TECHNICAL FIELD The present invention relates generally to a process for the recovery of usable, economically valuable concentrated iron products, including relatively pure iron product, such as direct reduced iron, and/or very pure product, such as pig iron, useful as the feedstock for iron and steel making processes, from industrial waste streams typically comprising heavy materials, such as iron oxide, cadmium, zinc and lead, and light materials, such as lime and ash.

BACKGROUND ART There exists a need for a method which will allow the recovery of an iron product from industrial waste streams which can be subjected to further treatments, resulting in a concentrated, relatively pure iron product, such as direct reduced iron, and/or a very pure iron product, such as pig iron, which can be used as the feedstock for other processes, such as a steel making process. The industrial waste streams of most interest for this invention include a typical electric arc furnace waste and basic oxygen furnace streams and the paniculate matter filtered or otherwise removed from various substeps of the disclosed process, particularly from the fumes of a reduction furnace, such as a rotary hearth furnace, or from a small scale blast furnace or cupola furnace. Producing an iron product with a minimum amount of impurities, such as zinc ferrite, lead and cadmium, is advantageous because the iron product can be used as the feedstock for steel production processes.

A method which results in the recovery of an iron product has additional value in that the iron product can be sold for use in other processes. Furthermore, recovery and retreatment of exhaust and other waste products from the present invention and from other processes and subprocesses has a beneficial effect on the environment, and a beneficial, economic effect on die cost of the steel making process. The exhaust may be further processed by filtering it through a bag house to capture the particulate materials, and then subjecting the captured materials to leaching to recover the iron and iron oxide which was not separated out during the separation step. The iron

materials then can be briquetted (compacted) and sent to a reduction furnace or a blast furnace.

Iron is smelted, or refined, in a furnace in which iron ore, coke and limestone are heated. Scrap iron also can be used as a feed to the iron smelting furnace. Prior to introducing scrap iron to the furnace, it is de-scaled of iron oxide, or rust. The mill scale, as it is called, is a waste product typically disposed of and not used in the iron production process. Finding an economical and/or beneficial use for this mill scale would provide iron and steel mills an opportunity to dispose of the mill scale. Likewise, used batteries provide a waste disposal problem and are not typically used in the steel making process. Rather than disposal in a landfill, it generally is preferable to recycle the used batteries, which are rich in iron oxide. Finding an economical and/or beneficial use for used batteries would reduce the quantity of such material sent to landfills and provide a recycle for usable components. All of these iron oxide rich materials can be added to the waste stream feed which is fed into the present process.

As can be seen, there exists a need for a method which separates iron oxide from other materials contained in a waste stream and processes the iron oxide to create DRI and/or pig iron and which will allow exhausts and fumes from reduction or pig iron furnaces or the like to be filtered in a baghouse or/and a wet scrubber so that the iron oxide which was not recovered during the separation step can be recovered by leaching the captured materials and recycled back to the process of the present invention. This need is addressed by the present invention.

BRIEF SUMMARY OF THE INVENTION In accordance with the present invention, a waste material combination typically comprising iron compounds, such as iron oxide, and other compounds, such as cadmium, zinc, lead, ash and lime is subjected to a series of steps including compaction, roasting, crushing and separation. The preferred waste material combination is EAF dust, or other furnace dusts from metals processing processes. To the dust, other waste materials can be added. For example, iron-rich wastes such as mill scale or used batteries, iron-poor wastes such as wastes from industrial

processes, and other wastes containing economically valuable constituents may be added to the dust for recovery of the metals and chemicals values.

Two basic series of steps are contemplated by this invention. The first series comprises subjecting the waste materials stream to a first compacting process whereby the waste materials stream is compacted into a compacted waste materials stream; roasting the compacted waste materials stream to a temperature greater than about 980°C in a reducing atmosphere to convert at least a portion of the iron compounds in the waste materials stream into a direct reduced iron product comprising iron and non-iron compounds and fuming off at least a portion of the non- iron compounds; providing the direct reduced iron product to a crushing process whereby at least a portion of the direct reduced iron product is crushed into particles of one-half inch mesh size or smaller; subjecting the direct reduced iron product to a separation process whereby a first portion of the direct reduced iron product comprising a portion of the iron compounds is separated from the remainder of the direct reduced iron product comprising a portion of the iron and the non-iron compounds; and then recovering the first portion of the direct reduced iron product as the more concentrated iron product.

The second series comprises subjecting the waste materials stream to a separation process whereby a first portion of the waste materials stream comprising a portion of the iron compounds is separated from the remainder of the waste materials stream comprising a portion of the iron and the non-iron compounds; subjecting the waste materials stream to a first compaction process whereby the waste materials stream is compacted into a compacted waste materials stream; roasting the compacted waste materials stream to a temperature greater than about 980°C to convert at least a portion of the iron compounds in the waste materials stream into a direct reduced iron product comprising iron and non-iron compounds and fuming off at least a portion of the non-iron compounds; providing the direct reduced iron product to a crushing process whereby at least a portion of the direct reduced iron product is crushed into particles of one-half inch mesh size or smaller; and then recovering the first portion of the direct reduced iron product as a more concentrated iron product.

The preferred separation processes are magnetic separation and flotation separation. If flotation is used, the heavy materials such as iron oxide, cadmium, zinc and lead sink to the bottom of the liquid suspension used in the flotation process while the lighter materials such as lime and ash cling to bubbles produced by passing air through the suspension and are removed as a froth product. The heavy materials then are compacted or briquetted with carbon and sent either to a reduction furnace, such as a rotary hearth furnace, to produce DRI or to a small scale blast furnace or cupola furnace to produce pig iron. The light products such as lime and ash, which also may contain some iron and other compounds, are leached and the majority of the non-iron compounds either go into solution or float on top of the solution, whereas any iron oxide contained in the material being leached remains undissolved and sinks. The undissolved iron oxide then is sent to the compacting step where it is compacted or briquetted with carbon and sent either to the rotary hearth furnace for producing DRI or to the small scale blast furnace or cupola furnace for producing pig iron. If magnetic separation is used, the iron-based materials are magnetically separated from the non-iron materials. The iron-based materials can then be briquetted with carbon and sent to the reduction furnace for producing DRI or/and to the small scale blast furnace or cupola furnace for producing pig iron. It is possible that some iron-based materials will remain with the non-iron materials even after magnetic separation. The non-iron products can be sent to a leaching process to separate any iron or iron oxide from the non-iron materials. Any iron or iron oxide which remains with the substantially non-iron materials does not go into solution and is subsequently separated and sent to the briquetting or compaction process. Once the iron oxide has been briquetted with carbon, the briquettes can be sent to the reduction furnace for producing DRI or/and to the pig iron furnace

When the briquettes or the material is roasted, or is liquefied in the pig iron furnace, fumes are released which can be captured in a bag house. The captured materials, which generally comprise lead, zinc and cadmium, then can be leached as discussed above, and the undissolved iron oxide can be recycled to the compacting or

briquetting process. The non-iron products and compounds then are subjected to further recovery steps for recovering metals and chemicals values.

