MXPA06005851A - Method of obtaining electrolytic manganese from ferroalloy production waste - Google Patents

Abstract

The invention relates to a method of obtaining electrolytic manganese from sludges resulting from the cleaning of gases that are released by ferroalloy production furnaces, having a high manganese content, using a process comprising the following steps:sulphation, leaching, purification, conditioning and electrolysis. The aforementioned process produces a manganese sulphate liquor which can be used for the already-known electrolysis process in order to obtain electrolytic manganese.

Description

PROCEDURE FOR THE OBTAINING OF ELECTROLYTIC MANGANESE FROM WASTE FROM THE MANUFACTURE OF FERROALATIONS OBJECT OF THE INVENTION The process object of the patent consists of obtaining electrolytic manganese from sewage sludge from the exhaust gases of the ferroalloy production ovens. The aim is to achieve the integrated management of a waste that is produced globally in significant quantities through the use of its manganese content, which is the main raw material in the production process in which it is generated. BACKGROUND OF THE INVENTION Manganese is a metal that is not found in free form in nature, but combined in minerals whose composition is found as oxide (pyrolusite, mainly) or carbonate (rhodochrosite, mainly). Traditionally, the production processes that have required the contribution of manganese have been carried out using these minerals in steel reduction furnaces, in order to take advantage of manganese as an alloying element or as a deoxidant and desulfurizer in steel production. However, in the late nineteenth century began to study different methodologies for obtaining pure manganese from manganese minerals, with the aim of improving the alloys in which it participated and expanding its field of application, developing several procedures: electrolysis aqueous manganese salts, electrothermy, carbothermia, aluminothermy and silicoterothermia. Among these are the US patents 2,511,507 for "TREATING MANGANESE ELECTROPLANTING SOLUTIONS "; 2,483,287 for" METHOD OF PURIFYING MANGANESE ELECTROLYTES "; 2,347,451" ELECTROLYTIC DEPOSITION OF MAGANESE "; 2,343,293" PROCESS FOR THE PURIFICATION OF MANGANOUS SULPHATE SOLUTIONS "; and UK 528,112" IMPROVEMENTS IN THE ELECTROLYTIC PRODUCTION OF MANGANESE "Of all of them , which allows to obtain a higher purity of manganese, has more affordable production costs and, therefore, is more used, it is the first of them, that is, the production of manganese by aqueous electrolysis of this metal salts or obtaining of electrolytic manganese This product is currently marketed with purities ranging between 99.5 and 99.9% metal.

The electrolytic route for obtaining manganese metal was first investigated by Davis in 1930. However, this process did not become important until 1939, when the demand for electrolytic manganese by steel producers (for the manufacture of weapons) he made the US Bureau of Mines will install a pilot plant in Knoxville (Tennessee). This plant was redesigned in 1940, and in 1944 it reached a production capacity of 1,500 t / year.

In Japan, the production of electrolytic manganese began in 1941. The U.S.Bureau of Mines built a second pilot plant in 1942 in Boulder City. For its part, The Electrolytic Manganese Corporation of Krugersdorp, South Africa, began producing it in 1955. Currently, most of the • electrolytic manganese that is consumed in the world is produced in China and South Africa.

The process of obtaining electrolytic manganese that has been developed at the laboratory level starts from the need to solve the biggest environmental problems derived from the manufacture of ferroalloys, which is the generation of waste as a consequence of the treatment of the exhaust fumes of the production furnaces. The most efficient way to treat these emissions is wet scrubbing, so that the particles contained in them are retained in water. The subsequent treatment of this water results in the obtaining of a residual product that has a high content of manganese that is difficult to use as a recyclable material due to its physical nature.

The problem described caused the petitioner company to commission four years ago to the Chair of Metallurgy of the University of "Oviedo (Spain) the realization of some feasibility tests for the extraction of manganese content of this waste by hydrometallurgical way, for later electrolytic recovery, and thus obtain a product with great added value Research has shown that by means of certain novelties on the previously mentioned methods it is possible to achieve this challenge.

PROCESS DESCRIPTION The starting material used in the method for obtaining electrolytic manganese object of the invention is the residue obtained in the purification of the exhaust gases of ferroalloy production ovens, mainly composed of: The process that has been devised consists of the following phases: 1) Sulfation 2) Leaching 3) Purification 4) Electrolysis 1) SULFATATION The initial industrial waste is subjected to an acid attack to dryness, obtaining on the one hand a byproduct consisting of the untapped materials and, on the other hand, the metal sulfates that contain ions of the different leachable metals present in the residue, mainly manganese. 2) LEACHING The leaching and filtering of this solid gives rise to a liquor that carries the sulphates and other soluble substances generated during the treatment in the furnace, and to the obtaining of a solid residue that is rendered inert by washing it. The exhaust gases from this oven are subjected to alkaline purification. 3) PURIFICATION The purification stage is essential for the solution to be suitable for electrolysis. Small amounts of unwanted metals in the solution would cause contamination of the deposit, or even impede electrodeposition reactions.

