FLISSAK WILIAM (BR)
DOS SANTOS JOSE ROBERTO (BR)
DE ALMEIDA ANTONIO LUIZ (BR)
FLISSAK WILIAM (BR)
DOS SANTOS JOSE ROBERTO (BR)
| KR100924296B1 | 2009-11-02 | |||
| US5431713A | 1995-07-11 | |||
| US3691038A | 1972-09-12 | |||
| BRPI0801716A | 2008-05-05 |
HAVLIK T ET AL: "Atmospheric leaching of EAF dust with diluted sulphuric acid", HYDROMETALLURGY, ELSEVIER SCIENTIFIC PUBLISHING CY. AMSTERDAM, NL, vol. 77, no. 1-2, 1 April 2005 (2005-04-01), pages 41 - 50, XP004777572, ISSN: 0304-386X, DOI: DOI:10.1016/J.HYDROMET.2004.10.008
JHA M K ET AL: "Review of hydrometallurgical recovery of zinc from industrial wastes", RESOURCES CONSERVATION AND RECYCLING, ELSEVIER SCIENCE PUBLISHER, AMSTERDAM, NL, vol. 33, no. 1, 1 August 2001 (2001-08-01), pages 1 - 22, XP004246483, ISSN: 0921-3449, DOI: DOI:10.1016/S0921-3449(00)00095-1
| CLAIMS PH YSICAL-CHEMICAL PROCESS FOR THE RECOVERY OF METALS CONTAINED STEEL INDUSTRY RESIDUES 1. The process of recovering of metals contained in aciary powder characterized by promoting the homogeneous mixture of aciary powder (EAF) with concentrated sulphuric acid, using a grinder and a stirrer associated with the calcination furnace (3) in order to prevent the agglomeration of particles in the reaction mass. 2. The process of recovering metals contained in aciary powder, according to claim 1 , characterized by developing under normal atmospheric pressure. 3. The process of recovering metals contained in aciary powder, according to claim 1 , characterized by developing under temperatures between 150° C and 250° C. 4. The process of recovering metals contained in aciary powder, according to claim 1 , characterized by promoting the elimination of organic compounds containing halogens such as chlorine and fluorine. 5. The process of recovering metals contained in aciary powder, according to claim 1 , characterized by promoting zinc precipitation under the form of a basic salt cake (27) by adjusting pH and adding ammonia for a preferred range between 6.0 and 7.5, more preferably at a pH between 6.5 and 6.7 and exactly at a pH of 6.6. 6. The process of recovering metals contained in aciary powder, according to claim 1 , characterized by presenting a calcination step (33) of zinc basic salt (27) for the production of zinc oxide (ZnO) (34) , at a preferred temperature between 800° C and 1200° C, more preferably at temperatures between 900° C and 1 100° C and exactly at a temperature of 1000° C. 7. The process of recovering metals contained in aciary powder, according to claim 1 , characterized by presenting a basic salt solubilization step with sulphuric acid for the production of a concentrated zinc solution, followed by the recovery of zinc sulphate heptahydrate [ZnS04.7H20] (30) by crystallization. |
CONTAINED STEEL INDUSTRY RESIDUES
Field of the invention
This invention relates to a physical-chemical process intended for the treatment of steel industry residues of electric arc furnaces (EAF), known as "aciary powder", for the recovery of metals of interest, such as zinc, iron and other ones contained therein through soluble sulphates in aqueous medium under specific conditions.
Background of the invention
In the current steel industry residues treatment process, called aciary electric arc furnace (EAF) powder, reagents are used in order to prevent the formation of pellets or lumps from part of the reaction mass, which decreases the efficacy of the open chemical reactions of the residues' metal constituents by the concentrated sulphuric acid. The chemical reagent accepted as efficient for this use is potassium chloride (KC1), once it originates a large mass of hydrogen chloride in gaseous form (HC1). This gas is very reactive thus requiring special equipment in order to prevent rapid wear through corrosion from occurring.
The process requires subsequent treatment steps through hydrometallurgy. The separation of metal constituents is conducted by controlling pH values, so that each metal can precipitate in the form of a specific compound. When potassium chloride is applied, the neutralizing agent should necessarily be potassium hydroxide (KOH) allowing thus the recovery of potassium sulphate (K 2 S0 4 ) at the end of the process.
The process proposed herein uses mechanic resources associated with the chemical process, able to avoid the formation of pellets or lumps. It relates to the adaptation of a milling device to the calcination reactor. Thus, the reactor starts to operate as a mechanical stirrer which homogeneously stirs the steel industry residues with the concentrated acid. This adequacy intends to grind the agglomerated material during the addition of sulphuric acid. In this system, the same efficacy of the open chemical reactions of the several residue constituents' crystal networks is maintained when compared to the previously described process.