Therefore, it is an object of the present invention to provide a method for recovering a concentrated iron product from an industrial waste stream, such as EAF and blast furnace dust, and for processing the iron and iron oxide to produce direct reduced iron and/or pig iron which can then be used in a steel making process.

It is another object of the present invention to provide a method for recovering iron and iron oxide from waste materials, such as fumes from a reduction furnace or small scale blast furnace or cupola furnace, which can be recycled to the process of the present invention for producing direct reduced iron and/or pig iron.

It is yet another object of the present invention to provide a method for recovering a concentrated iron product which can be used as is as a feedstock for a steel making process.

It is yet another object of the present invention to provide a method for recovering other metal and/or chemical values such as cadmium, zinc, and lead from an industrial waste stream.

It is yet another object of the present invention to provide a process which uses the waste streams of various industrial processes, particularly the iron and steel making processes, so as to achieve an economical, environmentally friendly recycle process in the iron or steel making industry.

It is yet another object of the present invention to provide a method for recovering iron and iron oxide from waste materials such as batteries and cars, to produce direct reduced iron and/or pig iron which can be used in a steel making process. It is yet another object of the present invention to provide a method for recovering an iron product such as direct reduced iron, pig iron and/or iron oxide from an industrial waste material stream which minimizes waste and pollution, and is economical, quick and efficient.

These and other objects of the present invention will become apparent from the following detailed description, drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic block diagram illustrating a process of the present invention.

Fig. 2 is a schematic block diagram illustrating alternative steps in the process of the present invention.

Fig. 3 is a schematic block diagram illustrating where the process of the present invention fits in in the overall recycle and recovery process for industrial waste streams.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiment of the present invention will now be described with reference to Figs. 1 and 2. A waste material stream 10 such as EAF dust typically comprises iron oxide, cadmium, zinc, lead, lime and ash. Waste material stream 10 also may be or comprise the stream from subprocesses 400 and 500, as described below and as shown in Fig. 3. The present invention generally replaces subprocess 100 and part of subprocess 200 shown in Fig. 3.

The first series of steps contemplated by this invention comprise the basic path of sending the waste stream 10 first to the compactor 60, 60A, then to the reduction furnace 14B, then to the crusher 80, and then to the separator 600, which can be a flotation separation process 600A or a magnetic separation process 600B. A second compactor 60B can be included after the separator 600.

The second series of steps contemplated by this invention comprise the basic path of sending the waste stream to the separator 600, then to the compactor 60, 60A, then to the reduction furnace 14B, and then to the crusher 80. The separated, more concentrated iron product, 602 or 83, respectively, then can be used as the feedstock for the ironmaking and steelmaking processes.

The first method for producing a more concentrated iron product from an iron- bearing waste materials stream generated from a steelmaking or ironmaking furnace, which waste materials stream comprises iron compounds and non-iron compounds, comprises the steps of:

a. subjecting the waste materials stream 10 to a first compacting process 60A whereby the waste materials stream is compacted or briquetted into a compacted waste materials stream 64; b. roasting 14B the compacted waste materials stream 64 at a temperature greater than about 980°C thereby converting at least a portion of the iron compounds in the waste materials stream 10 into a direct reduced iron product 76 comprising iron and non-iron compounds, and fuming off at least a portion of the non-iron compounds 70; c. providing the direct reduced iron product 76 to a crushing process 80 whereby at least a portion of the direct reduced iron product 76 is crushed into particles 81 of one-half inch mesh size or smaller; d. subjecting the crushed direct reduced iron product 81 to a separation process 600 whereby a first portion 602 of the direct reduced iron product comprising a portion of the iron compounds is separated from the remainder 604 of the direct reduced iron product (which comprises a portion of the iron and the non-iron compounds); and then e. recovering the first portion 602 of the direct reduced iron product as the more concentrated iron product 66, and discarding or recycling the remainder 604, or recycling the first portion 602 to the leaching process 100 for further consideration. In the first series of steps, the waste materials stream first is sent to a compacting process where the waste materials are compacted into pellets of a predetermined size. More specifically, the waste materials can be briquetted with carbon at temperatures ranging from 10°C to 250°C, preferably above 50°C. The briquettes or pellets then are sent to the reduction furnace 14B where they are converted into a direct reduced iron product, or to a pig iron furnace 14A to form pig iron. During the reduction process, fumes 70 are exhausted which typically comprise lead, zinc and cadmium. The fumes 70 are captured in a capture means 16, such as a baghouse or scrubber. The captured product 72 then is sent to leaching process 100, described below. The undissolved iron oxide 68 resulting from the leaching process 100 then is recycled to the compacting process 60A. The materials which go into

solution during the leaching process 100 constitute other values 74 which are recovered and may be further treated or used in other processes, such as subprocess 300, described below.

The direct reduced iron product 76 is optionally sent to a crusher 80 where it is ground into smaller pieces. The small pieces are introduced to the separation step 600 where iron compounds remaining may be separated from non-iron compounds, and the non-iron compounds sent back to the compacting step 60 or the leaching step 100. This step increases the iron concentration. The iron compounds then can be sent to a second compactor 60B for further compaction, to the leaching step 100 for further concentration, to another furnace also for further concentration, or to the ironmaker or steelmaker as the feedstock for the ironmaking or steelmaking process.

