MXPA99009396A - Method for utilizing ph control in the recovery of metal and chemical values from industrial waste streams - Google Patents

Abstract

An improved method for the recovery of metal and/or chemical values from an industrial waste stream containing zinc, cadmium, lead and/or iron compounds by heating the waste stream in a reducing atmosphere, treating the resultant fumes in an ammonium chloride solution, separating any undissolved components from the solution, adjusting the pH of the solution, if necessary, to less than about 6.3, displacing undesired metal ions from the solution using zinc metal, treating the solution to remove therefrom zinc compounds, adjusting the pH of the solution to about 6.5 to about 7.0, and further treating the zinc compounds and the undissolved components, as necessary, resulting in the zinc products and the optional iron-carbon feedstock.

Description

METHOD OF USING pH CONTROL IN RECOVERY OF VALUABLE METALLIC AND CHEMICAL MATERIALS OF THE INDUSTRIAL WASTEWATER EXTRACT OF THE RELATED APPLICATIONS This application is a continuation of the application with serial number 08 / 439,352 filed on May 11, 1995, currently pending. BACKGROUND OF THE INVENTION. 1. Field of the Invention The present invention generally relates to a process for the recovery of valuable metallic and chemical materials including, for example, essentially pure zinc oxide and a residual iron coal, from industrial wastewater comprising zinc and iron compounds. The present invention relates more specifically to the control of pH in a process which is subject to wastewater materials comprising zinc compounds; Compounds and / or iron components, such as electric arc furnace dust (EAF), to a combination of reduction and leaching steps in a recycling operation that recycles process solutions to reuse and recover valuable metals and / or chemicals . 2. Related Art The United States Patent for Burrows, now expired but assigned to a cession director of the present invention, discloses a method for the selective recovery of zinc oxide from industrial waste. The Burrows method involves leaching a waste material with an ammonium chloride solution at elevated temperatures, separating the iron from the solution, treating the solution with zinc metal and cooling the solution to precipitate the zinc oxide. The Burrows patent discloses a method for collecting EAF dust that is primarily a mixture of iron and zinc oxides and in a series of steps, separating the oxides of iron and other metals. However, the material obtained in the last step is a mixture of a small amount of zinc oxide, zinc hydrated phases that can include zinc oxide hydrates and zinc hydroxide, as well as other phases and a large amount of diamino zinc dichloride Zn (NFÍ3) 2Cl2 or other similar compounds containing zinc and chlorine ions. Currently, the Burrows method is not economically viable due to the guidelines established by the Environmental Protection Agency subsequent to the issuance of the Burro ws patent. Additionally, the Burrows method is not a continuous method and therefore, is not as economical as a continuous process. The first step in the Burrows patent is to treat the EAF powder with an ammonium chloride solution. The action of the treatment is the leaching of zinc oxide, lead oxide and cadmium oxide in the solution without any leaching of the iron oxides present. Burrows does not teach the control of the solubility of zinc compounds in the ammonium chloride solution more than the variation by temperature. As a result, the Burrows method does not disclose or contemplate the control of solubility by controlling the pH. Patent Number 4,071,357 to Peters discloses a method for the recovery of valuable metal materials which includes a steam distillation step and a calcination step for precipitating zinc carbonate and zinc oxide, respectively. Peters still discloses the use of a solution containing approximately equal amounts of ammonia and carbon to leach the chimney dust at room temperature, resulting in the extraction of only about half the zinc in the dust, almost 7% of the iron, less of 5% of lead and less than half of cadmium. Steam distillation precipitates zinc carbonate, other carbonates and iron impurities. Steam distillation results in an increase in the temperature that repels ammonia and carbon dioxide, resulting in the precipitation of iron impurities and then zinc carbonate and other dissolved metals. Conversely, the decrease in temperature precipitates a quantity of crystalline zinc compounds. The purity of the zinc carbonate obtained depends on the speed of the steam distillation and the efficiency of the separation of solids as a function of time. Peters does not disclose or contemplate the control of solubility by controlling the pH to control the amount and effect of precipitation. In addition to the advantages of temperature decrease, this process also uses steps to control the solubility of the product solution by varying the pH of the product solution. The co-pending application with Serial Number 08 / 439,352, of which this application is a continuation, describes a method for the recovery of zinc products from industrial wastewater by treating the wastewater with charcoal and a chloride solution of ammonium and the crystallization of