WO2015194980A2

WO2015194980A2 - A method of hydrometallurgical separation of iron and its compounds from non-ferrous metals and their compounds and a device for carrying out said method

Info

Publication number: WO2015194980A2
Application number: PCT/PL2015/050023
Authority: WO
Inventors: Andrzej STEFAŃSKI; Adam BĄCHÓR; Jerzy SIWEK
Original assignee: Zakład Hydrometalurgii "Hydromet" Spółka Z Ograniczoną Odpowiedzialnością
Priority date: 2014-06-17
Filing date: 2015-06-17
Publication date: 2015-12-23
Also published as: PL231506B1; WO2015194980A3; PL408584A1

Abstract

The invention relates to a method of hydrometallurgical separation of iron and its compounds from non-ferrous metals and their compounds in which the sludge is leached in an alkalised solution while being exposed to an alternating or direct current until its temperature reaches 40-45°C, then, preferably under the continuous of an alternating or direct current, thus obtained sludge solution is alkalised to achieve a pH in the range of 11.5-14.0, and then a liquid phase is separated from the solid phase, and then the separated solid phase is acidified with an aqueous solution of acetic acid and is subjected to deep leaching, and then the liquid phase is separated from the solid phase and finally thus obtained solid phase is washed with an alkaline solution in order to achieve pH in the range of 6.8-7.2, and then excess water is filtered off, obtaining a solid phase comprising iron, iron compounds, silica, and carbon suitable for repeated thermal treatment. The object of the invention is also a separator (B) comprising an open iron container forming a housing (15) of the separator, a centrifugal pump (14) setting the sludge pulp in motion and a battery of bag filters (21) or a battery of filter discs (16).

Description

A method of hydrometallurgical separation of iron and its compounds

from non-ferrous metals and their compounds

and a device for carrying out said method

TECHNICAL FIELD

The invention relates to a method of hydrometallurgical separation of iron and its compounds from non-ferrous metals and their compounds and is used in particular for treating or processing sludge and sediment of blast furnace and steelmaking origin, which are waste in the steel industry. Preferably, the method uses alternating current or direct current for leaching and/or alkalising.

The invention relates also to a separator being an element of the system of devices for carrying out the above-mentioned method,

PRIOR ART

Blast furnace sludge is an aqueous suspension of an ultrafine fraction of blast furnace dust. Its hydration exceeds 97%, and its composition is characterized by the fact that it contains toxic compounds. In the known furnace practice, blast furnace sludge is pumped to the settlers purifying water in the gas treatment circulation, and then after an optional concentration in settling tanks or filters is transferred to dumps that contribute to environmental pollution, in particular surface water and groundwater.

So far methods of dealing with the sludge are limited mainly to its disposal. For example Polish patent no. 80509 discloses that for the disposal of blast furnace sludge, molten blast furnace slag is poured into it, wherein the ratio of slag and sludge in dry matter amounts to about 100:2. The method described in this patent is used for the disposal of blast furnace sludge, however it does not allow for the extraction and reuse of metals contained in the sludge. Methods of separation of iron and its compounds from non-ferrous metals and their compounds in various systems as well as devices used for this purpose are known in the prior art. For example the description of Polish patent application No. P.231252 discloses a device for recovery of ferromagnetic metals from ferruginous sludge, wherein a magnetic drum is used for metal recovery. However, the solution according to this invention is not suitable for industrial application and it was necessary to develop a more effective method of recovering metals from blast furnace sludge.

On the other hand, a scientific publication by P. Ostrowska-Popielska et al. (P. Ostrowska-Popielska i A. Sorek, Prace IMZ 4, 2013) described a method of recovering zinc from BOF sludge using hydrometallurgical processes. This solution was tested in laboratory systems and it was necessary to develop techniques of recovering other metals on a large scale.

Despite the fact that methods of separating iron and its compounds from non-ferrous metals and their compounds already exist in the prior art, more efficient methods of separation are still being sought. In the context of environmental protection it is particularly important - to develop methods of separating iron and its compounds from non-ferrous metals and their compounds out of massive amounts of sludge and sediment of blast furnace and steelmaking origin, which is treated as waste in the steel industry. Physico-chemical form of this waste does not allow its reuse as an input for thermal treatment or granulation, due to the high content of non-ferrous metals and their compounds in its composition, in particular zinc with an average content ranging from 6 to 10% and due to the fact that it has a form of sol with a high water content, often exceeding 30%.