The first method can further comprise the additional steps of subjecting at least a portion 601 of the first portion of the direct reduced iron product to a second compaction process 60B resulting in a compacted concentrated product 63, providing at least a portion of the crushed waste materials stream 83 directly to an electric arc furnace or another furnace, and/or capturing at least a portion of the non-iron compounds 606 and subjecting the captured non-iron compounds 606 to subsequent processing steps 100, 300 to recover chemical and metal values. These subsequent processing steps can include leaching the captured non-iron compounds 606 in a solution comprising a leachant selected from the group consisting of ammonium chloride, sodium hydroxide, ammonium sulfate, ammonia/ammonium hydroxide, ammonium phosphate, potassium hydroxide, ammonia/ammonium oxalate, and ammonia/ammonium carbonate solutions. Further processing of leached compounds 74 also can be employed. Any iron compounds 68 can be recycled to the compacting process 60A.

The first compaction process 60A preferably operates at a temperature of between approximately 10°C and 250°C, preferably above 50°C, although operation outside of this temperature range is acceptable. A carbon compound C generally is added to the waste materials stream during the first compaction process 60A. The first compaction process 60A can be a briquetting process. The first portion of the

direct reduced iron product 76 alternatively can be provided to another furnace 14A, wherein the first portion of the direct reduced iron product 76 is heated to a temperature sufficient to liquefy the first portion of the direct reduced iron product 76, and removing at least a portion of any non-iron compounds 70a contained in the first portion of the direct reduced iron product stream as slag. Likewise, the first portion of the direct reduced iron product 76 can be provided to a steelmaker for use as an iron feedstock in the production of iron-based products.

The second method for producing a more concentrated iron product from an iron-bearing waste materials stream generated from a steelmaking or ironmaking furnace, which waste materials stream comprises iron compounds and non-iron compounds, is a rearrangement of the first method, and comprises the steps of: a. subjecting the waste materials stream 10 to a separation process 600 whereby a first portion 603 of the waste materials stream 10 comprising a portion of the iron compounds is separated from the remainder 604 of the waste materials stream comprising a portion of the iron and the non-iron compounds; b. subjecting the first portion 603 of the waste materials stream 10 to a first compaction process 60A whereby first portion 603 of the waste materials stream 10 is compacted into a first compacted waste materials stream 64; c. roasting 14B the first compacted waste materials stream 64 at a temperature greater than about 980°C in a reducing atmosphere thereby converting at least a portion of the iron compounds in the first compacted waste materials stream 64 into a direct reduced iron product 76 comprising iron and non-iron compounds, and fuming off at least a portion of the non-iron compounds 70; d. providing the direct reduced iron product 76 to a crushing process 80 whereby at least a first portion of the direct reduced iron product 76 is crushed into particles 83 of one-half inch mesh size or smaller; and then e. recovering the crushed direct reduced iron product 83 as a more concentrated iron product 63.

In the second series of steps, the waste materials stream is sent first to the separation process 600 where iron compounds remaining may be separated from non-

iron compounds, and the non-iron compounds sent to the leaching step 100. This step increases the iron concentration. The iron compounds 68 then are sent to the compacting process 60, 60A where the waste materials are compacted into pellets of a predetermined size 64. The pellets then are sent to the reduction furnace 14B where they are converted into a direct reduced iron product or to a pig iron furnace 14A. During the reduction process, fumes 70 are exhausted which typically comprise lead, zinc and cadmium. The fumes 70 are captured in a capture means 16, such as a baghouse or scrubber. The captured product 72 then is sent to leaching process 100. The undissolved iron oxide 68 resulting from the leaching process 100 then is recycled to the compacting process 60. The materials which go into solution during the leaching process 100 constitute other values 74A which are recovered and may be further treated or used in other processes, such as subprocess 300.

The direct reduced iron 76 produced in the reduction furnace 14B also can be liquefied in pig iron furnace 14A as indicated on Fig. 2. Alternatively, as shown in Fig. 1, the direct reduced iron product 76 then can be sent to a crusher 80 where they are ground into smaller pieces. The small pieces of concentrated iron product 83 then can be sent to the leaching step 100 for further concentration, to the EAF furnace also for further concentration, or to the ironmaker or steelmaker as the feedstock for the ironmaking or steelmaking process. Referring to Fig. 2, the briquettes 64 which are sent to the pig iron furnace

14A are liquefied to produce pig iron. During the liquification process, slag also is produced which typically comprises copper, manganese and other impurities which have not been previously separated out. Fumes 70a exhausted during the liquification process are captured by capture means 16. The captured materials then are sent to a leaching process, such as subprocess 100. The undissolved iron oxide 68a resulting from the leaching process then is recycled back to the briquetting process 60 and the briquettes 64 are sent to reduction furnace 14B, to the pig iron furnace 14A for producing direct reduced iron 76 or/and pig iron, or to the crusher 80 to be separated 600A again and further concentrated.

In accordance with another embodiment, the separation processes 600A and 600B can be bypassed. Therefore, although it is preferred that the waste material stream 10 first be subjected to a separation process prior to being briquetted, the waste materials 10 can be briquetted without first being subjected to the separation process 600. When the briquettes 64 are subsequently subjected to the reduction 14B or/and liquification processes 14A, the iron and iron oxide is separated from the other materials as either slag (in the liquification process) or fumes 70B (in the reduction process).

Unseparated exhaust fumes or other waste materials 10 are sent directly to the leaching process, such as subprocess 100. The waste materials are leached, as disclosed above, with the iron compounds and other heavies 68 being sent to the briquetting process 60.

Grinding 80 can be employed after compaction when flotation separation 600A is used; however it generally is more effective when magnetic separation 600B is used. This step can increase the iron concentration in the briquettes 64, causing a resulting increase in the quality of DRI produced in reduction furnace 14B or/and lowering the amount of slag created in pig iron furnace 14A. Further, the DRI 76 produced in reduction furnace 14B can be sent to intermediate grinding step 80 for further purification by reseparation in subprocess 600 and rebriquetting in briquetting step 60. The DRI then can be sent to reduction furnace 14B in a cyclical fashion for even higher purity, or to pig iron furnace 14A for the production of pig iron. Intermediate grinding step 80 also can be employed if the heavy materials 62a or iron- based products 62b are not as high in iron concentration as desired, so as to produce a briquette 64 of higher iron concentration. The second method also can comprise the additional steps of providing at least a portion of the crushed direct reduced iron product directly to an electric arc furnace or another furnace and/or capturing at least a portion of the non-iron compounds and subjecting the captured non-iron compounds to subsequent processing steps to recover chemical and metal values, as well as the other side processes mentioned above.

