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WO1994008057A1 - Procede permettant de mieux recuperer l'oxyde de zinc - Google Patents

Procede permettant de mieux recuperer l'oxyde de zinc Download PDF

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Publication number
WO1994008057A1
WO1994008057A1 PCT/US1993/008497 US9308497W WO9408057A1 WO 1994008057 A1 WO1994008057 A1 WO 1994008057A1 US 9308497 W US9308497 W US 9308497W WO 9408057 A1 WO9408057 A1 WO 9408057A1
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Prior art keywords
zinc
product solution
solution
temperature
compounds
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WO1994008057B1 (fr
Inventor
Allan S. Myerson
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Metals Recycling Technologies Corp
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Metals Recycling Technologies Corp
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Priority to AU48535/93A priority Critical patent/AU4853593A/en
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Publication of WO1994008057B1 publication Critical patent/WO1994008057B1/fr
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    • 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
    • C22B17/00—Obtaining cadmium
    • C22B17/04—Obtaining cadmium by wet processes
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B13/00—Making spongy iron or liquid steel, by direct processes
    • C21B13/006—Starting from ores containing non ferrous metallic oxides
    • 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
    • C22B13/00—Obtaining lead
    • C22B13/04—Obtaining lead by wet processes
    • C22B13/045—Recovery from waste materials
    • 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
    • C22B19/24—Obtaining zinc otherwise than by distilling with leaching with alkaline solutions, e.g. ammonia
    • 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
    • C22B19/26—Refining solutions containing zinc values, e.g. obtained by leaching zinc ores
    • 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
    • C22B19/30—Obtaining zinc or zinc oxide from metallic residues or scraps
    • 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
    • C22B19/34—Obtaining zinc oxide
    • 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
    • C22B3/12—Extraction of metal compounds from ores or concentrates by wet processes by leaching in inorganic alkaline solutions
    • C22B3/14—Extraction of metal compounds from ores or concentrates by wet processes by leaching in inorganic alkaline solutions containing ammonia or ammonium salts
    • 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
    • C22B5/00—General methods of reducing to metals
    • C22B5/02—Dry methods smelting of sulfides or formation of mattes
    • C22B5/10—Dry methods smelting of sulfides or formation of mattes by solid carbonaceous reducing agents
    • 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
    • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
    • C22B7/006—Wet processes
    • C22B7/008—Wet processes by an alkaline or ammoniacal leaching
    • 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
    • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
    • C22B7/02—Working-up flue dust
    • 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
    • Y02P10/10—Reduction of greenhouse gas [GHG] emissions
    • Y02P10/134—Reduction of greenhouse gas [GHG] emissions by avoiding CO2, e.g. using hydrogen
    • 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

Definitions

  • the present invention relates generally to a method for the recovery of essentially pure zinc oxide and specifically to a method utilizing a combination of leaching and roasting steps, for the recovery of essentially pure zinc oxide in a recycling operation from metal dust containing zinc compounds.
  • Zinc oxide typically is a coarse white or grayish powder which has a variety of uses including as an accelerator activator, as a pigment, as a dietary supplement and in the semiconductor field. Zinc oxide is found in commercial by-products including waste material streams such as fly ash and flue dust. Methods for recovering zinc oxides are known in the art, including recovering zinc oxide from industrial waste materials. Such previous methods have included leaching with mineral acid, caustic soda, ammonium hydroxide, and ammonium carbonate solutions. However, these methods have low yields of zinc oxide and typically do not recovery pure zinc oxide, the recovered zinc oxide being contaminated with other metal salts. Therefore, in order to obtain pure zinc oxide, subsequent roasting and evaporation processes were necessary.
  • U.S. Patent No. 3,849,121 to Burrows discloses a method for the selective recovery of zinc oxide from industrial waste.
  • the Burrows method comprises leaching the a waste material with an ammonium chloride solution at elevated temperatures, separating iron from solution, treating the solution with zinc metal and cooling the solution to precipitate zinc oxide.
  • the Burrows patent discloses a method to take metal dust which is mainly a mixture of iron and zinc oxides and, in a series of steps, to separate out the iron oxides and waste metals.
