KR20080022545A - 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. ® KIPO & WIPO 2008

Description

Separation of valuable metals from zinc leach residues {SEPARATION OF METAL VALUES IN ZINC LEACHING RESIDUES}

The present invention relates to a method for separating metals from Fe-bearing zinc leaching residues, especially neutral and weak acid leach residues.

Blends, which are impure ZnS ores, are the main starting material for the production of Zn. Typical industrial practice involves an oxidative roasting step, which produces ZnO with sulfates or oxides of impurities. In subsequent steps, ZnO in the roasted blend is placed in solution and leached to neutral or weak acid conditions to produce Zn-depleted residues referred to herein as neutral leaching residues and weak acid leaching residues, respectively. The residue typically comprises 2-10 wt% S, 30 wt% or less Zn, 35 wt% Fe, 7 wt% Pb and 7 wt% SiO ₂ .

However, some of the Zn in roasting reacts with Fe, which is present as a typical impurity in the blend, to form a relatively insoluble zinc ferrite. Therefore, leach residues contain, in addition to lead sulphate, calcium sulfate and other impurities, quite large Zn fractions in the form of ferrites. According to this embodiment, the method of recovering Zn from ferrite requires treatment of certain hydro-metallurgical residues using high acid concentrations of 50-200 g / l H ₂ SO ₄ . A disadvantage of this acidic treatment is that almost all Fe and other impurities besides Zn, such as As, Cu, Cd, Ni, Co, Tl, Sb, are dissolved. Since these elements interfere with the subsequent electrowinning of Zn even at low concentrations, they must be removed from the zinc sulfate solution. Cu, Cd, Co, Ni and Tl are precipitated by the addition of Zn powder and Fe is typically discarded as hematite, jarosite or goethite via hydrolysis. Because of the risk of heavy metal loss, the Fe-containing residues must be treated with a well-controlled landfill. However, landfill disposal of these residues poses significant environmental pressures, which leads to uncertainty in the sustainability of the process. Another drawback of this treatment is the loss of metals such as In, Ge, Ag and Zn in the Fe-containing residues.

Selective treatment of ferrite-containing residues is introduced into several plants using Waelz kilns, producing slag and fumes containing Zn and Pb. The process is described in 'Steelworks residues and the Waelz kiln treatment of electric arc furnace dust' (G. Strohmeier and J. Bonestell, Iron and Steel Engineer vol. 73, N ° 4, pp. 87-90). In the Baeltz kiln, zinc enters the form of ferrites and sulfates and is evaporated after being reduced by the CO generated by burning the coke. In the reaction zone of the kiln (iron is reduced to metal), the problem of overheating often occurs. In this case, the filling in the kiln is melted and adducts are formed, mainly by the formation of eutectic 2FeO.SiO ₂ -FeO, the melting point of which is approximately 1180 ° C. Dissolution of FeO further lowers the melting point and combines with zinc sulfide to reduce from zinc sulfate in the initial stage to form solid crusts. Furnace rotation is further hampered by the formation of large balls of carbonized iron which are formed as molten metal phase at approximately 1150 ° C. This leads to a reduced reduction of ZnO and iron oxide and is formed in the initial furnace stage from reduced zinc ferrite. Overheating promotes wear of the kiln's acid-resistant bricks. To limit the risk of overheating, the CaO / SiO ₂ ratio in the feed is monitored and set to a value of 0.8 to 1.8.

Although numerous Zn fuming processes have been described, recent literature has focused on the treatment of Zn-containing Fe secondary residues, such as EAF dust. In this respect, the Baelz Kiln is suitable but nevertheless its productivity is hindered by its sensitivity to overheating.

In WO2005-005674, a process for the separation and recovery of nonferrous metals from zinc-containing residues is described. The method comprises treating the residue in a direct reduction step, extracting Zn-containing and Pb-containing fumes, and treating the obtained metallic Fe-containing phase by an oxidizing smelting step. do. Direct reduction is carried out in a multiple hearth furnace operating at 1100 ° C in the reduction zone. One disadvantage of using such a reduction furnace is that reduction kinetics are limited by temperature. However, temperatures above 1100 ° C. cannot be reached in multiple stages.

JP2004-107748 describes a process for the treatment of zinc leach residues in rotary furnaces with a reduction temperature of less than 1250 ° C. The proportion of burner air is set within a limited range.

In US Pat. No. 5,906,671, Zn plant leach residues are treated in a rotary kiln at temperatures up to 1150 ° C. and aggregated together with alkaline earth and alkali metal complexes and reducing agents of alumina and silica oxides.

In US Pat. No. 5,667,553, the neutral leaching residual by-product of zinc electrosmelting is heat treated in the same way as EAF dust in a reduction furnace.

It is an object of the present invention to provide a process for separating metals contained in Fe-containing zinc leach residues, which does not have the disadvantages mentioned above. The method includes the following steps:

Preparing agglomerates comprising at least 5% by weight carbon and 2-10% by weight sulfur in addition to the Zn leach residue;

Fusing the aggregates in a static bed at a temperature of at least 1250 ° C. to produce reduced Fe-containing phases and Zn-containing fumes; And

Extracting the Zn-containing fume.

Zn leaching residue is preferably that to prepare the agglomerates dried to a moisture content of less than 12% by weight in H ₂ O, and even of not more than 5% by weight of H ₂ O.

The carbon content in the aggregate is preferably at least 15% by weight and the CaO equivalent is at least 10% by weight, even at least 15% by weight.

The strength of the pellets, expressed as Mass Pellet Strength, is preferably at least 5 kg, even 10 kg. In this way dust is avoided to be transported thereon, and fusing of the charge is well prevented at high process temperatures.

