LU83260A1 - PROCESS FOR THE DIRECT RECOVERY OF METAL ZINC TRIMMING AND POWDER, ESPECIALLY FINE PARTICLES - Google Patents

Description

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Process for the direct recovery of parings? and metallic zinc powder, in particular fine particles

The present invention relates to the recovery of metallic zinc which is a residue from the operations of treatment under the form of shaving and fine particle powder.

These metal residues cannot be directly recovered by a new fusion since the particles are entirely or partially coated with an oxide film or with other pollutants which prevent these particles from being directly charged in a melting furnace where finds molten metallic zinc "

Reference will subsequently be made to zinc powder, which is a residue from the treatment in the manufacture of galvanized steel. It is really an important and annoying case of recovery of metallic zinc; Of course, what is said for the present invention can also be applied to residues of metallic zinc having any other origin. Zinc powder which is a residue from the process of galvanizing steel has, in general, a size very fine particle size, j_equal or less than 400 mesh (37 p) ^ ü it is not possible to have it remelted because of its extreme fineness and also the oxide film or other compounds which coat each granule When the metallic powder is charged in a melting furnace, it actually floats on the molten metallic zinc and, almost immediately, it shines and forms zinc oxide without melting, even when the transformation into agglomerates (or bri-30 quettes) is used for the powder, the same negative results are obtained t the pieces float on the molten zinc, are not wetted by the metal bath because of the film which coats the metal particles ^ and the zinc that these mor these contain is oxidized, although more slowly, ’t“ “'" 1 - 2 - "f

For these reasons, the conventional technique of recovering metal from powders or small parings "uses the usual cycles, that is to say either by the hydrometallurgical route (dissolution of the powder in di-5 lu solutions of H2SO4, purification of the solution thus obtained and electrolytic deposition of metallic zinc from this electrolyte), either thermally, to obtain zinc in its oxide form to then treat it as a primary zinc oxide · 10 Finally , other recovery tests provided smell the zinc as a zinc salt, which is processed

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as mentioned above · *

These methods for recovering zinc, however, involve cost prices which are of the same order of magnitude as those required for primary zinc, all the more so since, in practice, the same treatment cycles as for zinc primary are followed ·

It is an object of the present invention to provide a method which consists in treating powders or trimmings of metallic zinc in order to detach it from the oxide shell and obtain it in an essentially metallic form.

Another object of the present invention is to provide a treatment for zinc powders or trimmings so that they can be reintroduced, after transformation into compressed products> or simply as they are, in the melting furnaces without any chemical treatment. additional·

The process according to the present invention comprises the processing stages detailed below. The first stage consists in leaching the metal powder in acid solutions which contain ammonium ions, such as aqueous solutions of ammonium chloride and / or d hydrochloric acid having a pH range of 4.1 h 4.65 · The concentrations of ammonium chloride are between 50 g / liter and 300 g / liter and preferably between 150 g 35 per liter and 250 grams per liter · _ / ^ '—p ^ - - 3 - it>

This leaching operation is carried out at temperatures close to ordinary temperature with contact durations of between 10 minutes and t> 0 minutes and, preferably, between 15 minutes and 30 minutes, the weight ratio of the agent leaching agent to the treated powder being maintained between 0.2 and 2, and preferably between 0.8 and 1.2 · The operation is carried out continuously or discontinuously in conventional devices, such as agitated vertical tanks, horizontal or substantially horizontal tanks having an axial feed system, plate reactors and the like

After leaching, the treated powder is separated by filtration or decantation. The leachate liquor is recycled and enriched with zinc by appropriate wringing operations and by supplementing it with a fresh solution in order to maintain its effectiveness at a desirable level.

The zinc powder treated in this way is substantially free of adherent oxide films and is impregnated with the leach liquor which protects it from further attack.

The subsequent processing stage consists in agglomerating the powder as obtained from filtration in the form of a cake (wet) and the wetting liquor is a useful auxiliary in order to improve the wettability of metal particles by the bath of molten zinc while simultaneously facilitating both melting and fluidification.

