CA2104736A1 - Process for high extraction of zinc from zinc ferrites - Google Patents
Process for high extraction of zinc from zinc ferritesInfo
- Publication number
- CA2104736A1 CA2104736A1 CA002104736A CA2104736A CA2104736A1 CA 2104736 A1 CA2104736 A1 CA 2104736A1 CA 002104736 A CA002104736 A CA 002104736A CA 2104736 A CA2104736 A CA 2104736A CA 2104736 A1 CA2104736 A1 CA 2104736A1
- Authority
- CA
- Canada
- Prior art keywords
- stage
- zinc
- solid
- jarosite
- liquid separation
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B19/00—Obtaining zinc or zinc oxide
- C22B19/20—Obtaining zinc otherwise than by distilling
- C22B19/22—Obtaining zinc otherwise than by distilling with leaching with acids
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
- C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
- C22B3/06—Extraction of metal compounds from ores or concentrates by wet processes by leaching in inorganic acid solutions, e.g. with acids generated in situ; in inorganic salt solutions other than ammonium salt solutions
- C22B3/08—Sulfuric acid, other sulfurated acids or salts thereof
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Metallurgy (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Environmental & Geological Engineering (AREA)
- Geology (AREA)
- Geochemistry & Mineralogy (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Inorganic Chemistry (AREA)
- Manufacture And Refinement Of Metals (AREA)
Abstract
Abstract of the Disclosure:
A process for high extraction of zinc from calcine containing zinc oxide and zinc ferrite, comprises the steps of leaching such calcine with a sulphuric acid bearing solution in a neutral leach stage followed by a low acid leach stage with a first solid-liquid separation stage between the neutral and low acid leach stages to dissolve the zinc oxide while leaving the zinc ferrite substantially undissolved, separating a residue containing the zinc ferrite in a second solid-liquid separation stage following the low acid leach stage, leaching the zinc ferrite with a sulphuric acid bearing solution at an initial acid concentration of 50-60 g/l and a temperature of 90°C up to boiling to simultaneously dissolve the zinc ferrite and precipitate the iron content of the ferrite as a jarosite by the addition of ammonia or other alkali ions to the leaching solution, separating a residue containing jarosite in a third solid-liquid separation stage, neutralizing the overflow of the third solid-liquid separation stage to a pH of about 1.4-1.8 with neutral leach underflow from the first solid-liquid separation stage or calcine at a temperature of at least 75°C to further precipitate iron as jarosite and reduce the soluble iron concentration to less than 4 g/l, and recycling the content of the neutralization/iron precipitation stage to the low acid leach stage.
A process for high extraction of zinc from calcine containing zinc oxide and zinc ferrite, comprises the steps of leaching such calcine with a sulphuric acid bearing solution in a neutral leach stage followed by a low acid leach stage with a first solid-liquid separation stage between the neutral and low acid leach stages to dissolve the zinc oxide while leaving the zinc ferrite substantially undissolved, separating a residue containing the zinc ferrite in a second solid-liquid separation stage following the low acid leach stage, leaching the zinc ferrite with a sulphuric acid bearing solution at an initial acid concentration of 50-60 g/l and a temperature of 90°C up to boiling to simultaneously dissolve the zinc ferrite and precipitate the iron content of the ferrite as a jarosite by the addition of ammonia or other alkali ions to the leaching solution, separating a residue containing jarosite in a third solid-liquid separation stage, neutralizing the overflow of the third solid-liquid separation stage to a pH of about 1.4-1.8 with neutral leach underflow from the first solid-liquid separation stage or calcine at a temperature of at least 75°C to further precipitate iron as jarosite and reduce the soluble iron concentration to less than 4 g/l, and recycling the content of the neutralization/iron precipitation stage to the low acid leach stage.
Description
210~73~
., "
PROCESS FOR ~EIGH DCTRACTION OF ZINC FROM
ZINC F13RP IT}3 S
., This invention relates to an improved process for a high extraction of zinc from zinc ferrites and efficient precipitation of ferric iron as jarosite.
~AC~GROUND OF THE INV~NTIO~
In the conventional roast-leach-electrowin route for the production of zinc, zinc oxide contained in the calcine (roasted concentrate) is dissolved in a neutral leaching stage, leaving undissolved zinc ferrites in the leach residue. Ferrites dissolution for further zinc recovery requires high temperature and acid concentration in a subseguent stage of the process. Iron, which also dissolves from the zinc ferrites, is precipitated for disposal through one of the following industrial processes:
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210~73~
- Jarosite - Conversion (jarosite) - Goethite - Hematite Only the Jarosite and Conversion processes produce a final jarosite residue; therefore the Goethite and Hematite processes are not considered in the present patent application.