zinc products to extract them from the solution. However, the crystallization of zinc compounds can be unpredictable and difficult to control at times. For example, the solubility of zinc compounds may vary depending on the composition of the wastewater. The increased solubility results in more difficulty to crystallize the compounds in the crystallization step. On the other hand, the decrease in solubility can lead to the premature crystallization of the compounds. Both problems reduce the operational efficiency and the economic viability of the process. Therefore, there is a need for a method of recovering valuable metals and chemicals that provides increased control of the solubility of the zinc compounds in an ammonium chloride solution. There is also a need for an improved zinc oxide purification method that utilizes the controlled precipitation of zinc oxide from an ammonium chloride solution. Furthermore, this need is also related to the processes to produce iron-based feeds from industrial wastewater. BRIEF SUMMARY OF THE INVENTION The present invention satisfies these needs in a method that recovers valuable metals and chemicals that contain wastewater, inter alia, zinc or zinc oxide and / or iron or iron oxide, in which the solubility of certain Zinc compounds are controlled by controlling the pH of the product solution. Essentially pure zinc oxide can be recovered, along with zinc metal if desired, and other valuable metallic elements contained in the waste material such as lead, copper, silver and cadmium. The solutions used in the processes are recycled in such a way that the processes do not have any liquid waste. The solids recovered from the process, called zinc oxide, zinc, valuable metals, and other residues, can be used in other processes. For example, some waste can be used directly as a feed for the typical iron or the steel production process. Briefly, the waste material, typically a volatile ash, vacuum dust or chimney dust, such as EAF powder, is heated and reduced to decompose the franklinite into zinc oxide and to reduce any iron oxide present in direct reduced iron. These fumes from the hot waste material, which typically comprise the majority of the solids from the waste materials, are leached with a solution of ammonium chloride, resulting in a solution of the product and undissolved materials. The solution of the product and the undissolved materials are separated, both being treated to recover valuable components. The zinc metal is added to the product solution to bond any lead and cadmium contained in the product solution. The remnant of the product solution is rich in zinc compounds, which can be recovered via a crystallization step. Undissolved materials contain inerts and some alkali salts. Wastewater materials and fumes from hot wastewater materials normally contain chloride in the form of alkali chlorides (sodium and potassium), zinc chlorides, lead chlorides and other complex metal salts. The leaching of this water from waste materials and / or fumes in an ammonium chloride solution can result in a product solution with a low pH (less than 6.3). Low pH translates into zinc compounds, namely, diamino dichloride zinc, more soluble in a given concentration and temperature and, therefore, more difficult to crystallize in the crystallization step. If the pH is higher, on the other hand, the solubility of the zinc compounds at a given concentration and temperatures is reduced, which leads to a premature crystallization of the zinc compounds. Therefore, the solubility of the zinc compounds at a given concentration and temperature can be controlled by monitoring and adjusting the pH at various stages of the process. Preferably, the pH of the product solution is kept low by the addition of a suitable acid until the product solution reaches the crystallizer. This will prevent the crystallization from occurring prematurely. Once the product solution reaches the crystallizer, a suitable base, such as ammonia, is added to decrease the solubility of the zinc compound and facilitate crystallization. The remnant of the product solution can be treated in two ways. The first, the remnant of the product solution can be cooled by precipitating the zinc components of the product solution as a mixture of the crystallized zinc compounds. These crystallized zinc compounds are separated from the product solution, washed and dried at elevated temperatures, resulting in zinc oxide product of 99% or more purity. Second, the remnant of the product solution can be subjected to electrolysis in which the zinc metal sits on the cathode of the electrolysis cell. Any remnant of the product solution after crystallization or electrolysis is recycled again to treat the incoming waste material. Both processes can be carried out in a continuous manner. Therefore, it is an object of the present invention to provide a method for recovering zinc metal, zinc oxide, DRI and / or iron oxide that is economical, easy and efficient. It is another object of the present invention to provide a zinc oxide purification process that utilizes the controlled precipitation of zinc oxide from an ammonium chloride solution. These and other objects, features and advantages of the present invention will be apparent to those skilled in the art when the