The solution being the object of the present invention aims to provide an efficient method for the separation of iron and its compounds from non-ferrous metals and their compounds applicable in particular to the recovery of these elements and their compounds from the sludge and sediment resulting from technological processes in metallurgy. DETAILED DESCRIPTION OF THE INVENTION

The object of the invention is a method of hydrometallurgical separation of iron and its compounds from non-ferrous metals and their compounds characterized in that: a) the sludge is leached in an alkalized solution with a pH in the range of 7.5-11.0 while being exposed to a current until its temperature reaches 40-45°C, then thus obtained sludge solution is alkalised to achieve a pH in the range of 11.5-14.0, and then

a liquid phase is separated, comprising zinc compounds and soluble compounds of metals from the group forming complex compounds, in particular compounds of aluminium, tin, germanium and gallium, from a solid phase comprising iron, iron compounds, silica and carbon; whereupon b) the separated solid phase is acidified with an aqueous solution of acetic acid to achieve a pH in the range of 4.5-5.0 and is subjected to deep leaching, and then a liquid phase, comprising zinc compounds, is separated from the solid phase, comprising iron, iron compounds, silica, and carbon; whereupon c) thus obtained solid phase is washed with an alkaline solution in order to achieve pH in the range of 6.8-7.2, and then the excess water is filtered off, obtaining a solid phase comprising iron, iron compounds, silica, and carbon suitable for repeated thermal treatment.

For the sludge pulp to reach the right temperature in the leaching process with an alkaline solution, that pulp can be heated or connected to an alternating current or a direct current of an appropriate voltage.

Preferably, when the alkalising in step a) occurs when the solution is additionally subjected to heating.

Preferably, when the alkalising in step a) occurs while the solution is subjected to AC or DC current. Also preferably, when the value of the AC or DC voltage is 2,5-70 V, and particularly preferably when it is 2.5-4.5 V. Preferably, when the sludge leaching is preceded by a preliminary filtration of the process water containing soluble compounds of metals from the group that forms complex compounds and compounds of calcium and magnesium from the sludge.

Preferably, when the process water obtained in the preliminary filtration is placed in a settling tank, and then it is treated with an alkalised base solution precipitating soluble metal compounds, particularly calcium and magnesium compounds. Thus obtained process water is used in the leaching and/or washing process.

During leaching, preferably under an alternating current or direct current, the temperature of the solution increases. Formation of soluble compounds of non-ferrous metals and the distribution of the water sol takes place. Additional alkalising of the solution is performed to dissolve the zinc hydroxide formed in the solution. As a result of separating the liquid phase from the solid phase, a solid phase is obtained comprising iron, iron compounds, silica, and carbon having a water content of approx. 10%, without the burden of non- ferrous metals, suitable for further thermal treatment.

Preferably, when the liquid phase is separated from the solid phase by vacuum through a filter forming a diaphragm between the electrodes.

Also preferably, when the alkaline sludge leaching uses a solution alkalised with a base NaOH or KOH.

Also preferably, when the initial pH of the solution, wherein the leaching occurs, is in the range of 8.5-9.5.

Preferably, when the process of separating the liquid phase from the solid phase occurs after alkalising and takes place at a pH in the range of 12.0-14.0.

If a current is not used to separate the liquid phase from the solid phase, soluble zincates and aluminates are created along with the simultaneous production of hydrogen. This process is more expensive and longer.

The object of the invention is also a separator characterized by the fact that it comprises an open iron container forming a housing of the separator, a centrifugal pump setting the sludge pulp in motion and a battery of bag filters or a battery of filter discs. Preferably, when the alternating current is connected to the separator's housing with the zero pole and correspondingly either an isolated movable filter disc ring or an isolated portable battery of a bag filter is connected with the phase pole of the alternating current.

Also preferably, when the direct current is connected to the separator's housing with the positive pole and correspondingly either an isolated movable filter disc ring or an isolated portable battery of a bag filter is connected with the negative pole of the direct current.

Preferably, when the capacity of the separator is between 2 and 4 m .

Preferably, when the housing of the separator is lined with a hard-wearing perforated material with holes.

An advantage of the solution according to the invention is that the separation of iron and its compounds from non-ferrous metals and their compounds using a hydrometallurgical method is a very efficient process, which can be used on a large scale in metallurgy for lingering sludge dumps. Application of the solution according to the invention helps to reduce environmental pollution. Application of the method according to the invention allows for the change in classification of metallurgical sludge, currently considered as waste, into a raw material used in further industrial processes.

The object of the invention has been visualised in the embodiments as well as in the accompanying drawings, not limiting however the scope of this application, in which:

Fig. 1 and 2 schematically illustrate the carrying out of the method according to the invention,

Fig. 3 illustrates a schematic structure of the separator in a version with disc filters presented in Example 1,

Fig. 4 illustrates a schematic structure of the separation element in the form of a disc filter presented in Example 1

Fig. 5 illustrates a schematic structure of the separator in a version with bag filters presented in Example 2,

Fig. 6 illustrates a schematic structure of the separation element in the form of a bag filter presented in Example 2 EMB ODIMENTS Example 1

A method of hydrometallurgical separation of iron and its compounds and non-ferrous metals and their compounds was carried out as illustrated in a flowchart constituting fig. 1 and fig. 2. Alternating current was used in performing the method according to the invention.

