Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Patent
1992-06-15
1995-04-18
Andrews, Melvyn J.
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
204112, 204114, 423140, 4231503, 423633, C22B 344
Patent
active
054074630
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for recovering cadmium (Cd) and nickel (Ni) from batteries, containing the following process steps: smaller than approximately 15 mm; acid, filtering and removing the residue; extraction; metallic Cd therefrom with the aid of electrolysis; (Fe).sup.++ -ions are converted into solid Fe.sup.+++ hydroxide, and filtering this off; filtrate with the aid of electrolysis or by increasing the pH. Such a, so-called hydrometallurgical, method is known.
The Ni-Cd batteries concerned consist of approximately 16 weight % of Cd, of approximately 34 weight % of Ni, of approximately 23 weight % of Fe, and for the rest of plastic and paper.
The size reduction takes place with the aid of a knife-mill, equipped with a retaining screen. The contents of the batteries are thus laid bare. When leaching the conditions are chosen in such a manner that the maximum amount of Cd and Ni goes into solution. The choice of four independent parameters is concerned here, i.e.: the temperature, the ratio between the quantities of acid and solid material, the strength of the acid and the residence-time in the leaching barrel.
The solvent extraction of Cd can be achieved with the aid of various extractants, for example with tributyl phosphate or with a tertiary amine. After the Cd has been removed from the leaching liquid the conversion of Fe.sup.++ into Fe.sup.+++ therein can be achieved with the aid of hypochlorite and at a pH of approximately 4.
The aim of the method is twofold: on the one hand to prevent the dangerous Cd from ending up in the environment, on the other hand to be able to re-use the relatively expensive Cd and Ni. Re-chargeable batteries in particular contain much Ni and Cd. With the aid of this known process approximately 275 kg of metallic Ni and 150 kg of metallic Cd can be recovered from each 1000 kg of batteries. An important factor for applying such a process or not is especially also the economy of the process.
The aim of the invention is to improve the indicated economy of the process. The improvement according to the invention is, that after step 1) the small pieces are separated into a coarse fraction with linear sizes of more than approximately 3 mm, a fine fraction with linear sizes of less than 3 mm and that the coarse fraction is separated into a magnetic and a non-magnetic fraction.
The coarse, magnetic fraction--approximately 50% of the weight of the batteries--appears to be very Fe rich, while virtually all of the Cd and Ni is situated in the fine fraction together with only a few weight percent of Fe, from the coarse, magnetic fraction the Fe can be recovered.
By removing the Fe at the first stage in this way the economy of the leaching process can be improved: because there is little Fe in the leaching liquid--approximately a factor 5 less than in the event that no separation into coarse and fine fractions is made--the production of hydrogen gas is now much smaller--still approximately 25%--and only approximately 30% of the usual quantity of acid is now necessary. The emission of salt to water becomes proportionally smaller.
After removal of the residue--in the order of 1% of the fine fraction and containing some Cd and Ni--a leaching liquid remains, which contains proportionally more Cd, more Ni and less Fe than in the case that no prior separation was carried out.
A further advantage turns out to be the fact that approximately 30% less extraction liquid is required for the solvent extraction process.
A further improvement is obtained if, according to a further characteristic of the method according to the invention, the stripping of the loaded extract liquid takes places with the aid of a diluted strong acid. The stripping efficiency turned out to increase from approximately 85% approximately 100%.
Yet another improvement of the process is acquired if, at step c), metallic Fe powder is added in order to reduce any Fe.sup.+++ which may be present. This prevents the Fe which is present from being extracted together with the Cd.
The invention will be explained further by a
REFERENCES:
patent: 5120409 (1992-06-01), Hanulik
Andrews Melvyn J.
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