There are two types of impurities that must be eliminated from the liquor, according to the way in which they must be dealt with.

A first group is formed by those that can be separated by a simple pH control. The aim is to bring the solution to pH conditions that require the precipitation of unwanted ions, following the Pourbaix diagrams (potential - pH), keeping the manganese in solution. With this, precipitation of virtually all iron and aluminum, as well as other less problematic pollutants such as cobalt or nickel, is guaranteed. . To increase the pH of the liquor, lime is added while stirring the pulp. The precipitate obtained is separated by filtration.

Finally, the solution is passed through an active C filter before being subjected to secondary purification.

The second group of pollutants is formed by basic metals that can not be completely eliminated by pH control, since the value that must be reached for their precipitation interferes with the precipitation pH of manganese.

The metals identified in this second group are headed by zinc, and are more noble than manganese. Its elimination is achieved by means of its precipitation in the form of sulfur at slightly acidic pH. This precipitation requires a sufficient residence time for the manganese sulphide that is formed but not excessive to redissolve to prevent redissolving impurities that had precipitated.

The liquor already purified is conditioned by adding a base until reaching an almost neutral pH, to enable its introduction into the electrolysis cell. Finally, part of this liquor is passed through a crystallizer to remove part of its calcium and magnesium content as ammoniacal salts. 4) ELECTROLYSIS Prior to its introduction into the cathodic cells of special electrolysis tanks, the liquor is completed with the following additives: Ammonium sulfate: it is added as a manganese stabilizer and buffering agent.

Hydroxylamine sulfate: antioxidant.

The electrolysis process is carried out in diaphragm tanks, in which the anolyte and the catholyte are separated by a semipermeable material.

Regarding the flow of liquors in the separated electrolyte cell, the catholyte, when passing through the diaphragm, feeds the anodic cell, so that the anolyte has a composition similar to the catholyte, although with a lower pH and remarkably depleted in manganese . The spent electrolyte is therefore suitable for recirculation to the process head. The vats should be kept at a certain temperature, and the electrolyte compositions should be kept homogeneous.

With the passage of time, the metal is deposited on the surface of the cathode, in the form of scales. The metal charge is separated by mechanical means.

While the electrolytic manganese flakes are deposited on the cathode, manganese dioxide accumulates on the anode. Once the process is finished, this product also requires washing with water and then separated by mechanical means. 1) Primary purification It is carried out in the same leach reactor and is achieved by increasing the pH of the solution. To separate the residue contained in the resulting pulp, which has both the untapped material and the precipitated impurities in the form of hydroxides (mainly Fe and Al), it is subjected to filtration in a filter press. The waste separated here requires a water wash to recover part of the manganese that it has dragged and to improve its chemical and physical characteristics for its later deposition. The washing water of these filtration cakes can be used as feed water to the mixer.

The electrolytic manganese obtained by the process is in the form of sheets and has an Mn content of 99.9%.

TESTS FOR OBTAINING MANGANESE SULFATE LIQUOR EXAMPLE A material with a humidity of 40% and a Mn content of 15% was started from 1 kg.

The material was mixed with 390 g. of sulfuric acid and 390 ml. of water in a ceramic container.

Subsequently, the mixture was poured onto a tray that was placed in an oven maintained at 300 ° C for 30 minutes.

The leaching was carried out with prepared synthetic anolyte. The residence time for the extraction of the Mn in this process was 1 hour, during which the pulp was kept under strong agitation. After that time, 70 g were added in the same leach reactor. of lime and left under stirring for half an hour, raising in this time the pH from 3.7 to 6.5. To separate the residue contained in the resulting pulp, which has both the untapped material and impurities precipitated in the form of hydroxides (mainly Fe and Al), it was subjected to a vacuum filtration. The waste separated here was subjected to a water wash to recover part of the manganese that it has dragged and to improve its chemical and physical characteristics so as to face its subsequent deposition. According to the characterization carried out, this waste is of inert kind according to the applicable norms.

To remove the content that may have both organic matter and traces of contaminants from the liquor separated in the filtration, it was passed through an active C filter.

The second purification phase consisted in the addition of 11.1 ce of sulfur and 0.65 g. of zinc sulfide bait. The precipitate obtained was separated by filtration. Thus 1.25 1. of liquor was obtained with the following chemical analysis: APPLICATIONS OF THE ELECTROLYTIC MANGANESE Electrolytic Manganese strength and ductility which provides (structural applications, resistant thin sheets, aeronautics, canned ...) is mainly used in the aluminum industry, and can be provided: in the master alloy, as injectable powder and briquettes mixed powder (or mechanical pre-alloy). Other uses of electrolytic manganese are: in the steel industry, as a desulphurizer and fine alloy for high performance stainless steels and HSLA steels; in the copper and nickel alloy industry; electrolytic manganese flakes as a catalyst for chemical reactions; production of manganite for the manufacture of variable resistances with temperature; manufacture of zinc-manganese ferrites for medium power electronic applications and as a pigment; manufacture of welding rods.

