EA013690B1 - Separation of metal values in zinc leaching residues - Google Patents

Abstract

The invention relates to the separation of metals in Fe-bearing zinc leaching residues, in particular neutral and weak acid leach residues. The process comprises the steps of : - preparing agglomerates containing, besides the Zn leaching residue, at least 5 wt% of carbon and 2 to 10 wt % of S; - fuming said agglomerates in a static bed at a temperature above 1250°C, thereby producing a reduced Fe-bearing phase and Zn-bearing fumes; and - extracting said Zn-bearing fumes. The high S content of the feed allows for a relatively high operating temperature without production of molten phases. This guarantees fast reduction and fuming kinetics, and permits the use of a compact technology such as a static bed furnace.

Description

The present invention relates to the extraction of metals present in iron-containing leaching of zinc, in particular in neutral and weakly acidic waste.

The main raw material in the production of zinc is zinc blende, representing contaminated ore дуη8. A typical industrial process involves a stage of oxidative roasting, in which Ζη обра is formed, as well as sulfates or oxides of impurities. At subsequent stages, the ΖηΟ contained in the burnt snag is transferred to the solution by leaching in a neutral or weakly acidic medium; the formation of zinc-depleted residues, referred to in the present description, respectively, neutral waste or slightly acid waste. These residues typically contain from 2 to 10 wt.% 8, up to 30 wt.% Η, 35 wt. % Those 7 wt. % Pb and 7 wt. % 8ίΟ ₂ .

However, in the firing process, a part of Ζη reacts with a Fe, a typical impurity contained in the blende, and forms zinc ferrite, which has a relatively low solubility. Therefore, after leaching, in addition to lead sulfate, calcium sulfate and other impurities, waste contains a significant proportion of Ζη in the form of ferrite. According to current practice, the extraction of Ζη from ferrite requires special hydrometallurgical waste treatment using high concentrations of acid (from 50 g / l to 200 g / l Η ₂ 8Ο ₄ ). The disadvantage of this acid treatment is that along with zinc, almost all of the iron, as well as other impurities, dissolves, for example, Άδ, Cu, Sat, N1, Co, T1, 8b. Since even low concentrations of these elements prevent the subsequent extraction of zinc by electrolysis, they must be removed from the zinc sulphate solution. C, Sb, Co, N1 and T1 are precipitated by adding powdered zinc, and Fe is typically removed in the form of hematite, jarosite or goethite by hydrolysis. Due to the danger of leaching heavy metals, these iron-containing wastes should be taken to waste storage facilities, the state of which should be carefully monitored. However, the accumulation of such waste is associated with a strong negative impact on the environment, which calls into question the permissibility of the above process. Another disadvantage of the treatment described above is the loss of valuable metals, such as Ιη, Ge, Hell and η, present in iron-containing wastes.

In some enterprises, an alternative method of processing ferrite-containing waste using furnaces Balti (\ Wae1x) is used. in which slag and smoke containing η and Pb are formed. Such a method is described in Shtromayera and Bonstella "Waste steelmaking and processing of EAF dust emissions in furnaces Balti" (81ee1 \\ 'og1 <5 teChbiek AIB 111e \ Uae1h PCU 1gea1teSh οί e1es1ps aga GITAS biy, O. 81goyte1eg AIB 1. Voie ^ eI οτοη aib 81ee1 B ^ sews νοί. 73, Νο.4, pp. 87-90). Zinc enters the Balti furnace in the form of ferrites and sulphate and is evaporated after reduction of CO, which is generated by burning coke. In the reaction zone of the furnace, where iron is reduced to the metal, often there are complications associated with overheating. In such cases, the materials loaded into the furnace melt and agglomerates form, mainly due to the formation of the 2PeΟ · 8 ^ Ο ₂ -PeΟ eutectic, having a melting point of approximately 1180 ° C. The dissolution of Re causes a further decrease in the melting point, and in combination with zinc sulphide formed from zinc sulphate at earlier stages, solid nastils are formed. The rotation of the furnace is additionally prevented by the formation of large pellets consisting of carburized iron, which are formed from the molten metal phase at approximately 1150 ° C. This, in turn, leads to a decrease in the efficiency of reduction of ΖηΟ and iron oxide, which are formed in the furnace sections overlying the direction of movement of the reduced zinc ferrites. Overheating accelerates the wear of the furnace refractory lining. In order to limit the risk of overheating, the .'3 отношение / 8ίΟ ₂ ratio in the starting material should be carefully controlled, which should be maintained between 0.8 and 1.8.

Although numerous zinc evaporation processes are described, the current literature focuses on the treatment of zinc-containing secondary iron waste, for example, dust emissions from electric arc furnaces. The Balti furnaces are well adapted for this treatment, but their performance is limited due to sensitivity to the effects of overheating.

