RU2389533C2 - Method of electrolytic production of manganese from ferrous alloys production wastes - Google Patents

Abstract

FIELD: process engineering. ^ SUBSTANCE: invention relates can be used in metallurgy, electronics and in production of pigments and welding electrodes. Wastes of production of ferrous alloys containing, mainly, manganese represent slimes of fume gases washing from furnaces producing ferromanganese and silicon manganese. Said wastes are directed for thermal sulphating 1 that comprises furnace processing of material fed from mixer wherein said wastes have been subjected to treatment by acid with flow rate approximating to stoichiometric. Teflon chutes are used inside the furnace to produce SO2. Then hydrometallurgical phase is performed consisting of vatting stage 2, primary 3 and secondary 4 washing stages and that of conditioning. Vatting is carried out at intensive mixing in reactor with coating that regulates acidity using anolyte of electolyser or synthetic anolyte. Primary washing stage 3 is carried out in the same reactor till pH increases to values approximating to neutral one by removing, mainly, iron and aluminium. Produced fine pulp is filtered in pressure filter, flushed by water, preferably, in the same pressure filter, to produce inert wastes. Fine pulp flushing water is added into the mixer or used again to concentrate manganese therein. At secondary flushing stage 4, zinc impurity is removed by settling ZnS. Solution obtained after conditioning 5, is directed to electrolysis 6 to produce electrolytic manganese. ^ EFFECT: possibility to recover wastes to produce 99,9%-pure manganese. ^ 5 cl, 6 dwg

Description

The method according to the invention relates to the electrolytic production of manganese from treated sludge from the exhaust gases of furnaces for the production of ferroalloys for any other industrial waste containing mainly manganese. The intention is to achieve integrated management of wastes that are produced worldwide in significant quantities through the use of their manganese content, which is the main raw material in the actual production process in which they are generated.

BACKGROUND OF THE INVENTION

Manganese is a metal that is not found in nature in a free state, but is preferably combined into minerals in the composition in which it is located, as an oxide (mainly pyrolusite) or carbonate (mainly rhodochrosite). Production processes that traditionally require manganese additives are carried out using these minerals in the iron and steel industry in furnaces with a reducing atmosphere, in order to use manganese as an alloy element or as a deoxidizing agent, or as a desulfurizing additive in steel production. However, at the end of the 19th century, various methods for obtaining pure manganese from manganese minerals began to be studied in order to improve the alloys it is composed of and to expand its scope, and several processes have been developed: aqueous electrolysis of manganese salts, electrothermal, carbothermal , aluminothermic and silicothermic processes.

Among the premises worthy of mention are US patents 2511507 "Processing solutions for electrolytic deposition of manganese"; 2483287 "Method for the purification of manganese electrolytes"; 2347451 "Electrolytic deposition of manganese"; 2343293 "Method for the purification of solutions of manganese sulfate"; and UK patent 528112 "Improvements in the electrolytic production of manganese."

Of all these processes, the one that makes it possible to obtain manganese of the highest purity has very affordable production costs, and therefore is the most used process, is the first process, that is, the production of manganese through the aqueous electrolysis of salts of this metal or the production of electrolytic manganese. This product is currently sold with a purity between 99.5 and 99.9% metal.

The electrolytic route for producing manganese metal was first investigated by Davis in 1930. However, this process did not become important until 1939, when the need for steel producers in electrolytic manganese (for the manufacture of weapons) forced the U.S. Mining Bureau to install a pilot plant in Knoxville (Tennessee). This installation was modernized in 1940, and in 1944 it reached a capacity of 1,500 t / year. In Japan, electrolytic manganese production began in 1941. The U.S. Mining Bureau built a second pilot plant in 1942 in Boulder City. From my side. Electrolytic Manganese Corporation in Krugersdorp, South Africa, began production in 1955. Currently, most of the electrolytic manganese consumed worldwide is produced in China and South Africa.

The method for producing electrolytic manganese, which was developed at the laboratory level, is delayed due to the need to eliminate the biggest environmental disadvantage that is obtained in the manufacture of ferroalloys for any other industrial waste having mainly manganese, which is the production of waste generated in the result of the exhaust gas treatment of industrial furnaces. The most effective way to treat these secretions is to wet clean the gas, so that the particles contained in it are retained by water. Subsequent treatment of this water leads to waste having a high manganese content, which is difficult to use as a recoverable material, due to their physical nature.

The described drawback forced the interested company to entrust the Department of Metallurgy of the University of Oviedo (Spain) four years ago with the task of testing the viability of extracting the manganese content from these wastes through a hydrometallurgical route for its subsequent electrolytic reduction, and thus to obtain a product of high value. The study clearly showed that through certain innovations in the previously mentioned methods, this problem can be solved.