An apparatus (details not shown, but within the ability of one skilled in the art after reading this specification) for producing this more concentrated iron product from an iron-bearing waste materials stream generated from a steelmaking or ironmaking furnace, which waste materials stream comprises iron compounds and non-iron compounds, also is contemplated. The apparatus for carrying out the first method comprises: a. means for compacting the waste materials stream into a compacted waste materials stream; b. roasting means for converting at least a portion of the iron compounds in the compacted waste materials stream into a direct reduced iron product; c. means for crushing the direct reduced iron product whereby at least a portion of the direct reduced iron product is crushed into particles of one-half inch mesh size or smaller; and d. means for separating a first portion of the crushed direct reduced iron product from the remainder of the direct reduced iron product.

The apparatus can further comprise means for leaching the remainder of the waste materials stream such that a portion of the non-iron compounds goes into solution and the iron compounds do not go into solution. The leachant is selected from the group consisting of aqueous solutions of ammonium chloride, sodium hydroxide, ammonium sulfate, ammonia/ammonium hydroxide, ammonium phosphate, potassium hydroxide, ammonia/ammonium oxalate, and ammonia/ammonium carbonate solutions.

The apparatus for carrying out the second method comprises: a. means for separating a first portion of the waste materials stream comprising a portion of the iron compounds from the remainder of the waste materials stream comprising a portion of the iron and the non-iron compounds; b. means for compacting the first portion of the waste materials stream into a compacted waste materials stream; c. roasting means for converting at least a portion of the iron compounds in the compacted waste materials stream into a direct reduced iron product; and

d. means for crushing the direct reduced iron product whereby at least a portion of the direct reduced iron product is crushed into particles of one-half inch mesh size or smaller.

The apparatus also can further comprise means for leaching the remainder of the waste materials stream such that a portion of the non-iron compounds goes into solution and the iron compounds do not go into solution.

The separation process can be either flotation separation 600A or magnetic separation 600B. When flotation is used, the heavy materials which generally comprise iron oxide, cadmium, zinc and lead sink to the bottom of the liquid suspension whereas the light materials which typically comprise lime, ash and silica cling to bubbles produced by passing air through the liquid suspension and are removed as a froth product. The heavy materials 62a are sent to the briquetting process 60 where they are compacted or briquetted with carbon C at a temperature ranging from approximately 50°F to 250°F. The briquettes 64 then are sent to a reduction furnace 14B, such as a rotary hearth furnace, or/and to a pig iron furnace 14A for producing direct reduced iron or/and pig iron, respectively. The light materials 66a separated during the flotation step are sent to a leaching process, such as subprocess 100, where they are leached with a leachant such as ammonium chloride or sodium hydroxide. Other suitable leachants include ammonium chloride, sodium hydroxide, ammonium sulfate, ammonia/ammonium hydroxide, ammonium phosphate, potassium hydroxide, ammonia/ammonium oxalate, and ammonia/ammonium carbonate solutions. During the leaching process, any iron oxide contained in the light materials 66a does not go into solution whereas other materials such as zinc, lead and cadmium compounds dissolve. Still other materials, such as the lights (lime and ash), do not go into solution, but float on the top of the solution. The undissolved iron oxide 68 then is separated from the solution and the lights and sent to the compacting process 60 where it is compacted or briquetted with the heavy materials and then sent to the reduction furnace 14B or/and to the pig iron furnace 14A.

14

When magnetic separation 600B is used, most of the iron-based products are separated from the non-iron products. The iron-based products 62b are sent to the compacting process 60 where it is compacted or briquetted with carbon C at a temperature from 50°F to 250°F. The briquettes 64 then are sent to the reduction furnace 14B or/and to the pig iron furnace 14A, as discussed above. The substantially non-iron product 66b (which may contain some iron product) is sent to a leaching process, such as subprocess 100. During the leaching process, the iron oxide does not go into solution whereas certain non-iron products dissolve. The undissolved iron oxide 68 then is sent to the compacting process 60. Further, it should be noted that the process may involve only flotation and DRI production, only flotation and pig iron production, only magnetic separation and DRI production, or only flotation and pig iron production. The process and Figs, disclosed herein combine these processes for clarity, simplicity and to show their relatedness, but in no way is it necessary to have magnetic separation, flotation, DRI production and pig iron production all in the same process.

PREFERRED EMBODIMENT AS COUPLED WITH A COMPLETE IRON PRODUCT AND CHEMICAL VALUES RECOVERY

AND RECYCLE METHOD 0 The present invention also can be coupled to the complete process shown in

Fig. 2 and disclosed in more detail below for the recovery of other usable economically valuable products from industrial waste streams typically comprising zinc compounds and iron compounds. Primary recovery and recycle processes are disclosed and claimed in patents and patent applications filed by the present inventors 5 and assigned to the assignee of this invention and specification.

In general, the recovery and recycling process of this invention utilizes the iron-rich materials produced by the process as a feedstock ultimately to a steel mill. The iron-rich materials either are processed to a higher purity iron product which may be fed directly to a steel mill as the feed, or are fed directly to a small scale blast 0 furnace or a cupola furnace. Fumes and other non-iron compounds exhausted from the furnace and other processing steps can be processed by a baghouse or/and by a wet

scrubber or other capturing means and the captured materials then are recycled. Fumes emanating from the furnace 14A contain particulate matter, and may include potentially valuable zinc, cadmium, and lead constituents. The fumes are filtered in a baghouse, either at the steel mill's baghouse or at an independent baghouse. The filter cake, which is an iron-poor mixture, may be combined with the initial waste feed (such as EAF dust) to this general process and/or other iron-rich materials, and processed further.

