CA2025161A1

CA2025161A1 - Method for selectively recovering lead, zinc and calcium from materials in which they are contained as oxide or salts not soluble in water

Info

Publication number: CA2025161A1
Application number: CA002025161A
Authority: CA
Inventors: Angelo Delalio; Silvano Cossali
Original assignee: Individual
Current assignee: ECONOMETAL Srl
Priority date: 1989-10-20
Filing date: 1990-09-12
Publication date: 1991-04-21
Also published as: IT1236233B; GB9022673D0; FR2653450A1; DE4033232A1; GB2238528A; IT8905221A1; IT8905221A0; ES2026406A6

Abstract

A METHOD FOR SELECTIVELY RECOVERING LEAD ZINC AND CALCIUM FROM
MATERIALS IN WHICH THEY ARE CONTAINED AS OXIDES OR SALTS NOT
SOLUBLE IN WATER
ABSTRACT

A method for selectively recovering lead zinc and calcium from materials containing them as oxides or salts not soluble in water, which includes leaching the above mentioned materials with ammonium chloride solution at its boiling temperature, separating the insoluble solid and treating the obtained solution with carbon dioxide and ammonia to precipitate separately lead, zinc and calcium carbonates from which carbon dioxide is recovered by calcination or by leaching in acids.

Description

2025~61 DESCRIPTION OF THE INVENTION

This invention discloses a method for selectively recovering lead, zinc and calcium from materials containing such metals as oxides or salts that are not soluble in water as e.g. the Waelz oxides and generally the oxides obtained from enrichment thermal treatments of materials containing lead and zinc, electric-steel furnaces dusts, materials from roasting processes on lead and zinc ~inerals, oxidized zinc ores.
The typical average composition of the above mentioned materials are described in the following table:

Table ~yp- of material Quantity ~%) Zinc Lead Calcium Others Waelz oxides 40-65 5-10 1-5 up to 100%
Oxldes ~rom plaoma 40-60 5-12 2-3 up to 100%
Tetronics proceoo oxldeo ~rom plasma 53 9 1-4 up to 100%
~ibur Howden proceoo Oxldeo ~rom Flame 37-46 5-8 1-4 up to 100%
Reactor process Electric-steel 5-35 1-10 1-20 up to 100%
furnaceo d~u~ts Zinc Calcine 55-65 1-4 0.5-3 up to 100%
Ox$dized zinc ores 30-50 0.5-5 0.5-5 up to 100%
(Smithsonite) Low grade oxidized 8-20 1-5 10-30 up to 100%
zinc ores 2~5161 Among the methods for recovering such metals from the above mentioned materials there are:

- Leachinq oxidized zinc materials by sulphuric acids (traditional processes for producing electrolytic zinc) in which lead and calcium remain in the residue as sulphates.

- Double stage leaching in autoclave oxidized zinc materials (U S.
patent no. 4,610,721).
- Leaching with chlorine and electrolysis of zinc chloride in molten salts (Process at low temperature, by B.K. Thomas and D.
G. Fray, England).

- Leaching in strong alkaline ambient (caustic soda) followed by the electrolytic extraction of zinc as dust in alkaline bath (U.S. patent no. 3,743,501 and Promozinc process, France). In the~e proce~ses, calcium remains as residue.

- Carboammoniacal loaching (U.S. patent no. 4,071,357) in which lead and calclum remain ln the residue as carbonates.

The Imperial Smeltlng proce~es which can treat, on a large production scale ~minimum 200,000 ton/year), Waelz oxides calcinated and roa~ted ~rom minerals, yielding metals which need rurther re~ining processes.

- The Plasma process (Scan Dust) which produces zinc metal at Prime Western grade.
- The Waelz ~urnace ~HTR proce~s, U.S.A.7 and Berzelius proce~, Germany), pla~ma processe~ ~Tetronics, England and Tibur Howden, Canada) and the Flame Reactor Process ~F.R.P. Hor~ehead Resource~
Development, USA) which produces enriched materlals.

202~161 Among the above mentioned methods, eome of them only achieve an enrichment of the mentioned metal~, othere produce metals of low quality when compared to that obtained by electrolysis or in a form barely marketable, other methods again extract only zinc with reagent consumption for lead and calcium that remain in the residue. Thi~ invention provides a method to process materials containing oxides or ~alts of lead, zinc and calcium not soluble in water, and to obtain ~eparately the~e elements in a marketable form.