In both the Jarosite and Conversion processes, iron is precipitated at a high temperature (95-105C) as jarosite. In the Jarosite process, the conventional practice consists of dissolving the zinc ferrites in a high-acid-leach and neutralizing with calcine in a following stage to precipitate iron. This process is well known and documented and many different fl~wsheets using jarosite precipitation have been developed in the zinc industry. The process generally suffers from losses of zinc undissolved from the calcine added to the iron precipitation stage and therefore requires additional steps such as a jarosite acid wash to increase zinc recovery. In the Conversion process such as disclosed in Canadian patent No. 1,217,638 granted February 10, 1987, zinc extraction and iron precipitation take place simultaneously without the addition of a neutralizing agent. The major drawback of this process is the limited initial acid concentration (35-45 g/l) which can be 210~73~ ~
tolerated to achieve efficient iron precipitation. The leaching rate of zinc ferrites may be increased by increasing the acid concentration of the solution.
However, increasing the acid concentration also increases the soluble iron concentration in the final solution.
SnMMaRY OF TH~ INVENTION
In the present invention, it has been found that high overall zinc extractions (>99~) and low iron concentration in the final solution can be achieved through a new conversion-type process. The so-called High Acid Conversion (HAC) process consists of leaching calcine containing zinc oxide and zinc ferrite with sulphuric acid in a neutral leach stage followed by a low-acid-leach stage with a first solid-liquid separation stage between the neutral and low acid leach stages to dissolve zinc oxide while leaving the zinc ferrite substantially undissolved, separating a ferritic residue in a second solid-liquid separation stage following the low acid leach stage, simultaneously dissolving the ferritic residue at an initial acid concentration of 50-60 g/l and precipitating iron as jarosite at a temperature of 90C up to boiling by the addition of ammonia or other alkali ions, followed by separation of the jarosite residue in a third solid-liquid separation stage. The overflow of the third solid-liquid separation stage is neutralized to a pH
of about 1.4-1.8 with neutral leach underflow and/or ", ., ~ i .
~.,-, . ~ , .
~10~7~
calcine to further precipitate iron as jarosite and the neutralized solution is recycled to the low-acid~leach stage. It was found that a temperature of 75C in the neutralization step was sufficient to achieve effective precipitation of iron as jarosite.
The underflow from the second solid-liquid separation stage can be washed by counter-current decantation and/or filtration prior to solids disposal.
' ~ The zinc ferrite leaching is preferably continued for a period of about five to seven hours with recycled jarosite seed. The jarosite residue is separated after such period of about six to seven hours.
The neutralization to pH 1.8 is preferably done during the first hour of retention in the neutralization/precipitation stage.
SHORT D~SQIPTION OF THI~ DRAWINS:8 The invention will now be disclosed, by way of example, with reference to flowsheets illustrated in the accompanying drawings in which:
¦ 20 Figure 1 is a flowsheet of a conventional leach-¦ jarosite-process;
Figure 2 is a flowsheet of a conventional leach-conversion process; and Figure 3 is a flowsheet of the new high-acid conversion process.
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~1047~
D~TAIL D~SCRIP~ION OF TH~ INV~N~ION
In the conventional leach-jarosite process illustrated in Figure 1, calcine containing zinc oxide and zinc ferrite is leached with spent electrol~te in a so-called neutral leach stage 10 to dissolve zinc oxide whileleaving the zinc ferrite substantially undissolved. The zinc ferrite residue is separated in a solid-liquid separation stage 12. The overflow from the solid-liquid separation stage 12 is an impure zinc solution which is purified in subsequent stages and sent to electrolysis for zinc recovery. The underflow from the solid-liquid separation stage 12 is a zinc ferrite residue which is fed to a so-called high acid leach stage 14 where the zinc ferrite is dissolved with spent electrolyte and additional sulphuric acid. The solution from ~he high acid leach stage 14 is separated in a second solid-liquid separation stage 16 and neutralized with calcine in a pre-neutralization stage 18. The neutralized zinc sulphate solution is separated in a third solid-liquid separation stage 20. The underflow from the solid-liquid separation stage 20 is recycled to the high acid leach stage while the overflow is contacted with calcine and alkali ions (ammonium, sodium or potassium) in a jarosite precipitation stage 22. The zinc contained in the zinc oxide is transformed to sulphates while zinc ferrites remain undissolved and the soluble iron is precipitated as ~ 21~47~
jarosite. The content of the jarosite precipitation stage is passed through a fourth solid-liguid separation stage 24. The overflow from the solid-liguid separation stage is recycled to neutral leach stage 10 while the underflow ; 5is subjected to a jarosite acid wash stage 26 to increase zinc recovery. The output of the jarosite wash stage is subjected to a fifth solid-liquid separation stage 28.
The overflow from the solid-liquid separation stage Z8 is recycled to jarosite precipitation while the jarosite underflow is discarded.
