IT8905221A1 - METHOD FOR THE SELECTIVE RECOVERY OF LEAD, ZINC AND CALCIUM FROM MATERIALS CONTAINING THEM IN THE FORM OF OXIDES OR WATER INSOLUBLE SALTS - Google Patents

Description

DESCRIPTION_of the invention having as title: METHOD FOR THE SELECTIVE RECOVERY OF LEAD, ZINC AND CALCIUM FROM MATERIALS CONTAINING THEM IN THE FORM OF OXIDES OR SALTS INSOLUBLE IN WATER

SUMMARY - Method for the selective recovery of lead, zinc and calcium from materials containing them in the form of oxides or water insoluble salts and comprising the leaching of said materials with a solution of ammonium chloride maintained at the boiling temperature, the separation of the insoluble solids and the treatment of the solution obtained with carbon dioxide and ammonia to separately precipitate the carbonates of lead, zinc and calcium from which carbon dioxide is recovered by calcium, national or acid leaching.

DESCRIPTION OF THE INVENTION The invention relates to the selective recovery of lead, zinc and calcium from materials which contain_SQtto.forms_of.oxides or_insoluble_sals_ JLn_water_ such as:,. of lead and zinc oxidized minerals of zinc.

The aforementioned materials have typical average analyzes as described in the following table:

TABLE _ CONTENT IN PERCENTAGE (%) TYPE OF MATERIAL ZINC LEAD CALCIUM OTHERS

Process oxides

Waelz type_ _ 40-65 5-10 1-5 _ Rest 100% Process oxides

plasma Tetronics 40-60. 5-12_ 2-3 Rest at 100? Oxides, from process to _

plasma Tibur__Howden_ 53 1 = 4 _ Ras.tD_a_lD0% _ Oxides from _prpcess

tFlame Reactor Process 37-46_ 5-8_ l = 4__ Res.to_a_100? _ _F_umi_of steel plant 5-35_ 1 = 10_ 1-20. Res.to_a_100? _ Roasted Blenda. 55 = f 0., 5 = 3_? Res.to_a_100? Minerals, obs? Data ^ _di_

zinc (Calamine) 30-50 0.5-5 0.5-5 _ Rest 100% Oxidized minerals

poor 8? 20 1-5 10-30 Rest at 100? Between ? methods of recovering these metals from the aforementioned materials include:

? leaching with sulfuric acid on oxidized zinc materials (traditional processes for the production of electro-lithic zinc) in which lead and calcium remain in the residue as sulphates

- two-stage leaching in autOQ.lay_e_on.mater.iali. .sidates of zinc _ (. U .5. Patent_4..61Q .._ 721_U ^ S.A ...)

- chlorine leaching and electrolysis of zinc chloride in molten salts (low temperature process by B.K. Thomas and D.G_. Fray ENGLAND)

- leaching in a strong alkaline environment (caustic soda) which provides for the electrolytic extraction of zinc in the alkaline bath? flax in powder form {U.S. Patent 3,743,501 U.S.A. e_ Promozinc process FRANCE) j in these processes the calcium remains in the residue.

- carboammonia leaching (U.S. Patent 4.071.357 U.S.A. in which lead and calcium remain in the residue as carbonates. - Imperiai Smelting which can treat Waelz oxides, calcined and roasted by minerals on a large production scale (minimum 200,000 tons / A), producing metals that require further refining processes.

- plasma process (Scan Dust SWEDEN) which produces Prime Western grade zinc metal.

? Waelz furnace (HTR U.S.A process .. Berzelius GERMA-NIA process), plasma processes (Tetronics ENGLAND, Tibur Howden CANADA) and Flame Reactpr Process (F.R.P. Horsehead Resource Develqpement U.S.A.) that produce enriched materials Among the above-mentioned methods some produce only a enrichment of the metals in question, some perform a quality metal extraction? lower than those obtained electrolytically or in poorly marketable forms and some carry out only the extraction of zinc with consumption of reagents for lead and calcium which remain in the residue.

The present invention makes it possible to process materials containing oxides or insoluble salts of lead, zinc and calcium and to obtain these elements separately in the form of marketable products.

