RU2604080C2 - Method of nickel-cadmium-iron alkaline storage batteries negative electrodes electrode mass processing - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to hydrometallurgy and can be used during making of non-waste technologies of hazardous substances disposal and environmental protection. In disclosed method of alkaline storage batteries negative electrodes electrode mass processing, containing nickel, cadmium and iron oxides, their leaching is performed by treating with acid solution at high temperature and stirring, separation of solution from cake, precipitation of obtained cadmium hydroxide solution, its separation, obtained precipitate washing and drying. At that, leaching is performed with sulphamic acid solution with concentration of not more than 1.95 mol/l at temperature of 25-95°C for 0.5-2 hours and S:L ratio equal to 1:10, and dried cadmium hydroxide precipitate is annealed at temperature of 540-610 °C.

EFFECT: providing comprehensive and low-waste disposal of toxic wastes, complete and selective extraction of cadmium.

6 cl, 12 ex

Description

The invention relates to hydrometallurgy, disposal of hazardous waste, environmental protection, and in particular to methods of processing the electrode mass of the negative electrodes of alkaline batteries containing nickel, cadmium and iron oxides, followed by the preparation of cadmium compounds.

In connection with the observed increase in the volume of decommissioned spent nickel-cadmium-iron alkaline batteries that have a negative impact on the environment in temporary storage, the problem of processing the negative electrode mass of these batteries containing toxic components such as cadmium and nickel is very urgent. These metals not only have a negative impact on human health, but also pollute the environment, including groundwater, for many years they are stored in the soil and not washed out of it. Recycling such waste will help preserve the environment and supply valuable raw materials for batteries, providing essentially waste-free technology.

A known method of processing negative electrodes of alkaline batteries, based on the hydrometallurgical separation of cadmium and iron oxides [RF Patent No. 2372411], in which cadmium is leached with a solution of sodium ethylene diamine tetraacetate at pH 9.0-9.5, followed by the removal of ethylene diamine tetraacetate from the solution by molecular precipitation sulfuric acid at a pH of 1.0-1.6, after which the cadmium is precipitated in the form of hydroxide by adding alkali to a solution of pH more than 9.8.

The main disadvantages of this method are the poor filterability of the precipitate of ethylenediaminetetraacetic acid when it is isolated from a cadmium-containing solution, the increased consumption of an expensive reagent - sodium hydroxide, due to the need to transfer strongly acidic solutions to a strongly alkaline region, and the incompleteness of cadmium release.

According to the method of [RF Patent No. 2164956], scrap of spent nickel-cadmium batteries is heated and oxidized with atmospheric oxygen at a temperature of 690-900 ° C, cooled and subjected to magnetic separation, then leached: from the magnetic fraction with concentrated solutions of mineral acids - nickel, and from non-magnetic - concentrated solutions of ammonia salts - cadmium. The disadvantage of this method is the low degree of extraction of cadmium due to non-selective leaching, the use of highly concentrated solutions of mineral acids, in the presence of iron impurities, the technological scheme is complicated by the introduction of operations for cleaning from iron.

The closest technical solution is the method [RF Patent No. 2344520]. Extracted from the negative electrodes of used alkaline batteries, the active mass is directed to the leaching of metals by sulfuric acid 20-22 mass. % with mechanical stirring at a ratio of T: L = 1: 6 and a temperature of 85-95 ° C, cadmium and iron are transferred into the solution, then they are precipitated with sodium hydroxide and ferrous iron is converted to ferric iron by atmospheric oxygen. Next, the conversion of iron hydroxides to oxides is carried out by changing the temperature of the process, the conversion of cadmium hydroxide to the base salt; sulfuric acid leaching; separation from iron by filtration.

The main disadvantages of the prototype are the complexity and multi-stage technology due to the lack of selective action of sulfuric acid and the transition to a solution of significant amounts of iron, the separation of which from sulfate solutions is problematic, the need to repeat the deposition and filtering of hard-to-filter precipitates of iron hydroxides, high risk when working with sulfuric acid solutions, great amount of effluents that worsen the environment.