Figure 2 is a flowsheet of a conventional leach-conversion process wherein zinc extraction and iron precipitation take place simultaneously without the addition of a neutralizing agent (pre-neutralization stage 15 18 of the flowsheet of Figure 1). In the flowsheet of IFigure 2, calcine containing zinc oxide and zinc ferrite Iis leached with spent electrolyte in a first neutral leach stage 30 to dissolve most of the zinc oxide while leaving the zinc ferrite substantially undissolved. The zinc 20ferrite is separated in a solid-liquid separation stage 32. The overflow from the solid-liguid separation stage 32 is an impure zinc solution which is purified in subsequent stages and sent to electrolysis for zinc recovery. The underflow from the solid-liguid separation 25stage 32 is fed to a low acid leach stage 34 where it is leached with spent electrolyte to increase zinc recovery.
"
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-~ 2~0473~
- The content of the low acid leach stage 34 is separated out in a second solid liquid separation stage 36. The overflow from the second solid-liquid separation stage is recycled to neutral leach while the underflow is fed to a so-called conversion stage 38 wherein zinc ferrite is contacted with spent electrolyte and sulphuric acid with the addition of ammonia or other alkali ions to simultaneously leach zinc and precipitate iron without the addition of a neutralizing agent, as disclosed in the above mentioned Canadian patent No. 1,217,638. The content of the conversion stage 38 i5 fed to a third solid-liquid separation stage 40. The overflow from the solid-liquid separation stage 40 is recycled to low acid leach stage 34 while the underflow is jarosite which may be discarded.
The major drawback of this conversion process is the limited initial acid concentration (35-45 g/l) which can be tolerated to achieve efficient iron precipitation.
The leaching rate of zinc ferrites could be increased by ¦ 20 increasing the acid concentration of the solution but ¦ increasing the acid concentration also increases the soluble iron concentration in the final solution. This second phenomenon results in higher circulating loads of iron to the low-acid-leach stage 34 and to the neutral leach stage 30 and is therefore undesirable.
The drawbacks of the normal conversion process ~', ' . ~' ,' ' . , ' ~ ',, ' ~,- ," :' ",' " ' ' ' ' ' . ' ., ' ' ' f~ ~10~73~
are overcome in the flowsheet illustrated in Figure 3, whereby (1) the zinc ferrites are leached with spent electrolyte and sulphuric acid to give >99~ overall zinc extraction and (2) ferric iron is precipitated to a final concentration of <4 g/l soluble iron. The neutral and low acid leach stages of the new conversion process are identical to the normal conversion process. However, the conversion stage is a high acid conversion stage 42 wherein zinc ferrite is leached with spent electrolyte and sulphuric acid at an initial acid concentration of 50-60 g/l and a high temperature of 9~-105C with the addition of ammonia or alkali metal ions to simultaneously dissolve the zinc ferrite and precipitate iron as jarosite. The content of the high acid conversion stage is separated in a solid-liquid separation stage 44. The underflow can be washed by counter-current decantation and/or filtration prior to solids disposal. The overflow from solid-liquid separation stage 44 is neutralized with neutral leach underflow from the first solid~ uid separation stage 32 or calcine to further precipitate iron as jarosite, and recycled to low acid leach stage 34. Surprisingly a temperature of about 75C in the neutralization stage 46 was sufficient to achieve effective precipitation of iron as jarosite to a final concentration of <4 g/l in only three hours.
The process can be operated using existing ;: ~ . : . .
;~
~ ` ~10~7 .. g equipment of a conventional Conversion process; no additional solid-liquid separation equipment is required.
Since jarosite can be precipitated effectively at only 75C, heating of the solution to neutralization is not necessary. When the capacity of neutral leach solid-.~
liquid separation stages is considered a bottleneck, the ! use of neutral leach underflow in the neutralization stage can allow the possibility of increasing plant throughputs with only minor changes to the piping system; no additional calcine feeding system is needed if the i existing one has sufficient capacity.
The invention will now be disclosed with reference to the following examples:
~xamDle 1 (a) High-Acid Conversion Stage A slurry was prepared by mixing 750 ml of LAL
(low acid leach) solution (112 g/l Zn, 5.7 g/l Fe, 10.8 g/l H2SO4), 375 mL of conversion circuit solution (95 g/l Zn, 4.5 g/l Fe, 13.2 g/l H2SOg), 825 ml of spent electrolyte (40 g/l Zn, 185 g/l H2SO4), 141 ml of water, j with 280.5 g of LAL solids (ferritic residue; 18.5% Zn, 42.2~ Fe) and 225 g of jarosite seed (1.37% Zn, 35.7% Fe).
The acid concentration was maintained at 50-60 g/l during the first hour of additions of concentrated sulphuric acid; the mixture was allowed to react for a total of seven hours at 98-100C. A total of 28 g of ammonium : : : , ~ :: ~ :: :
., ~ , .
~ 21 0~ 7~
hydroxide solution containing 29% NH3 was added after two and three hours. The final solids assayed 1.5% Zn, corresponding to an overall zinc extraction (neutral leach, LAL, conversion) of 99.1%. The soluble iron and S acid contents of the final solution were 15 g/l and 37 g/l respectively.