1) The material is mixed with a solution of ammonium chloride, which contains from 5 to 85 gr. for 100 gr. of water, the whole is brought and maintained at the boiling temperature corresponding to an operating pressure from 0.7 to 2 ATA until it comes out more? ammonia from the solution itself. In this phase, reactions such as:

MeO 2NH CI = MeCl H 0 2NH

- 4 2 2 3

MeCO 2NH CI MeCl H 0 CO 2NH

3 4 2 2 - 2? 3? MeSiO 2NH CI = MeCl H 0 SiO 2NH

3 4 2 2 2 3 MeOFe 0 2NH CI MeCl H 0 Fe 0 2NH 2 3 4 2 -2 2 3 - 3 where Me stands for Ca, Zn, Pb and any other bivalent metals present as impurities. The ammonia that develops in this phase is used in the following phases 2) _4) _5). At the end of the operation, the chloride solution is separated from the residue consisting of silica, ferric oxide and non-solubilized materials.

2) The solution obtained in 1) is treated with ammonia and carbon dioxide maintaining a pH from 5.7 to 6.0; there is thus the precipitation of lead carbonate according to the reactions: NH C (> HO NH HCO

NH HCO

A --- 3? ? ?

PbCl2 - + - tNH-4) 2CO.g = __PbCQ_ ._2NH .CJ_

Lead carbonate cos? precipitate is separated from

.solution and washed with ammonia solution to purify it of any carbonate, of coprecipitated zinc which is thus between-

_sforma.t-Q_J.n_ soluble complex zincQ ^ ammonium .._ * _ -3) The solutions obtained in 2), from which? the lead carbonate has been separated, are treated with zinc dust which precipitates the residual lead in the form of "cements", not precipitated as a carbonate, and any metals pi? nobles_ of zinc (Cd, Ni, Cu_ecc.). _

_ 11 "cements * 1 are separated from the solution.

4) The solution obtained in 3) is treated with ammonia and carbon dioxide at a pH from 6.0 to 6.5; yes it has cos? _the_pre_Q? -citation of_carbpnatp_ of zinc. According to the reactions

NH _ + _ CO_ H O _ = NI

.-NH._H.CO _ * NH (NH) CO _

4 3 3 4 2 3

The zinc carbonate is separated from the solution._

5) The solution obtained in 4) is treated with ammonia and carbon dioxide at a pH higher than _si_hft._cos? precipitation of calcium carbonate according to the reactions: NH CO H 0? NH HCO

--3- - 2 -2-? * 4 '

NH HCO NH (NH) CO

-4- 3- 3- 4 "2 3

CaCl (NH) CO CaCO 2NH CI

The zinc possibly not precipitated in 4) is at this point kept in solution why? under the operating conditions described in this phase, the soluble zinc-ammonium complex is formed.

The calcium carbonate is separated from the solution.

6) The solution obtained in 5). from which the metals were precipitated_ed JLn which? ammonium chloride was restored according to the reactions described in 2) _j4) 5). can be reused in lj for a & _new operation_of_lis.ci?iation ...

7) _The carbonate_of_pismbo. Obtained JLn J?.) __ is_calcinated_for_ .to obtain _oxide or_11s. in both ideasi ai otterr? carbon dioxide to be used (in phases 2) 4) 5).

8) The zinc carbonate obtained in 4) is calcined to obtain. oxide or leached in mineral acids (for example sulfuric acid) and extracted as electrolytic zinc: in both cases it will be obtained? carbon dioxide to be used in phases 2) 4) 5)

.9) The calcium carbonate obtained in 5) is calcined to obtain oxide; it will have? cos? carbon dioxide to use!

- in phases 2) 4) 5).

The process according to the present invention will be now better understood with reference to the following example; . given merely as an illustration of some of its particular embodiments, on dust from smoke abatement from electric furnaces for the production of steel.

EXAMPLE OF APPLICATION OF THE INVENTION - The object of the invention relates for example to a recovery of lead and zinc from steelworks fumes coming from electric furnaces. The steelworks fumes used for the example have the following composition: Zinc 18.6%

Lead 4.3?

Football 2.0%

Iron 39.0%

Cadmium 0.07 a /

To an aqueous solution containing 400 grams per liter of ammonium chloride, 450 grams per liter of steelworks fumes are added; the whole is brought and maintained to abolition at a pressure of 1 ATA. When from the solution does not develop more? ammonia separates the solid by filtering it while hot. The solid obtained washed with boiling water has a composition: Zinc 8.0%

Lead 1.1%

Calcium 1.3%

Iron 50.0%

Cadmium 0.006%

Aimnonium bicarbonate and ammonia are added to the filtered solution, maintaining a pH lower than 6.0; there is precipitation of lead carbonate which is separated by filtration. To the filtered solution which now contains:

Zinc 54 gr / 1

Lead 1,5 gr / 1

Calcium 4,4 gr / 1 _ _

zinc dust is added which completely precipitates the lead and the pi? zinc nobles (Cd, Cu etc.) in the form of "cements1 * which are separated by filtration. __ Ammonium bicarbonate and ammonia are added to the filtered solution, maintaining a pH of 6.5; zinc carbonate precipitates which it is separated by filtration The filtered solution now contains: Zinc 23 g / l

Calcium 4.2 g / l This solution is brought to a pH higher than 6.5 with ammonia and ammonium carbonate and calcium carbonate precipitates which is separated by filtration. The resulting solution can? be reused ._for_a new leaching.

