FR2482137A1 - PROCESS FOR THE DIRECT RECOVERY OF TRIM AND METAL ZINC POWDER, IN PARTICULAR FINE PARTICLES - Google Patents

Abstract

THIS PROCESS ALLOWING DIRECTLY RECOVERY OF THE CROWN AND THE METAL ZINC POWDER, PARTICULARLY HAVING FINE PARTICLES, INCLUDES THE FIRST STAGES OF A LEACHING OF THE SAID POWDERS IN A SOLUTION OF AMMONIUM CHLORIDE THEN THE TREATMENT OF THEN THE SEPARATION, AFTER WHAT, THIS POWDER THUS SEPARATED IS AGGLOMERATED AND INTRODUCED IN A FUSION OVEN. APPLICATION OF THIS PROCEDURE TO RECOVER METAL ZINC POWDER FROM PROCESSING RESIDUES IN THE MANUFACTURING OF GALVANIZED STEEL.

Description

- 1 - Process -for the direct recovery of clipping and powder

  The present invention relates to the recovery of metallic zinc which is a residue of the processing operations in the form of clipping and fine-particle powder.

  These metal residues can not be directly

  recovered by a new melting process since the particles are wholly or partly coated with an oxide film or other pollutants which pock these particles directly into a melting furnace.

molten metal zinc.

  We will refer later to the zinc powder which is a residue of the treatment in the manufacture of galvanized steel: it is really an important and annoying case of recovery of zinc metal well understood what is said for the present The zinc powder, which is a residue of the galvanizing process of steel, generally has a very fine particle size, which is equal to or smaller than the 400 mesh (37). P)] and it is not possible to have it recast because of its extreme

  finesse and also oxide film or other

  which coat each individual granule, When the metal powder is charged into a melting furnace, in fact, it floats on the molten metal zinc and, almost immediately, it burns and forms the oxide of

zinc without melting.

  Even when the transformation into agglomerates (or

  cords) is used for the powder, the same negative results are obtained s the pieces float on the molten zinc, are not wetted by the metal bath because of the peel which coats the metallic particles and the zinc that these pieces contain is oxidized although more slowly,

  then is transformed into zinc oxide.

- 2 -

  For these reasons, the classical technique of recovering

  metal from powders or small shavings

  uses the usual cycles, that is to say either by the hydro-

  metallurgy (dissolution of the powder in di-

  H2SO4, purification of the solution thus obtained and

  electrolytic deposition of metallic zinc from this elec-

  trolyte), either thermally, to obtain the zinc in its oxide form and then treat it as a primary zinc oxide.

  Finally, other recovery tests provided

  zinc in the form of a zinc salt, which is treated

as mentioned above.

  These processes for zinc recovery involve

  however, cost prices which are of the same order of magnitude

  than those required for primary zinc, especially since, in practice, the same cycles of treatment as for

primary zinc are monitored.

  It is an object of the present invention to provide a method of treating zinc metal powders or trimmings in order to detach it from the oxide shell.

  and to obtain it in an essentially metallic form.

  Another object of the present invention is the provision of

  treatment of zinc powders or shavings so that they can be reintroduced, after processing into compressed products or simply as they are, in the ovens

  melting without any additional chemical treatment.

  The method according to the present invention comprises the processing steps detailed below. The first step is to leach the metal powder into acidic solutions that contain ammonium ions, such as aqueous solutions of ammonium chloride and / or hydrochloric acid.

  buffered having a pH range of 4.1 to 4.65. The con-

  ammonium chloride concentrations are between 50 g / liter and 300 g / liter and preferably between 150 grams

per liter and 250 grams per liter.

  This leaching operation is carried out at temperatures close to ordinary temperature with contact times of between 10 minutes and 60 minutes and,

  preferably between 15 minutes and 30 minutes, the report

  the lubricating agent has the treated powder being

  between 0.2 and 2, and preferably between 0.8 and 1.2, the

  is carried out continuously or discontinuously in

  conventional methods, such as agitated vertical tanks,

  horizontal or substantially horizontal vessels having a system

  axial feeding system, plate reactors and

Analogs.

  After leaching, the treated powder is separated

  by filtration or decantation. The leaching liquor is

  cycled and is enriched with zinc by

  rage and by supplementing with a fresh solution

  to maintain its effectiveness at a desirable level.

  Zinc powder treated in this way is sensitive

  is free of adhering oxide films and is

  caused by the leach liquor that protects it from attacks

later.