(b) Neutralization/Iron Precipitation Stage One litre of final solution from a High Acid Conversion test (10 g/l Fe, 31 g/l H2SO4) was mixed with g of jarosite seed; the slurry temperature was maintained at 80C. The pH was increased to 1.8 and maintained constant for one hour by adding Neutral Leach underflow which contained 344 g/l solids; the slurry was allowed to react for two additional hours without any pH
adjustment. The final acid and soluble iron concentrations were 12 g/l and 3.9 g/l respectively. The final solids consisted of jarosite and zinc ferrites with traces of Fe2O3 and SiO2.
(c) Low-Acid Leach on Neutralization Residue The final solids from the neutralization/
precipitation test were subjected to a Low-Acid-Leach (75C, 14.5 g/l H2SO4, 100 g/l solids) with a sample of LAL solution (14.5 g/l H2SO4, 2.4 g/l Fe). No iron dissolution was observed after 30 minutes, showing the stability of the solids (jarosite and zinc ferrites) under LAL conditions; the soluble iron and solids concentrations ... :. . : , - . . . .
:~ ~ , . , , , . -,,. ,. , , . . : ::
;i ~ , - . . . . .
~ 210 4 ~ 3 ~
remained unchanged at 2.4 g/l and 100 g/l respectively.
Exzm~le 2 The final iron concentration in solution can be further decreased by increasing the amount of jarosite seed and/or temperature:
(a) a final concentration of 3.6 g/l iron was obtained by carrying out a test as in Example 1 (b), with 100 g of jarosite seed;
(b) a test also carried out as in Example 1 (b), but at 90C, resulted in a final iron concentration of 2.4 g/l.
~xamDle 3 A test was carried out in a way corresponding to Example 1 (b), but at 90C with an initial solution containing 15 g/l soluble ferric iron; the final iron concentration was 1.7 g/l.
The examples mentioned above demonstrate that higher zinc extractions ~>99%) can be achieved in this new two-stage Conversion process while controlling the final soluble iron concentration to <4 g/l. For comparable overall zinc extractions, the final solution produced by the conventional Conversion process contains 10.8-11 g/l soluble ferric iron.
,, ~ ;
, .
,:.~- : ' , . :
,
., "
PROCESS FOR ~EIGH DCTRACTION OF ZINC FROM
ZINC F13RP IT}3 S
., This invention relates to an improved process for a high extraction of zinc from zinc ferrites and efficient precipitation of ferric iron as jarosite.
~AC~GROUND OF THE INV~NTIO~
In the conventional roast-leach-electrowin route for the production of zinc, zinc oxide contained in the calcine (roasted concentrate) is dissolved in a neutral leaching stage, leaving undissolved zinc ferrites in the leach residue. Ferrites dissolution for further zinc recovery requires high temperature and acid concentration in a subseguent stage of the process. Iron, which also dissolves from the zinc ferrites, is precipitated for disposal through one of the following industrial processes:
, ,, ~ -~"-~
:, ,: - ,: . . :
210~73~
- Jarosite - Conversion (jarosite) - Goethite - Hematite Only the Jarosite and Conversion processes produce a final jarosite residue; therefore the Goethite and Hematite processes are not considered in the present patent application.
In both the Jarosite and Conversion processes, iron is precipitated at a high temperature (95-105C) as jarosite. In the Jarosite process, the conventional practice consists of dissolving the zinc ferrites in a high-acid-leach and neutralizing with calcine in a following stage to precipitate iron. This process is well known and documented and many different fl~wsheets using jarosite precipitation have been developed in the zinc industry. The process generally suffers from losses of zinc undissolved from the calcine added to the iron precipitation stage and therefore requires additional steps such as a jarosite acid wash to increase zinc recovery. In the Conversion process such as disclosed in Canadian patent No. 1,217,638 granted February 10, 1987, zinc extraction and iron precipitation take place simultaneously without the addition of a neutralizing agent. The major drawback of this process is the limited initial acid concentration (35-45 g/l) which can be 210~73~ ~
tolerated to achieve efficient iron precipitation. The leaching rate of zinc ferrites may be increased by increasing the acid concentration of the solution.
However, increasing the acid concentration also increases the soluble iron concentration in the final solution.
SnMMaRY OF TH~ INVENTION
In the present invention, it has been found that high overall zinc extractions (>99~) and low iron concentration in the final solution can be achieved through a new conversion-type process. The so-called High Acid Conversion (HAC) process consists of leaching calcine containing zinc oxide and zinc ferrite with sulphuric acid in a neutral leach stage followed by a low-acid-leach stage with a first solid-liquid separation stage between the neutral and low acid leach stages to dissolve zinc oxide while leaving the zinc ferrite substantially undissolved, separating a ferritic residue in a second solid-liquid separation stage following the low acid leach stage, simultaneously dissolving the ferritic residue at an initial acid concentration of 50-60 g/l and precipitating iron as jarosite at a temperature of 90C up to boiling by the addition of ammonia or other alkali ions, followed by separation of the jarosite residue in a third solid-liquid separation stage. The overflow of the third solid-liquid separation stage is neutralized to a pH
of about 1.4-1.8 with neutral leach underflow and/or ", ., ~ i .