  • the material obtained in the last step is a mixture of a small amount of zinc oxide, hydrated zinc phases which can include hydrates of zinc oxide and zinc hydroxide, as well as other phases and a large amount of diamino zinc dichloride Zn( H 3 ) 2 Cl2 or other similar compounds containing zinc and chlorine ions.
  • the Burrows method is not economically viable because of Environmental Protection Agency guidelines established subsequent of the issuance of the Burrows patent. Additionally, the Burrows method is not a continuous method and, therefore, is not economical as a continuous process.
  • Waste metal process dust typically has varying amounts of lead, cadmium and other metals contained in the dust. For various reasons, it is desirable to remove such metals from the waste metal dust, for example to recycle the lead and cadmium and/or to prevent introduction of the lead and cadmium into the atmosphere.
  • the Burrows patent includes a method for removing dissolved lead and cadmium from the ammonium chloride solutions which have been used to treat the waste metal dust. In the Burrows method, powdered zinc dust is added to the ammonium chloride solutions and an electrochemical reaction results in which lead in elemental form deposits on the surface of the powdered zinc dust.
  • U.S. Patent No. 4,071,357 to Peters discloses a method for recovering metal values which includes a steam distillation step and a calcining step to precipitate zinc carbonate and to convert the zinc carbonate to zinc oxide, respectively. Peters further discloses the use of a solution containing approximately equal amounts of ammonia and carbon to leach the flue dust at room temperature, resulting in the extraction of only about half of the zinc in the dust, almost 7% of the iron, less than 5% of the lead, and less than half of the cadmium.
  • the solubility of zinc (or zinc oxide) is relatively high in NH 4 C1 solution which is important to the efficiency of the present process in terms of the rate of the leaching, the mass of dust that can be processed, and the ability to recycle the solution.
  • the rate of the leaching (which is a dissolution process) is a function of the difference between the zinc concentration in solution and the saturation concentration; the higher the saturation concentration the more rapid the leaching.
  • the present process leaches for only 1 hour, while the Peters process leaches for at least several hours.
  • the ammonium chloride solution has the added property that the solubility of zinc (or zinc oxide) in the solution declines rapidly with temperature, which is the basis for the crystallization-based separation which is used later in the process.
  • Lead and lead oxide, as well as cadmium and cadmium oxide, are soluble in the ammonium chloride solution while iron oxide is virtually insoluble.
  • 95-100% of the zinc present as zinc oxide is extracted, compared to about 55% in Peters; 50-70% of the lead present is removed, compared to less than 5% in Peters: as is 50-70% of the cadmium, compared to less than half in Peters.
  • Peters does not remove a significant amount of the impurities so as to leave an acceptably clean effluent.
  • Peters indicates that his residue, which is high in lead and is a hazardous waste, is discarded.
  • the present process produces a material which can be used by the steel producer as they use scrap metal.
  • Peters adds powdered zinc to the solution, which has a tendency to clump reducing the surface area available for the dissolution of the zinc and the plating of the lead and cadmium.
  • the present process teaches a method to minimize this effect through the use of an organic dispersant.
  • Peters steam distills the filtrate, resulting in an increase in temperature which drives off ammonia and carbon dioxide, resulting in the precipitation of iron impurities and then zinc carbonate and other dissolved metals.
  • the purity of the zinc carbonate obtained depends on the rate of steam distillation and the efficiency of solids separation as a function of time.
  • Peters also precipitates iron impurities, zinc carbonate and other carbonates, while the present process only crystallizes zinc salts. Any metal impurities (less than 1%) are surface absorbed or lattice substituted.
  • the filtrate from the cementation step is already hot (90-110°C) and contains a large amount of dissolved zinc with small amounts of trace impurities.
  • crystallization is based on differential solubility, and none of the impurities is present in a concentration which can crystallize, the zinc salts are virtually free of any metal impurities.
  • the final purification step in Peters is a calcining of the zinc carbonate at 600°C to zinc oxide.
  • the mixture of zinc oxide hydrates and diamino zinc dichloride are suspended in hot (90-100°C) water.
  • the zinc oxide is not soluble; however, the zinc diamino dichloride is very soluble and completely dissolves.
  • the remaining solid which is zinc oxide hydrates is then filtered and dried at 100-200°C to remove the water of hydration. The result is a very pure zinc oxide powder of controlled particle size.
  • the present invention satisfies these needs in a method which recovers essentially pure zinc oxide from waste material containing zinc or zinc oxide.
