FR2556368A1 - DECHLORATION OF STARTING MATERIALS FOR ZINC PRODUCTION - Google Patents

Abstract

THE INVENTION RELATES TO A PROCESS FOR DECHLORURING AND OXIDIZING BY-PRODUCTS. THE STARTING MATERIAL CONTAINING CHLORINE IS INTRODUCED IN A REACTOR 1 AND HEATED TO 750C BY MEANS OF A HOT GAS 4 SUPPLYING THE REACTOR, SO AS TO EVAPORATE THE ZINC CHLORIDE, AFTER WHICH THE ZINC CHLORIDE IS SUPPRESSED THROUGH A GAS OUTPUT 6 AT TOP 7 OF REACTOR, AND A ZINC AND ZINC OXIDE DECHLORIDE PRODUCT IS SUPPLIED FROM REACTOR 1 AT A LOWER LEVEL 5. APPLICATION TO THE PRODUCTION OF ZINC.

Description

Dechlorination of starting materials for the production of zinc.

  The invention relates to a method for

  and the oxidation of by-products as a starting material for zinc, consisting of ash, oxides and the like. It is estimated that in Europe alone there is between 000 and 60 000 tonnes of zinc ash, in addition to all other zinc-containing wastes. Zinc ash is produced as waste in the manufacture of zinc and contains about 60% zinc in the form of metal and oxide. A serious drawback with respect to the processes known to date is that the zinc ash contains significant amounts of chlorine in the form of zinc chlorides and other chlorides,

volatile.

  Zinc ash is a starting material

  very interesting in the manufacture of zinc, mainly

  for secondary industries, provided that the ash can be completely free of chlorine, since chlorine is a poison. In current processes, zinc ash is generally subjected to heat treatment in a rotary kiln to remove volatile chlorine compounds. The dechlorinated product is then. used to make

  zinc oxide, used as a pigment or in the

duction of charges.

  The process mentioned above, however, has only limited possibilities of recovering useful constituents of zinc ash, with a correct yield. Rotary kilns have a very low capacity and are not perfectly gas-tight,

  which causes undesirable pollution of the environ-

  ment. Processes carried out in rotary kilns

  also produce large quantities of gas, essen-

  because the heat is generated by combustion

tion.

  Accordingly, the invention aims to

  propose a process that allows the recovery of

  of exploitable constituents, from starting materials containing chlorine, and which eliminates or reduces

  disadvantages related to known methods.

  For this purpose, the invention proposes a process characterized in that the starting material for zinc, containing chlorine, is fed into a reactor,

  is heated to around 750 C, the thermal energy required

  being provided by a high energy gas heated in a plasma generator; and that the zinc chloride is drawn off at the top of the reactor and the dechlorinated zinc oxide at a lower level of the reactor. The energy-rich gas is preferably an oxidizing gas, so that it can oxidize all the metallic zinc present

  in zinc oxides, and thus avoids deposits.

  According to a first embodiment of the invention,

  The zinc-containing starting material, containing chlorine, is charged in powder form over a gas-permeable grid, below which is introduced a gas which has been heated by means of a plasma generator. gas being supplied with a flow rate to maintain a fluidized bed above the grid while at the same time the energy supplied to the plasma generator is controlled so as to maintain a temperature of about 750 C in the upper part of the reactor, a dechlorinated product comprising zinc oxide being withdrawn through

  a gas evacuation at the top of the reactor.

  According to another embodiment of the invention, the starting material containing chlorine is charged with

  in the form of briquettes or pieces through an intro

  gas-tight ducting at the top of the reactor, and the dechlorinated zinc oxide is withdrawn from the reactor by the bottom thereof, through a gas-tight extraction means, the expulsion of the gaseous zinc chloride formed being effected by supplying thermal energy by means of a hot gas in a plasma generator, the quantity of gas supplied being suitable for maintaining a

  temperature of about 750 C at the top of the reactor.

  The following description, next to the drawings

  annexed by way of non-limitative examples will allow

  understand how the invention can be put into practice.

  Figure 1 is a block diagram concerning

  dechlorination and oxidation of pulverized by-products

  as starting material for zinc, and

  FIG. 2 is a schematic diagram relating to

  dechlorination and oxidation of by-products as starting material for zinc, in the form of

briquettes.

  As mentioned above, the zinc starting materials may be derived from processes for the manufacture of zinc, and then contain zinc ash. Zinc-containing waste is, however, also obtained in the form of chemical compounds and in the form of metal chips, plastics, etc. Depending on the type of waste considered, the material

  can be loaded, as needed, in a fine form-

  divided, in which case it is possible to use a reactor operating on the principle of fluidised beds, see Figure 1, or the material can be briquetted and loaded into a reactor operating according to the principle

  tank furnaces, see the process according to Figure 2.

  In the process according to FIG. 1, a fluidized bed reactor is used. The starting material for the zinc, containing chlorine, is loaded in finely divided form in the reactor 1 through an inlet 2 situated above a bottom or gate 3 permeable to gases; by finely divided here means a base material having been ground into particles of a size not exceeding, preferably, the 5 mm. The particles must, however, be large enough not to be entrained by the fluidizing gas, and the size of the particles must be able to produce the necessary residence time in the reactor, by means of the fluidizing gas which is conferred a high energy in a generator of plasma 4 and which is then injected into the reactor 1 at a level below the gate, at a

  pressure above ambient pressure.