In \ νΟ2005-005674 a method for the separation and extraction of non-ferrous metals from zinc-containing wastes is described. The described method includes the stages of direct recovery of waste, extraction of the Ζη- and Pb-containing vapors and oxidative melting of the resulting metallic iron-containing phase. Direct reduction is carried out in a multi-malt furnace at a working temperature in the reduction zone of 1100 ° C. The disadvantage of using such a reducing furnace is that the kinetics of reduction is limited by the effect of temperature. However, it is not possible to reach temperatures exceeding 1100 ° C in a multiple-hearth furnace.

Patent 1P2004-107748 describes a method for treating zinc-containing waste in a rotary hearth furnace at a reduction temperature of up to 1250 ° C. At the same time, the air flow rate in the burners is set within a limited range.

According to patent I85,906,671, after zinc leaching, wastes are processed in a rotary kiln at temperatures up to 1150 ° С after agglomeration together with complexes of aluminum and silicon oxides with alkaline earth and alkali metals and a reducing agent.

According to patent I85,667,553 neutral leaching waste — the side products of zinc electrolysis — is heat treated in a reduction furnace in the same way as dusty

- 1 013690 throws arc electric furnaces.

The object of the present invention is a method for the extraction of metals present in iron-containing leaching of zinc, devoid of the aforementioned disadvantages. This method includes the steps of:

obtaining an agglomerate containing, along with leaching zinc leaching, not less than 5% by weight of carbon and from 2 to 10% by weight of sulfur;

evaporating said agglomerate in a fixed bed at temperatures above 1250 ° C to obtain reduced iron-containing phase and zinc-containing vapors; and removal of the mentioned zinc-containing vapors.

Before leaching of the agglomerate, leaching of zinc wastes should preferably be dried to a moisture content of less than 12 wt.% H ₂ O or even less than 5 wt. % H ₂ O.

The carbon content in the agglomerate is preferably at least 15 wt.%, And the equivalent of CaO is at least 10 wt.% Or even at least 15 wt.%.

The strength of the granules, expressed in terms of the mass strength of the granules (Gs8 Pe11e1 8 (gspd1P). Preferably should not be less than 5 kg or even 10 kg. This prevents dust entrainment and more efficiently prevents melting of the charge at high operating temperatures.

Evaporation should be carried out at a temperature not lower than 1300 ° C in an atmosphere containing carbon monoxide.

The method is almost ideally suitable for processing neutral or weakly acid leaching of zinc.

The method according to the present invention can be implemented in a rotary hearth furnace; optionally, it may be followed by a subsequent melting and oxidation process of the reduced iron-containing phase.

To ensure the total sulfur content within the required range, it may be necessary to introduce a sulfur-containing component into the waste. A typical additive in such cases may be gypsum. The use of a carbon source with a high sulfur content may also be envisaged in such cases.

As shown in the examples below, the high sulfur content of the starting material ensures operation at relatively high temperatures without the formation of molten phases. This eliminates the danger of formation of wall accretions near the exit from the furnace. High temperatures guarantee fast kinetics of reduction and evaporation, which makes it possible to use compact technology, for example, to use a fixed bed oven. In addition, sintering of agglomerate is prevented in this type of kiln, dust generation is largely eliminated, and dust pollution is limited.

Example 1

The example below illustrates the extraction of various non-ferrous metals contained in the calcined and then leached zinc blende.

Approximately 1000 g of weakly acid leaching waste (^ AB), consisting mainly of zinc ferrite (2nO-D ₂ O ₃ ), lead sulphate (Pb8O ₄ ), calcium sulphate (Ca8O ₄ ), zinc sulphate (ΖηδΟ ₄ ) and impurities , for example, CaO, 81O ₂ , MgO, A1 ₂ O ₃ , Cu ₂ O, 8πO, dried to a moisture content below 5 wt.% H ₂ O and mixed with 15 wt.% CaO or an equivalent amount of gypsum and 25% (wt.) PET coke having a purity greater than 85%. This mixture was pressed into briquettes by squeezing between two hydraulic rollers under a pressure of 20 kN / cm ² , obtaining solid shiny briquettes having a mass index of granules of 20 kg.

The evaporation stage was performed in an induction furnace in order to simulate the process that takes place in a rotating hearth furnace. For this purpose, a 1Pbi MI-3000 type furnace with a maximum power of 15 kW and an operating frequency of 2000 Hz was used. The internal diameter of the furnace was 180 mm, and the graphite crucible into which the briquettes were loaded had an internal diameter of 140 mm.

Approximately 400 g of briquettes were placed on the bottom of a pure graphite crucible so that the surface of the crucible was covered with a single layer of material. Then the crucible was placed in an induction furnace and a control thermocouple was installed between briquettes so that it did not touch the bottom of the crucible. Cover the crucible with a lid of refractory material. The volatile metals were subsequently burned over the crucible and trapped in the form of flue dust using a filter.