  • the waste material typically including Franklinite and Magnetite
  • the waste material is roasted at temperatures greater than 500°C for a predetermined period of time, before and/or after the material is added to an ammonium chloride solution at a temperature of about 90°C or above.
  • the roasting causes a decomposition of Franklinite into zinc oxide and other components.
  • the roasting process generally comprises the steps of adding heat to the waste material and/or passing heated reducing gases through the waste material. Although all reducing gases are suitable, hydrogen and carbon dioxide are preferred, as well as mixing carbon (activated) with the material and roasting in a gas containing oxygen.
  • the zinc and/or zinc oxide dissolves in the ammonium chloride solution along with other metal oxides contained in the waste material, such as lead oxide and cadmium oxide.
  • the resultant solution is filtered to remove the undissolved materials, such as iron oxides and inert materials such as silicates, which will not dissolve in the ammonium chloride solution, and then dried at a temperature of at least 100°C for at least 60 minutes.
  • finely powdered zinc metal can be added to the resultant, solution at a temperature of about 90°C or above.
  • a dispersant may be added at this point to prevent the finely powdered zinc metal from flocculating and becoming less effective.
  • lead metal and some cadmium plates out on the surface of the zinc metal particles.
  • the addition of sufficient powdered zinc metal results in the removal of virtually all of the lead from the resultant solution.
  • the resultant solution is filtered to remove the solid lead, zinc and cadmium.
  • the filtrate then is cooled to a temperature of between about 20°C and 60°C resulting in the crystallization of a mixture of zinc compounds.
  • the crystallization step helps to achieve a high purity zinc oxide of controlled particle size.
  • the filtrate can be cooled to its final temperature by controlling the cooling profile. The use of a reverse natural cooling profile is preferred as its results in a more desirable nucleation to crystal growth ratio.
  • This mixture contains a significant amount of diamino zinc dichloride, or other complex compounds which involve zinc amino complexes, as well as hydrated zinc oxide and hydroxide species.
  • the solid precipitate is filtered from the solution, the solution recycled, and the solid precipitate washed with water at a temperature between about 25°C and 100°C.
  • the diamino zinc dichloride dissolves in the wash water leaving the majority of the hydrated zinc oxide species as the precipitated solid.
  • the precipitated solid then is filtered from the solution, the resulting solution being recycled, and the solid precipitate placed in a drying oven at a temperature of between about 100°C and 200°C, resulting in a dry white zinc oxide powder.
  • Yet another object of the present invention is to provide a method for recovering zinc oxide in which the leaching and washing solutions are recycled for further use.
  • Still another object of the present invention is to provide a method for recovering zinc oxide which also results in the precipitation in elemental form of any lead and cadmium metals contained in the starting materials.
  • a further object of the present invention is to provide a method for recovering zinc oxide in which iron oxide contained in the starting materials is not put into solution.
  • An additional object of the present invention is to provide a method for recovering zinc oxide in which lead, cadmium and other metals contained in the starting materials can be removed from the process using a minimal amount of powdered zinc dust.
  • Yet another object of the present invention is to provide a method for recovering zinc oxide in which the powdered zinc dust added to the intermediate solutions is kept dispersed using water soluble polymers which act as antiflocculants or dispersants.
  • Still another object of the present invention is to provide a method for recovering zinc oxide in which Franklinite is decomposed to zinc oxide and other materials through roasting.
  • a final object of the present invention is to provide a method for recovering zinc oxide which is economical, quick and efficient.
  • Fig. IA is an X-ray diffraction of the precipitate obtained in Example 1 (many phases).
  • Fig. IB is an X-ray diffraction of the precipitate after drying ZnO + Zn(NH 3 ) 2 Cl 2 .
  • Fig. 1C is an X-ray diffraction of the precipitate after washing and drying ZnO.
  • Fig. 2A is an X-ray diffraction of the precipitate obtained in Example 4 (many phases).
  • Fig. 2B is an X-ray diffraction of the precipitate after drying ZnO + Zn(NH 3 ) Cl 2 .
  • Fig. 2C is an X-ray diffraction of the precipitate after washing and drying ZnO.