Process description

The starting material used in the method for producing electrolytic manganese, as an object of the invention, is the waste obtained by cleaning the exhaust gases of furnaces for the production of ferroalloys, which mainly consist of:

% % MnO 5-50 S 0-10 SiO ₂ 5-40 K ₂ O 0-8 Cao 2-14 Na ₂ O 0-5 Al ₂ O ₃ 1-12 C 2-15 MgO 1-11 FeO 0-5

This method consists of the following phases:

Sulphation

Leaching

Cleaning

Electrolysis

1) SULFATION

The initial industrial waste is subjected to etching in acid before drying, on the one hand, a by-product is made up of non-etched materials, and, on the other hand, metal sulfates containing ions of various metals that can be leached and which are present in the waste, mainly way manganese.

2) leaching

Leaching and filtering of this solid leads to the formation of a solution that removes sulfates and other soluble substances produced during processing in the furnace, and to the production of solid wastes that become inert by washing them. The exhaust gases from this furnace are alkaline cleaned.

3) CLEANING

The purification step is absolutely necessary so that the solution is suitable for electrolysis. Small amounts of undesirable metals in the solution lead to contamination of the electrolytic coating, or even prevent electrolytic deposition reactions.

There are two types of impurities that must be removed from the solution in accordance with the method by which they must be handled.

The first group consists of those that can be separated simply by adjusting the pH. Acceptance of the conditions for the pH of the solution leads to the deposition of unwanted ions, in accordance with the diagrams Pourbaix (potential - pH), keeping manganese in solution. In this way, precipitation of virtually all of the iron and aluminum, as well as other less problematic contaminants such as cobalt or nickel, is achieved. To increase the pH of the solution, lime is added while the pulp is mixed. The resulting precipitate is separated by filtration.

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

The second group of contaminants is the base metals, which cannot be completely removed by adjusting the pH, since the value that is necessary to achieve their deposition reaches the pH of the deposition of manganese.

The metals identified with this second group are headed by zinc, and they are more inert than manganese. Their removal is achieved by their precipitation in the form of sulfide at a slightly acidic pH. This precipitation requires a residence time sufficient for the manganese sulfide that has been formed to re-dissolve, but not excessive to prevent the re-dissolution of the impurities that have precipitated.

The already purified solution is conditioned by adding a base until an almost neutral pH value is reached in order to allow its introduction into the electrolyzer. Finally, part of this solution is passed through a crystallizer to remove part of its calcium and magnesium content, like ammonium salts.

4) ELECTROLYSIS

Before introducing the solution into the electrolytic cells with the cathode of special tanks for electrolysis, the conditioning of the solution with the following additives is completed.

Ammonium sulfate: added as a manganese stabilizer and a buffering agent.

Hydroxylamine Sulfate: Antioxidant.

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

As for the flow of solutions in a separate electrolyzer, the catholyte, when passing through the diaphragm, feeds the electrolyzer with the anode, so the anolyte has a composition similar to catholyte, although with a lower pH and noticeably depleted in manganese. The used electrolyte is therefore suitable for recycling to the beginning of the process. The cells must be maintained at a certain temperature, and the composition of the electrolytes must be maintained homogeneous.

Over time, the metal deposits on the surface of the cathode in the form of flakes. The metal load is separated by mechanical means.

While electrolytic manganese flakes are deposited on the cathode, manganese dioxide accumulates on the anode. When the process ends, this product also requires rinsing with water and is subsequently separated by mechanical means.

Primary cleaning

It is carried out in the leaching reactor itself and is achieved by increasing the pH of the solution. In order to separate the waste contained in the resulting pulp, which contains uncoated material, as well as precipitated impurities in the form of hydroxides (mainly Fe and Al), it is filtered by a filter press. The waste separated here requires washing with water in order to regenerate the part of the manganese that has been carried away, and to improve its chemical and physical properties before its subsequent precipitation.

Wash water from these filter cake can be used as additional water in the mixer.

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

TESTS FOR OBTAINING Manganese Sulfate Solution

EXAMPLE

1 kg of material with a moisture content of 40% and a Mn content of 15% was used as the starting material.

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

The mixture was then poured onto a tray that was introduced into an oven maintained at 300 ° C. for 30 minutes.

Leaching was performed with prepared synthetic anolyte. In this process, the residence time for the extraction of Mn was 1 hour, during which the pulp was maintained with vigorous stirring. After this time, 70 g of lime was added to the same leach reactor, and it was left under stirring for half an hour, at which time the pH increased from 3.7 to 6.5 at that time. In order to separate the wastes contained in the resulting pulp, which contains both the etched material and the precipitated impurities in the form of hydroxides (mainly Fe and Al), it was subjected to vacuum filtration.

The waste separated here was washed with water to recover some of the manganese that had been entrained and to improve its chemical and physical properties before its subsequent precipitation. In accordance with the study, these wastes are of an inert type in accordance with the applicable standards.

To remove from the solution separated by filtration, its content, which can be either organic material or traces of contaminants, was passed through an activated carbon filter.

The second cleaning phase included the addition of 11.1 cm ^{3 of} sulfide and 0.65 g of zinc sulfide primer. The resulting precipitate was separated by filtration. 1.25 L of the solution was thus obtained with the following chemical analysis.