following Detailed Description of a Preferred Specimen is read in conjunction with the figures. DETAILED DESCRIPTION OF AN EXEMPLARY OF PREFERENCE. The terminology used in this specification is for the purpose of describing only particular specimens and does not intend to be borderline. As used in the specification and the appended claims, the singular forms "a", "an" and "the" include plural references unless the context otherwise clearly dictates otherwise. The "effective amount" of a compound as provided in this specification is intended to be a sufficient amount of the compound to provide the desired result. As noted below, the exact amount required will vary, depending on the composition of the wastewater in the compound used. Thus, it is not always possible to specify an exact "effective amount". However, an appropriate effective amount can be determined by one of ordinary skill in the art using only routine experimentation. The term "suitable" is used to refer to a moiety that is compatible with the appropriate compounds for the stated purpose. The convenience for the stated purpose can also be determined by someone with ordinary skill in the art using only routine experimentation. The method to recover valuable metals and chemicals disclosed here is best carried out to recover these valuable wastewater from industries or other processes. A typical industrial wastewater used is a chimney dust where the load contains galvanized steel, which has the following percentage of composition: TABLE 1 Chimney Dust Analysis Component Percentage in Weight zinc oxide 30.00 iron oxide 40.00 lead oxide and lead chloride 6.48 inert materials1 9.10 sodium oxide and sodium chloride 5.00 calcium oxide 2.80 potassium oxide and potassium chloride 3.00 manganese oxide 1.29 tin oxide 1.13 aluminum oxide 0.38 magnesium oxide 0.33 chromium oxide 0.16 copper oxide 0.06 silver 0.05 unidentified materials2 0.22 Silicon material as slag, with clogged carbon granules. molybdenum, antimony, indium, cadmium, germanium, bismuth, titanium, nickel and boron Generally, the present process is a continuous improved method for the recovery of valuable metals and chemicals in wastewater comprising zinc and iron compounds, silicon material and salts that comprise the steps of: a. heating the waste material at a high temperature in a reduced atmosphere; b. treatment of the fumes from the heating step with an ammonium chloride solution at an elevated temperature to form a solution of the product comprising dissolved zinc compounds and an undissolved material comprising salts of silicon material and, depending on the Feeding composition, small amounts of iron compounds; c. separation of the product solution from undissolved materials; d. determination of the pH of the product solution and if the pH of the product solution is higher than 6.3 then add an effective amount of a suitable compound to the product solution to obtain a pH less than 6.3; and. add zinc metal to the product solution where any leads and cadmium ions contained in the product solution are displaced by the zinc metal and precipitated from the product solution as lead and cadmium metals; F. Separate the product solution from lead and cadmium metals; g. add an effective amount of a suitable compound to the product solution to obtain a pH of 6.5 A 7.0; h. decrease the temperature of the product solution to precipitate the zinc component as a mixture of the crystallized zinc compounds; and i. Separate the crystallized zinc compounds from the product solution.

The crystallized zinc compounds can be further processed to produce one or more high purity zinc-based products. Undissolved materials can be used as they are or later treated to feed the process of iron and / or steel. The remnant of the product solution can also be treated later to recover valuable additional and / or chemical metals. The initial leaching step can be carried out in the fumes produced by the step reduction or raw powder. One skilled in the art will recognize that various combinations of reduction-leaching-reduction or leaching-reduction-leaching are compatible with this method, as described in related applications. A two-stage leaching process will provide greater zinc oxide fields and a two-stage (reduction) heating process will provide larger fiepo-based feed fields. A solution of ammonium chloride in water is prepared in known amounts and concentrations. If the two-step leaching process (leach-reduce-leach) is used, the feedstock, such as the residual chimney dust material described in Table 1 or any other source of feed material containing zinc, oxide of zinc, iron and / or iron oxide mixed with other metals, is added to the ammonium chloride solution at a temperature of about 90 ° C or higher. Otherwise, the feed material is first reduced by heating the feed material in a reduced atmosphere. The iron oxide is reduced to ferrous oxide (FeO) in the reduction step to ensure the non-solubility of the iron. Zinc and / or zinc oxide are dissolved in the ammonium chloride solution together with the other metal oxides, such as lead oxide and cadmium oxide. The ferrous oxide and the remaining iron oxide do not dissolve in the ammonium chloride solution. The solubility of zinc oxide in the ammonium chloride solutions is shown in Table p.