  • a typical industrial waste stream used is a flue gas where the charge contains galvanized steel, having the following percent composition:
  • siliceous material such as slag
  • carbon granules occluded molybdinum, antimony, indium, cadmium, germanium, bismuth, titanium, nickel and boron.
  • ammonium chloride solution in water is prepared in known quantities and concentrations.
  • the feed material which contains the zinc species such as the dust described immediately above or the waste material flue dust described in Table I or any other feed material source containing zinc or zinc oxide mixed with other metals, is added to the ammonium chloride solution at a temperature of about 90 ⁇ C or above.
  • the zinc and/or zinc oxide dissolves in the ammonium chloride solution along with other metal oxides, such as lead oxide and cadmium oxide.
  • the solubility of zinc oxide in ammonium chloride solutions is shown in Table II.
  • the zinc oxide, as well as smaller concentrations of lead or cadmium oxide, are removed from the initial dust by the dissolution in the ammonium chloride solution.
  • the solid remaining after this leaching step contains zinc, iron, lead and cadmium, and possibly some other impurities.
  • the remaining solid is then roasted in a reducing atmosphere, typically at a temperature greater than 420°C and often at 700°C to 900°C.
  • the reducing atmosphere can be created by using hydrogen gas, simple carbon species gases such as carbon dioxide, or by heating the material in an oxygen containing gas in the presence of elemental carbon. Typical roasting times are from 30 minutes to 4 hours.
  • the waste dust first may be roasted and second may be leached, omitting the first leaching step.
  • the dust After the dust has been roasted, it is subjected to another leaching step in 23% by weight ammonium chloride solution in water at a temperature of at least 90°C. Any zinc or zinc oxide formed during the roasting step dissolves in the ammonium chloride solution. The zinc oxide and ammonium chloride solution then is filtered to remove any undissolved material. After filtering, for analysis, the solid may be separated out and dried at a temperature of over 100°C, typically between 100°C and 200°C, for about 30 minutes to 2 hours, typically 1 hour.
  • Powdered zinc metal alone may be added to the zinc oxide and ammonium chloride solution in order to remove the solid lead and cadmium.
  • the zinc powder typically aggregates to form large clumps in the solution which sink to the bottom of the vessel. Rapid agitation typically will not prevent this aggregation from occurring.
  • any one of a number of water soluble polymers which act as antiflocculants or dispersants may be used.
  • a number of surface active materials also will act to keep the zinc powder suspended, as will many compounds used in scale control. These materials only need be present in concentrations of 10 - 1000 ppm.
  • Suitable materials include water soluble polymer dispersants, scale controllers, and surfactants, such as lignosulfonates, polyphosphates, polyacrylates, polymethacrylates, maleic anhydride copolymers, polymaleic anhydride, phosphate esters and phosponates.
  • surfactants such as lignosulfonates, polyphosphates, polyacrylates, polymethacrylates, maleic anhydride copolymers, polymaleic anhydride, phosphate esters and phosponates.
  • Flocon 100 and other members of the Flocon series of maleic-based acrylic oligmers of various molecular weights of water soluble polymers, produced by FMC Corporation also are effective. Adding the dispersants to a very high ionic strength solution containing a wide variety of ionic species is anathema to standard practice as dispersants often are not soluble in such high ionic strength solutions.
  • the filtrate then is cooled to a temperature of between about 20°C and 60°C resulting in the crystallization of a mixture of zinc compounds.
  • the mixture contains a significant amount of diamino zinc dichloride, or other complex compounds which involves zinc amino complexes, hydrated zinc oxides and hydroxide species. Crystallization helps to achieve a high purity zinc oxide of controlled particle size, typically through control of the temperature-time cooling profile. Reverse natural cooling, that is cooling the solution slower at the beginning of the cooling period and faster at the end of the cooling period, is preferred to control the nucleation to crystal growth ratio and, ultimately, the crystal size distribution.
  • the precipitated crystallized solid is filtered from the solution and washed with water at a temperature of between about 25°C and 100°C. The filtered solution is recycled for further charging with feed material.
  • the diamino zinc dichloride dissolves in the water. The solubility of diamino zinc dichloride in water is shown in Table III.
  • the zinc, lead and cadmium contained in the feed materials are amphoteric species, by using ammonium chloride solution these species will go into solution, while any iron oxide present in the feed material will not go into solution.