An alternative method of removing the particulate matter from the exhausts is the use of a wet scrubber 16, such as a venturi scrubber. The exhaust constituents soluble in water will be removed from the exhaust by the recirculated water. The loaded recirculated water then may be introduced to an ammonium chloride or sodium hydroxide leach step. Alternatively, the wet scrubber can use an ammonium chloride or sodium hydroxide solution instead of water. The particulate matter soluble in ammonium chloride, such as for example zinc, cadmium, and lead constituents, or in sodium hydroxide, will be removed in the ammonium chloride solution or sodium hydroxide solution, respectively, in the wet scrubber. The loaded ammonium chloride solution or sodium hydroxide solution then can be combined with the leaching step discussed above, resulting in an exceptional increase in the recycle of waste streams from, for example, the steel making process. Recovery and retreatment of exhaust and other waste products from the present invention and from other processes and subprocesses has a beneficial effect on the environment, and a beneficial, economic effect on the cost of the steel making process.

Scrap iron, mill scale, and used batteries also can be combined with waste materials stream 10 or used as a feed to the iron smelting furnace. Additionally, iron- poor materials can be added to the waste materials stream 10 for the present invention. Iron-poor materials comprising chemical values recoverable in the present process can be added, resulting in the recycle of waste streams which otherwise would be disposed of in. for example, landfills, and the recovery of chemical values which otherwise would be wasted.

The preferred iron-poor waste feed stream is taken from fumes emanating from industrial processes. For example, fumes from reduction furnaces 14B and from the iron and steel making processes typically are filtered in baghouses 16. Other industrial processes also produce fumes which may be filtered in baghouses. The waste product removed from the fumes in the baghouses may be subjected to the present process for recovery of chemical values and production of an iron-rich product. Likewise, the fumes emanating from direct-reduced iron reduction furnaces may be filtered, with the filtrate recycled to the present process. Alternatively, the fumes may be cleaned using a recirculating water or ammonium chloride solution wet scrubber. The loaded recirculating water or ammonium chloride solution (the scrubbant) may be recycled to the leach step of the present invention. Alternatively, a sodium hydroxide leach step can be used, depending on the chemical values to be recovered. a. Leaching Step The combined waste material is leached with an ammonium chloride or other suitable leachant solution resulting in a product solution (leachate) and undissolved materials (precipitate). In the leaching step, 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, including iron oxides and inert materials such as silicates, which will not dissolve in the ammonium chloride solution. The product solution and the undissolved materials are separated, with both the product solution and the undissolved materials being further treated to recover valuable components. For example, the remaining product solution can be treated to produce a zinc oxide product of 99% or greater purity. Alternatively, the remaining product solution can be subjected to electrolysis in which zinc metal plates onto the cathode of the electrolysis cell. Any remaining product solution after crystallization or electrolysis can be recycled back to treat incoming waste material.

To assist in the formation of a more usable direct reduced iron, the undissolved materials can be pelletized with carbon or sodium silicate, or another suitable

material, at the end of or after the roasting step. Carbon, in the form of activated carbon, carbon dust, carbon pellets or the like, also can be introduced to the ammonium chloride and waste material mixture during the leaching process. Carbon also can be introduced to the dried undissolved material cake. When the iron oxide and carbon are heated under a reducing atmosphere, such as CO or CO ₂ or other common reducing gases, the carbon will react with the iron oxide, assisting in reducing the iron oxide to DRI. Combining any of these methods can result in an even purer direct reduced iron product.

Prior to being leached by the ammonium chloride solution, the waste material mixture, which typically includes franklinite and magnetite, may be preroasted at temperatures greater than 500°C for a predetermined period of time. The preroasting causes a decomposition of the franklinite zinc oxide-iron oxide complex into zinc oxide, iron oxide and other components. The preroasting process generally comprises the steps of adding heat to the waste material mixture and/or passing heated reducing gases through the waste material mixture. Although all reducing gases are suitable, hydrogen and carbon-containing gases such as carbon dioxide are preferred, as well as mixing carbon (activated) with the waste material mixture and preroasting in a gas containing oxygen. While some iron oxide is reduced from Fe ₂ O ₃ and Fe ₃ O ₄ to FeO, no elemental iron is produced during the preroasting step. Additionally, iron and iron oxides are not soluble to any degree in the basic ammonium chloride solution.

The invention also provides a method by which iron-rich by-products produced by the recovery process are reduced in a reduction furnace which reduces the iron oxide to DRI. Fumes exhausted by the reduction furnace are filtered through a baghouse or/and a wet scrubber. The materials captured by the baghouse or/and wet scrubber then may be recycled back into the leaching step of the recovery process of the present invention where they are used in the recovery process. The solid particles captured by the baghouse may be combined with the primary waste stream feed, such as EAF dust, or, alternatively, fed as a separate primary feed to the ammonium chloride leach. The loaded scrubbant liquid from the wet scrubber may be combined with the primary ammonium chloride leachant or, alternatively, if an ammonium

chloride solution is used as the scrubbing liquid, used as the primary ammonium chloride leachant.

If the fumes are filtered through a baghouse, the captured materials will be solids which are placed into the waste material stream whereby they are added to the ammonium chloride solution of the leaching step. If the fumes are filtered through a wet scrubber, the captured materials will be discharged from the wet scrubber in a liquid stream directly into the ammonium chloride solution of the leaching step. Alternatively, if ammonium chloride is used as the scrubbing liquid, the ammonium chloride scrubbant may be used as the leaching (digesting) solution. If the scrubbant becomes too loaded, make-up ammonium chloride can be added. If the wet scrubber uses an ammonium chloride solution as the scrubbing liquid, it should be maintained at approximately 90°C and 23% by weight ammonium chloride in water. b. General Method Including A Leach

By taking an iron cake comprising for the most part iron oxides, and roasting it at elevated temperatures under a reducing atmosphere, a product can be made which is equivalent to direct reduced iron. In general terms, by heating the iron cake above 980°C up to about 1260°C, and typically no higher than 1315°C, a direct reduced iron product is formed. This direct reduced iron product then can be pelletized with carbon or with a sodium silicate, or other suitable compound, after it comes out of the furnace. The final product then can be used as a feedstock for steel mills without any additional treatment.