TABLE II Solubility of ZnO in a 23% solution of NH4CI Temperature in "C g Dissolved / 100 g of H2O 90 14.6 80 13.3 70 8.4 60 5.0 50 3.7 40 2.3 18% -23% by weight of ammonium chloride solution in water at a temperature of at least 90 ° C provides the best solubility of zinc oxide, with 23% by weight of ammonium chloride solution as the most preferred . Concentrations of ammonium chloride below 23% do not dissolve the maximum amount of zinc oxide from the flue dust and concentrations of ammonium chloride greater than 23% tend to precipitate ammonium chloride together with zinc oxide when cool the solution. Iron oxide and inert materials such as silicate will not dissolve in the preferred solution.

At least a portion of zinc oxide, as well as lower concentrations of lead or cadmium oxide, can be extracted from the initial powder by dissolving in the ammonium chloride solution in a first leaching step. The solid remaining after the leaching step contains zinc, iron, lead, cadmium and possibly some other impurities. The remaining solid is then heated in a reduced atmosphere, typically at a temperature higher than 420 ° C and often from 700 ° C to 900 ° C. Preferably, the feed material is first heated in a reduced atmosphere, at the temperature previously mentioned. The reduction of the atmosphere can be created using hydrogen gas, simple carbon species such as carbon dioxide, or by heating the material in an oxygen gas container in the presence of elemental carbon. The carbon is preferably in the form of powder or pellets. Typical warm-up times are from 30 minutes to 4 hours. Typical feed powder contains 15% to 30% zinc by weight. The X-ray defraction indicates the existence of certain crystalline phases in the powder, specifically zinc oxide. The positive identification of the iron phase is complicated by the possible structural types (eg, the spinal-type iron phases show almost identical defraction patterns). The combination of chemical analysis and X-ray defraction indicates that the feed powders typically comprise a combination of magnetite (iron oxide: Fß3?). Both phases have very similar spinal structures. The zinc within the franklinite, (Fe, Mn, Zn) (FeMn) 2 ° 4, can not be extracted by dissolution with the ammonium chloride. In addition, no simple extraction process will extract zinc from this stable oxide phase. Although franklinite is very stable to oxidation (all elements in the highest oxidation state), it is relatively easy to destroy this compound by reduction at elevated temperatures.

The reduction step can be carried out before the initial leaching step, or between a first and second leaching step. The residual dust is heated to temperatures higher than 500 ° C. This temperature causes a reaction that causes a decomposition of the phase of the stable franklinite within the zinc oxide and other components and still does not allow to complete the reduction of the zinc oxide to zinc metal. The resulting zinc oxide can be extracted by sublimation or extraction with an ammonium chloride solution, as by the steps detailed above in the general process. The material resulting after the extraction has less than 15 by weight of zinc. Moreover, when heated in a reduced atmosphere, the zinc oxide will be reduced to form direct reduced iron. The powder can be reduced using many conventional reduction processes, such as direct and indirect heating and passing hot gases through the dust. For example, non-explosive gas reduction mixtures, such as for example hydrogen gas and nitrogen or carbon dioxide, can pass through the dust. Hydrogen gases are not the only species that can be used for reductive decomposition of franklinite and reduction of iron oxide. It is possible to use coal or species containing simple coal, including reducing gases containing coal and elemental coal. The heterogeneous gas phase reductions are faster than the solid state reductions at lower temperatures and therefore suggest the use of carbon monoxide. Carbon monoxide can be generated in situ by mixing the franklinite powder with carbon and heating it in the presence of oxygen at elevated temperatures. The oxygen concentration is controlled to optimize CO production. Carbon monoxide can be introduced as a separate resource to more clearly separate the rate of carbon monoxide preparation from the decomposition rate of Franklinite. The zinc oxide then prepared can be extracted either by extraction of ammonium chloride or by sublimation. The reduction process can also be carried out to complete the reduction using carbon at high temperatures and bringing together the zinc metal that will mix at very low temperatures (420 ° C) and boil at 907 ° C. In this process, the zinc metal obtained can easily be converted, if desired, into rust by scorching air. After the