  • Other solutions such as strong basic solutions having a pH greater than about 10 or strong acidic solutions having a pH less than about 3, also can be used to dissolve the zinc, lead and cadmium species; however, if strong acidic solutions are used, iron oxide will dissolve into the solution, and if strong basic solutions are used, iron oxide will become gelatinous.
  • the lead and cadmium can be removed from the ammonium chloride solution through an electrochemical reaction which results in the precipitation of lead and cadmium in elemental form.
  • the crystallization step of the present process can be done continuously in order to increase the throughout and maximize the zinc oxide yield after the washing and drying step.
  • Example 1-7 do not include roasting and Examples 8-13 include roasting.
  • Examples 10-12 also show variations on the crystallization step, and Example 13 also illustrates the recycle results.
  • X-ray diffraction analyses of the zinc oxide prepared according to these examples indicate the recovery of high purity zinc oxide.
  • a metal dust of composition listed in Table I of the Burrows patent is added to 23% by weight NH 4 C1 solution (30g NH 4 C1 per lOOg H 2 0) , as discussed in the Burrows patent, in the amount of 1 gram of dust per 10 grams of solution.
  • the solution is heated to a temperature of 90°C and stirred for a period of 1 hour, during which the zinc oxide in the dust dissolves.
  • the remaining solid which has a composition of approximately 60% iron oxide, 5% calcium oxide, 5% manganese, 30% other materials, is filtered out of the solution.
  • Powdered zinc is then added to the filtrate at 90°C, causing the precipitation of waste metals, the precipitate containing about 60% lead, 40% zinc, 2% cadmium and 8% other metals.
  • the waste metals are then filtered out and the filtrate is cooled to room temperature (between about 18°C and 30°C) over a period of about two hours.
  • the solution then contains a white precipitate which is not essentially pure zinc oxide but is a mixture of hydrated zinc phases and diamino zinc dichloride.
  • Example 2 A metal dust of composition listed in Table I is added to 23% by weight NH 4 C1 solution (30g NH C1 per lOOg H 2 0) . 1 gram of dust is used per 10 grams of solution. The solution is heated to a temperature of 90°C and stirred for a period of 1 hour. During this period the zinc oxide in the dust dissolves. The remaining solid, having a composition of approximately 60% iron oxide, 5% calcium oxide, 5% manganese, 30% other materials, is filtered out of the solution. Powdered zinc is then added to the filtrate at 90°C. This causes the precipitation of waste metals, the waste metal precipitate containing about 60% lead, 40% zinc, 2% cadmium and 8% other metals. The waste metals are then filtered out and the filtrate is cooled to room temperature (between about 18°C and 30°C) over a period of about two hours. The solution then contains a white precipitate.
  • X-ray diffraction of the precipitate indicates that it is a mixture of hydrated zinc phases and diamino zinc dichloride.
  • the hydrated zinc phases are virtually insoluble in water, however the measurements in Table III show that diamino zinc dichloride is quite soluble in water.
  • a portion of the white precipitate was dried and, as shown in Fig. IB, zinc oxide and diamino zinc dichloride, as well as some other components, are present. The white precipitate is then filtered from the solution and resuspended in water at
  • the ZnO recovered by this Example also had the following components: lead: 866 ppm potassium: 45 ppm calcium: less than 25 ppm manganese: less than 25 ppm chromium: less than 25 ppm
  • Example 1 The procedure of Example 1 is followed until the step in which the zinc containing filtrate is cooled.
  • the diamino zinc dichloride Since the diamino zinc dichloride is more soluble then the majority of the other possible precipitates in the ammonium chloride solution (except for zinc chloride which is so soluble that it will not appear), the diamino zinc dichloride appears as a larger fraction of the solid as the temperature declines.
  • the filtrate was divided into fractions and each fraction cooled to a different temperature. The resulting solids were then filtered, resuspended in water at 90°C for one hour, filtered and dried. The result was 99%+ zinc oxide in all cases, however the yield changed with temperature to which the fraction was cooled as follows:
  • Example 4 ZnO also can be recovered from the wash water used in the process.
  • Fifty grams of dried zinc phase precipitate (the solid obtained after cooling to room temperature) obtained using the procedure of Example 1 is added to lOOg of H 2 0 at 90°C.
