JP2008545888A - Separation of valuable metal from zinc leaching residue - Google Patents

Abstract

The present invention relates to separation of metals in Fe-containing zinc leaching residues, particularly neutral and weakly acidic leaching residues. The method comprises:-producing an agglomerate comprising, in addition to Zn leaching residue, at least 5 wt% carbon and 2-10 wt% S;-said agglomerate in a fixed bed at a temperature above 1250C Fume, thereby producing a reduced Fe-containing phase and Zn-containing fume; and-extracting said Zn-containing fume. The high S content feed allows for relatively high operating temperatures without producing a melt phase. This ensures rapid reduction and humming reaction rates, and allows the use of small technologies such as fixed bed furnaces.
[Selection figure] None

Description

  The present invention relates to the separation of metals in Fe-containing zinc leaching residues, especially neutral and weakly acidic leaching residues.

Sphalerite, a ZnS ore containing impurities, is the main starting material for Zn production. A typical industrial practice involves an oxidative roasting process in which ZnO is produced with an impurity sulfate or oxide. In a subsequent step, the ZnO in the roasted sphalerite is brought into the solution by leaching under neutral or weakly acidic conditions, whereby neutral leaching residues and weakly acidic are respectively referred to herein. Zn-depleted residues, referred to as leaching residues, are produced. These residues contain 2 to 10% by mass of S, 30% by mass or less of Zn, 35% by mass of Fe, 7% by mass of Pb and 7% by mass of SiO ₂ .

However, during roasting, some of the Zn reacts with Fe, which is a typical impurity in sphalerite, to form a relatively insoluble zinc ferrite. The leach residue thus contains a substantial fraction of ferrite-form Zn in addition to lead sulfate, calcium sulfate and other impurities. According to current practice, recovery of Zn from ferrite requires a specific wet-metallurgical residue treatment using high acid concentrations of H ₂ SO _{4 from} 50 to 240 g / l. The disadvantage of this acid treatment is that it dissolves almost all other impurities such as Fe and As, Cu, Cd, Ni, Co, Tl, Sb in addition to Zn. Even though these elements are in low concentrations, they must be removed from the zinc sulfate solution to prevent subsequent Zn electrowinning. While Cu, Cd, Co, Ni and Tl are precipitated by the addition of Zn powder, Fe is usually discarded by hydrolysis as hematite, jarosite (iron alumite), goethite (goethite). Due to the risk of heavy metal spillage, these Fe-containing residues must be disposed of in well-managed landfills. These residue landfills, however, are exposed to severe environmental pressures, making the sustainability of the process uncertain. Another drawback of the above treatment is the loss of metals such as In, Ge, Ag and Zn in the Fe-containing residue.

Another treatment of ferrite-containing residues has been applied in some factories, using Weelz kilns, which produce slag and Zn and Pb-containing fumes. The process is described in "Electric arc furnace dust steelwork residue and Welz kiln treatment", G. Strohmeier and J.M. Bonestell, Iron and Steel Engineer Vol. 73, No4, pp. 87-90. In the Welts kiln, zinc is in the form of ferrite and sulfate, and after being reduced by CO generated by coke combustion, it is evaporated. Overheating problems often arise in the kiln reaction zone where iron is reduced to metal. In that case, mainly due to the formation of eutectic 2FeO.SiO ₂ —FeO having a melting point of about 1180 ° C., the charge in the kiln is dissolved and deposits are formed. The dissolution of FeO further lowers the melting point, and a solid shell is formed through a combination with zinc sulfide, which is reduced from zinc sulfate in the initial stage. Furnace rotation is further hindered by the formation of giant spheres of iron carbide formed as a molten metal phase at about 1150 ° C. This further leads to reduced reduction of ZnO and iron oxide formed from reduced zinc ferrite in the early stages of the furnace. Overheating promotes kiln brick wear. In order to counter the risk of overheating, the CaO / SiO ₂ ratio in the feed needs to be closely monitored to be adjusted to a value between 0.8 and 1.8.

Although a large number of Zn fuming processes are described, recent literature concentrates on the treatment of Zn-containing Fe secondary residues such as EAF dust. Although Wertz kilns are suitable in this respect, their productivity is hampered by their overheat sensitivity.