powder is reduced by heating in a reduced atmosphere, the fumes created by the heating step typically comprise the majority of the solids in the powder and are subjected to a leaching step in 18% to 23% ammonium chloride solution in water at a temperature of at least 90 ° C. Any zinc or zinc oxide formed during the reduction step dissolve in the ammonium chloride solution. The zinc oxide and the ammonium chloride solution are then filtered to remove any undissolved material, including iron oxide. Because of the temperature at which the zinc compounds (specifically, for example, diamino zinc chloride) crystallize at a given concentration of zinc decreased with pH, the pH of the product solution remains below 6.3 before the crystallizer reaches the lower pH will prevent premature crystallization of zinc compounds. Premature crystallization reduces the rate of zinc recovery and can clog transfer lines or other parts of the recovery apparatus. The pH can be determined through knowledge of the composition of the waters of the waste material, by direct measurement or by other known methods. As stated above, the pH of the product solution will often be low due to the chlorides present in the waste material waters. However, if necessary to further reduce the pH of the product solution, one skilled in the art will recognize suitable compounds to be added to the product solution in an effective amount to reduce the pH. The presently preferred compound is hydrochloric acid (HCl). For example, the zinc-rich smoke powder of a rotary hearth furnace has a typical composition of approximately: 70% ZnO 6% Pb 3% Na 3% K 11% Cl 3% Insoluble 4% Other When the dust is leached with 20% solution of ammonium chloride, the resulting product will have a pH of 5.9 - 6.3. This solution of the product will not crystallize prematurely before the crystallizer due to its lower pH and therefore does not need adjustment of pH. However, as discussed below, an upward pH adjustment will be necessary in the crystallizer. While one skilled in the art will recognize that the pH of the product solution can be adjusted at various stages of the process, care must be taken to do so before undissolved materials including iron oxide are removed. If the pH is acidified strongly at this point, the oxide of the willow can dissolve in the solution. This is preferable to keep iron oxide and other iron compounds out of the solution for ease of recovery and use in other processes.

To recover the zinc oxide, while filtering the zinc oxide and the ammonium chloride solution is still hot, that is at a temperature of 90 ° C or higher, finely powdered zinc metal is added to the solution. Through an electrochemical reaction, any lead metal and cadmium in solution are plated on the surfaces of the zinc metal particles. The addition of sufficient powdered zinc metal results in the extraction of virtually all the leads from the solution. The solution is then filtered to extract the solid lead, copper, zinc and cadmium. Powdered zinc metal should only be added to zinc oxide and the ammonium chloride solution to extract solid lead and cadmium. However, zinc dust is typically added to form large groups in the solution that sinks to the bottom of the container. Typically rapid agitation will not prevent this aggregation from occurring; however, mixing with high shear forces can. To keep the zinc powder suspended in the zinc oxide and the ammonium chloride solution, any of a number of water-soluble polymers that act as antiflocculants or dispersants can also be used. In addition, a number of active surface materials will also act to keep zinc dust suspended, as will many compounds used in the control scale. These materials only need to be present in concentrations of 10 - 1000 ppm. Various suitable materials include water-soluble dispersion polymers, scale controllers and surfactants, such as lignosulfonates, polyphosphates, polyacrylates, polymethacrylates, maleic anhydride copolymers, polymaleic anhydride, ester phosphates and phosphates. A discussion of these diverse materials can be found in the literature, such as Drew, Principles of Industrial Residual Treatment, pages 79-84, which is incorporated herein for reference. Also effective are Flocon 100 and other members of the Flocon series of maleic acrylic oligomers of various molecular weights of water soluble polymers produced by the FMC Corporation. Adding dispersants to a very high strong ionic solution containing a wide variety of ionic species is anathema to standard practice since dispersants are often not soluble in such strong ionic solutions. In this stage is a filtrate rich in zinc compounds and a precipitate of lead, cadmium and other products. The filtrate and the precipitate are separated, with the precipitate being treated later, if