~.,-, . ~ , .
~10~7~
calcine to further precipitate iron as jarosite and the neutralized solution is recycled to the low-acid~leach stage. It was found that a temperature of 75C in the neutralization step was sufficient to achieve effective precipitation of iron as jarosite.
The underflow from the second solid-liquid separation stage can be washed by counter-current decantation and/or filtration prior to solids disposal.
' ~ The zinc ferrite leaching is preferably continued for a period of about five to seven hours with recycled jarosite seed. The jarosite residue is separated after such period of about six to seven hours.
The neutralization to pH 1.8 is preferably done during the first hour of retention in the neutralization/precipitation stage.
SHORT D~SQIPTION OF THI~ DRAWINS:8 The invention will now be disclosed, by way of example, with reference to flowsheets illustrated in the accompanying drawings in which:
¦ 20 Figure 1 is a flowsheet of a conventional leach-¦ jarosite-process;
Figure 2 is a flowsheet of a conventional leach-conversion process; and Figure 3 is a flowsheet of the new high-acid conversion process.
~ " .
~1047~
D~TAIL D~SCRIP~ION OF TH~ INV~N~ION
In the conventional leach-jarosite process illustrated in Figure 1, calcine containing zinc oxide and zinc ferrite is leached with spent electrol~te in a so-called neutral leach stage 10 to dissolve zinc oxide whileleaving the zinc ferrite substantially undissolved. The zinc ferrite residue is separated in a solid-liquid separation stage 12. The overflow from the solid-liquid separation stage 12 is an impure zinc solution which is purified in subsequent stages and sent to electrolysis for zinc recovery. The underflow from the solid-liquid separation stage 12 is a zinc ferrite residue which is fed to a so-called high acid leach stage 14 where the zinc ferrite is dissolved with spent electrolyte and additional sulphuric acid. The solution from ~he high acid leach stage 14 is separated in a second solid-liquid separation stage 16 and neutralized with calcine in a pre-neutralization stage 18. The neutralized zinc sulphate solution is separated in a third solid-liquid separation stage 20. The underflow from the solid-liquid separation stage 20 is recycled to the high acid leach stage while the overflow is contacted with calcine and alkali ions (ammonium, sodium or potassium) in a jarosite precipitation stage 22. The zinc contained in the zinc oxide is transformed to sulphates while zinc ferrites remain undissolved and the soluble iron is precipitated as ~ 21~47~
jarosite. The content of the jarosite precipitation stage is passed through a fourth solid-liguid separation stage 24. The overflow from the solid-liguid separation stage is recycled to neutral leach stage 10 while the underflow ; 5is subjected to a jarosite acid wash stage 26 to increase zinc recovery. The output of the jarosite wash stage is subjected to a fifth solid-liquid separation stage 28.
The overflow from the solid-liquid separation stage Z8 is recycled to jarosite precipitation while the jarosite underflow is discarded.
Figure 2 is a flowsheet of a conventional leach-conversion process wherein zinc extraction and iron precipitation take place simultaneously without the addition of a neutralizing agent (pre-neutralization stage 15 18 of the flowsheet of Figure 1). In the flowsheet of IFigure 2, calcine containing zinc oxide and zinc ferrite Iis leached with spent electrolyte in a first neutral leach stage 30 to dissolve most of the zinc oxide while leaving the zinc ferrite substantially undissolved. The zinc 20ferrite is separated in a solid-liquid separation stage 32. The overflow from the solid-liguid separation stage 32 is an impure zinc solution which is purified in subsequent stages and sent to electrolysis for zinc recovery. The underflow from the solid-liguid separation 25stage 32 is fed to a low acid leach stage 34 where it is leached with spent electrolyte to increase zinc recovery.
"
,f - ' ,.-i . . ", , , , . :
,;, ~ ~ ........ . . . .. .
-~ 2~0473~
- The content of the low acid leach stage 34 is separated out in a second solid liquid separation stage 36. The overflow from the second solid-liquid separation stage is recycled to neutral leach while the underflow is fed to a so-called conversion stage 38 wherein zinc ferrite is contacted with spent electrolyte and sulphuric acid with the addition of ammonia or other alkali ions to simultaneously leach zinc and precipitate iron without the addition of a neutralizing agent, as disclosed in the above mentioned Canadian patent No. 1,217,638. The content of the conversion stage 38 i5 fed to a third solid-liquid separation stage 40. The overflow from the solid-liquid separation stage 40 is recycled to low acid leach stage 34 while the underflow is jarosite which may be discarded.
The major drawback of this conversion process is the limited initial acid concentration (35-45 g/l) which can be tolerated to achieve efficient iron precipitation.
