DE2913893A1 - Sepn. of cadmium and nickel - by fractional cementation in soln. contg. sodium chloride, and using double treatment with aluminium shot - Google Patents

Abstract

An aq. soln. is made contg. min 50 g/l Cd, and also Ni, both metals being present as sulphates. At least 40 g/l NaCl is added to the soln., and its pH adjusted to 2.4-2.5 at 25-30 degrees C; Al shot is then added to ppte. Cd which is filtered off. The filtrate (I) contains the Ni; and more NaCl is added to obtain >=120 g/l NaCl. The pH is again adjusted to 2.4-2.5 and the soln. heated to >=55 degrees C., followed by adding Al shot to ppte. the Ni. When the initial soln. contains 40-100 g/l Cd, the same amt., viz. 40-100 g/l of NaCl is pref. used; and the Cd ppte. is pref. treated with fresh soln. contg. Cd- and Ni- sulphates.

Description

Process for the separation of cadmium and nickel

by fractional cementation. The present invention relates to a wet chemical process for the separation of cadmium and nickel, which is different from other processes due to their particular economy and a wide range of applications differs.

According to the state of the art, it is the one most frequently used in practice Method for cadmium-nickel separation the electrolytic separation of the two metals. Under suitable conditions, the cadmium can be cathodically deposited from acidic baths while the nickel remains in solution.

This process is designed to be a continuous, high throughput operation which allows amortization of the high investment costs required. However, this condition is often not the case, as is the case with cadmium extraction, for example from lyes from discontinuously occurring secondary raw materials (e.g. Ni-Cd cells). Furthermore, the separation by electrolysis is not complete; part of the cadmium remains in solution. After all, this is the maximum possible nickel concentration in this Case due to the requirement of a low nickel content (a few g / l Ni) in the deposited Cadmium metal limited.

Another possibility for separating cadmium and nickel in the form of aqueous solution of their salts consists in the precipitation of cadmium sulfide with hydrogen sulfide in the acidic range. Here, however, the cadmium occurs in the form of a product, which does not work well, i.e.

can be brought into solution. This method is also technically complex and, due to two process steps, burdened with high costs. Some of the known processes can be used less as separation methods than as cleaning processes be addressed. So it is possible to get small amounts of nickel from cadmium salt solutions separated by precipitation with sodium cyanide. A cadmium sulfate solution with 200 g / l However, Cd must not contain more than about a g / l Ni. At higher nickel contents this process can no longer be used, as there are significant amounts with the nickel Cadmium can be precipitated as cyanide.

The use of specific reagents for nickel precipitation, e.g. Diacetyldioxime, is only of interest for the laboratory or for the separation entirely lower tightness of nickel on an operational scale. It has also been tried to be different To exploit the stability of the hexamine complexes of cadmium and nickel for a separation (DP 2 001 985 and DE-OS 2.601.766) Here there are two facts that are considered negative are to be assessed. The resulting cadmium carbonate contains cadmium per 100 parts still 2 - 6 parts of nickel and from the nickel solution must be to a precipitate To obtain the ammonia to be driven off in gaseous form. Regarding the latter finding the same applies as for electrolytic separation. The procedure is to one tied to continuous high throughput operation that has an amortization of the required high investment costs allowed.

The object of the present invention is to avoid all Disadvantages of the known processes wet chemical separation of in the form of mixtures of the aqueous solutions-their sulfates-present elements cadmium and nickel, in particular in the presence of concentrations of these metals, such as those in common sulfur Acid leaching process of cadmium-nickel secondary raw materials (e.g. used nickel-cadmium cells or nickel-cadmium sintered plate waste). These usual Concentrations are between 10 and 80 g nickel and 120 - 150 g cadmium per liter of solution.

These conditions were made possible by a process of fractional cementation to be met. After the tension series of the elements come practically to cementation of cadmium and nickel only the elements zinc or aluminum are considered: Red. Oxide. E (volts) Al Al +++ + 3 e - 1.67 Zn Zn ++ + 2 e - 0.76 Cd Cd ++ + 2 e - 0.40 Ni Ni + 2 e - 0.25 In fact, cadmium and nickel can be added from acidic sulfur solutions metallic aluminum or zinc can be deposited as cement. But always will Cadmium and nickel deposited together, just as it was after the position of the Elements in the above voltage series can be expected.

It has now been found, surprisingly, that if certain process conditions are observed, fractional cementation of cadmium and nickel from sulfate solutions is still possible. The application therefore relates to a process for separating the elements cadmium and nickel, which are present in the form of mixtures of the aqueous solutions of their sulfates, by cementing the cadmium present in a concentration of at least 50 9 Cd per liter of solution and subsequently depositing the nickel. The process is characterized in that the cadmium is first separated from these solutions by adding aluminum powder to the cadmium-nickel solution, the cadmium being separated as cement, with the proviso that before the cementation begins, an amount of at least 40 9 sodium chloride per liter of solution of the sulphates is added so that the pH the solution is adjusted to 2.4-2.5 and that the temperature of the solution is also kept during the cementation in the range between 25 and 300 C, is then separated from the cadmium cement, and then the nickel in the filtrate by adding aluminum powder as cement, with the proviso that before the start of cementation so much common salt is added that the total concentration is at least 120 g NaCl per liter of solution, that the pH of the solution is regulated to 2.4-2.5 and that a A temperature of at least 550 C is set and this temperature is maintained during the cementation and the nickel cement is separated after the cementation has ended.