Mn (g / l) 45 Zn (ppm) fifteen Ca (ppm) 250 Mg (g / l) 3,5 Fe (ppm) <1

APPLICATIONS OF ELECTROLYTIC Manganese

Electrolytic manganese is mainly used in the aluminum industry, it provides strength and ductility (structural applications, durable thin sheets, aeronautics, canning ...), and it can be supplied: as a main alloy, as an input powder or in mixed-powder briquettes (or mechanical preliminary alloy). Other applications of electrolytic manganese are: in the steel industry, as a desulfurizing additive and high-quality alloying additive for high-quality stainless steels and HSLA steels; in the industry of copper and nickel alloys; electrolytic manganese flakes as a catalyst for a chemical reaction; manganite production for the manufacture of thermoregulating variable resistors; manufacture of manganese-zinc ferrites for medium power applications and as a pigment; production of welding electrodes.

PROCESS DIAGRAMS

Description of diagrams of a preferred embodiment of the invention.

Figure 1 shows a flow diagram of a process that starts with a sulfation phase (1), followed by a hydrometallurgical phase consisting of four stages: leaching (2), primary treatment (3), secondary treatment (4) and conditioning (6 ) to finally reach the electrolysis phase (6) to obtain electrolytic manganese.

Figure 2 schematically shows a diagram corresponding to the sulfation phase (1), including processing in the furnace (8) of the material supplied by the mixer (9), and the produced gases being forcedly extracted from the specified furnace (8) through the chimney (10) and neutralized in the scrubber (11) with a suitable reagent.

Figure 3 schematically shows the stages of leaching (2) and primary treatment (3), in which the product resulting from the phase (1) sulfation is processed in a tank (12) with a coating that regulates acidity, and the resulting pulp passes through a filter a press (13), where the washing of the filter cake can be additionally countercurrent. This washing is carried out with water supplied from the tank (14), which can subsequently be used both in the initial mixture of the process and in the leaching phase. Inert waste is collected in a pan (15) at the bottom of the filter press.

4 corresponds to a secondary purification step (4), in which the primary solution from the previous step is filtered in an activated carbon filter (16) before it is taken into the secondary purification tank (17), where the remaining impurities precipitate in the form of sulfides, which are separated by another filtering process (18), whereby in the end a purified solution (19) and production waste (20) - ZnS are obtained.

Figure 5 schematically shows the conditioning step (5) in which the purified solution is subjected to an increase in pH in the tank (21) by the introduction of ammonium sulfates and hydroxylamine to subsequently process it in a crystallizer (22), in which favorable conditions are created for the precipitation of ammonium salts ( 24) Ca and Mg from the solution and which is provided with an outlet (23) to remove the liquor from which these salts are isolated.

6 schematically shows the phase (6) of the electrolysis of the solution, which is processed in an electrolyzer (26) equipped with catholyte heated by the action of the heat exchanger available in the supply tank (25). The electrolyzer is an electrolyzer with a diaphragm made of polyester, and two anodes and one cathode are immersed inside, the latter being inside its own compartment. There is an immersion tank (28) to flush the cathode after deposition of electrolytic Mn on its surface. On the other hand, the anode sludge in the cell accumulates and is removed from the double bottom of the cell, and passes for processing into the tank (27) for flocculation of the sludge.

Claims (5)

1. A method of producing electrolytic manganese from waste products of ferroalloys containing mainly manganese, comprising a hydrometallurgical phase consisting of leaching stages, primary and secondary purifications and conditioning, as well as an electrolysis phase, the primary purification stage being carried out in the same reactor as the stage leaching, until the pH rises to values close to neutral, characterized in that the waste is used as a slurry for washing exhaust gases from ferromarg furnaces Nanosecond and silicomanganese, before the hydrometallurgical phase, a thermal sulfation phase is carried out, which includes treating in a furnace material supplied from a mixer, in which these wastes are treated with acid with a flow close to the stoichiometric, impurities such as mainly iron and aluminum, and in the secondary purification step, the zinc impurity is removed by precipitation of ZnS to obtain an electrolysis solution. 2. The method of producing electrolytic manganese according to claim 1, characterized in that when the thermal sulfation phase is carried out inside the furnace, Teflon trays are used and SO _{2 is} produced as a result of exothermic reactions. 3. The method of producing electrolytic manganese according to claim 1, characterized in that the leaching is carried out with an anolyte of the electrolyzer or, alternatively, a synthetic anolyte, with vigorous stirring in an acid-coated reactor. 4. The method of producing electrolytic manganese according to claim 1, characterized in that the pulp obtained as a result of the primary cleaning is filtered in a filter press and rinsed with water, preferably in the filter press itself, receiving inert waste. 5. The method of producing electrolytic manganese according to claim 4, characterized in that the pulp washing water is added to the mixer used in the initial phase of the process, or reused several times in a row to concentrate manganese in it.

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