc-containing materials recommended for Weltz processing by chemical composition.

The iron content in Waelz oxide from the furnace observed (the main indicator by which mechanical dust removal is estimated) with the beginning of loading the granulated charge decreased from 3-4 to less than 1% (before testing, the cake after the press filter and coke breeze were separately loaded into the furnace, mixed with flux and pulverulent materials by means of a grab charge, recycled dust was loaded separately). Measurements of the temperature of the furnace casing during the test period did not show growth accrued.

Due to the close contact of coke particles and zinc-containing material in the granules, the effectiveness of the carbon reducing agent increased. Loading the mixture prepared by the proposed method, it was possible to steadily conduct the Waelz process with a consumption of coke breeze 350-400 kg per 1 ton of zinc-containing material (before that, the usual consumption rate was 430-450 kg / t).

The verification of the method was carried out as follows.

A mixture consisting of zinc cake, coke breeze, recyclable materials, limestone, and dusty zinc-containing materials through a chute installed on the top head of the furnace was loaded into a 41 × 2.5 m tube rotary kiln. The mixture due to the rotation and tilt of the furnace moved along the length of the furnace, passing successively the drying, metal reduction and clinker zones. In contrast to the movement of the mixture passed dust and gas flow. Dust was captured by bag filters, and the cleaned gas was released through the pipe into the atmosphere. From the discharge end of the furnace, where the clinker was unloaded, air was additionally supplied to the furnace to provide the required amount of oxygen in the reaction space of the furnace for burning solid carbonaceous reducing agent (coke) and oxidizing metal vapors and organosulfur compounds.

The mixture was fed into the furnace in different ways: by grabbing the charge of coke, fluxes and pulverized materials with feeding the mixture through a separate hopper, zinc cake filtered on a LAROX press filter through another hopper, and circulating material through a separate estrus flow. According to the proposed method, the mixture was thoroughly mixed and granulated in a turbopaste mixer. The ratio of the components of the charge in the tests was maintained as follows: 1 kg of zinc cake accounted for 400 kg of coke breeze, 50 kg of limestone, 70 kg of recycled dust or recycled dust together with dusty materials.

The table below shows comparative data on the welting of a mixture prepared in different ways.

Table Test method Humidity cake / charge,% Humidity,% Productivity of the furnace (according to the charge), t / h The output of working material,% by weight of the mixture Weltz-oxide yield from cake,% Iron in Waelz-oxide,% Proposed 17 - 6.86 2-3 29-31 0.5-1.0 Without mixing and granulation (cake after the press filter, the remaining components are mixed with a grab) 22 12 6.6 6-7 33-35 3-4

From the above data it follows that when mixing and granulating the cake, the productivity of the Waelz kiln really increases, the yield of the circulating material decreases, the quality of the Waelz oxide improves (by the example of reducing the content of the non-combustible component - iron).

Claims (2)

1. The method of pyrometallurgical processing of zinc cakes, including the stages of their dehydration on press filters and Waelz with a dosage of coke breeze, fluxes, circulating dusts, characterized in that the dosage to the zinc cakes of the charge components is performed in a mixer in a turbulent mode of motion with particle collisions at a speed rotation of the blades of the mixing device from 6 to 10 rpm./s. 2. The method according to claim 1, characterized in that dusty zinc-containing materials are added to zinc cakes, chemical composition recommended for processing by Waelz.