Fuming is advantageously carried out at temperatures above 1300 ° C. in an atmosphere containing carbon monoxide. The process is ideally suited for treating neutral or weak acid Zn leach residues.

The method of the invention can be carried out in a rotary furnace; The process by which the reduced Fe-containing phase is melted and oxidized can optionally be carried out.

Therefore, an S-containing component is added to the residue to adjust its total S content to the required range. Gypsum is a typical additive in this case. It is conceivable in this case to use S-rich carbon sources.

As demonstrated in the examples below, the high S content in the feed allows for relatively high operating temperatures without creating a melt phase. Therefore, there is no risk of the formation of adducts at the discharge port of the furnace. High temperatures ensure fast reduction and fusing kinetics, and compact technologies such as stationary bed furnaces can be used. In addition, the shape of the furnace preserves the accumulation of aggregates, greatly avoids the formation of dust and limits the contamination of the fume.

Example 1

The following examples illustrate methods for separating different nonferrous metals contained in roasted and subsequently leached blends.

Mainly zinc ferrite (ZnO.Fe ₂ O ₃ ), lead sulfate (PbSO ₄ ), calcium sulfate (CaSO ₄ ), zinc sulfate (ZnSO ₄ ) and impurities (e.g. CaO, SiO ₂ , MgO, Al ₂ O ₃ , Cu Approximately 1000 g of Weak Acid Leaching (WAL) residue consisting of ₂ O, SnO) is dried to a water content of up to 5% by weight of H ₂ O, 15% by weight of CaO or even gypsum and 25% by weight. Is mixed with PET coke (purity> 85% C). The mixture is compacted into coal briquettes by compressing between two hydraulic rolls at a pressure of 20 kN / cm 2 to form hard, polished briquettes with a mass pellet strength of 20 kg.

The fuming step is carried out in an induction furnace to simulate the process occurring in a rotary furnace. An Indutherm MU-3000 furnace with a maximum power of 15 kW and a frequency of 2000 Hz is used. The inner furnace diameter is 180 mm and the graphite crucible carrying the coal briquettes is 140 mm.

Approximately 40 g of coal briquettes are placed in the bottom of a clean graphite crucible and the crucible surface is applied with a single layer material. The crucible is then placed in an induction furnace, and the thermocouple to be monitored is mounted between the coal briquettes without touching the bottom of the crucible. The crucible is coated with a refractory plate. The fume metal is post-burned on the crucible and collected in the filter under the formation of dust.

The reactor and material were heated to 1300 ° C. as measured by a Pt / PtRh10 thermocouple mounted between coal briquettes. Below 600 ° C., heating is carried out under a protective N ₂ gas atmosphere at a gas flow rate of 200 l / h. At 600 ° C. to 1300 ° C., CO is injected into the crucible at a flow rate of 200 l / h.

Samples are taken 30 minutes after reaching 1300 ° C. The sample is quenched in liquid N ₂ to stop all reactions and freeze minerals. The composition of the feed and product is set forth in Table 1 below. Elemental distributions for the products are set forth in Table 2 below.

The experimental results clearly show that after 30 minutes of roasting, Zn, Pb and In effectively fuse from the coal briquettes and Fe, Cu, As and F are concentrated in the reduced residue. Good selectivity for As and F is particularly interesting in terms of the subsequent treatment of the fume by hydrometallurgical means.

Example 2

This example illustrates the important role of S coal briquettes, which avoids softening and melting of materials during the roasting process without losing selectivity.

The two mixtures are prepared using zinc ferrite with 5 wt.% SiO ₂ and synthetic S-glass zinc leach residues comprising:

15 weight% CaO and 25 weight% finely ground coke (mixture 1);

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

The two mixtures are compacted into coal briquettes and fuse according to the procedure of Example 1.

Coal briquettes containing only about 0.3 wt.% S (corresponding to Mixture 1) are smelted to form a low smelting phase such as 2FeO.SiO ₂ . However, coal briquettes (corresponding to Mixture 2) comprising about 6.5% by weight of S does not show formation of the phase due to the presence of an appropriate amount of S.

Claims (10)

A method for separating valuable metals from a Fe-containing Zn leach residue, The method is Preparing agglomerates comprising at least 5% by weight carbon and 2-10% by weight sulfur in addition to the Zn leach residue; Fusing the aggregates in a static bed at a temperature of at least 1250 ° C. to produce reduced Fe-containing phases and Zn-containing fumes; And Extracting said Zn-containing fume. The method of claim 1, How to make up to 12% by weight prior to the step of preparing the agglomerates H ₂ O, preferably, further comprises the step of drying the Zn leaching residue to a moisture content of H ₂ O less than 5% by weight, characterized. The method according to claim 1 or 2, Wherein the aggregate comprises at least 15% by weight of carbon. The method according to any one of claims 1 to 3, The aggregate further comprises a Ca compound, wherein the compound provides at least 10 wt%, preferably at least 15 wt% CaO equivalents in the aggregate. The method according to any one of claims 1 to 4, The agglomerate is a pellet characterized by having a mass pellet strength of at least 5 kg, preferably briquettes having a mass pellet strength of at least 10 kg. The method according to any one of claims 1 to 5, The fusing temperature is at least 1300 ° C. The method according to any one of claims 1 to 6, The purging is carried out in an atmosphere containing carbon monoxide. The method according to any one of claims 1 to 7, Zn leach residue is a neutral or weak acid Zn leach residue. The method according to any one of claims 1 to 8, The fusing step is carried out in a rotary hearth furnace. The method according to any one of claims 1 to 9, Treating the reduced Fe-containing phase with an oxidizing smelting step.