The technical result of the invention is:

- comprehensive and low-waste disposal of toxic man-made materials;

- obtaining the final product of processing - cadmium oxide, suitable for various purposes and, including, to return to the production of the electrode mass of alkaline batteries;

- ensuring the complete separation of cadmium from iron at the beginning of the process;

- selectivity and a high degree of extraction of cadmium from the source material;

- simplification of the process by reducing the number of stages;

- improving working conditions and improving production safety by eliminating sulfuric acid.

The technical result is achieved by the fact that in the method of processing the electrode mass of the negative electrodes of alkaline batteries, including their leaching with an acid solution at elevated temperature and stirring, precipitation of cadmium hydroxide, its separation, washing and drying of the precipitate obtained, according to the invention, leaching is carried out with a sulfamic acid solution with a concentration not more than 1.95 mol / l at a temperature of 25-95 ° C for 0.5-2 hours and a T: W ratio of 1:10, the dried precipitate of cadmium hydroxide is calcined at a temperature round 540-610 ° C, and part of the filtrate, containing sulfamic acid, is recycled to the leaching.

The precipitate of cadmium hydroxide, it is advisable to dry at a temperature of 100-150 ° C.

For leaching of electrode mass with high - not less than 73 mass. %, cadmium content, it is advisable to use sulfamic acid with a concentration of 0.65-1.95 mol / L. Before leaching the electrode mass with a low, not more than 10 mass. %, its cadmium content is fired at a temperature of 600 ± 10 ° C, and sulfamic acid with a concentration of not more than 0.12 mol / L is used for leaching. This allows you to selectively extract cadmium from waste with any content, even with a very small amount, which is a very difficult technological task. To reduce the duration of the process and reduce energy consumption, leaching is carried out at a temperature of 90-95 ° C in two stages lasting 30 minutes each with an intermediate decantation to T: W 1: 3 and adding a fresh portion of sulfamic acid solution. In order to retain nickel in the solution and reduce its content in the final product, the solution was treated with complexing agent Trilon B (EDTA) before precipitation of cadmium hydroxide.

The concentration of sulfamic acid is calculated by stoichiometry to the content of cadmium oxide in the waste material, which provides selective transfer of cadmium into the solution. When leaching, up to 96.5% cadmium and, in part, nickel passes into the solution, and all the iron remains in the cake. The solution containing cadmium and nickel is separated from the cake by decantation and filtration. Subsequent precipitation of cadmium compounds is carried out by known methods, for example, precipitated with a solution containing sodium hydroxide or a mixture of hydroxide and sodium carbonate.

The proposed method is based on the well-known property of cadmium to form water-soluble salts - sulfamates. Thus, US Pat. No. 3,331,273 describes the preparation of metal sulfamates, including nickel, cadmium and iron, by reacting fine powders of these metals with sulfamic acid in an aqueous medium by heating, stirring and blowing with air. The degree of acid consumption is controlled by the pH value. At the same time, a high degree of conversion is achieved - at least 97%.

However, the authors of this patent did not have the task of isolating individual metal sulfamates from a multicomponent mixture containing the corresponding oxides. In addition, the description indicates the inappropriateness of applying temperatures above 65 ° C due to the hydrolysis of sulfamic acid.

The material to be recycled in this application is the knocking out of alkaline batteries from the battery lamellas (negative electrode plates). In appearance, it is a powder with a wide distribution of particle sizes: from 1.0 μm to 1.5 mm, but larger clumps are also found - up to 3 cm.

The electrode mass is made by repeatedly repeating the operation of mixing several components, the main of which are cadmium oxide and iron oxide (III). Nickel hydroxide, manganese oxide, graphite powder, a homogenizer and a plasticizer are also added to the mixture. During operation, the electrode mass is exposed to alkaline electrolyte and multidirectional electric current (discharge-charge cycle). In this case, electrochemical reactions occur in the electrode mass, which are not completely reversible due to harsh conditions of discharge and charge, as well as other reasons. The consequence of this is irreversible changes in the composition and structure of the electrode mass, causing a decrease in the operational characteristics of the battery and the need for its subsequent replacement. However, the changes occurring in the electrode mass are still very superficially studied.

Thus, the components of the electrode mass undergo changes both during its manufacture and during operation. Therefore, such a material of complex composition will not exhibit the same chemical properties as the original individual metal oxides.

Compared to the original electrode mass, the material is poor in cadmium content and rich in iron, since it was subjected to preliminary heat treatment in the presence of a reducing agent — carbon. However, information on the chemical properties of such a material is not available in the literature.