The leaching rate of zinc ferrites could be increased by ¦ 20 increasing the acid concentration of the solution but ¦ increasing the acid concentration also increases the soluble iron concentration in the final solution. This second phenomenon results in higher circulating loads of iron to the low-acid-leach stage 34 and to the neutral leach stage 30 and is therefore undesirable.
The drawbacks of the normal conversion process ~', ' . ~' ,' ' . , ' ~ ',, ' ~,- ," :' ",' " ' ' ' ' ' . ' ., ' ' ' f~ ~10~73~
are overcome in the flowsheet illustrated in Figure 3, whereby (1) the zinc ferrites are leached with spent electrolyte and sulphuric acid to give >99~ overall zinc extraction and (2) ferric iron is precipitated to a final concentration of <4 g/l soluble iron. The neutral and low acid leach stages of the new conversion process are identical to the normal conversion process. However, the conversion stage is a high acid conversion stage 42 wherein zinc ferrite is leached with spent electrolyte and sulphuric acid at an initial acid concentration of 50-60 g/l and a high temperature of 9~-105C with the addition of ammonia or alkali metal ions to simultaneously dissolve the zinc ferrite and precipitate iron as jarosite. The content of the high acid conversion stage is separated in a solid-liquid separation stage 44. The underflow can be washed by counter-current decantation and/or filtration prior to solids disposal. The overflow from solid-liquid separation stage 44 is neutralized with neutral leach underflow from the first solid~ uid separation stage 32 or calcine to further precipitate iron as jarosite, and recycled to low acid leach stage 34. Surprisingly a temperature of about 75C in the neutralization stage 46 was sufficient to achieve effective precipitation of iron as jarosite to a final concentration of <4 g/l in only three hours.
The process can be operated using existing ;: ~ . : . .
;~
~ ` ~10~7 .. g equipment of a conventional Conversion process; no additional solid-liquid separation equipment is required.
Since jarosite can be precipitated effectively at only 75C, heating of the solution to neutralization is not necessary. When the capacity of neutral leach solid-.~
liquid separation stages is considered a bottleneck, the ! use of neutral leach underflow in the neutralization stage can allow the possibility of increasing plant throughputs with only minor changes to the piping system; no additional calcine feeding system is needed if the i existing one has sufficient capacity.
The invention will now be disclosed with reference to the following examples:
~xamDle 1 (a) High-Acid Conversion Stage A slurry was prepared by mixing 750 ml of LAL
(low acid leach) solution (112 g/l Zn, 5.7 g/l Fe, 10.8 g/l H2SO4), 375 mL of conversion circuit solution (95 g/l Zn, 4.5 g/l Fe, 13.2 g/l H2SOg), 825 ml of spent electrolyte (40 g/l Zn, 185 g/l H2SO4), 141 ml of water, j with 280.5 g of LAL solids (ferritic residue; 18.5% Zn, 42.2~ Fe) and 225 g of jarosite seed (1.37% Zn, 35.7% Fe).
The acid concentration was maintained at 50-60 g/l during the first hour of additions of concentrated sulphuric acid; the mixture was allowed to react for a total of seven hours at 98-100C. A total of 28 g of ammonium : : : , ~ :: ~ :: :
., ~ , .
~ 21 0~ 7~
hydroxide solution containing 29% NH3 was added after two and three hours. The final solids assayed 1.5% Zn, corresponding to an overall zinc extraction (neutral leach, LAL, conversion) of 99.1%. The soluble iron and S acid contents of the final solution were 15 g/l and 37 g/l respectively.
(b) Neutralization/Iron Precipitation Stage One litre of final solution from a High Acid Conversion test (10 g/l Fe, 31 g/l H2SO4) was mixed with g of jarosite seed; the slurry temperature was maintained at 80C. The pH was increased to 1.8 and maintained constant for one hour by adding Neutral Leach underflow which contained 344 g/l solids; the slurry was allowed to react for two additional hours without any pH
adjustment. The final acid and soluble iron concentrations were 12 g/l and 3.9 g/l respectively. The final solids consisted of jarosite and zinc ferrites with traces of Fe2O3 and SiO2.
(c) Low-Acid Leach on Neutralization Residue The final solids from the neutralization/
precipitation test were subjected to a Low-Acid-Leach (75C, 14.5 g/l H2SO4, 100 g/l solids) with a sample of LAL solution (14.5 g/l H2SO4, 2.4 g/l Fe). No iron dissolution was observed after 30 minutes, showing the stability of the solids (jarosite and zinc ferrites) under LAL conditions; the soluble iron and solids concentrations ... :. . : , - . . . .
:~ ~ , . , , , . -,,. ,. , , . . : ::
;i ~ , - . . . . .
~ 210 4 ~ 3 ~
remained unchanged at 2.4 g/l and 100 g/l respectively.
Exzm~le 2 The final iron concentration in solution can be further decreased by increasing the amount of jarosite seed and/or temperature:
(a) a final concentration of 3.6 g/l iron was obtained by carrying out a test as in Example 1 (b), with 100 g of jarosite seed;
(b) a test also carried out as in Example 1 (b), but at 90C, resulted in a final iron concentration of 2.4 g/l.