Claims (2)

CLAIMS 1) A method for the selective recovery of lead, ~ zinc ~ and calcium from materials containing them in the form of oxides or water-insoluble salts such as: Waelz oxides and generally oxides from enrichment heat treatments from materials containing them lead and zinc, dust from the abatement of fumes from electric furnaces in steel mills, materials from roasting of lead and zinc minerals, oxidized minerals of zinc_o_. 2) A method as described in claim N? 1 and which consists of: a) treatment of said materials with an ammonium chloride solution maintained at a high temperature in order to solubilize the oxides and salts of lead, zinc and calcium as such and to allow the ammonia produced to escape from it from reactions. b) separation from the solution of ferric oxide, silica and insoluble residues. c) addition of ammonia and carbon dioxide to the solution obtained in b) maintaining a pH lower than 6.0 in order to precipitate lead carbonate. _ d) separation of the lead carbonate from the solution. e) washing the lead carbonate separated in d) with ammonia solution so as to dissolve any co-precipitated zinc carbonate in c). f) treatment of the solution obtained in d) with zinc powder to precipitate the residual lead and any more metals. noble zinc in the form of "cements". g) separation of the "cements" precipitated in f) from the solution, h) treatment of the solution obtained in g) with ammonia and carbon dioxide, maintaining a pH from 6.0 to 6.5 in order to precipitate zinc carbonate. i) separation of the carbonate d? zinc from the solution. 1) treatment of the solution obtained in i) with ammonia and carbon dioxide at a pH higher than 6.5 in order to precipitate calcium carbonate m) separation of the calcium carbonate from the solution. n) recovery of carbon dioxide by calcination or acid leaching of lead carbonate. o) recovery of carbon dioxide by calcination or acid leaching of zinc carbonate. p) recovery of carbon dioxide by calcination of calcium carbonate. q) recycling of the carbon dioxide recovered in n) o) p) in the precipitation phases of the carbonates c) h) 1). _ r) recovery of the ammonia obtained in a) in the precipitation phases of the carbonates c) h) 1). -'3) A method as described in claim N? 2 in_a) where said ammonium chloride solution? at a concentration of 5 to 85 grams per 100 grams of water. . 4) A method as described in claim_N? 2_in a) _ where said high temperature goes from 80 ° C_ to the boiling temperature of the solution. 5) A method as described in claim N? 4 where said boiling temperature? that corresponding to an operating pressure of the system from 0.7 to 20 ATA. 6) A method as described in claim, N? 2_ in a) where said high temperature is maintained for a time from 0.5 hours to that necessary to completely distil the ammonia from the solution. 7) A method as described in claim N? 2 and that includes a) the treatment of the solution obtained as, in claim N? 2 in b) with ammonia and carbon dioxide at a pH lower than 6.5 to simultaneously precipitate the carbon dioxide. lead and zinc. b) separation of lead and zinc carbonates from the solution c) treatment of lead and zinc carbonates with solution. of ammonia in a way to dissolve the zinc carbonate and the zinc-ammonium-carbonate complex. d) separation of the p? ombo carbonate from the solution containing the zinc-ammonium-carbonate complex. e) stripping the ammonia from the solution containing the. _ <1 zinc-ammonium-carbonate complex _ so as to precipitate carbonate d? zinc. 8) A method as described in claim NP - ^. In.c) h 1) and in claim N? 7 in a) where said ammonia and carbon dioxide can also be in the form of ammonium carbonate or ammonium bicarbonate or ammonium carbamate or d? mixtures of them with ammonia or carbon dioxide approx. 9) A method which comprises the treatment of the solution obtained as in claim N? 2 in b) with zinc powder to precipitate the lead. .10) A method as described in claim ^ N? J2 in a) where said ammonium chloride solution can be be replaced by the solutions obtained as in claim N? 2 in d) g) i) m) and as in claim N? 7 in b) ._