Thus, one skilled in the art cannot expect that all components of the electrode mass will react with sulfamic acid in the same way as the corresponding metals in US Pat. No. 3,331,273.

In USSR author's certificate 730850 it is proposed to use solutions of sulfamic acid with a concentration of 80 to 200 g / l at a temperature of 18 ° C for the selective extraction of zinc from dusts. Zinc from the resulting sulfamate solutions is precipitated with hydrogen sulfide to produce zinc sulfide and the regeneration of sulfamic acid in solution. However, the information disclosed in this document cannot be used for the selective extraction of cadmium, which, being an element of the same group of the Periodic System as zinc, also forms water-soluble sulfamate, and when the corresponding multicomponent mixture is leached, it goes into solution together with zinc .

The authors of the present invention have found such process parameters (temperature range, sulfamic acid concentrations, process duration, T: G ratio) that ensure the achievement of the above technical result.

Studies have shown that the degree of hydrolysis of sulfamic acid and its depth depends not only on temperature, but also on its concentration, as well as on the duration of the process. In the method according to the invention, almost all the acid is consumed in the first 30 minutes and its concentration drops to tenths of a percent, which allows the process to be carried out at sufficiently high temperatures - up to 95 ° C. The ratio of T: W will provide acceptable hydrodynamic leaching conditions.

The invention is illustrated by the following examples.

Example 1. The electrode mass of the negative electrodes of Nickel-cadmium-iron alkaline batteries, containing, mass. %: Cd - 73, Ni - 2.5, Fe - 0.3, Mn - 0.9, C - 3.1, oxygen - 12.1, moisture - 8.1, the phase composition of which is represented by cadmium and nickel oxides , manganese and iron (III), were leached with a solution of sulfamic acid with a concentration of 0.65 M at a ratio of T: W = 1: 10 for 2 hours at a temperature of 90 ° C, while cadmium passes into the solution (extraction 49.3%) and nickel (2.9% recovery), cadmium hydroxide was precipitated from the solution with concentrated sodium hydroxide solution, the precipitate was washed, dried, calcined at a temperature of 540 ° C, and cadmium oxide was obtained.

Example 2. The electrode mass of the negative electrodes of nickel-cadmium-iron alkaline batteries of the same composition as in example 1, was leached with a solution of sulfamic acid with a concentration of 1.3 M at a ratio of T: W = 1: 10 for 2 hours at a temperature of 90 ° C cadmium (96.5% recovery) and nickel (21% recovery) are transferred to the solution, cadmium hydroxide was precipitated from the solution with concentrated sodium hydroxide solution, the precipitate was washed, dried, calcined at a temperature of 540 ° C, and cadmium oxide was obtained.

Example 3. The electrode mass of the negative electrodes of nickel-cadmium-iron alkaline batteries of the same composition as in example 1, was leached with a solution of sulfamic acid with a concentration of 1.95 M at a ratio of T: W = 1: 10 for 2 hours at a temperature of 90 ° C cadmium (96.5% recovery) and nickel (96.5% recovery) are transferred to the solution, cadmium hydroxide was precipitated from the solution with concentrated sodium hydroxide solution, the precipitate was washed, dried, calcined at 540 ° C, and cadmium oxide was obtained with an admixture of nickel oxide.

The above examples show that the optimal concentration of sulfamic acid in the treatment of waste with a high concentration of cadmium is 1.3 M, which corresponds to the equivalent cadmium content in the starting material. At an acid concentration below 0.65 M, cadmium leaching is slow and not complete, but at a concentration exceeding 1.9 M, nickel passes into the solution, i.e. cadmium selectivity decreases.

Example 4. The electrode mass of the negative electrodes of nickel-cadmium-iron alkaline batteries of the same composition as in example 1, was leached with a solution of sulfamic acid with a concentration of 1.3 M at a ratio of T: W = 1: 10 for 0.5 hours at a temperature of 90 ° C, cadmium (extraction 93.2%) and nickel (extraction 26.7%) are transferred to the solution, cadmium hydroxide was precipitated from the solution with concentrated sodium hydroxide solution, the precipitate was washed, dried, calcined at a temperature of 540 ° C, and oxide was obtained cadmium.