As discussed below, the additional step of roasting the iron cake, which is the undissolved precipitate, to reduce the iron oxide and to drive off any zinc, cadmium, and lead, and other impurities, is added to the end of a zinc oxide recovery process. The resulting iron product may have been reduced from several forms of me iron, such as FeO, Fe ₂ O ₃ , or Fe ₃ O ₄ , reduced to an iron extremely usable as the feedstock for steel mills. The waste material, such as the combination of iron poor materials from a baghouse or wet scrubber and EAF flue dust, is leached using ammonium chloride, and the remaining undissolved precipitate is, for the most part, an iron oxide cake. This iron oxide cake can be sent to the compacting step 60A for processing

according to the invention. Iron-rich materials also may be added to be leached and further processed. During the roasting of the undissolved precipitate, the bond to the non-leachable zinc oxide-iron oxide complex, franklinite, contained in the undissolved precipitate is broken, and the zinc oxide compounds are exhausted in the off gas and captured in a pollution control device, such as a baghouse, leaving the iron oxide cake as the residue. The iron oxide cake is roasted at an elevated temperature, causing the reduction of the iron oxide, leaving the iron metal values. The iron then can be mixed with a binder and formed into briquettes or cubes to be used as the feedstock. The exhausted impurities then can be recycled to recover, for example, zinc oxide, cadmium metal, and lead metal.

A typical industrial waste materials stream 10 is a flue gas where the charge contains galvanized steel, having the following percent composition:

TABLE I

Analysis of Flue Dust

Component Percent By Weight

Zinc Oxide 39-40

Iron Oxide 36-37

Lead Oxide 5-6

Inert Materials 9-10

Calcium Oxide 2-3

Potassium Oxide 2-3

Manganese Oxide 1-2

Tin Oxide 1-2

Aluminum Oxide 0-1

Magnesium Oxide 0-1

Chromium Oxide 0-1

Copper Oxide 0-1

Silver 0-1

Unidentified Materials 0-1

General Process Description

Generally, the present process is a continuous method for the recovery of an iron product feedstock from waste material streams. The basic process steps comprise: a. combining a typical industrial process waste material stream, such as from a metal or metal product process, with an iron rich or iron poor waste material, such as from a reduction furnace or the iron and steel making processes; b. treating the waste material combination with an ammonium chloride solution at an elevated temperature to form a product solution and an undissolved precipitate comprising iron oxide; c. separating the product solution from the undissolved precipitate comprising the iron oxide; and d. subjecting the undissolved precipitate to the method for producing a more concentrated iron product disclosed above, resulting in the recovery of a relatively pure iron product.

Iron poor waste material, if in solid form such as from a baghouse, is added to Basic Process Step a. Alternatively, iron poor waste material, if in solution form such as from a wet scrubber, is added to Basic Process Step b.

To the basic process steps, a number of additional steps may be added depending on the process conditions and iron properties desired. The additional steps include, either individually or in some combination:

1. preroasting the solid waste material at an elevated temperature;

2. preroasting the solid waste material at an elevated temperature and in a reducing atmosphere; 3. pretreating the solid waste material with an ammonium chloride solution at an elevated temperature to form a product solution and an undissolved precipitate comprising iron oxide; and/or

4. preroasting the solid waste material at an elevated temperature and optionally in a reducing atmosphere, and then pretreating the waste material with an

ammonium chloride solution at an elevated temperature to form a product solution and an undissolved precipitate comprising iron oxide.

To the basic process steps, additional iron product purification steps may be added. For example: 1. elemental carbon can be added during the leaching step or steps to initiate the reduction of the iron oxide into direct reduced iron during the leaching step or steps; and/or

2. elemental carbon can be added to the undissolved precipitate after it has been separated from the product solution. Referring to Fig. 3, a preferred embodiment of the complete iron products and chemical values recycle and recovery process is shown. Subprocess 100, the digestion and filtration steps, generally comprises the process disclosed and claimed in related U.S. Patent No. 5,464,596, which also is disclosed above. Subprocess 200, the direct reduced iron production steps, generally comprises the process disclosed and claimed in related U.S. application Serial No. 08/348,446, which also is disclosed above. The present process as shown in Figs. 1 and 2 generally replaces subprocesses 100 and 200, with subprocess 100 being used as a side recovery process for zinc and other chemical and metal values. Subprocess 300, the chemical values recovery steps, when combined with subprocess 100, generally comprises the process disclosed and claimed in related U.S. Patent No. 5,453,111, which also is disclosed above. Subprocess 400, the enhanced direct reduced iron production steps, when combined with subprocess 200, generally comprises the process disclosed and claimed in related U.S. Patent No. 5,571,306, which also is disclosed above.

Subprocess 500 comprises a feed process to the present invention. Feed streams such as iron poor waste fume streams from electric arc furnaces 12 and other furnaces such as reduction furnaces or smelters are filtered in a capture means 16, such as a baghouse or scrubber. Other feed streams such as iron rich direct reduced iron and pig iron, as well as scrap iron and steel, are subjected to the iron or steel making process. Exhaust fumes from such processes, which typically include an electric arc furnace or other reduction furnace, also can be filtered in a capture means

16. The constituents filtered out in capture means 16 comprise a waste feed to subprocess 100.

In subprocess 100, for recovering chemical and metal values from the exhausts 70 from the present process, the exhausts are leached in digester 18 with ammonium chloride, preferably at approximately 90°C and approximately 23% by weight concentration. Constituents soluble in ammonium chloride go into solution, while constituents insoluble in ammonium chloride, such as iron oxides, precipitate out. The precipitates are filtered from the solution in filter 20. The filtered solution is sent to cementer 22, and subjected to subprocess 300 to recover other chemical values. The precipitate, which is an iron cake (IC), can be sent to the compacting step 60A.

In a full subprocess 200, the precipitate is dried and crushed in dryer/crusher 24. Exhaust gases from dryer/crusher 24 may be sent to a capture means 16 such as baghouse, but more typically are sent to an air scrubber such as air scrubber 26 for cleaning, as the exhaust gases from dryer/crusher 24 typically do not have a significant quantity of recoverable constituents. The dried and rushed precipitates can be compacted in a compactor and also sent to a reduction furnace or smelter 14 to produce DRI.

Exhaust fumes from the furnace 14 (or 14A in Figs. 1 and 2) can be sent to scrubber 34 (a subset of capture means 16), which preferably is a recirculating wet scrubber using water or an aqueous ammonium chloride solution. Exhaust fumes from EAFs such as EAF 12 also can be sent to scrubber 34. In scrubber 34, the exhaust fumes are scrubbed and the scrubbed off-gas released. The water or aqueous ammonium chloride solution containing the constituents scrubbed from the exhaust fumes is sent either to cementer 22 or digester 18, depending on purity; more pure solutions typically are sent to digester 18, while less pure solutions typically are sent to cementer 22.