desired, to capture chemical values. The filtrate can be treated in several ways, of which two are preferred. First, the filtrate can be cooled resulting in the crystallization and recovery of zinc oxide. Second, the filtrate can be subjected to electrolysis resulting in the generation and recovery of metallic zinc. To facilitate crystallization, the pH of the product solution rises from 6.5 to 7.0 immediately before crystallization. By increasing the pH of the product, the solution reduces the solubility of the zinc compounds at a given concentration and temperatures and then the crystallization increases. One skilled in the art will recognize suitable compounds to be added to the product solution in an amount effective to increase the pH. The present compounds are preferably ammonium hydroxide and ammonia. Adding these compounds results in the formation of additional ammonium chloride, which increases the pH. The filtrate can be treated to crystallize diamino zinc dichloride and other complex compounds. This can be done in a continuous batch or crystallizer by cooling the filtrate between 20 ° C and 60 ° C. Then it is added to diamino zinc dichloride from 25 ° C to 100 ° C of water to decompose it into zinc oxide and ammonium chloride. The amount and temperature of the water controls the decomposition of the diamine salt into zinc oxide and thus affects the particle size and chloride content as described in related applications. The solid hydrated zinc oxide species are filtered from the solution and dried at a temperature of 100 ° C - 350 ° C for 5 seconds at 5 minutes. Like zinc, the lead and cadmium contained in the feed materials are amphoteric species, using the solution of ammonium chloride these species will go into the solution, while any iron oxide present in the feed material will not go into the solution. Other solutions, such as strong basic solutions that have a pH greater than 10 or acidified solutions that have a pH less than 3, can also be used to dissolve the zinc, lead and cadmium species; however, if strong acidified solutions are used, the iron oxide will dissolve in the solution, and if the strong base solutions are used, the iron oxide will become gelatinous. Lead and cadmium can be extracted from the ammonium chloride solution through an electrochemical reaction that results in the precipitation of lead and cadmium in elemental form. The difference in solubility between diamino zinc dichloride and zinc oxide in water and in ammonium chloride solutions allows the selective dissolution of diamino zinc dichloride so that the pure zinc oxide can be extracted. This can also be used in the crystallization step to improve the relative amounts of diamino zinc dichloride and the form of zinc oxide species. Significantly, all the zinc can be recycled, so that all the zinc will eventually be converted to zinc oxide. The crystallization step can be done continuously to increase it and maximize the zinc oxide field after the washing and drying step.

During the crystallization step, it is preferable to use a natural reverse cooling profile. Such a profile is the opposite form to that which is observed by natural cooling. In a natural reverse cooling profile, cooling is slower at the beginning and faster at the end; In a natural cooling profile, cooling is faster at the beginning and slower at the end. The temperature control with a natural reverse cooling curve results in an average average sized glass greater than by linear cooling or natural cooling, which improves the filtration rate. To produce pure zinc oxide from residual powders containing zinc efficiently and safely and with an effective cost, the process recycles all the zinc that is not extracted from the leachate in the crystallization step. In addition, diamino zinc dichloride and ammonium chloride redissolved in water in the wash step are also recycled. The recycling of zinc increases the overall concentration of zinc in liquid solution in the process. This allows the crystallizer to operate at a higher temperature due to the rapid change in the solubility of the zinc oxide with temperature in the ammonium chloride solution. Recycling has the advantage that the solution can be made relatively saturated for certain materials present in the powder, such as CaO. When this happens, CaO does not leach more from the dust, but remains with the iron. This increases the value since CaO is still present and will not have to be added when the iron block is fed into an oven when making the steel. Another important advantage is that there is no liquid wastewater in this process. The only products that are solid (blocks of iron, zinc oxide or other metals), are then sold for uses in various industrial processes. No waste is produced since all the liquids are recycled.