  • the diamino zinc dichloride dissolves while only a small amount of the other zinc phases dissolve (due to the ammonium chloride which is part of the diamino zinc dichloride) .
  • the remaining solid is filtered out and is dried resulting in 99%+ zinc oxide.
  • the filtrate is cooled to room temperature and the solid filtered out.
  • the solid is again a mixture of hydrated zinc phases and Zn(NH 3 ) 2 Cl 2 .
  • the solid is washed in 90°C water, filtered and dried resulting in 99% ZnO.
  • the yield is 40% ZnO.
  • the source of the zinc does not have to be dust. If pure ZnO is added to a 23% NH 4 C1 solution, the result is the same. As an example, saturated solutions of ZnO in 23% ammonium chloride solutions were prepared at temperatures ranging from 40°C - 90°C, using the solubility data of Table II. These solutions were then cooled to room temperature over a period of 1 - 2 hours. The resulting solid was filtered, washed in 90°C water, and dried. As before, and as shown in Fig. 2A, the original solid was a mixture of hydrated zinc phases and diamino zinc dichloride. As shown in Fig. 2C, the final product was 99% ZnO.
  • Fig. 2B shows the analysis of the intermediate zinc oxide and diamino zinc dichloride precipitate. The yields obtained as a fraction of the original solid precipitate are listed below:
  • Example 2 shows the present procedure run in a continuous crystallization process to increase the through put and to maximize the zinc oxide yield.
  • the procedure of Example 1 is followed until the step in which the waste metals are precipitated out of the zinc oxide containing solution.
  • Fifty gallons of the solution are used as the feedstock for a continuous crystallization process.
  • the solution initially at about 90°C, is pumped into a 1-gallon jacketed crystallizer equipped with baffles and a draft tube at a rate of 1 gallon per hour.
  • the crystallizer jacket temperature is maintained at about 55 ⁇ C by use of a constant temperature circulating bath.
  • the solution and the product crystals are removed continuously so as to keep the volume of material present in the crystallizer constant.
  • the temperature in the crystallizer is maintained at about 60°C.
  • the product solution flows through a filter which collects the solid.
  • the solid product then undergoes the washing and drying steps as discussed in Example 1.
  • the yield of zinc oxide from this continuous crystallization process is about 60% of the total mass of the solid crystallized.
  • the crystallizer can be operated at lower temperatures; however, lower temperatures decrease the final yield of zinc oxide obtained as shown in Example 2.
  • the flow rate employed also can be altered along with the crystallizer jacket temperature to minimize crystallization on the crystallizer vessel walls.
  • these variables, along with the crystallizer jacket temperature can be used to alter the crystal size distribution.
  • Example 7 Metal dust of the composition shown in Table I is digested in 23% ammonium chloride solution at about 90°C
  • One gram of zinc metal dust is used per 10 grams of ammonium chloride solution. After one hour the remaining solid is filtered out of the solution.
  • 500 cc of the solution is put into each of two vessels with stirrers and the temperature of the solutions is maintained at 90°C.
  • 500 ppm of Flocon 100 is added to one of the vessels, while nothing is added to the other vessel.
  • Four-tenths of a gram (0.4g) of 200 mesh zinc dust then is added to each of the two solutions. In the solution containing the Flocon 100, the zinc dust remains suspended, while in the solution containing any additive the zinc dust clumps together (flocculates).
  • the solids are filtered out of each of the solutions, weighed and analyzed.
  • the mass of solid from the solution which contained the dispersant was 1.9 grams and comprised approximately 21% zinc, 75% lead, 2% cadmium and the remaining, amount other metals.
  • the mass of solid obtained from the solution with no dispersant was 1.2 grams and comprised approximately 33% zinc, 63% lead, 2% cadmium and the remaining amount other metals. From this example, it can be seen that the additional step of adding a dispersant increases the amount of lead and other metals removed from the waste stream in solution.
  • the zinc dust obtained from various sources have shown by chemical analysis to contain from 20% - 25% zinc by weight. X-ray powder diffraction indicates clearly the existence of certain crystalline phases in this dust, specifically zinc oxide. The positive identification of the iron phase is complicated by the possible structural types (i.e. Spinel type iron phases showing almost identical diffraction patterns).
  • the zinc oxide (as well as smaller concentrations of lead or cadmium oxide) are removed from the initial dust by dissolution in a concentrated ammonium chloride solution (23% ammonium chloride) .