Analysis of the state of arts
The Brazilian patent application PI 0801716-6, in the secrecy period, shows a chemical process for the treatment of "aciary powder", for the recovery of metals of interest contained therein by obtaining soluble sulphates in aqueous medium. Such process uses reagents, notably potassium chloride ( C1) in order to prevent the formation of pellets or lumps, which decrease the efficacy of the open chemical reactions of the residues' metal constituents by the concentrated sulphuric acid. The process proposed herein is presented as an upgrade of that process, once it eliminates the need of such reagents by including a new mechanical stirring and milling step in the calcination furnace.
Description of the drawings
Fig. 1 shows the general process flow chart, where the several single operations and the several products (9, 15, 18, 21 , 26 and 30) generated in the process through the calcination (3) of the raw material (EAF) in acid medium by adding sulphuric acid (H 2 S0 4 ), are noted.
Brief description of the invention
The process can be described as the production of salts or sulphates from aciary powder (EAF) constituent metals using dry concentrated sulphuric acid, under normal pressure and moderate temperatures. It consists in promoting the direct reaction of concentrated sulphuric acid with the aciary powder (EAF), maintaining a homogeneous mixture without the presence of water avoiding the agglomeration of the particles by means of a grinder associated to the calcination reactor (3), which operates in parallel with a mechanical stirrer, eliminating the need to add potassium chloride as a dispersive agent and the use of potassium hydroxide for the neutralization of solutions in the hydrometallurgy steps.
This mechanical adequacy allowed the neutralizing agent to be replaced by liquefied ammonia thus obtaining a significant decrease in weight and cost of reagents and eliminating the need of special equipment resistant to corrosion.
Another advantage relates to a decrease in mass, which can reach levels up to 95% when a second surfactant calcination (7) is performed. Thus, almost all the metals contained in the aciary powder (EAF) can be recycled, once the remaining mass, around 5%, refers to a lead concentrate (9) with a Pb content between 30% and 40% which can be recycled for the casthouses or transformed into chemical products such as acetate, nitrate, oxide or lead sulphate.
This technological innovation also allows the replacement of potassium hydroxide (KOH) in the neutralizing steps by liquefied ammonia gas (NH 3 ). The mass reduction in the reagent consumption is approximately 3 fold, i.e., for each mol of neutralized sulphuric acid, two moles of potassium hydroxide are spent. In case of using liquefied ammonia, two moles are required, equivalent to just 34 g of NH 3 . Another benefit from the process development is related to the circuit dilution once potassium hydroxide (KOH) should be used in the form of a diluted aqueous solution, while ammonia is doses in the form of gas, without adding water to the circuit, being able to work with more concentrated solutions, thus saving energy in zinc and ammonia sulphates crystallization (29 and 25, respectively). The reagents costs, which represent a significant decrease, should further be considered.
Detailed description of the invention
The process consists in the production of salts or sulphates from aciary powder (EAF) constituent metals using dry concentrated sulphuric acid, under normal pressure and moderate temperatures, where the direct reaction of concentrated sulphuric acid with aciary powder (EAF) is promoted, maintaining a homogeneous mixture without the presence of water, avoiding particle agglomeration by using a grinding device, coupled with the calcination reactor (3), operating in parallel with a mechanical stirrer.
It is necessary to dry the material in a drying furnace (2) until the humidity is lower than 2% in mass for subsequent milling in a mill (2) until a granulometry of 45 micra is reached. Following this preparation, the material is fed into the pre-heated calcination furnace (3) at a temperature of around 120° C. The stirrer and grinder are started and the concentrated sulphuric acid is continuously fed to the reactor (3) until a ratio of 1.1 kg of acid to 1 kg of residue is reached.
In this process, the reaction of opening the crystal networks of the constituents starts occurring as the acid is fed. For being exothermic reactions, the temperature of the reaction mass reaches values between 230° C and 250° C. Under these conditions, when the addition of acid is completed, almost all the residue constituents were transformed into their respective sulphates. The organic components, such as dioxins and furans are also chemically destroyed and transformed into carbon dioxide (C0 2 ), water vapor, molecular chlorine (Cl 2 ) and/or hydrogen chloride (HC1), molecular fluorine (F 2 ) and/or hydrogen fluoride (HF). All the produced gases are absorbed by a lime milk [Ca (OH) 2 ] suspension (32), circulated in a column (31 ) containing plastic spheres. In the top of the column there is an exhauster which aspirates all the gases making them leach through the bed, in a counter flow against the lime milk (32). Only water vapor, free from components that are harmful to the environment, are released in the atmosphere.