The reactor and the material were heated to 1300 ° C, determining the temperature using a platinum-platinum-rhodium thermocouple P1 / RF1110. installed between the briquettes. Up to 600 ° C, heating was performed in a protective atmosphere of Ν ₂ at a gas flow rate of 200 l / h. In the temperature range from 600 to 1300 ° C, CO was injected into the crucible at a flow rate of 200 l / h.

After 30 min after reaching a temperature of 1300 ° C, samples were taken. These samples were cooled in liquid nitrogen, stopping all reactions and fixing the mineralogical composition. The composition of the starting material and products are presented in table. 1. The distribution of elements by product is presented in table. 2

- 2 013690

Table 1. Composition of the starting material and products

Componeite Weight (G1 Composition,% (May.) Raw material Pb Si Az Ζη Re Ιη Cao 8Yu ₂ eight WITH R Waste \ uae 1000 5.1 1.74 0.1 28 15 0.02 1.61 5.46 5.9 0.05 0.01 PET-coke 250 5.27 87,8 Gypsum 190 41 24 OD Briquettes 1440 3.5 1.50 0.2 nineteen 10.9 0.02 6.7 3.75 6.8 14.6 0.02 Products Recovered waste 365 1.0 4.05 0.47 2.3 thirty <0.01 18.0 10.5 14.6 7 0.02 Top dust 270 eleven 0.03 0.07 66 0.15 0.07 <0.01 0.19 1.0 0.043 <0.03

Table 2. Distribution of elements by products

Distribution,% (May.) Products Pb Si Az Ζη Re Ιη Cao & S ₂ eight WITH R Recovered waste 10.9 99.5 90.1 4.5 99.6 <13 > 99.2 98.7 95.2 99.5 > 71 Top dust 89.1 0.05 9.9 95.5 0.4 > 87 <0.8 1,3 4.8 0.5 <29

The results of the experiments clearly show that after 30 minutes of roasting, Ζη, Pb and Ιη are effectively removed from the briquettes as vapors, while Pe, Cu, and P are concentrated in the recovered waste. Of particular interest from the point of view of the subsequent treatment of flue dust by hydrometallurgical methods has a high selectivity for R.

Example 2

This example illustrates the crucial importance of the presence of sulfur in the briquettes, since it helps to prevent softening and melting of the material in the calcination process without loss of selectivity.

Two mixtures using synthetic waste leaching zinc were prepared containing no sulfur and comprising zinc ferrite doped with 5 wt% 8ίΟ and ₂ wt% of CaO and 25% by weight fine-particulate coke (mixture 1)...;

36.7% by weight of gypsum and 25% by weight of finely ground coke (mixture 2).

Both mixtures were pressed into briquettes and evaporated according to the procedure described in Example 1.

Briquettes corresponding to mixture 1, containing only about 0.3 wt.% 8, were melted at this treatment, which indicates the formation of low-melting phases, for example, 2ReO-81O ₂ . In contrast, in briquettes corresponding to a mixture of 2 containing approximately 6.5% by weight of 8, the formation of such phases was not observed due to the presence of an adequate amount of 8.

Claims (10)

CLAIM 1. A method for extracting valuable metals present in iron-containing zinc leaching waste, comprising the steps of producing an agglomerate containing, along with zinc leaching waste, at least 5 wt.% Carbon and 2 to 10 wt.% Sulfur; evaporating said agglomerate in a fixed bed at temperatures above 1250 ° C to obtain reduced iron-containing phase and zinc-containing vapors; and removal of the mentioned zinc-containing vapors. 2. The method according to claim 1, further comprising a step of drying the zinc leaching waste before the step of obtaining the agglomerate to a moisture content of less than 12% by weight of H ₂ O, preferably less than 5% by weight of H2O. 3. The method according to claim 1 or 2, characterized in that the agglomerate contains at least 15 wt.% Carbon. 4. The method according to any one of claims 1 to 3, characterized in that the agglomerate additionally contains a compound Ca, and this compound ensures the presence in the agglomerate at least 10 wt.%, Preferably at least 15 wt.% Equivalent to CaO. 5. The method according to any one of claims 1 to 4, characterized in that the agglomerate is a granule having a mass strength of not less than 5 kg granules, preferably briquettes having a mass strength of not less than 10 kg granules. 6. The method according to any one of claims 1 to 5, characterized in that the evaporation temperature is at least 1300 ° C. 7. The method according to any one of claims 1 to 6, characterized in that the evaporation is carried out in an atmosphere containing carbon monoxide. - 3 013690 8. The method according to any one of claims 1 to 7, characterized in that the leaching waste of zinc are neutral or weakly acid waste leaching of zinc. 9. The method according to any one of claims 1 to 8, characterized in that the evaporation stage is performed in a rotary hearth furnace. 10. The method according to any one of claims 1 to 9, further comprising a stage of oxidative melting of the reduced iron phase.