~xamDle 3 A test was carried out in a way corresponding to Example 1 (b), but at 90C with an initial solution containing 15 g/l soluble ferric iron; the final iron concentration was 1.7 g/l.
The examples mentioned above demonstrate that higher zinc extractions ~>99%) can be achieved in this new two-stage Conversion process while controlling the final soluble iron concentration to <4 g/l. For comparable overall zinc extractions, the final solution produced by the conventional Conversion process contains 10.8-11 g/l soluble ferric iron.
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Claims (5)
1. A process for high extraction of zinc from calcine containing zinc oxide and zinc ferrite, comprising the steps of:
a) leaching said calcine with a sulphuric acid bearing solution in a neutral leach stage followed by a low acid leach stage with a first solid-liquid separation stage between the neutral and low acid leach stages to dissolve said zinc oxide while leaving the zinc ferrite substantially undissolved;
b) separating a residue containing said zinc ferrite in a second solid-liquid separation stage following said low acid leach stage;
c) leaching said zinc ferrite with a sulphuric acid bearing solution at an initial acid concentration of 50-60 g/l and a temperature of 90°C up to boiling to simultaneously dissolve the zinc ferrite and precipitate the iron content of the ferrite as a jarosite by the addition of ammonia or other alkali ions to the leaching solution;
d) separating a residue containing jarosite in a third solid-liquid separation stage;
e) neutralizing the overflow of said third solid-liquid separation stage to a pH of about 1.4-1.8 with neutral leach underflow from the first solid-liquid separation stage or calcine at a temperature of at least 75°C to further precipitate iron as jarosite and reduce the soluble iron concentration to less than 4 g/l, and f) recycling the content of said neutralization/iron precipitation stage to the low acid leach stage.
a) leaching said calcine with a sulphuric acid bearing solution in a neutral leach stage followed by a low acid leach stage with a first solid-liquid separation stage between the neutral and low acid leach stages to dissolve said zinc oxide while leaving the zinc ferrite substantially undissolved;
b) separating a residue containing said zinc ferrite in a second solid-liquid separation stage following said low acid leach stage;
c) leaching said zinc ferrite with a sulphuric acid bearing solution at an initial acid concentration of 50-60 g/l and a temperature of 90°C up to boiling to simultaneously dissolve the zinc ferrite and precipitate the iron content of the ferrite as a jarosite by the addition of ammonia or other alkali ions to the leaching solution;
d) separating a residue containing jarosite in a third solid-liquid separation stage;
e) neutralizing the overflow of said third solid-liquid separation stage to a pH of about 1.4-1.8 with neutral leach underflow from the first solid-liquid separation stage or calcine at a temperature of at least 75°C to further precipitate iron as jarosite and reduce the soluble iron concentration to less than 4 g/l, and f) recycling the content of said neutralization/iron precipitation stage to the low acid leach stage.
2. A process as defined in claim 1, wherein zinc ferrite leaching is continued for a period of about five to seven hours at a jarosite seed to ferrite ratio of about 0.8-1.2.
3. A process as defined in claim 2, wherein the jarosite residue is separated after said six to seven hours of operation.
4. A process as defined in claim 3, wherein the jarosite residue obtained in said third solid-liquid separation stage is washed prior to disposal.
5. A process as defined in claim 2, wherein neutralization to pH 1.4-1.8 is done during the first hour.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002104736A CA2104736A1 (en) | 1993-08-24 | 1993-08-24 | Process for high extraction of zinc from zinc ferrites |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002104736A CA2104736A1 (en) | 1993-08-24 | 1993-08-24 | Process for high extraction of zinc from zinc ferrites |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2104736A1 true CA2104736A1 (en) | 1995-02-25 |
Family
ID=4152202
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002104736A Abandoned CA2104736A1 (en) | 1993-08-24 | 1993-08-24 | Process for high extraction of zinc from zinc ferrites |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2104736A1 (en) |
Cited By (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1998006879A1 (en) * | 1996-08-12 | 1998-02-19 | Outokumpu Base Metals Oy | Method for leaching zinc concentrate in atmospheric conditions |
