Method for the recovery of group IA salts during the treatment of industrial process waste streams

A method for the production of Group IA salts during a process for the recycling of industrial waste streams containing Group IA compounds and iron and/or zinc compounds, by heating the waste stream in a reducing atmosphere, treating the exhaust fumes from the heating step with an ammonium chloride leaching solution resulting in a Group IA salt containing precipitate, and recovering the Group IA salts from the precipitate.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to a process for the recovery of 
usable economically valuable products from industrial waste streams 
typically comprising zinc compounds and iron compounds. The present 
invention relates specifically to a process for the recovery of Group IA 
salts from industrial waste streams comprising Group IA compounds along 
with zinc compounds and iron compounds, in an overall process in which a 
relatively pure iron or direct reduced iron product feedstock and a very 
pure zinc oxide product are produced. 
The specific improvement of the present invention is an additional process 
for recovering sodium chloride and potassium chloride from a waste 
material cake resulting after a waste stream from a metals-related 
industrial process has been treated to remove a significant portion of any 
iron and zinc compounds. 
2. Prior Art 
Industrial waste streams typically contain components which have economic 
value if they can be recovered in an economic fashion. For example, U.S. 
Pat. No. 3,849,121 to Burrows, now expired but which was assigned to a 
principal of the assignee of the present invention, discloses a method for 
the selective recovery of zinc oxide from industrial waste. The Burrows 
method comprises leaching a waste material with an ammonium chloride 
solution at elevated temperatures, separating iron from solution, treating 
the solution with zinc metal and cooling the solution to precipitate zinc 
oxide. The Burrows patent discloses a method to take EAF dust which is 
mainly a mixture of iron and zinc oxides and, in a series of steps, to 
separate out and discard the iron oxides and waste metals, so that the 
resulting zinc-compound-rich solution can be further treated to recover 
the zinc compounds. 
Waste metal process dust typically has varying amounts of other components, 
in various forms, such as Group IA elements including sodium and 
potassium, contained in the dust. The Burrows patent does not teach the 
treatment or recovery of any values from the discarded iron oxide 
containing precipitates, and does not discuss any method of recovering 
Group IA salts, such as sodium chloride and potassium chloride, from the 
process. 
U.S. Pat. No. 4,071,357 to Peters discloses a method for recovering metal 
values which includes a steam distillation step and a calcining step to 
precipitate zinc carbonate and to convert the zinc carbonate to zinc 
oxide, respectively. Peters further discloses the use of a solution 
containing approximately equal amounts of ammonia and carbon to leach the 
flue dust at room temperature, resulting in the extraction of only about 
half of the zinc in the dust, almost 7% of the iron, less than 5% of the 
lead, and less than half of the cadmium. However, Peters does not disclose 
a method for further treating the removed components not containing zinc 
compounds, nor of recovering Group IA salts from the process. 
As can be seen, there exists a need for a method which will allow the 
continuous treatment of exhausts and fumes from reduction furnaces or the 
like to recover Group IA salt values. This need is addressed by the 
present invention. 
BRIEF SUMMARY OF THE INVENTION 
The present invention satisfies this need in a method which recovers Group 
IA salts in conjunction with the recovery of a relatively pure iron 
product from a waste material or a combination of waste materials from 
industrial processes, such as waste streams from electric arc furnaces, 
typically containing zinc or zinc oxide and iron or iron oxide, and 
exhaust fumes from reduction furnaces, which typically are iron-poor. The 
non-iron solids and feed and product solutions used and/or produced in the 
overall process can be recycled such that the process has minimal solid or 
liquid wastes. Other solids can be recovered by treating other compounds 
in the waste materials, for example zinc oxide, zinc, metal values, and 
other residues, all of which can be used in other processes. As an 
alternative embodiment, iron-rich waste products, such as for example mill 
scale and used batteries, also can be added to the waste stream feed of 
the present process. 