1) The material i~ added to an ammonium chloride solution (which contain from 5 to 85 gr. of ammonium chloride per 100 gr. of water) and the whole is brought and kept at the boiling temperature, corresponding to a pressure that can be between 0.7 and 20 ata, up to the time when ammonia is completely removed ~rom tho solution. During thi~ ~tep, the following reactions tak- place:

M-0 + 2NH~Cl -~ MeCl~ + H20 + 2NH~
MoC0~ + 2NH~Cl -~ MeCl2 + H~0 + C0~ + 2NH, MeS10, + 2NH4Cl -~ MeCl~ + H~0 + sio~ + 2NH3 MeOFe20, + 2NH~Cl -~ MeCl~ + ~0 + Fe~03 + 2NH~

where Me ~tand~ for Ca, Zn, Pb and other bivalent metals po~ibly pre~ent a6 impuritie~. The ammonia, which i8 developed durlng thi~ ~tep, i~ used during the following 6tep~ 2), 4) and 5).

At the end o~ thi~ ~tep, the ¢hloride ~olution i~ separated ~rom the re~idue compo~ed of ~llica, ferric oxide, and non ~olubillzed materlal~.

2 ~ 2 ~ ~ 61 2) Thz solution obtained in 1) is treated with ammonia and carbon dioxide keeping the pH between 5.7 and 6.0, precipitating the lead carbonate according to the following reactions:

NH3 + C0z + ~0 -> NH~HC0 NH4HC03 + NH3 -> (NH~)~C0~
PbC12 + (NH~)2C03 -~ PbC03 + 2NH~Cl The lead carbonate i8 then separated from the solution and washed with ammonia solution to purify it from zinc carbonate possibly coprecipitated which is transformed in a soluble zinc ammonium complex.

3) The solution obtained in 2), from which lead carbonate has been separated is treated with zinc powder to precipitate as "cements" the residual lead, that was not precipitate as carbonate in step 2), and other metal more noble than zinc (Cd, Ni, Cu, etc.) possibly present. The "cements" are then separated from the solution.

4) The ~olution obtained in 3) ls treated with ammonia and carbon dioxide at a pH between 6.0 and 6.5 in order to precipitate zinc carbonate according to the ~ollowing reactions:

NH, + C02 + H20 -> NH4HC03 NH4HCOa ~ NHa -~ (NH4)2COa ZnCl2 + (NH4)2C03 -~ ZnC03 + 2NH4Cl The zinc carbonate is then separated ~rom the solution.

5) The solution obtained in 4) i~ treated with ammonia and carbonic dioxide at a pH higher than 6.5 and calcium carbonate precipitates according to the ~ollowing reactions:

2Q2~

N~ia + C2 + P20 -> NH~Hco3 NH4HCO3 + NH3 -> (NH4) 2CJ
CaCl2 + (NH4) 2C03 -> CaCO, + 2NH~Cl The zinc possibly not precipitate in step 4) does not precipitate here (and then it remains in the solution) because under the described condition the soluble zinc-ammonium complex is formed. The calcium carbonate i8 then ~eparated from the solution.

6) The solution obtained in step S), from which the metals has been preclpitated and in which ammonium chloride has been restored according to the reactions de~cribed ln steps 2), 4) and 5) may be re-used in 1) for a new leaching process.
7J The lead carbonate obtained in step 2) is either calcinated in order to obtain lead oxide or leached in mineral acids (e.g.
~luoboric acid) and then extracted as electrolytic lead: in both ca~e~ carbon dioxide i~ obtained to be used in steps 2), 4) and 5).

8) The zinc carbonate obtained in step 5) is either calcinated to obtain zinc oxide~ or leached in mineral acids (e.g. sulphuric acid) and then extracted a~ electrolytic zinc; in both cases carbon dioxide ls recovered to be used in steps 2), 4) and 5).

9) The calclum carbonate obtained in 5) is calcinated to obtain calcium oxide and carbon dioxide is recovered to be used in step~ 2, 4) and 5).
The invention above described will be better understood by the ~ollowing example, which i6 ~u~t illu~trative o~ ~ome particular embodiments o~ the invention on electric-~teel ~urnaces dust~;
however, the pre~ent example has not to be con~trued as limiting 2~2~6~

the invention to the condition or ~aterials therein used.

EXAMPLE

This invention provide a method for recovering, e.g. lead and zinc from the electric-steel furnaces dusts. The dusts used in the present example, have the following composition:

Zinc18.6%
Lead4.3%
Calcium2.0%
Iron39.0%
Cadmium0.07%
The dust i5 added, in a proportion of 450 g/l, to an aqueous ~olution which contain 400 g/l of ammonium chloride; the whole is brought and kept at the boiling temperature at a pressure of 1 ata:
when no more ammonia will di~tillate from the ~olution, the solid 1~ ~oparatod by a hot filtration. The solid obtained, washed with bolllng water, i~ ~ound to have the following composition:

Zin¢ 8.0%
Lead~.1%
Calclum1.3%
Iron50.0%
Cadmium0.006%

Ammonium bicarbonate and ammonia are added to the filtered ~olution, keeping the pH lower then 6.0; lead carbonate precipitate and i~ then ~eparated by filtration.