  In WO2005-005674, a method for separating and recovering non-ferrous metals from zinc-containing residues was disclosed. The method includes a step of subjecting the residue directly to a reduction step, a step of extracting Zn- and Pb-containing fumes, and a step of subjecting the obtained metal Fe-containing phase to an oxidation refining step. Direct reduction is carried out in a multi-stage hearth furnace operating at 1100 ° C. in a reduction furnace. One disadvantage of using such a reduction furnace is that the reduction reaction rate is limited by temperature. However, temperatures above 1100 ° C. cannot be reached in a multi-stage hearth furnace.

  Japanese Patent Application Laid-Open No. 2004-107748 describes a method for treating zinc leaching residues in a rotary hearth furnace at a reduction temperature of 1250 ° C. or less. The air ratio of the burner is set within a limited range.

  In US Pat. No. 5,906,671, Zn plant leaching residue is formed at a temperature of 1150 ° C. or less in a rotary kiln after agglomerating the alkaline earth and alkali metal complexes of alumina and silicon oxide with a reducing agent. Is processed.

In US Pat. No. 5,667,553, the neutral leaching residue, which is a byproduct of zinc electrowinning, is heat treated in a reduction furnace in the same manner as EAF dust.
International Publication No. 2005-005674 Pamphlet JP 2004-107748 A US Pat. No. 5,906,671 US Pat. No. 5,667,553 “Steelwork residue and Weltz kiln treatment of electric arc furnace dust”, G. Strohmeier and J.M. Bonestell, Iron and Steel Engineer Vol. 73, No4, pp. 87-90

The object of the present invention is to provide a method for separating a metal contained in an Fe-containing zinc leaching residue that does not have the disadvantages described above. The method is:
-Producing an agglomerate comprising, in addition to Zn leaching residue, at least 5 wt% carbon and 2-10 wt% S;
-Fuming said agglomerates in a fixed bed at a temperature above 1250 ° C, thereby producing a reduced Fe-containing phase and a Zn-containing fume; and
-Extracting said Zn-containing fume;
including.

Zinc leaching residue prior to manufacture of the agglomerates, preferably below H ₂ O 12% by mass, is further dried to a moisture content of H below ₂ O 5 wt%.

  A carbon content of at least 15% by weight in the agglomerates is preferred, as is a CaO equivalent of at least 10% by weight and even at least 15% by weight.

  The strength of the pellets, expressed as mass pellet strength, is preferably at least 5 kg and even 10 kg. This method prevents dust carryover and better prevents charge melting at high process temperatures.

Huming is advantageously performed in air-containing carbon monoxide at a temperature of at least 1300 ° C.

  The method is ideally suited for the treatment of neutral or weakly acidic zinc leaching residues.

  The method of the invention can be carried out in a rotary hearth furnace; it can optionally be followed by a process of melting and oxidizing the reduced Fe-containing phase.

  It may therefore be necessary to add S-containing components to the residue in order to bring the total S content to the required range. In this case, gypsum is a typical additive. The use of an S-rich carbon source can also be envisaged in this case.

  As will be apparent from the examples below, a high S content feed allows for relatively high operating temperatures without producing a melt phase. Thus, there is no risk of deposit formation at the furnace discharge port. The high temperature ensures a rapid reduction and humming reaction rate, which allows the use of small technologies such as fixed bed furnaces. This type of furnace further maintains the integrity of the agglomerates, greatly avoids the production of dust and stops subsequent fume contamination.

  The following examples illustrate the separation of different non-ferrous metals contained in roasting followed by leached zinc blende.

Mainly zinc ferrite (ZnO.Fe ₂ O ₃ ), lead sulfate (PbSO ₄ ), calcium sulfate (CaSO ₄ ), zinc sulfate (ZnSO ₄ ) and CaO, SiO ₂ , MgO, Al ₂ O ₃ , C
About 1000 g of weakly acidic leaching (WAL) residue consisting of impurities such as u ₂ O, SnO, etc., is dried to a moisture content of less than 5% by weight of H ₂ O, 15% by weight of CaO or equivalent of gypsum and> 85 Mixed with 25% by weight PET coke with% C purity. This mixture is compressed into briquettes by pressing between two hydraulic rolls at a pressure of 20 kN / cm ² , 20
A hard and glossy briquette with a mass pellet strength of kg was obtained.