The calcinated material, primarily composed by the sulphates of metals present in the original residue, is transferred to a reactor (4) for aqueous leaching, where all the metal sulphates are solubilized, except lead and calcium sulphates. The pulp resulting from leaching is filtered in filter press (5a), while the filtrate is taken to a tank (10) of metal sulphates solution for treatment through hydrometallurgy, recovering iron in a precipitation tank (1 1 ) as paragoetite (13), which is subsequently dehydrated through drying (14), transforming into hematite ( 15) to be applied as pigment or recycled in blast furnaces of steel industries.
Copper (1 8), in its turn, is recovered as copper sponge concentrate for subsequent transformation into copper pentahydrate (CuS0 4 .5H 2 0). Manganese (21) is recovered as bioxide concentrate (Mn0 2 ) to be transformed into manganese sulphate monohydrate (MnS0 4 .H 2 0). Zinc (30) is precipitated as a basic salt [ZnS0 4 .3Zn(OH) 2 .4H 2 0] for subsequent recovery as zinc oxide (ZnO) or crystallized zinc sulphate heptahydrate (ZnS0 4 .7H 2 0) and ammonia e recovered at the end of the process as crystallized ammonia sulphate [(NH 4 ) 2 S0 4 ] (26).
The cake (6) resulting from the first leaching (3) of the calcinated material represents 15% o the mass of aciary powder (EAF) residue fed to the process. It is directed to the second calcination step (7) in a furnace which is similar to the first one, but with lower size. The second calcination (7) is performed under the same conditions as the first (3) one and the gases are also absorbed in a column (31) containing plastic spheres, with the circulation of a lime milk suspension (32).
Similarly, this second calcinate is submitted to aqueous leaching (8) for the extraction of more soluble sulphates that have been formed. The pulp is also filtered in filter press (5b). The filtrate is directed to the tank (10) of sulphate solution; the cake is washed with water and directed to the tank of water from the various washings for a new leaching process.
Such cake, resulting from the second aqueous leaching (8), represents only 5% of the initial residue mass which was fed to the first calcination furnace (3), allowing a total mass decrease of 95%, constituting a lead concentrate (9) with contents between 30 - 40%.
The solution from the first (4) and the second leaching (8) from the two calcinates, containing all the soluble sulfates from metals present in the original aciary powder (EAF) is oxidized with a small amount of hydrogen peroxide (H 2 0 2 ) for the transformation of ferrous sulphate (FeS0 4 ), eventually present, into ferric sulphate [Fe 2 (S0 4 ) 3 ]. Subsequently, the solution is fed into a reactor (1 1 ) in a point which is immediately below the stirrer helices, which is the region presenting the highest turbulence and which provides the rapid homogenization of the reagents with the entire reaction volume. Oxidation can also be conducted by air bubbling close to the point at which the solution is added to the reactor (1 1 ). The temperature inside the reactor ( 1 1 ) is maintained between 60° C to 70° C by means of a superheated vapor passage tubing. pH is maintained between 3.0 and 3.5 by ammonia gas (NH 3 ) bubbling. Under such conditions, the concentration of ferric irons (Fe 3+ ) inside the reactor ( 1 1 ) is null, once all these ions are instantaneously precipitated in the form of paragoetite (13) and the ammonia is transformed into ammonia sulphate according to the following chemical reaction:
Fe 2 (S0 4 ) 3 + 6NH 3 + 4H 2 0 - 2F60.0H! + 3(NH 4 ) 2 S0 4
Paragoetite ( 13) is a crystalline ferric oxide hydrate (Fe 2 0 3 .H 2 0) which easily flocculates and decants providing a good solid/liquid separation and with a high filtration rate. The pulp is filtered in filter press (5c) and the solution ( 16) is directed to a cementation process (17) with zinc powder. The cake is washed with hot water for the extraction of soluble sulphates, being directed to the tank containing water from the washings. This cake is further washed with ammonia solution in order to decompose jarosite which, eventually, can be formed in paragoetite precipitation (13) reactor ( 1 1) and, also, in order to solubilize a small amount of basic zinc and copper sulphates which are formed in the working pH. The cake is still submitted to a third wash with hot water for the extraction of all the soluble sulphates which can still be present.