  A dechlorinated product, in the form of zinc oxide, is then withdrawn through the spillway 5, while

  that the gaseous zinc chloride formed is drawn off through

  towards the gas outlet 6 at the top 7 of the reactor.

  The gaseous zinc chloride then passes through a dust separator 8, in the form of a hopper, then it

  is brought into contact with water in a venturi washer 9.

  The pH of the resulting zinc chloride solution is adjusted to 10 in a vessel, so as to obtain zinc dihydroxide. The purified gas can then be

  recycled into the process or vented to the atmosphere.

  The dust separated in the hopper 8 contains essentially zinc oxide, and is recovered

  in common with the dechlorinated zinc oxide produced.

  The gas used must be an oxidizing gas, and

can be air for example.

  The temperature in the upper portion 11 of the fluidized bed is preferably about 750 C. The temperature in the wash station is about room temperature. The dechlorinated zinc oxide, which is withdrawn through the spillway 5, is evacuated through

  to a gas-tight valve device of known type.

  In the process illustrated in FIG. 2, the chlorine-containing starting material 21 for obtaining zinc is loaded in the form of briquettes or pieces at the top of the reactor 22, through a conventional gas-tight inlet 23. The reactor functions as a shaft furnace in which the briquette material is a charge 24 which continuously flows through the reactor. As in the method described above, the energy required is provided by means of heated gas

  in a plasma generator 25, the supply of the

  energy is regulated so as to maintain a temperature

  approximately 750 ° C at the top 26 of the reactor. Zinc gaseous chloride is withdrawn through an outlet

  gas 27 at the top of the reactor, while oxy-

  de-chlorinated zinc is discharged through a valve

  29 gas-tight bottom 28 of the reactor.

  In the latter case, when the starting material is in the form of briquettes, a dust separator is useless because the minimal quantities of dust possibly entralnés by the gas can be easily captured in the venturi washer 30, where the zinc chloride contained in the gas is collected

  in the form of an aqueous solution which can be

  vertie in zinc hydroxide, adjusting the pH of the solution in a vase 31. During the washing process

  mentioned, the temperature is about 30 C.

  The resulting gaseous waste can either be released into the atmosphere or compressed and recycled into the atmosphere.

process.

  Thus, the two embodiments of the process according to the invention allow the recovery of zinc and exploitable zinc oxides from all industrial waste, which no current technique can achieve in a cost-effective manner.

Claims (12)

  Process for the dechlorination and oxidation of by-products constituting a starting material for obtaining zinc, characterized in that the material   starting material containing chlorine is loaded into a reaction   (1), heated to about 750 C by introduction of   gas in the reactor so as to evaporate the chlorine   zinc chloride present; the gaseous zinc chloride is discharged from the reactor through an outlet (6) at the top (7) of the reactor; and zinc and zinc oxide dechlorinated are drawn from the reactor below   of the outlet (5) for the gaseous zinc chloride.   2. Method according to claim 1, characterized   in that the hot gas is heated in a genera-   plasma reactor (4) located outside the reactor (1).   3. Process according to claims 1 and 2,   characterized in that the reactor (1) is a reactor fluidized bed.   4. Method according to claim 3, characterized in that the starting material for obtaining zinc, containing chlorine, is introduced into the reactor (1) in a finely divided form at a level higher than the grid (3) permeable to gases; the hot gas is introduced at a level below the grid (3) with a flow rate suitable for maintaining a fluidized bed above the grid (3), while the energy level of the gas   is regulated so as to maintain a temperature of about   750 C at the top of the reactor; oxide   of dechlorinated zinc produced is discharged through a   evening (5); and the gaseous zinc chloride is evacuated to   through an outlet (6) at the top (7) of the reactor (1).   5. Method according to claim 4, characterized in that the starting material for obtaining zinc,   containing finely divided chlorine has a   particles up to 5 mm.   6. Process according to any one of the claims   1 to 5, characterized in that the gaseous zinc chloride   passes through a dust filter (8).   7. Process according to any one of the   cations 1 to 6, characterized in that the gaseous zinc chloride is brought into contact with water in a venturi scrubber (9) at a temperature of about 30 C, in order to   to obtain an aqueous solution of zinc chloride.   Process according to any one of the claims   cations 1 to 7 characterized in that the energy-rich gas is an oxidizing gas for oxidizing zinc, present   in the starting material, in zinc oxide, in order to avoid deposit.   9. Process according to claim 7, characterized in that the pH of the zinc chloride solution is adjusted so as to convert this solution to dihydroxide of zinc.   10. A method according to any of the claims   cations 1 and 2, characterized in that the starting material for obtaining zinc, containing chlorine, is introduced into the reactor in pieces,   and that the reactor comprises a tank.   11.Procédé according to claim 10, characterized in that the outgoing gas is brought into contact with   water in a venturi scrubber at a temperature of   30 C, in order to obtain a solution of chloride of zinc.   12. The method of claim 11, characterized   rised in that the pH of the zinc chloride solution   is adjusted to convert this solution to dihy- zinc oxide.   13. Process according to any one of the   cations 1 to 12, characterized in that the washed gas is   compressed and recycled in the process.