Preliminary filtration of process water from the sludge and the separation of calcium and magnesium compounds

In the first stage diluted sludge Sz from a gas treatment installation is fed into separator A to pre-separate the excess process water from sludge Sz in the form of sol. Then sludge Sz is mechanically transported into separator B. Water is discharged via line 1 to settling tank E, where it is subjected to alkalising with a base NaOH 13. As a result of alkalising mainly calcium and magnesium compounds precipitate. The content of calcium and magnesium compounds in the moist mass was measured three times. Measurement results are shown in Table 1.

Table 1. Precipitation of calcium and magnesium compounds by alkalising.

Calcium and magnesium compounds are separated from the solution in centrifuge G and transported for further processing via line 3. Alkalised aqueous solution with a pH of 8.5 is returned to separator B via line 2.

Basic leaching

Then basic leaching is carried out in separator B which contains disc filters (fig. 3). Ratio by weight of the aqueous solution to sludge is 1: 1, wherein volume ratio 5: 1. The sludge solution is put in motion using pump 14 (fig. 3). An alternating current is fed with the zero pole to the grounded housing 15 and with the phase pole to the isolated disc elements 16. The leaching was carried out under an AC voltage of 2.5 to 4.0 V. A series of tests was conducted measuring the relation between the transition of Zn into the solution and time at a voltage of 3.5 V, the results of which are shown in Table 2.

Table 2. Basic leaching - the relation between the Zn content [% ] in the sludge in three tests and the leaching time at the temperature of 40-45° C

During leaching the undissolved non-ferrous metals and their compounds are converted into a solution forming soluble complex compounds, and the water is converted from sol into liquid. Then the solution is alkalised to a pH in the range ofl l,5-14 feeding a concentrated solution of NaOH via line 5. Then the zinc compounds are completely dissolved.

Filtered compounds are transported via line 4 to settling tank F. Sludge Sz with a zinc content of 1 - 1.5% is discharged into separator C for deep treatment.

Precipitation of non-ferrous metal compounds from the electrolyte and crystallisation of Glauber's salt hydrate

In the settling tank F dissolved compounds of non-ferrous metals fed via line 4 are acidified with sulphuric acid fed via line 7 at the temperature of 40°C to pH in the range of 7.5-8.0.

As a result, mainly gelatinous zinc and aluminium compounds are released, which were separated with centrifuge G and discharged via line 6 for separate processing. The remaining electrolyte solution was discharged via line 8 into settling tank H and acidified with sulphuric acid fed via line 7 to complete neutralisation, e.g. obtaining pH of approx. 7.0. Then the temperature is lowered below 30°C, thereby forming a crystalline salt hydrate, which is then dried up. Water is discharged via line 9 for re-use, for example, to dilute acids or to dissolve bases.

Deep treatment of iron sludge with acetic acid

In separator C sludge Sz is acidified with an aqueous solution of acetic acid fed via line 10 to obtain pH of the solution in the range of4.5-5.0, causing elution of zinc compounds. The relation between the elution of zinc compounds to filtration time is presented in Table 3.

Table 3. Deep leaching - the relation between Zn content [% ] in the sludge and filtration time.

Electrolyte of resulting acetates was discharged via line 11. Filtered iron sludge was transferred into separator D.

Washing and neutralisation of iron sludge with intense drying

In separator D NaOH is fed via line 2 and water is fed via line 9 to obtain pH 7.0, wherein such a solution is filtered and discharged via line 11. Whereas filtered iron sludge is discharged via line 12 for repeated thermal treatment.

Separators B, C, i D shown in fig. 1 i 2 have the same structure with the exception that only separator B is connected to the alternating current. Separators are connected in series and, where appropriate, to increase the efficiency of the system, they may be made into parallel batteries.

The principle of operation of the device according to the invention

Implementation of the method according to the invention for separating sludge being metallurgical waste of high gravity applies a specially-designed separator for continuous filtration (fig. 3) in a version with disc filters used to separate a liquid phase compromising non-ferrous metal compounds from the solid phase.

A separator with disc filters comprises: an open iron housing 15 of a separator lined with a hard-wearing material (as in example 2) constituting a housing 15 of a separator with a capacity of 2 to 4 m , a battery of filter discs 16 and a centrifugal pump 14 setting the sludge pulp in motion. Sludge Sz and solution of reactants Re are fed into the separator and as a result of filtration electrolyte E and separated sludge OSz are formed. Low- voltage alternating current is connected with the zero pole to the separator's housing 15 that is grounded and with phase pole to an isolated movable filtration disk ring 16.