Example 5. The electrode mass of the negative electrodes of nickel-cadmium-iron alkaline batteries of the same composition as in example 1, was leached with a solution of sulfamic acid with a concentration of 1.3 M at a ratio of T: W = 1: 10 for 1.0 hour at a temperature of 90 ° C, cadmium (recovery 96.0%) and nickel (recovery 45.7%) are transferred to the solution, cadmium hydroxide was precipitated from the solution with concentrated sodium hydroxide solution, the precipitate was washed, dried, calcined at a temperature of 540 ° C, and oxide was obtained cadmium.

Example 6. The electrode mass of the negative electrodes of nickel-cadmium-iron alkaline batteries of the same composition as in example 1, was leached with a solution of sulfamic acid with a concentration of 1.3 M at a ratio of T: W = 1: 10 for 6.0 hours at a temperature of 90 ° C, cadmium (extraction 96.5%) and nickel (extraction 30.0%) pass into the solution, cadmium hydroxide is precipitated from the solution with concentrated sodium hydroxide solution, the precipitate is washed, dried, calcined at 540 ° C, and oxide is obtained cadmium.

The results presented in examples 4 to 6 show that the duration of the process, which is necessary to achieve the highest degree of cadmium leaching, lies in the range from 0.5 to 2.0 hours. For less than 0.5 hours, the leaching reaction is insufficient. More than 2 hours to continue the process is impractical, because the degree of extraction at the selected temperature reaches its maximum value.

Example 7. The electrode mass of the negative electrodes of nickel-cadmium-iron alkaline batteries of the same composition as in example 1, was leached with a solution of sulfamic acid with a concentration of 1.3 M at a ratio of T: W = 1: 10 for 2.0 hours at a temperature of 25 ° C, cadmium (extraction 92.6%) and nickel (extraction 24.3%) pass into the solution, cadmium hydroxide was precipitated from the solution with concentrated sodium hydroxide solution, the precipitate was washed, dried, calcined at a temperature of 540 ° C, and oxide was obtained cadmium.

Example 8. The electrode mass of the negative electrodes of nickel-cadmium-iron alkaline batteries of the same composition as in example 1, was leached with a solution of sulfamic acid with a concentration of 1.3 M at a ratio of T: W = 1: 10 for 2.0 hours at a temperature of 50 ° C, while cadmium (recovery 96.5%) and nickel (recovery 37.6%) pass into the solution, cadmium hydroxide was precipitated from the solution with concentrated sodium hydroxide solution, the precipitate was washed, dried, calcined at 540 ° C, and oxide was obtained cadmium.

The results presented in examples 5, 7 and 8 show that a sufficiently high extraction of cadmium and a relatively low extraction of nickel in solution is already achieved at 25 ° C. However, to increase the intensity of leaching and subsequent precipitation of the cadmium compound, the reaction mass is heated to 90 ± 5 ° C. Above this temperature, the solution may boil, which is undesirable due to intense foaming and vaporization.

Examples 9 and 10 illustrate the processing of "poor" samples of electrode mass.

Example 9. The electrode mass of the negative electrodes of Nickel-cadmium-iron alkaline batteries, containing, mass. %: Cd - 6.6, Ni - 6.6, Fe - 30%, Mn - 7.0, C - 2.0, oxygen - 40.5, moisture - 7.3, the phase composition of which is represented by cadmium oxides, nickel, manganese and iron (III) were leached with a solution of sulfamic acid with a concentration of 0.12 M at a ratio of T: W = 1: 10 for 2 hours at a temperature of 90 ° C, while cadmium 64.3% and nickel 0 passed into the solution , 5%, cadmium hydroxide was precipitated from the solution with a concentrated sodium hydroxide solution, the precipitate was washed, dried, calcined at a temperature of 540 ° C, and cadmium oxide was obtained.

Example 10. The electrode mass of the negative electrodes of nickel-cadmium-iron alkaline batteries of the same composition as in example 9, was preliminarily fired at 600 ° C for 2 hours, and then leached with a solution of sulfamic acid with a concentration of 0.12 M at a ratio of T: W = 1: 10 for 2 hours at a temperature of 90 ° C, with cadmium 86.8% and nickel 5.0% passing into the solution, cadmium hydroxide was precipitated from the solution with a concentrated sodium hydroxide solution, the precipitate was washed, dried, calcined at a temperature 540 ° C, received oxide ka Miya.