The process can also be operated to produce a block of high quality iron coal as a residual product. The iron oxide contained in wastewater does not go into the solution in the ammonium chloride solution, but is filtered from the product solution as an undissolved material. This iron oxide block can be used as a feeder for a steel mill; however, it becomes more valuable if it is reduced by reaction with elemental carbon to produce an iron coal or a directly reduced iron product. A preferred method for producing such iron ore or directly reduced iron product from the waste material is to add carbon to the product solution where the carbon will not go into the solution and then separate the solution from the product from any undissolved material present in the product solution that includes any iron oxide and carbon. The combination of carbon and iron oxide results in the reduction of iron oxide, producing directly reduced iron (DRI). Generally the iron oxide and the carbon product are pressed into a block for ease of use and handling. The reduction process produces vapors, from zinc, lead, cadmium and other impurities, that has to be condensed into the powder. These impurities can be sent to the vacuum cleaner at the end of the steel production process, mixed into the original waste powder and then sent to the first leach step, in a recycled form. Alternatively, the vapors of gases and dust that are generated from the reduction step can be sent to a separate vacuum in a separate installation. Smoke gases from furnaces in steel mills and reduction furnaces are typically poor in iron, but comprise other valuable components. The smoke gases of the ovens are an excellent resource of poor residual materials in iron useful for the recovery in the present process. Smoke gases can be filtered in a vacuum cleaner, with the resulting filtering that is added to the wastewater feed of the present process, or with the resulting filtrate that is the primary feed of the present process. The fumes gases can also be purified in a wet scrubber, with the resulting charge of purified solution that is added to the leaching ammonium chloride of the present process. If an ammonium chloride purifying solution is used instead of water, the charged ammonium chloride purifying solution can be used as a leaching agent of the present process. The process can also be operated to recover zinc metal by replacing the crystallization steps with an electrolysis step. A preferred method for the recovery of zinc oxide from waste material waters, comprising zinc compounds using electrolysis, comprises clamping the solution of the final product to electrolysis to extract zinc metal from said solution of the combined product. The solution of the product from the leaching steps comprises zinc ions in solution such as Zn2 +. When the product solution is subjected to electrolysis in an electrolytic cell containing an anode and a cathode, the zinc metal is electrodeposited on a cathode. Although it is preferable to have the cathode made of zinc metal, the cathodes of other materials will also allow the electrodeposition of the zinc metal from the solution of the combined product. Any of the electrolysis cells discussed in the literature is adequate, as long as said cells are configured for the electrolysis of the zinc ion containing solutions. The product solution also contains sodium, potassium, magnesium, calcium and other soluble solutions. These solubles can be recovered by introducing an electrolyte in the leaching step or in the ammonium chloride storage tanks that receive the solution of the recycled product. As ammonium chloride is used as the leach, the ammonium salts in solution are the preferred electrolyte. For example, if some ammonium sulfates are added, one can precipitate calcium sulfate. Ammonium sulfate is the preferred electrolyte to add because the process already uses ammonium in the form of ammonium chloride. Preferred electrolytes include ammonium sulfate, ammonium hydroxide or ammonium carbonate to precipitate various solubles. The foregoing description establishes the best mode of the invention as known to the inventor at this time, as is obvious to those skilled in the art to make modifications to this process without departing from the spirit and scope of the invention and its equivalents as established in the claims that are added.

Claims (27)

1. CLAIMS 1. A method for recovery of valuable metals and / or chemicals from waste material waters comprising zinc compounds, comprises the steps of: a. Heating said waste material to an elevated temperature in a reduced atmosphere, thereby producing fumes comprising zinc, lead and cadmium; b. Treat said fumes with an ammonium chloride solution at an elevated temperature to form a first solution of the product comprising dissolved zinc and first undissolved materials; c. determining the pH of said first solution of the product and if the pH of said product solution is greater than 6.3, then an effective amount of a suitable first compound is added to said first solution of the product to obtain a pH of less than 6.3; d. adding zinc metal to the first product solution where any of the lead and cadmium ions contained within said first product solution are displaced by said zinc metal and precipitated out of said first product solution as lead and cadmium metals, leaving a second solution of the product: e. adding an effective amount of the second appropriate compound to said second product solution to obtain a pH of 6.5 to 7.0; and f decreasing the temperature of said second product solution thereby precipitating the zinc as a mixture of crystallized zinc, leaving a third product solution.
2. 2. The method as described in Claim 1, wherein said first appropriate compound in step c is selected from the group containing hydrochloric acid and sulfuric acid.
3. 3. The method as described in Claim 2, wherein said second appropriate compound in step e is selected from the group consisting of ammonium hydroxide and ammonia.
4. 4. The method as described in Claim 3, wherein said first product solution of step d is maintained at a temperature of at least 90 ° C.
5. 5. The method as described in Claim 4, wherein the concentration of said ammonium chloride solution in step b is 18-23% by weight of ammonium chloride.
6. 6. The method as described in Claim 5, wherein the waste materials are heated to a temperature of at least 500 ° C.
7. 7. The method as described in Claim 1, wherein said first product solution is separated from said undissolved materials before determining the pH of said first product solution.