SCHEMES OF THE PROCESS Description of the schemes of a preferred embodiment of the invention.

Figure 1 shows the block diagram of the process that begins with the sulphation phase (1), followed by the hydrometallurgical phase that consists of four stages: leaching (3), primary purification (4), secondary purification (5) and conditioning (6) to finally reach the electrolysis phase (7) for obtaining the electrolytic manganese.

Figure 2 shows schematically the diagram corresponding to the sulphation phase (1), which consists of the treatment in furnace (8) of the material supplied by a mixer (9), generating gases that are forcefully extracted from said oven (8) through a chimney (10) and neutralized in a washing column (11) with the appropriate reagent.

Figure 3 schematizes the stages of leaching (3) and primary purification (4), in which the product resulting from the sulphated phase (1) is treated in a tank (12) with antacid coating, obtaining a pulp that is made passing through a filter press (13), in which the washing of the filter cakes can also be carried out countercurrently. This washing is carried out with water supplied from a tank (14), which can later be used both in the initial mix of the process and in the leaching phase. The inert waste is collected in the tank (15) from the bottom of the filter press.

Figure 4 corresponds to the secondary purification stage (5), in which the primary liquor of the previous stage is filtered with an activated carbon filter (16), prior to its conduction to the secondary purification tank (17) , in which the remaining impurities are precipitated in the form of sulfides that are separated through another filtration process (18), finally obtaining purified liquor (19) and a residual product, ZnS (20).

Figure 5 schematically shows the conditioning step (6) in which the purified liquor is subjected to an increase in pH in a tank (21), to be subsequently treated in a crystallizer (22), in which it is favored the precipitation of ammoniacal salts (24) of Ca and Mg of the liquor.

Figure 6 shows schematically the electrolysis phase (7) of the liquor that is treated in a cell (26) supplied with catholyte heated by the action of an existing heat exchanger in the feed tank (25). The cell is made of a polyester diaphragm and inside it are submerged two anodes and a cathode, the latter being inside its own compartment. To effect the washing of the cathode after the deposition of electrolytic Mn on its surface, an immersion tank (27) is available. On the other hand, anodic sludge from the cell accumulates and evacuates from the double bottom it possesses, becoming treated in a tank (28) for sludge flocculation.

Claims (6)

1. - Procedure for obtaining electrolytic manganese from residues from the manufacture of ferroalloys, more specifically manganese contained in the sludge from the exhaust gases of ferromanganese and silico-manganese production ovens obtaining a product of high added value, which is CHARACTERIZED because it consists of an initial phase of sulphation, a hydromethalurgic phase composed of four stages - leaching, primary purification, secondary purification and conditioning and a final phase of electrolysis and in which: A non-hazardous waste is made to disappear, producing another of half inert weight and which has the property of being self-compacting. - A process of thermal sulphation is used, with consumption of almost stoichiometric acids. - It promotes the elimination of impurities, iron and aluminum, mainly by pH control, minimizing the amount of equipment and time to be used. It promotes the elimination of impurities of basic metals, zinc mainly, by means of its precipitation in the form of sulfides suitable for other uses. That allows to obtain electrolyzed solutions that under standard conditions produce manganese with a purity of 99.9%.

2. - Method for obtaining electrolytic manganese from residues from the manufacture of ferroalloys, according to claim 1 the sulphation phase is CHARACTERIZED; because it is done in an oven in which exothermic reactions take place inside the oven and on Teflon pans, generating S02 gases.

3. - Method for obtaining electrolytic manganese from residues of the manufacture of ferroalloys, according to claim 1 wherein the stages of leaching and primary purification are CHARACTERIZED because the leaching is carried out with spent anolyte of the electrolysis cell or alternatively with synthetic anolyte.

4. - Process for obtaining electrolytic manganese from residues from the manufacture of ferroalloys, according to claim 4, wherein the said leaching stage is CHARACTERIZED because anolyte is used as a leaching agent and is carried out in a reactor with a coating antacid with strong agitation.

5. - Method for obtaining electrolytic manganese from residues of the manufacture of ferroalloys, according to claim 4 in which primary purification stage is CHARACTERIZED because it is carried out in the same reactor of leaching simultaneously to raise the pH of the pulp to values close to neutral pH and the resulting pulp is then subjected to filtering in a filter press and washing water, preferably in the filter press itself, obtaining an inert waste.

6. - Procedure for obtaining electrolytic manganese from residues from the manufacture of ferroalloys, according to claim 6 the washing water of the pulp is CHARACTERIZED because it can be used as a water supply to the mixer in the initial phase of the process or reuse successive times to go concentrating it in manganese.