The filter element of the disc ring part (Fig. 4) contains an iron element 17 constituting a frame of a disc part being also a current pole, backing fabric 18 and filter cloth 19 resistant to acids and bases constituting a diaphragm.

Example 2

Structure of the separator for cyclic filtration (fig. 5) is the same as in Example 1 except for the fact that instead of disc filters 16 bag filters 21 were used. A separator in a version with bag filters comprises an open iron container lined with a hard-wearing perforated (with holes) material constituting a housing 15 of the separator, a centrifugal pump 14 setting the sludge pulp in motion and a battery of bag filters 21 moved to the next container to discharge the sludge. Sludge Sz and a solution of reactants Re are fed to the container. As a result of separation electrolyte E is obtained. Low-voltage alternating current is connected with the zero pole to the separator's housing 15, that is grounded and with the phase pole to an isolated portable battery of bag filters 21.

The filtering element of a bag filter (fig. 6) comprises an iron pipe 22 being simultaneously an alternating current pole, a plastic pipe 23 with holes over its entire length and a backing fabric 18 resistant to acids and bases. The bag 21 is made of a material resistant to chemicals and is also a diaphragm.

Claims

A method of hydrometallurgical separation of iron and its compounds from non-ferrous metals and their compounds characterized in that: a) the sludge is leached in an alkalised solution with a pH in the range of 7.5-11.0 while being exposed to a current until its temperature reaches 40-45°C, then thus obtained sludge solution is alkalised to achieve a pH in the range of 11.5-14.0, and then a liquid phase is separated, comprising zinc compounds and soluble compounds of metals of the group that forms complex compounds, in particular compounds of aluminium, tin, germanium and gallium, from a solid phase comprising iron, iron compounds, silica and carbon; whereupon b) the separated solid phase is acidified with an aqueous solution acetic acid to achieve a pH in the range of 4.5-5.0 and is subjected to deep leaching, and then s liquid phase comprising zinc compounds is separated from the solid phase, that comprising iron, iron compounds, silica, and carbon; whereupon c) thus obtained solid phase is washed with an alkaline solution in order to achieve pH in the range of 6.8-7.2, and then excess water is filtered off, obtaining a solid phase comprising iron, iron compounds, silica, and carbon suitable for repeated thermal treatment.

The method according to claim 1 characterized in that the alkalising in step a) occurs when the solution is additionally subjected to heating.

The method according to claim 1 characterized in that the alkalising in step a) occurs when the solution is subjected to AC or DC current.

The method according to claim 1 characterized in that the value of AC or DC voltage is in the range of 2.5-70 V.

The method according to claim 4 characterized in that the value of AC or DC voltage is in the range of 2.5-4.5 V. - 2-

6. The method according to claim 1 characterized in that the sludge leaching is preceded by a preliminary filtration of the process water containing soluble compounds of metals form the group that forms complex compounds and compounds of calcium and magnesium from the sludge.

7. The method according to claim 1 characterized in that the process water obtained in the preliminary filtration is placed in the settling tank (E), and then is treated with an alkalised base solution precipitating soluble metal compounds, particularly calcium and magnesium compounds.

8. The method according to claim 7 characterized in that the process water is used in the leaching and/or washing process.

9. The method according to claim 1 characterized in that the liquid phase is separated from the solid phase by vacuum through a filter forming a diaphragm between the electrodes.

10. The method according to claim 1 characterized in that the alkaline sludge leaching uses a solution alkalised with a base NaOH or KOH.

11. The method according to claim 1 characterized in that the initial pH of the solution, wherein the leaching occurs, is in the range of 8.5-9.5.

12. The method according to claim 1 characterized in that the process of separating the liquid phase from the solid phase occurs after the alkalisation and takes place at a pH in the range of 12.0-14.0.

13. A separator (B) characterized in that it comprises an open iron container forming a housing (15) of the separator, a centrifuge pump (14) setting the sludge pulp in motion and a battery of bag filters (21) or a battery of filter discs (16).

14. The separator according to claim 13 characterized in that an alternating current is connected to the grounded separator housing (15) with the zero pole and correspondingly either an isolated movable filter disc ring (16) or an isolated portable battery of bag filters (21) is connected with the phase pole of the alternating current. - 3-

The separator according to claim 13 characterized in that a direct current is connected to the grounded separator's housing (15) with the positive pole and correspondingly either an isolated movable filter disc ring (16) or an isolated portable battery of bag filters (21) is connected with the negative pole of the direct current.

The separator according to claim 13 characterized in that the capacity of the separator is between 2 and 4 m .

The separator according to claim 13 characterized in that the separator's housing (15) is lined with a hard-wearing perforated material with holes.