| WO2002046481A1 (en) * | 2000-12-08 | 2002-06-13 | Outokumpu Oyj | Method for the hydrolytic precitpitation of iron |
| CN100387733C (en) * | 2006-08-03 | 2008-05-14 | 云南冶金集团总公司技术中心 | Method of extractin zinc from low grade zinc ore |
| RU2482198C1 (en) * | 2012-01-17 | 2013-05-20 | Общество с ограниченной ответственностью "УралЭкоМет" (ООО "УралЭкоМет") | Method to process sludge of neutralisation of acid mine waters |
| CN103290214A (en) * | 2013-05-28 | 2013-09-11 | 中国恩菲工程技术有限公司 | Method for depositing iron from ferruginous zinc sulfate solution |
| RU2535267C1 (en) * | 2013-07-11 | 2014-12-10 | Федеральное государственное бюджетное учреждение науки Институт химии и технологии редких элементов и минерального сырья им. И.В. Тананаева Кольского научного центра Российской академии наук (ИХТРЭМС КНЦ РАН) | Method of purifying nickel chloride solution from manganese |
| CN104946903A (en) * | 2015-07-06 | 2015-09-30 | 中南大学 | Method for recovering metal resource from zinc calcine through reduction roasting-leaching-zinc sinking |
| RU2601526C1 (en) * | 2015-06-29 | 2016-11-10 | Общество с ограниченной ответственностью "НВП Центр-ЭСТАгео" | Combined method of rebellious lead-zinc ores processing |
| RU2604289C1 (en) * | 2015-07-08 | 2016-12-10 | Лидия Алексеевна Воропанова | Method of purifying nickel electrolyte from impurities of iron (iii), cobalt (iii) and copper (ii) by extraction |
| RU2617086C1 (en) * | 2016-03-11 | 2017-04-19 | Айтбер Махачевич Бижанов | Method of selective iron oxide and zinc oxide extraction from gas treatment sludges and dusts of metallurgical units |
| RU2617471C1 (en) * | 2016-03-16 | 2017-04-25 | Федеральное государственное бюджетное учреждение науки Институт химии и технологии редких элементов и минерального сырья им. И.В. Тананаева Кольского научного центра Российской академии наук (ИХТРЭМС КНЦ РАН) | Method for cobalt extracting from sulfate solution containing nickel and cobalt |
| RU2620418C1 (en) * | 2016-01-18 | 2017-05-25 | Лидия Алексеевна Воропанова | Method of processing of zinc cake |
| CN114737064A (en) * | 2022-03-17 | 2022-07-12 | 云南云铜锌业股份有限公司 | Zinc jarosite hydrometallurgy method |
-
1993
- 1993-08-24 CA CA002104736A patent/CA2104736A1/en not_active Abandoned
Cited By (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1998006879A1 (en) * | 1996-08-12 | 1998-02-19 | Outokumpu Base Metals Oy | Method for leaching zinc concentrate in atmospheric conditions |
| WO2002046481A1 (en) * | 2000-12-08 | 2002-06-13 | Outokumpu Oyj | Method for the hydrolytic precitpitation of iron |
| US7118719B2 (en) | 2000-12-08 | 2006-10-10 | Outokumpu Technology Oy | Method for the hydrolytic precipitation of iron |
| CN100387733C (en) * | 2006-08-03 | 2008-05-14 | 云南冶金集团总公司技术中心 | Method of extractin zinc from low grade zinc ore |
| RU2482198C1 (en) * | 2012-01-17 | 2013-05-20 | Общество с ограниченной ответственностью "УралЭкоМет" (ООО "УралЭкоМет") | Method to process sludge of neutralisation of acid mine waters |
| CN103290214A (en) * | 2013-05-28 | 2013-09-11 | 中国恩菲工程技术有限公司 | Method for depositing iron from ferruginous zinc sulfate solution |
| RU2535267C1 (en) * | 2013-07-11 | 2014-12-10 | Федеральное государственное бюджетное учреждение науки Институт химии и технологии редких элементов и минерального сырья им. И.В. Тананаева Кольского научного центра Российской академии наук (ИХТРЭМС КНЦ РАН) | Method of purifying nickel chloride solution from manganese |
| RU2601526C1 (en) * | 2015-06-29 | 2016-11-10 | Общество с ограниченной ответственностью "НВП Центр-ЭСТАгео" | Combined method of rebellious lead-zinc ores processing |
| CN104946903A (en) * | 2015-07-06 | 2015-09-30 | 中南大学 | Method for recovering metal resource from zinc calcine through reduction roasting-leaching-zinc sinking |
| RU2604289C1 (en) * | 2015-07-08 | 2016-12-10 | Лидия Алексеевна Воропанова | Method of purifying nickel electrolyte from impurities of iron (iii), cobalt (iii) and copper (ii) by extraction |
| RU2620418C1 (en) * | 2016-01-18 | 2017-05-25 | Лидия Алексеевна Воропанова | Method of processing of zinc cake |
| RU2617086C1 (en) * | 2016-03-11 | 2017-04-19 | Айтбер Махачевич Бижанов | Method of selective iron oxide and zinc oxide extraction from gas treatment sludges and dusts of metallurgical units |
| RU2617471C1 (en) * | 2016-03-16 | 2017-04-25 | Федеральное государственное бюджетное учреждение науки Институт химии и технологии редких элементов и минерального сырья им. И.В. Тананаева Кольского научного центра Российской академии наук (ИХТРЭМС КНЦ РАН) | Method for cobalt extracting from sulfate solution containing nickel and cobalt |
| CN114737064A (en) * | 2022-03-17 | 2022-07-12 | 云南云铜锌业股份有限公司 | Zinc jarosite hydrometallurgy method |
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