In the preferred embodiment, the furnace 12, 14, 14A off-gases comprise ZnO and other particulate impurities. If the off-gases are scrubbed in scrubber 34, the water balance is maintained using a temperature control such as heat exchanger 36. Additionally, the concentration of ZnO and other solubles in the scrubbing liquid may

be controlled by the addition of water W to the cementer 22, or ammonium chloride to the scrubber 34. As discussed above, if an ammonium chloride solution is used as the scrubbing liquid, it is preferred to maintain the solution at approximately 90°C and approximately 23% NH ₄ C1. Optional Preroasting Process

An optional preroasting step can be carried out prior to an initial leaching step, or between a first and second leaching step, or both. The powder containing the franklinite and magnetite, such as the waste dust or the combination of waste dust and the iron oxide rich material, 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 solid waste material can be preroasted using many conventional roasting processes, such as, for example, direct or indirect heating and the passing of hot gases through the dust.

Leaching Treatment The exhausts can be subjected to an ammonium chloride leach. An ammonium chloride solution in water is prepared in known quantities and concentrations. The majority of the exhausts, including any zinc and/or zinc oxide, lead oxide, cadmium oxide, and other metal oxides, dissolves in the ammonium chloride solution. The iron oxide does not dissolve in the ammonium chloride solution. As an example, the solubility of zinc oxide in ammonium chloride solutions is shown in Table II.

TABLE II Solubility of ZnO in 23% NH ₄ C1 solution Temperature °C £ Dissolved/100 g

90 14.6

80 13.3 70 8.4

60 5.0 50 3.7

40 2.3

A 18-23% by weight ammonium chloride solution in water at a temperature of at least 90°C provides the best solubility for a waste stream comprising a significant quantity of zinc oxide and is prefeπed. Concentrations of ammonium chloride below about 18% do not dissolve the maximum amount of zinc oxide from the waste material, and concentrations of ammonium chloride above about 23% tend to precipitate out ammonium chloride along with the zinc oxide when the solution is cooled. The zinc oxide, as well as smaller concentrations of lead or cadmium oxide, are removed from the exhausts by the dissolution in the ammonium chloride solution. The solid remaining after this leaching step contains iron oxides and some impurities including silicates, zinc, lead, cadmium, and possibly some other impurities. The iron oxides can be sent to the compacting step 60A, while the non-iron compounds can be sent to the values recovery step 300.

If the iron poor material is removed from the industrial waste stream using a wet scrubber, the prefeπed wet scrubber is an ammonium chloride solution wet scrubber. By using an ammonium chloride wet scrubber, the loaded scrubbing solution, ammonium chloride, can be combined directly with the ammonium chloride leachant, or sent directly to the cementation step for removal of certain non-iron products. Depending on the degree of loadedness of the ammonium chloride

scrubbing solution, pure make-up ammonium chloride solution can be added to increase the effectiveness of the ammonium chloride leachant.

Optional Recovery of Zinc Oxide To recover the zinc oxide from the product solution in subprocess 300, while the filtered zinc oxide and ammonium chloride solution is still at a temperature of 90°C or above, finely powdered zinc metal is added to the solution. Through an electrochemical reaction, any lead metal and cadmium in solution plates out onto the surfaces of the zinc metal particles. The addition of sufficient powdered zinc metal results in the removal of virtually all of the lead of the solution. The solution then is filtered to remove the solid lead, zinc and cadmium.

Zinc powder typically aggregates to form large clumps in the solution which sink to the bottom of the vessel. To keep the zinc powder suspended in the zinc oxide and ammonium chloride solution, water soluble polymers which act as antiflocculants or dispersants, surface active materials, and/or compounds used in scale control, may be used. These materials only need be present in concentrations of 10 - 1000 ppm. Various suitable materials include water soluble polymer dispersants, scale controllers, and surfactants, such as lignosulfonates, polyphosphates, polyacrylates, polymethacrylates, maleic anhydride copolymers, poiymaleic anhydride, phosphate esters and phosponates. Flocon 100 and other members of the Flocon series of maleic-based acrylic oligomers 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. At this stage there is a filtrate rich in zinc compounds and a precipitate of lead, cadmium and other products. The filtrate and precipitate are separated, with the precipitate being further treated, if desired, to capture chemical values. The filtrate may be treated in several manners, two of which are prefeπed. First, the filtrate may be cooled resulting in the crystallization and recovery of zinc oxide. Second, the

filtrate may be subjected to electrolysis resulting in the generation and recovery of metallic zinc.

To recover zinc oxide, 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 prefeπed 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 water. Very little of the hydrated zinc oxide dissolves in the water. This resultant solution then is filtered to remove the hydrated zinc oxide species. The solid hydrated zinc oxide species filtered from the solution is placed in a drying oven at a temperature of over 100°C. After a sufficient drying period, the resultant dry white powder is essentially pure zinc oxide. The filtrate from the solution is recycled for charging with additional zinc compound mixture.

The zinc oxide may be dried at approximately 100°C. To ensure that the material is free of chloride, however, it is preferable to heat the zinc oxide to a higher temperature. Diamino zinc dichloride decomposes at 271°C and ammonium chloride sublimes at 340°C. Therefore, heating the zinc oxide to a temperature above 271°C is useful. The drying temperature should be kept below approximately 350°C to prevent the sublimation of significant amount of ammonium chloride. Therefore, it is preferable to dry the zinc oxide at a temperature in the range of 271°C to 350°C. Typically, the zinc oxide should be dried in this temperature range for approximately 2 to 60 minutes, and preferably from 5 to 20 minutes. A 10 minute drying time has been found to be a satisfactory average.

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 difference in solubility between diamino zinc dichloride and zinc oxide in water and in ammonium chloride solutions allows the selective dissolution of the diamino zinc dichloride such that pure zinc oxide can be recovered. This also can be used in the crystallization step to improve the relative amounts of diamino zinc dichloride and zinc oxide species form. Significantly, all of the zinc can be recycled so that all of the zinc eventually will be converted into zinc oxide. The crystallization step can be carried out continuously to increase the throughput and maximize the zinc oxide yield after the washing and drying step. 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 takes the filtrate from the cementation step at 90-

100°C. This filtrate contains the dissolved zinc with small amounts of trace impurities such as lead and cadmium. In order to prepare a pure zinc oxide it is necessary to prevent the formation of solvent inclusions inside the grown crystals. 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.