  The subsequent processing stage consists in agglomerating

  the powder as obtained from the filtration in the form of a cake (wet) and the damping liquor is an auxiliary

  useful for improving the wettability of metal particles

  by the fused zinc bath while at the same time facilitating

  at the moment to the law the fusion and the fluidification.

  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

  The agglomeration is carried out under a pressure of 1000 to 105 to 2000 ppm, and agglomerates with a specific gravity are obtained.

  between 5.8 and 5.9o These agglomerates are fed directly

  in the melting furnace without any additional treatment.

  silent. The present invention is illustrated by the example

  descriptive and not limiting thereafter.

  In a plastic tank having a volume of about 100 liters, equipped with a stirrer and filled with 60 liters of a solution of ammonium chloride (concentration grams per liter), is introduced continuously for about minutes and while stirring the liquor, 50 kg of powder

  zinc (containing 94% of zinc metal).

  Once the bill is over, we continue shaking for another ten minutes and then leave the solid products

to be deposited.

  The supernatant liquor is recovered by siphoning and, after having. has been suitably supplemented with fresh ammonium chloride, is recycled; the wet powder is removed

  and transformed directly into agglomerates. The agglomeration machine

  used is a mnachline of the discon-

  tinu capable of exerting a total pressure of 40 tons, which, when distributed over an area of 28.2 cm2 (diameter of a 6 cm agglomerate) gives a unit pressure of about

1400 105 pascals.

  We obtain 79 agglomerates weighing approximately 550 g each

  and having a volume of about 110 cm)

  viron 6 cm for a thickness of about 4 cm).

  The liquor drained during the transformation into agglomerates

  The melt was also collected and recycled while the amounts of ammonium chloride remaining in each agglomerated are about 2 g / l in an induction melting furnace having a total capacity of 100 kg of molten metal, filled exactly kg

  molten zinc, at the regulated temperature of about 50

  510 C, we introduce from 10 agglut (res chlaque laws, then waiting for the% emperature of the metal bath to reach the displayed value again.) With the -type of oven thus used,

  the amalgamation of all 79 agglomerates takes 50 to 60 minutes.

  The test gives 82.5 kg of metallic zinc and 5.8 kg of tuthie, the latter still containing 4 kg of zinc, especially in the form of zinc oxide and partly in the form of zinc chloride. 50 kg of starting zinc powder (94% reducing capacity) containing 47 kg of zinc metal is as follows: 42.5 kg of zinc metal corresponding to 90.4% of the metal of the powders and 85% of the starting powder, and 4 kg of zinc in the form of zinc oxide corresponding to 8.5% of the powders. The process according to the present invention is extremely simple and inexpensive, since it is practically possible to completely remove the powder. : powder and cleavage of zine metaelliqe of the envelopo of oxide, without any appreciable attack of the metal in this forms the consumption myenne related to the chloride deam

  monium is limited to 3 kg per ton of powder ...

  metal die for a powder having u. 93% to 94% reducing power reaches 90% of the initial weight of the liquid. The small amount of zinc which does not appear in the supplement is not lost, however, since it is recovered from the dewatered products of the liquor. washing and from the tuthie that is usually formed when the zinc is melted by

conventional methods.

  A significant feature of the present invention is that whenever it is desired to have all the purified zinc, or a portion thereof, in the form of a powder, it is possible from the very first stage of treatment of to get such a product because it takes

  perform only one leachate stage and one

  1. A process for the direct recovery of fine zinc metal powder and cleavage, characterized by the fact that these powders are first leached into an acidic solution containing ammonium ions and having a fold of

  4.1 to 4, b5, where the powder thus treated is separated by filtration.

  tion, that the cake thus obtained from the treated powder is agglomerated, after which the agglomerates thus obtained

  are introduced into the melting furnace.

  . Process for the direct recovery of powder and clipping, ha fine particles, d (metal zinc according to claim 1, characterized by the fact that the leach solution is an ammonium chloride solution and / or a

  hydrochloric acid buffered solution having a

  between 0 and 300 grams per liter, and preferably

  between 150 and 250 grams per liter.

  3. Process according to claims 1 and 2, characterized

  rised by the fact 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 report

  weight weight of the leach liquor 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 the claims

  1 to 3, characterized by the fact that agglomeration is effected

  killed by agglomerating the wet cake of the leached powder under a pressure of 1000 to 2000 pascals.