8. 8. The method as described in Claim 1, wherein said second product solution is separated from the lead and cadmium metals before adding said second appropriate compound to said second product solution.
9. 9. The method as described in Claim 3, wherein said zinc metal is powder.
10. 10. The method as described in Claim 3, wherein the temperature of said second product solution is decreased in step f in a controlled manner at 20 ° and 60 ° C using a reversible natural cooling profile to precipitate zinc.
11. 11. The method as described in Claim 1, wherein the crystallization step f is carried out continuously.
12. 12. The method as described in Claim 1, wherein said reducing atmosphere comprises carbon.
13. 13. The method as described in Claim 1, wherein it further comprises the steps of: g. washing said zinc precipitate with a water wash thereby solubilizing certain zinc compounds in a zinc compound containing the solution and then, h. drying said solid residues of zinc at a temperature of at least 100 ° C where said resulting product is zinc oxide of 99% or more purity.
14. 14. The method as described in Claim 13, wherein said zinc precipitate is separated from said third product solution before washing said zinc precipitate.
15. 15. The method as described in Claim 13, wherein the solid residues of zinc are separated from said zinc-containing solution prior to drying said zinc residues.
16. 16. The method as described in Claim 13, wherein during said drying step, said solid zinc residues are dried at temperatures between 100 ° and 350 ° C.
17. 17. The method as described in Claim 1, wherein it further comprises the steps of pretreating said waste material a first time with an ammonium chloride solution at an elevated temperature to form an initial product solution comprising dissolved zinc and non-waste materials. dissolving initials separating said initial product solution from said initial materials, and subjecting said undissolved materials to the steps of the process of Claim 1 and said initial product solution to the steps of the caf process of Claim 1.
18. 18. A method for the recovery of valuable metal and / or chemicals from wastewater comprising zinc, cadmium and lead, comprising the steps of: a. treating said residual material waters with an ammonium chloride solution at an elevated temperature to form a first product solution which comprises dissolved zinc, cadmium and lead compounds and first undissolved materials; b. separating said first product solution from said first undissolved materials; c. determining the pH of said first solution of the product and if the pH of said product solution is greater than 6.3, then an effective amount of a suitable first compound is added to said first solution of the product to obtain a pH of less than 6.3; d. adding zinc metal to the first product solution where any of the lead and cadmium ions contained within said first product solution are displaced by said zinc metal and precipitated out of said first product solution as lead and cadmium metals, leaving a second solution of the product: e. separating said second product solution from the lead and cadmium metals; F. adding an effective amount of a second suitable compound for said second product solution to obtain a pH of 6.5 to 7.0; and g. decreasing the temperature of said second product solution thereby precipitating the zinc products as a mixture of crystallized zinc, leaving a third product solution.
19. 19. The method as described in Claim 18, wherein said first appropriate compound in step c is selected from the group containing hydrochloric acid and sulfuric acid.
20. 20. The method as described in Claim 19, wherein said second appropriate compound in step f is selected from the group containing ammonium hydroxide and ammonia.
21. 21. The method as described in Claim 20, wherein said first product solution of step d is maintained at a temperature of at least 90 ° C.
22. 22. The method as described in Claim 21, wherein the concentration of said ammonium chloride solution in step a is 18-23% by weight of ammonium chloride.
23. 23. The method as described in Claim 3, wherein said zinc metal is powder.
24. 24. The method as described in Claim 20, wherein the temperature of said second product solution is decreased in step g in a controlled manner at 20 ° and 60 ° C using a reversible natural cooling profile to precipitate zinc.
25. 25. The method as described in Claim 19, wherein the crystallization step h is carried out continuously.
26. 26. The method as described in Claim 18, wherein it further comprises the steps of: h. separating said precipitated zinc compounds from said third product solution; i. washing said solid zinc compounds with a water wash thereby solubilizing certain zinc compounds in a solution containing the zinc. j. separating the solid residues of zinc from said solution containing zinc; and then: k. drying said solid residues of zinc at temperatures of at least 100 ° C where said resulting product is zinc oxide of 99% purity or more.
27. 27. The method as described in Claim 26, wherein during said drying step said solid zinc remains are dried at temperatures between 100 ° and 350 ° C.