Example 11. The electrode mass of the negative electrodes of nickel-cadmium-iron alkaline batteries of the same composition as in example 1, was leached with a solution of sulfamic acid with a concentration of 1.3 M at a ratio of T: W = 1: 10 for 30 minutes at a temperature of 90-95 ° C, the solution was decanted to a ratio of T: W = 1: 3 and a new portion of a solution of sulfamic acid with a concentration of 1.3 M was added to the remaining reaction mass at a ratio of T: W = 7.5 and a second leaching stage was carried out for 30 minutes and temperature 90-95 ° C. The total recovery of cadmium is 96.50% and nickel 97.0%. The reaction mass was filtered, the filtrate was combined with the decantate of the first stage, and cadmium hydroxide was precipitated from the resulting solution with concentrated sodium hydroxide solution, the precipitate was washed, dried, calcined at a temperature of 540 ° C, and cadmium oxide was obtained.

Example 12. The same as example 11, but in order to reduce the consumption of precipitant and increase the yield of cadmium in the precipitate, a concentrated solution of a mixture of sodium hydroxide and sodium carbonate in a ratio of 1: 4.5 was used as a precipitant. At this ratio, sodium carbonate is in stoichiometric amount to precipitate cadmium carbonate. The precipitation of cadmium in this case does not exceed 78%. To increase the cadmium yield in the precipitate, an excess of sodium carbonate in the precipitating solution equal to 20, 40, and 60% of stoichiometry was used, as well as a different order of mixing the working solution with the precipitating solution — direct and reverse.

The precipitation of cadmium in the direct precipitation: with a 20% excess of sodium carbonate - 91.39%;

with a 40% excess - 94.81%;

with a 60% excess - 96.1%;

The precipitation of cadmium during reverse deposition: with a 20% excess of sodium carbonate - 94.91%.

In order to reduce the nickel content in the final product, the composition of the solution was adjusted before cadmium deposition, which consists in adding to the solution the complexing agent Trilon B (EDTA) in an amount calculated from the nickel content in the solution. In this case, nickel selectively binds to the complex compound and remains in solution during the deposition of cadmium. The nickel / cadmium ratio in the final product was reduced by about 6 times to a value of 0.01.

Thus, from the examples and the results presented therein, it follows that the proposed method allows us to implement a method for processing the electrode mass of the negative electrodes of nickel-cadmium-iron alkaline batteries and to obtain the specified technical result.

The compliance of the product obtained by the claimed method with the requirements for cadmium oxide for the manufacture of an active mass of alkaline batteries is confirmed by the Act and Protocol No. 38 of 09/27/2013 of comparative tests conducted at JSC "Plant" AIT "in Saratov.

Claims (6)

1. A method of processing the electrode mass of the negative electrodes of alkaline batteries containing nickel, cadmium and iron oxides, including their leaching by treatment with an acid solution at elevated temperature and stirring, separation of the solution from cake, precipitation of cadmium hydroxide from the resulting solution, its separation, washing and drying the precipitate obtained, characterized in that the leaching is carried out with a solution of sulfamic acid with a concentration of not more than 1.95 mol / l at a temperature of 25-95 ° C for 0.5-2 hours and a ratio of T: W, equal ohm 1:10, while the dried precipitate of cadmium hydroxide is calcined at a temperature of 540-610 ° C. 2. The method according to p. 1, characterized in that the precipitate of cadmium hydroxide is dried at a temperature of 100 ± 5 ° C. 3. The method according to p. 1, characterized in that for leaching the electrode mass with at least 73 wt.% Cadmium content, sulfamic acid with a concentration of 0.65-1.95 mol / L is used. 4. The method according to p. 1, characterized in that before leaching the electrode mass with not more than 10 wt.% Cadmium content, it is fired at a temperature of 600 ± 10 ° C, and for leaching using sulfamic acid with a concentration of not more than 0.12 mol / l 5. The method according to p. 1, characterized in that the leaching is carried out at a temperature of 90-95 ° C in two stages lasting 30 minutes each with an intermediate decantation to T: W 1: 3 and a fresh portion of sulfamic acid solution is added. 6. The method according to p. 1, characterized in that before the precipitation of cadmium hydroxide, the solution is treated with a complexing agent in the form of Trilon B.