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This stage can be carried out with conventional methods provided that individual and coherent particles can be obtained. According to a preferred method, the transformation into agglomerates is carried out under a pressure of 1000 to 2000 bars, and agglomerates having a density of between 5.8 and 5.9 are thus obtained. These agglomerates are fed directly into the oven. The present invention is illustrated by the example jCi ~ '- ».

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i. , '! * - 4 - descriptive and non-limiting below.

EXAMPLE

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Into a plastic tank having a volume 1 of approximately 100 liters, equipped with a stirrer and filled with 560 liters of an ammonium chloride solution (concentration 200 grams per liter), continuously introduced for approximately 10 minutes and while stirring the liquor, 50 kg of zinc powder (containing 94 fe of metallic zinc)

Once the addition is complete, continue to agitate • OJ for another ten minutes and then allow the solid products to settle ·

The supernatant liquor is recovered by siphoning and, after having been suitably supplemented with fresh ammonium chloride, is recycled; the wet powder is removed and transformed directly into agglomerates. The agglomerating machine used is a machine of the discontinuous operating type capable of exerting a total pressure of 40 tonnes, which, when it is distributed over an area of 28.2 cm ^ (diameter of an agglomerated 6 cm) gives a unit pressure of approximately h 20 1,400 bars ·

79 agglomerates are obtained weighing approximately 650 g each and having a volume of approximately 110 cm-> to 115 cnt * (diameter of approximately 6 cm for a thickness of approximately 4 cm).

The liquor drained during the transformation into agglomerates was also collected and recycled while the quantities of ammonium chloride remaining in each agglomerate are approximately 2 g ·

In an induction melting furnace with a total capacity of 100 kg of molten metal, filled with exactly 40 kg of molten zinc, at the regulated temperature of approximately 50 ° C. to 510 ° C., 8 to 10 agglomerates are introduced each. times, then wait for the temperature of the metal bath to reach the displayed value again. With the type of oven thus used, the melting of all 79 agglomerates takes 50 to 60 minutes. 35; The test gives 82.5 kg of metallic zinc and 5.8 kg of _ ".

• - 5 - “tuthie, the latter still containing 4 kg of zinc, mainly in the form of zinc oxide and partly in the form of zinc chloride ·

The complement compared to the 50 kg of starting zinc powder 5 (reducing power 94 fo) containing 47 kg of metallic zinc is as follows: 42.5 kg of metallic zinc corresponding to. 90.4; i ”of the metal of the powders and to, 85 μl of the starting powder, and 4 kg of zinc in the form of zinc oxide corresponding to 8.5 # of the 10 powders. The process according to the present invention is extremely simple and inexpensive, since in practice it allows ridding! completely wipe off the powder and the metal zinc trim from the oxide shell, without any appreciable attack of the metal in this form *

The average consumption in relation to ammonium chloride is limited to 3 kg per tonne of powder treated. The metal yield for a powder having a reducing power of 93% at 94 ’fo reaches 90 ° / o of the initial weight of the powder. The small amount of zinc which does not appear in the supplement is not lost however, since it is recovered from the wrung products of the wash liquor and from the tuthie which is generally formed when zinc is Molten by conventional methods · ”25 A not insignificant characteristic of the present invention resides in the fact that each time that it is desired to have all of the purified zinc, or a part of it, in the form of powder, it is possible from the very first stage of treatment to obtain such a product, since it is necessary to carry out only a single stage of leaching and a final drying operation * 'J · -' ---

Claims (2)

3 · Process according to claims 1 and 2, characterized in that the leaching stage is carried out with contact times of 10 minutes to 60 minutes, and preferably between 15 minutes and 30 minutes, the weight ratio of the liquor leaching to the treated powder being maintained between 0.2 and 2, and preferably between 0.8 and 1.2. 4, Method according to any one of claims 25 1 to 3, characterized in that the agglomeration is effected— * - * killed by transforming the wet cake of the powder leached into agglomerates under a pressure of 1000 to 2000 bars · t