  In order to simulate the process occurring in a rotary hearth furnace, a fuming process was performed in an induction furnace. An Induther Mu-3000 furnace with a maximum power of 15 kW and a frequency of 2000 Hz was used. The inner diameter of the furnace was 180 mm, and the graphite crucible holding the briquette had an inner diameter of 140 mm.

  About 400 g of briquette was placed at the bottom of a clean graphite crucible so that the crucible surface was covered with a single phase of raw material. A crucible was installed in the induction furnace and a monitoring thermocouple was installed between the briquettes without touching the bottom of the crucible. The crucible was covered with a heat resistant plate. The fumed metal was post-combusted above the crucible and trapped in the filter under the formation of smoke.

The reactor and feed were heated to 1300 ° C. as measured by a Pt / PtRh10 thermocouple attached between briquettes. Heating was performed up to 600 ° C. under a protective N ₂ gas atmosphere at a gas flow rate of 200 l / h. From 600 ° C. to 1300 ° C., CO was blown into the crucible at a flow rate of 200 l / h.

30 minutes after reaching 1300 ° C., a sample was taken out. These samples were quenched in liquid N ₂ to stop all reactions and freeze the mineralogy. The feed and product compositions are shown in Table 1. Table 2 shows the component distribution throughout the product.

  The results of the examples clearly show that after 30 minutes of roasting, Zn, Pb and In are efficiently discharged from the briquette while Fe, Cu, As and F are concentrated in the reduction residue. It is. The excellent selectivity for As and F is particularly interesting in view of subsequent processing of the fumes by wet scouring techniques.

Example 2
This example illustrates the critical role of briquette S in preventing raw material softening and melting during the roasting process without compromising selectivity.

5% by weight of SiO ₂ and:
-15% by weight of CaO and 25% by weight of finely ground coke (mixture 1); or -36.7% by weight of gypsum and 25% by weight of finely ground coke (mixture 2)
It was prepared using a synthetic S-free zinc leaching residue containing zinc ferrite containing.

  Both mixtures were compressed into briquettes and fumed according to the procedure of Example 1.

The briquette corresponding to mixture 1 containing only about 0.3% by weight of S is 2FeO.SiO ₂
It seemed to scour and show the formation of a low scouring phase. However, the briquettes corresponding to mixture 2 containing about 6.5% by weight of S did not show any formation of such phases, thanks to the presence of a suitable amount of S.

Claims (10)

-Producing an agglomerate comprising, in addition to Zn leaching residue, at least 5 wt% carbon and 2-10 wt% S;
-Fuming said agglomerates in a fixed bed at a temperature above 1250C, thereby producing a reduced Fe-containing phase and a Zn-containing fume; and
-Extracting said Zn-containing fume;
A method for separating metal valuables in Fe-leaching Zn leaching residue. Further, before the step of producing agglomerates, the Zn leach residue, the H less than ₂ O 12% by weight, preferably includes a step of drying to a moisture content of less than H ₂ O 5% by weight, according to claim 1, wherein the method of. The method according to claim 1, wherein the agglomerates contain at least 15% by mass of carbon. 4. The agglomerate further comprising a Ca compound which results in a CaO equivalent of at least 10% by weight, preferably at least 15% by weight, in the agglomerate. The method described in 1. 5. A method according to any one of the preceding claims, characterized in that the agglomerates are pellets 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 claim 1, wherein the fuming temperature is at least 1300 ° C. The method according to claim 1, wherein the fuming is performed in an atmosphere containing carbon monoxide. The method according to claim 1, wherein the Zn leaching residue is a neutral or weakly acidic Zn leaching residue. The method according to claim 1, wherein the fuming process is performed in a rotary hearth furnace. The method according to any one of claims 1 to 9, further comprising a step of subjecting the reduced Fe-containing phase to an oxidation scouring step.