It is best to measure the addition of Al / 100 9 Cd (Y) as a function of the Cd concentration (x) in the Cd-Ni solution according to 1 Y = a + bx, where a = 88.463.10-4 and b = 2.352.10-4.

At cadmium concentrations within the limits of 40 9 - 100 g cadmium per liter of solution, the saline concentration is best equal to the present one Cadmium concentration selected.

The resulting cadmium cement can according to the invention Procedure can be treated again with fresh cadmium nickel solution.

It has also proven to be advantageous that the Nickel cementation present total concentration of table salt 120 - 150 9 NaCl per Liters of solution.

Finally, the resulting nickel cement can be used again as required of the Easis process described with fresh, flowing from the cadmium cementation Nickel solution can be modified.

The process according to the invention is carried out as follows before: Sufficient common salt is dissolved in the cadmium nickel sulphate solution that the weight ratio Cd: NaCl is 1: 1, i.e. the same concentrations of Cd and NaCl are present.

This regulation is limited in that it is also undercut a concentration of 40 g cadmium per solution nevertheless an amount of common salt of 40 9 per liter of solution must be present, on the other hand it must be present if one is exceeded Content of 100 9 cadmium per liter of solution is sufficient if the amount of table salt is 100 9 per liter of solution remains limited. The cadmium nickel solution is brought to a temperature brought between 25 and 300 C. A pH of 2.4-2.5 is set in the solution.

After the solution is prepared in this way, proceed with the cementation started by adding aluminum grit in portions. The temperature must also be kept in the temperature range of 25-300 ° C. during this process. This is based on the dependence of the nickel content shown in the drawing, FIG. 1 of cadmium cement from temperature and nickel concentration. The pH of the solution, which increases by approx. 0.5 units during the cementation, to towards the end of the cementation to decrease slightly again does not need to be readjusted. The need of aluminum grit is around 20 o per 100 9 cadmium. Only at concentrations from less than 50 9 cadmium per liter of solution, the relative consumption of aluminum powder increases at. This is evident from the measured curve shown in the drawing, FIG. 2 emerged. It shows the relationship between the Al requirement / 100 9 Cd and the Cd concentration in the Cd-Ni solution and roughly follows the arithmetic relationship mentioned above.

After the aluminum grit has been entered, it is another hour stirred. A final cadmium concentration of approx. 1 9/1 is then reached. then the cadmium cement is allowed to settle and the supernatant solution by decanting separated, filtered and provided for cementation of the nickel.

The cadmium cement obtained can then be mixed with new cadmium nickel solution (so-called fresh liquor) stirred for one hour under the conditions described above will. Most of the excess aluminum still in the cement is consumed by this further cementation process.

The fresh liquor is separated from the cadmium cement by decanting and subjected to cadmium cementation as described above. The cadmium cement will slurried with water and filtered off. The cadmium yield is about 98%. The following can be specified as a type analysis for the dried cement: 80% Cd 1% Ni 1 to 2% Al.

From the cadmium-free solution available for cementation of the nickel If the solution contains iron, this is initially achieved by precipitation of the D-isene (III) hydroxide deposited in a known manner and separated off by filtration. For preparation after the nickel cementation, enough common salt is added to the solution that (under Offsetting the amount already added before the cadmium cementation) a total concentration of at least 120 9 NaCl per liter of solution, regardless of the nickel concentration, is achieved. The temperature is adjusted to 55-600 ° C. and the pH is adjusted to 2.4 - 2.5 brought. Then the nickel cementation begins by adding in portions from Aluminum grit. The temperature is within the specified limits held in order, on the one hand, to achieve a delay-free onset of the cementation and on the other hand to avoid the precipitation of basic aluminum salts. The pH needs not to be adjusted. For every 100 9 nickel, 200 - 250 9 aluminum are needed. After one hour of stirring, a final nickel concentration of about 100 mg Ni per liter of solution reached. The cemented solution is made by decanting separated from the nickel cement.

The aluminum hydroxide can be precipitated from it in a known manner, which can be deposited or used in any way. The nickel cement is one hour at pH 1.5 and otherwise below that described for nickel cementation Conditions with new nickel solution flowing off from the cadmium cementation process treated, with a large part of the excess contained in the nickel cement Aluminum is consumed. Then this nickel becomes fresh liquor by decanting separated from cement and goes to nickel cementation. The nickel cement is made with Slurried water and filtered off. It is a cement with the following typical Data obtained (in the dry matter): 50 - 60% Ni 2% Cd 5 - 10% al.