2~25~l6~

The filtered solution has the following composition:

Zinc 54 g/l Lead 1.5 g/l Calcium 4.4 g/l Zinc powder i6 then added to precipitate, as "cements", lead and the metals more noble then zinc (such as Cd, Cu, etc.) which will be separated by filtration.
Ammonium bicarbonate and ammonia are added to the filtered solution keeping the pH at 6.5: under these conditions, the precipitation of zinc carbonate take place and the solid is separated by filtration. The filtered solution has at present the following composition:

Zinc 23 g/l Lead 4.2 g/l ~hi~ ~olution iB brought to a pH higher then 6.5, with ammonia and ~monium carbonate to preclpitate aalcium carbonate which i~
separated by ~iltration. The resulting solution may be re-used for a new loaching process.

Claims

1. A method for selectively recovering lead, zinc and calcium from materials in which they are contained as oxides or as salts not soluble in water such as, e.g. the Waelz oxides and generally the oxides obtained from enrichment thermal treatments of material containing lead and zinc; Electric-steel furnaces dusts; the materials from roasting processes of lead and zinc minerals; oxidized zinc ores.

2. A method as described in claim 1, which comprises:

a) the treatment of the above mentioned materials with an ammonium chloride solution kept at high temperature in order to solubilize (as chlorides) the oxides and the various salts of lead, zinc and calcium and to distillate the ammonia produced by the reactions;

b) the separation of ferric oxides, silica and the insoluble residues, from the solution;

c) the addition, to the solution obtained in step b), of ammonia and carbon dioxide at a pH lower than 6.0, in order to precipitate lead carbonate;
d) the separation of the lead carbonate from the solution;

e) washing the lead carbonate, separated in step d), with ammonia solution in order to solubilize the zinc carbonate possibly co-precipitated in step c);

f) the treatment of the solution obtained in step d) with zinc powder in order to precipitate as "cements" the residual lead and other metals, more noble then zinc, possibly present;

g) the separation from the solution of the "cements"
precipitated in step f);

h) the treatment of the solution obtained in step g) with ammonia and carbon dioxide at a pH between 6.0 and 6.5 in order to precipitate zinc carbonate;
i) the separation of zinc carbonate from the solution;

j) the treatment of the solution obtained in i) with ammonia and carbon dioxide at a pH higher than 6.5, to precipitate calcium carbonate;
k) the separation of calcium carbonate from the solution;

l) recovering carbon dioxide either by calcining or by leaching in acids the lead carbonate;

m) recovering carbon dioxide either by calcining or by leaching in acids the zinc carbonate;

n) recovering carbon dioxide by calcining the calcium carbonate;

o) recycling the carbon dioxide recovered in steps 1), m) and n) during the precipitation of the carbonates in steps c), h) and j);

p) recycling the ammonia obtained in step a) during the precipitation of the carbonate in step c), h) and j).

3. A method as described in claim 2, step a), where the concentration of the ammonium chloride solution ranges from 5 g. to 85 g. per 100 g. of water.

4. A method as described in claim 2, step a), where the high temperature therein mentioned ranges from 80°C to the boiling temperature of the above mentioned solution.

5. A method, as described in claim 4, where the boiling temperature therein mentioned is that corresponding to a working pressure ranging from 0.7 to 20 ata.

6. A method as described in claim 2, step a), where the high temperature therein mentioned is maintained for a time ranging from thirty minutes to the time necessary to completely distillate the ammonia from the solution.

7. A method as described in claim 2, which comprises:

a) the treatment of the solution obtained in claim 2, step b), with ammonia and carbon dioxide at a pH lower than 6.5, to coprecipitate, at the same time, lead and zinc carbonate;

b) the separation of lead and zinc carbonate from the solution;

c) the treatment of the lead and zinc carbonate with an ammonia solution in order to dissolve the zinc carbonate as zinc-ammonium-carbonate complex;

d) the separation of lead carbonate from the solution containing the zinc-ammonium-carbonate complex:

e) stripping the ammonia from the solution containing the zinc-ammonium-carbonate complex in order to precipitate zinc carbonate.

8. A method as described in claim 2, step c), h) and ;) and in claim 7, step a), where the ammonia and carbon dioxide, therein mentioned, may also be under the form of ammonium carbonate or ammonium bicarbonate or ammonium carbammato or their mixtures with ammonia and carbon dioxide.

9. A method comprising the treatment of the solution obtained as in claim 2, step b) with zinc powder to precipitate lead.

10. A method ad described in claim 2, step a), where the ammonium chloride therein mentioned may be replaced by the solution obtained as in claim 2, step d), g), i) and k) and as in claim 7, step b).