The following reactions provide a better idea of this double objective of the ammonia washing:
Jarosite decomposition
2NH 4 Fe 3 (S0 4 )2(OH) 6 + 6NH 3 -» 3Fe 2 0 3i + 4(NH 4 ) 2 S0 4 + 3H 2 0
Decomposition of basic zinc and copper salts
ZnS0 4 .3Zn(OH) 2 .4H 2 0 + 24NH 3 Zn(NH 3 ) 6 S0 4 + 3Zn(NH 3 ) 6 (OH) 2 + 4H 2 0
CuS0 4 .3Cu(OH) 2 .4H 2 0 + 24NH 3 -> Cu(NH 3 ) 6 S0 4 + 3Cu(NH 3 ) 6 (OH) 3 + 4H 2 0
Following these washings, the paragoetite cake (13) is calcinated at 180° C in a rotary furnace (14) for dehydration and transformation into hematite (15), which is a red pigment, according to the following reaction:
2FeO.OH - Fe 2 0 3 + H 2 0 †
When paragoetite (13) is dehydrated at temperatures higher than 180° C, other pigments can be obtained such as brown and black.
The solution (16) of the tank, free from iron, is continuously transferred to the reactor (17) for copper removal by cementation with zinc powder. The copper cement ( 18) is filtered in a filter press producing a copper sponge concentrate which is directed to the copper sulphate pentahydrate production unit. The filtrate (19), free from copper, is directed to another tank. This solution, free from iron and copper, is fed into a rector (20) for manganese oxidation with potassium permanganate, or another appropriate-, oxidizing agent, and precipitation of manganese bioxide (21 ) through pH control between 3.5 and 4.5, also using liquefied ammonia (NH ). The chemical reaction below illustrates this operation: 3MnS0 4 + 2KMn0 4 + 4NH 3 + 2H 2 0 5Mn0 2i + 2(NH 4 ) 2 S0 4 + K 2 S0 4 The pulp is filtered in filter press (5e), the washed cake and the resulting solution are directed to the tank containing water from the washings.
The solution (22) obtained from the aforementioned operations is purified, particularly containing zinc sulphate and ammonia sulphate. It is transferred to a reactor (23) where zinc is precipitated as a basic salt (27), by controlling pH between 6.0 and 7.5 by adding liquefied ammonia (NH 3 ). The temperature is maintained between 70° C and 80° C. The basic zinc salt (27), precipitated under these conditions is easily decanted and has a good filtration rate. The following chemical reaction illustrates this operation: 4ZnS0 4 + 6NH 3 + 10H 2 O + 3(NH 4 ) 2 S0 4 The pulp is filtered in filter press (5f) and the filtrate (24), containing just ammonia sulphate (26), is directed to a tank. The basic salt cake (27) is washed in the filter with water which is directed to the tank containing water from the washings.
The resulting basic zinc salt (27) can be used as a raw material for the production of zinc sulphates, zinc oxide, metal zinc and other products. For the production of zinc sulphate (30), the basic salt cake (27) is transferred to a reactor (28), repulped with a small volume of water and acidulated with sulphuric acid until pH between 4.0 - 4.5 to be transformed into a concentrated pure zinc sulphate solution, according to the following reaction:
ZnS0 4 .3Zn(OH) 2 .4H 2 0 + 3H 2 S0 4 -» 4ZnS0 4 + 10H 2 O
This zinc sulphate concentrated solution is evaporated until the salt heptahydrate (ZnS0 .7H 2 0) is crystallized and cooled for subsequent centrifugation of such crystals (30) in a centrifuge (29) for separation. The parent water returns to the evaporator and the crystals (30) are stored into appropriate silo for subsequent packaging into bags.
For the production of zinc oxide (34), the basic salt cake (27) is calcinated at temperatures between 750° C and 1.000° C in a furnace (33), thus generating zinc oxide (34). Upon calcinations, dehydration and thermal decompositon of the basic salt compound occurs, generating zinc oxide (34), sulphur dioxide, oxygen and water vapor. The sulphur dioxide is absorbed by a manganese bioxide pulp, generating manganese sulphate monohydrate (MnS0 4 .H 2 0). The decomposition reaction is showed below: ZnS0 4 .3Zn(OH) 2 .4H 2 0 -> 4ZnO + S0 2 † + 0 2 T + Η 2 Ο τ
The zinc basic salt filtration solution (24) containing the whole ammonia sulphate (26) is transferred to a tank where it is evaporated until ammonia sulphate [(NH 4 ) 2 S0 4 ] (26) is crystallized. The crystals are separated by centrifugation in a centrifuge (25) and the parent water returns to the evaporators and the crystals (26) are stored in appropriates silos for subsequent packaging into bags.
This invention is not limited to the representations commented or illustrated herein, and should be understood in its wide scope. A number of changes and other representations of the invention will come to mind of those who are familiar with the art to which this invention pertains, having the benefit of the teaching presented in the previous descriptions and attached drawings. In addition, it is to be understood that the invention is not limited to the specific disclosed form and that changes and other forms are understood as included in the scope of the attached claims. Although specific terms are employed here, they are use only in a generic and descriptive form and not for the purpose of limitation.
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