This nickel cement can be used in processes that are common in nickel smelters are, are further processed The obtained by the process according to the invention Cadmium cement dissolves at a satisfactory rate without the addition of oxidizing agents in sulfuric acid with most of the nickel remaining undissolved. So becomes a Obtain cadmium sulfate solution, which in addition to 150 g cadmium per liter of solution (a concentration as it is usually aimed at for the production of cadmium compounds) only still contains around 500 mg of nickel per liter of solution. Such Solution can be economically subjected to the usual fine cleaning, by precipitating the nickel as nickel diacetyl dioxime.

The advantages of the new process are in particular the following: It can be operated continuously without any loss of profitability be waived; the process can be carried out with the simplest of equipment; it inexpensive bulk chemicals can be used; it can be found in the cadmium concentrate reach a nickel content which is 1.25 parts by weight Ni per 100 parts by weight Cd does not exceed; the process is environmentally friendly without complex precautions to operate; the recovered Cd and nickel concentrates can easily after usual procedures are further processed.

The invention is further developed in the following by means of an exemplary embodiment explained.

Example 1 3500 ml of one from the leaching of sintered plates with diluted Sulfuric acid-derived cadmium nickel sulfate solution with a content of 157.2 9/1 Cd and 13.8 9/1 Ni are adjusted to pH 2.5 with sodium hydroxide solution and heated to 300.degree.

After 350 9 table salt have been dissolved in this solution, are with stirring 112 9 aluminum grit entered, being ensured by cooling is that the temperature does not exceed 300 C and not fall below 250 C.

After the aluminum has been introduced, the mixture is stirred for 1 hour.

The solution then still contains 1 g / l Cd. The deposited cadmium cement is then allowed to serve. The supernatant solution is separated off by decanting and provided for the cementation of the nickel. The cadmium cement is then treated with new cadmium nickel solution in the manner described above without further aluminum powder is added. Then the cement is allowed to settle again and the supernatant solution is separated off by decanting. The cadmium cement will filtered off and washed with a little water. There are 601.5 9 (tr.) Cadmium cement obtained with 92.5% Cd and 0.26% Ni. In comparison to the starting solution for cadmium cement the ratio of cadmium to nickel has shifted from 100: 9 to 100: 0.28. The decantate from the cadmium cementation, 2940 ml, is now used for the nickel cementation subject. For this, the pH of the solution is adjusted to 2.5 and 147 9 sodium chloride entered, so that a concentration of 150 9/1 NaCl is reached. Then will with stirring at a minimum temperature of 550 C 100 9 aluminum grit is added, where- the temperature increases in accordance with the entry rate and this is dimensioned so that the reaction is not too violent. After the The addition of aluminum grit is then stirred for one hour. The nickel free solution will then through Decanting separated; aluminum can be made from it be precipitated as hydroxide. The nickel cement is made with fresh, from the cadmium cementation originating nickel solution under the conditions of nickel cementation without any further Addition of aluminum semolina stirred for one hour. This solution is then turned through Decanting separately from the cement to be fed to the nickel cementation. Of the Nickel cement is filtered off and washed with a little water.

It weighs 90 9 dry and contains 51.6% Ni and 9% Al.

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Claims (6)

Process for the separation of cadmium and nickel by fractional cementation Patent claims 1. Process for the separation of the elements cadmium and nickel, which are present in the form of mixtures of the aqueous solutions of their sulphates, by cementation of the cadmium present in a concentration of at least 50 g of Cd per liter of solution and subsequent deposition of the nickel, characterized in that the cadmium is first deposited from these solutions by adding aluminum powder to the cadmium-nickel solution as cement, with the proviso that before the start of cementation, an amount of at least 40 g of sodium chloride is added per liter of solution of the sulfates so that the The pH of the solution is adjusted to 2.4-2.5 and that the temperature of the solution is also kept in the range between 25 and 300 ° C. during the cementation, then separated from the cadmium cement, and then the nickel in the filtrate by adding aluminum grit as cement, with the proviso that before the start of cementation enough common salt is added that the total concentration is at least 120 g NaCl per liter of solution, that the pH of the solution is regulated to 2.4-2.5 and that furthermore a temperature of at least 550 C is set and this temperature is maintained during the cementation and the nickel cement is separated after the cementation is complete. 2. The method according to claim 1, characterized in that the Al additive / 100 g Cd (Y) as a function of the Cd concentration (x) in the Cd-Ni solution according to y = 1 a = a + bx, where a = 88.463.10 and b = 2.352.10. 3 The method according to claim 1 or 2, characterized in that at Cadmium concentrations within the limits of 40 g - 100 g cadmium per liter of solution the salt concentration is chosen to be equal to the present cadmium concentration. t. Method according to claims 1-3, characterized in that the resulting cadmium cement in accordance with the provision in claim 1 again We treat fresh cadmium nickel sulfate solution. 5. Process according to claims 1-4, characterized in that the total concentration of table salt present during the Nicely Cementation 120 - 150 g NaCl per liter is. 6. Process according to claims 1-5, characterized in that the resulting nickel cement again in accordance with the provision in claim 1 fresh nickel solution flowing out of the cadmium cementation is treated.