  • the roasting step can be carried out prior to the initial leaching step, or between a first and second leaching step.
  • the powder containing the Franklinite and Magnetite such as the waste duct, is heated to temperatures greater than 500 ⁇ C. This temperature causes a reaction which causes a decomposition of the stable Franklinite phase into zinc oxide and other components, and yet does not allow for the complete reduction of zinc oxide to zinc metal.
  • the resulting zinc oxide can be removed by sublimation or extraction with an ammonium chloride solution, such as by following the steps detailed above under the general process.
  • the resulting material after extraction has less than 1% by weight zinc.
  • the dust can be roasted using many conventional roasting processes, such as, for example, direct or indirect heating and the passing of hot gases through the dust.
  • non-explosive mixtures of reducing gases such as for example hydrogen gas and nitrogen or carbon dioxide
  • Hydrogen gas is not the only species that may be used for reductive decomposition of Franklinite. It is possible to use carbon or simple carbon containing species. Heterogeneous gas phase reductions are faster than solid state reductions at lower temperatures and therefore suggest the use of carbon monoxide.
  • the carbon monoxide can be generated in situ by mixing the Franklinite powder with carbon and heating in the presence of oxygen at elevated temperatures. The oxygen concentration is controlled to optimize CO production.
  • the carbon monoxide may be introduced as a separate source to more clearly separate the rate of carbon monoxide preparation from the rate of Franklinite decomposition.
  • the prepared zinc oxide can then be removed by either ammonium chloride extraction or sublimation.
  • the roasting process also can be performed to complete reduction by using carbon at high temperatures and collecting zinc metal that will melt at very low temperatures (420 ⁇ C) and boil at 907°C.
  • zinc metal is obtained that can, if desired, be readily converted to the oxide by air roasting.
  • Example 8 A dust containing 19.63% Zn, 27.75% Fe, 1.31%
  • Example 9 A dust with composition given in Table I is leached in 23% ammonium chloride solution for 1 hour at 100°C.
  • the solid remaining (which contained 14% Zn) was placed in a quartz boat and heated to 700°C in an atmosphere of 8% hydrogen, 92% argon in mixture.
  • the material was cooled and reheated at 100°C in 23% ammonium chloride solution at 100°C.
  • the solid was separated, dried and analyzed for zinc. The zinc was found to be less than 1%.
  • the leached-roasted-leached material then can be subjected to the remainder of the general process to recover zinc oxide.
  • the purpose of the crystallization/washing step is to produce a high purity zinc oxide of controlled particle size. This is accomplished through control of the temperature-time profile during cooling in the crystallization.
  • the crystallization step in the process takes the filtrate from the cementation step at 90-110°C.
  • This filtrate contains the dissolved zinc with small amounts of trace impurities such as lead and cadmium.
  • trace impurities such as lead and cadmium.
  • Solvent inclusions are pockets of liquid trapped as a second phase inside the crystals. Control of crystallization conditions can be employed to reduce these impurities. An example is given below.
  • Example 10 A dust of composition given in Table I is taken through the leaching and cementation steps. After cementation the filtrate is at 100 ⁇ C. 500 ml of this filtrate is placed in a jacketed stirred vessel with the jacket temperature at 100°C. The temperature is lowered in the crystallizer as follows:
  • the cooling profile in Example 10 is known as a reverse natural cooling profile. Such a profile is the opposite shape as that which is observed by natural cooling. In a reverse natural cooling profile, the cooling is slower at the beginning and faster at the end; in a natural cooling profile, the cooling is faster at the beginning and slower at the end.
  • This type of cooling profile also is used to control the crystal size distribution (CSD) of the zinc oxide obtained.
  • the cooling profile controls the ratio of nucleation (birth of a new crystal) to crystal growth (growth of existing crystals). The ratio of nucleation/growth determines the final CSD.
  • a 23% ammonium chloride solution at 100°C containing 11 wt% dissolved ZnO is divided into 4 portions. Each portion is placed in a jacketed agitated vessel.