Recycle To produce pure zinc oxide from waste dust containing zinc efficiently and in a safe and cost effective way, the process recycles all zinc which is 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 due to the rapid change in zinc oxide solubility with temperature in ammonium chloride solution.

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. Another important advantage is 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.

Further Sodium Hydroxide Leach Once the essentially pure zinc oxide has been recovered, a further zinc oxide purification process is utilized which is based on the solubility of zinc oxide in a concentrated sodium hydroxide solution. The solubility of zinc oxide in sodium hydroxide increases significantly with increasing sodium hydroxide concentration. For example, a 16 molar sodium hydroxide solution (640g per liter) will dissolve 4 mole (320g) of zinc oxide. If this solution is then diluted by a factor of 4, the solubility will decline so that approximately 180g of zinc oxide/zinc hydroxide will precipitate. The zinc oxide purification process utilizes this phenomenon to produce zinc oxide which is at least 99.8% pure.

In the first step, zinc oxide is dissolved in a 50% - 70% sodium hydroxide solution. Since most metals are not soluble in concentrated sodium hydroxide, most of the metal impurities in the zinc oxide will not dissolve, including manganese, iron and cadmium. Lead and calcium are soluble in concentrated sodium hydroxide and therefore will dissolve, as will chloride. The solution is then filtered to remove the undissolved materials which are then sent to the metals recovery section of the plant.

The solution then is diluted with water by a factor ranging from 3 to 30, but preferably 3 to 8, and optimally around 4, which appears to be optimum from the point of view of product recovery and energy costs. The best mode for the dilution step is performed hot at a temperature at or above 70°C and preferably at temperatures ranging from 80°C to 100°C at atmospheric pressure. Temperatures below 70°C, and temperatures above 100°C at pressures greater than atmospheric, may be used, but are not as economically as advantageous as in the prefeπed range. The hot temperatures cause the formation of zinc oxide to be favored over the formation of zinc hydroxide. The resulting zinc oxide crystals which form are then filtered out, sent to a wash tank

where they are washed with water, and then sent to a dryer where they are dried, preferably at a temperature of 160°C.

The diluted sodium hydroxide solution is then sent to an evaporator condenser where the solution is concentrated back to 50% - 70% sodium hydroxide and then reused. When a steady state has been achieved, this step results in the formation of sodium chloride crystal which will be filtered out of the solution and recovered. This is because sodium chloride formed by the chloride present in the zinc oxide is less soluble in concentrated sodium hydroxide solution than in dilute sodium hydroxide. After the sodium chloride is filtered out, the concentrated solution can be reused in the purification process. Periodically, lead will be removed from the sodium hydroxide solution by cementation. This involves the addition of zinc dust which will displace the lead in solution. The lead will then be filtered out and sent to the lead recovery portion of the plant.

By controlling the rate of dilution of the sodium hydroxide solution or its method of addition during the zinc oxide crystallization step, it is possible to control the particle size hence the surface area of the zinc oxide produced. Furthermore, it should be observed that the zinc oxide purification process is not limited to the purification of zinc oxide recovered by the zinc oxide recovery process of the present invention and can be used to purify zinc oxide provided from any source. Additionally, by selecting the method of addition of the intermediate solution, preferably sodium hydroxide, during the zinc oxide crystallization step, it is possible to control the particle size hence the surface area of the zinc oxide produced. It has been found that the smaller the droplet size in which the solution is added, the smaller the particle size (larger surface area). By dispersing the sodium hydroxide into droplets by a hydraulic atomizer, the particle size can be controlled. Additionally, at a constant droplet size, vigorous mixing will result in a larger surface area. The principle can be employed through selection of the appropriate droplet size and amount of mixing, to obtain highly purified zinc oxide with a predetermined surface area. This general relationship is shown in Table III.

TABLE III Approximate Droplet Size Approximate Surface Area

250 microns 2.0 m /g

180 microns 3.0 m ² /g 150 microns 4.0 m /g

100 microns 10.0 m ² /g

As the concentration of the sodium hydroxide increases, the number of moles of zinc oxide which can be dissolved in the sodium hydroxide solution increases. As the sodium hydroxide solution is diluted, the number of moles which can be dissolved in the solution decreases, i.e., the zinc oxide in the solution begins to precipitate. This solubility characteristic of zinc oxide in sodium hydroxide is used by the present invention to purify zinc oxide by first dissolving the zinc oxide in a highly concentrated solution of sodium hydroxide and filtering out the impurities which do not dissolve, and then by diluting the sodium hydroxide solution to cause the zinc oxide to precipitate. By controlling the rate of dilution, the particle size and surface area of the zinc oxide produced can be controlled.

Production Of Zinc Compounds From Zinc Oxide Zinc oxide can be used to make a number of other zinc compounds. This is the basis for subprocess 300. Those include, zinc acetate, zinc borate, zinc bromate, zinc carbonate, zinc chloride, zinc chromate, zinc hydroxide, zinc nitrate, zinc phosphate, zinc stearate, zinc gluconate, zinc sulfate, and zinc EDTA salt. This list is not exhaustive and many other zinc compounds can be made by adding the appropriate reactants to the zinc oxide slurry.

Commercial zinc oxide is usually made by combustion of zinc vapor in air and is collected as a dry powder. The zinc oxide prepared as described herein is a precipitate in aqueous solution. This allows a range of downstream chemicals to be manufactured by addition of the appropriate acid to the zinc oxide slurry. Well known methods of producing zinc compounds by the addition of the appropriate acid can be used in the cuπent invention.

The zinc compounds can be manufactured directly without having to suspend or dissolve the dry zinc oxide. Synthesis of zinc compounds by this method also obviates the need to dry zinc oxide obtained from the purification process described above. Both simple commodity chemicals and specialty products having a particular

5 physical or chemical properties can easily be made by employing this process in conjunction with the methods to control particle size of the zinc oxide described above.

Although the present invention has been described in accordance with particular embodiments, it will be apparent to those skilled in the art that the

) embodiments discussed above are merely exemplary and that modifications can be made to the processes discussed above which are within the spirit and scope of the present invention.