  • the cooling profiles in each vessel are given below:
  • the purpose of this process is to produce pure zinc oxide from waste dust containing zinc. To do so this efficiently and in a safe and cost effective way, the process recycles all zinc which in not removed from the leachate in the crystallization step. In addition, the diamino zinc dichloride which is redissolved in water in the washing step also is recycled. The recycle of zinc increases the overall zinc concentration in liquid solution in the process. This allows the crystallizer to operate at a higher temperature. This is due to the rapid change in zinc oxide solubility with temperature in ammonium chloride solution.
  • An example of the process with recycle is given below: Example 13
  • the steady state zinc concentration can be raised to 7g/100g of solution. If the outlet of the crystallizer is kept at 60°C, 3g/100g solution of solid will crystallize (the solid is a mixture of zinc oxide and diamino zinc dichloride). The system does not have to be cooled further since this is an efficient way to operate to conserve energy (one does not have to cool then reheat the solution) . In addition, operating at the higher Zn concentration improves the ratio of ZnO/diamino zinc dichloride produced in the crystallizer.
  • the recycle has the advantage that the solution becomes saturated relative to certain materials present in the dust, such as CaO. When this occurs, CaO no longer is leached from the dust but remains with the iron in the iron cake. This increases the value of the cake since CaO is still present and will not have to be added when the iron cake is fed to a furnace in steel making. Another important advantage in that there is no liquid effluent in this process. The only products are solid (iron cake, zinc oxide, waste metals), which are then sold for use in various industrial processes. No waste is produced since all liquid is recycled.

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Abstract

L'invention se rapporte à un procédé permettant de récupérer l'oxyde de zinc provenant de déchets industriels de composants divers, y compris le zinc, le plomb, le fer et le cadmium, en calcinant les déchets à une température élevée, en les traitant avec une solution de chlorure d'ammonium maintenue à une température élevée, en séparant les composants non dissous de la solution, en traitant la solution avec du métal de zinc pour déloger les ions métalliques non désirés de la solution, en refroidissant la solution afin de précipiter les composés de zinc, en lavant les composés de zinc précipités pour retirer les composés non désirés tels que le dichlorure de diamino-zinc, et en séchant le composé de zinc restant qui est de l'oxyde de zinc essentiellement hydraté; l'on obtient de l'oxyde de zinc essentiellement pur.
PCT/US1993/008497 1992-09-29 1993-09-07 Procede permettant de mieux recuperer l'oxyde de zinc Ceased WO1994008057A1 (fr)

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AU48535/93A AU4853593A (en) 1992-09-29 1993-09-07 Method for the enhanced recovery of zinc oxide

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US07/953,645 1992-09-29

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN100368571C (zh) * 2005-11-23 2008-02-13 中南大学 一种铁-锌和锰-锌的分离方法
EP2814993B1 (fr) * 2012-02-15 2019-07-24 Steel Dynamics Investments, LLC Procédé pour la production d'oxyde de zinc à partir de minerai
WO2024194463A1 (fr) * 2023-03-22 2024-09-26 Belzinc Procédé de récupération de zinc

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3849121A (en) * 1971-11-30 1974-11-19 W Burrows Zinc oxide recovery process
US5120523A (en) * 1989-11-16 1992-06-09 Agency Of Industrial Science & Technology, Ministry Of International Trade & Industry Method for dissolution of metal
US5205004A (en) * 1990-11-28 1993-04-27 J. Nesbit Evans & Co. Ltd. Vertically adjustable and tiltable bed frame

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3849121A (en) * 1971-11-30 1974-11-19 W Burrows Zinc oxide recovery process
US5120523A (en) * 1989-11-16 1992-06-09 Agency Of Industrial Science & Technology, Ministry Of International Trade & Industry Method for dissolution of metal
US5205004A (en) * 1990-11-28 1993-04-27 J. Nesbit Evans & Co. Ltd. Vertically adjustable and tiltable bed frame

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN100368571C (zh) * 2005-11-23 2008-02-13 中南大学 一种铁-锌和锰-锌的分离方法
EP2814993B1 (fr) * 2012-02-15 2019-07-24 Steel Dynamics Investments, LLC Procédé pour la production d'oxyde de zinc à partir de minerai
WO2024194463A1 (fr) * 2023-03-22 2024-09-26 Belzinc Procédé de récupération de zinc
BE1031460B1 (fr) * 2023-03-22 2024-10-21 Belzinc Procédé de récupération de zinc

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