A waste materials stream such as electric arc furnace (EAF) dust or the 
flue dust disclosed in Table I herein, is subjected to a combination of 
processing steps, resulting ultimately in the recovery of certain Group IA 
salts. An enriched iron compound (an enriched iron cake or EIC) which can 
be used as a feedstock for steel mills, and other products of value, also 
can be produced from the general process, and are disclosed in and/or 
covered by other patent applications and patents assigned to Metals 
Recycling Technologies Corporation of Atlanta, Georgia US, the assignee of 
this invention. The EIC typically is rich in direct reduced iron (DRI). 
Preferably, the precipitate containing iron oxides is removed from a 
process for the recovery of zinc oxide and zinc metal from industrial 
waste streams. During the recovery process, carbon compounds can be added 
to the waste stream, and a cake product is produced from the undissolved 
iron and carbon compounds, which also can be used as a feedstock for steel 
mills. 
In a preferred embodiment of the process, the waste material stream is 
heated in a reducing atmosphere in a reduction furnace, resulting in the 
reduction of the iron compounds into DRI, and the production of combustion 
products. The DRI can be fed directly to a steel mill as a feed source, 
and the combustion products, typically in the form of exhaust dusts and 
fumes, are recovered in a filter means, such as a baghouse or wet 
scrubber. The exhaust dusts and fumes comprise the majority of the Group 
IA salt constituents, and the non-iron compounds, such as zinc, cadmium, 
copper, lead, and calcium compounds. 
EAF dust, either alone or in combination with iron-rich waste materials, 
mill scale, used batteries, or other iron-rich or iron-poor waste 
materials may be used as the initial feed for the process. This combined 
waste first is heated in a reducing atmosphere, reducing any iron oxides 
present to usable DRI. The exhaust vapor from the DRI process is condensed 
and comprises mainly zinc, lead and cadmium oxides and Group IA chlorides. 
This waste material then is leached with an ammonium chloride solution 
resulting in a product solution (leachate) and undissolved materials 
(precipitate). At steady state the Group IA species reach saturation in 
the ammonium chloride solution and therefore do not dissolve, remaining 
with the solids in the filter cake. 
In the leaching step, the Group IA salt constituents reach their saturation 
concentration in the ammonium chloride solution and precipitate out. The 
leachate comprises metal oxides contained in the waste material, such as 
lead oxide and cadmium oxide, and zinc and/or zinc oxide. The product 
solution and the undissolved materials are separated, with the product 
solution and the undissolved materials being further treated to recover 
Group IA salts and other valuable components, as appropriate. 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. 
When processing EAF dusts, zinc-containing wastes and fumes from rotary 
hearth furnaces, upon reaching steady state, the filter cake obtained 
after the first leaching step contains sodium chloride and potassium 
chloride since these have reached their saturation concentration in the 
ammonium chloride solution. The filter cake comprises true insolubles, 
which are mainly silicates, and water soluble salts, which are mainly 
sodium chloride and potassium chloride. The salts can be recovered by: 
1. Washing the filter cake with water, dissolving all water soluble salts; 
2. Optionally cementing out heavy metals such as lead using powdered zinc; 
and 
3. Crystallizing out sodium chloride and potassium chloride salts either 
singly or mixed by selective evaporative crystallization or spray drying. 
The salts then can be dried and bagged and sold. 
Therefore, it is an object of the present invention is to provide a waste 
material recovery process which recovers chemical values including Group 
IA salts from industrial waste streams, recycles exhaust fumes from 
furnaces such as electric arc furnaces and reduction furnaces, recycles 
exhaust fumes from industrial processes such as iron and steel making 
processes, and recycles other waste materials, including both iron-rich 
and iron-poor waste materials, to produce valuable products. 
Another object of the present invention is to provide a method for 
recovering Group IA salts from the precipitate from an ammonium chloride 
leach used to recover zinc oxide. 
These objects and other objects, features and advantages of the present 
invention will become apparent to one skilled in the art after reading the 
following Detailed Description of a Preferred Embodiment.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
The method disclosed herein is carried out in its best mode in treating the 
waste material from the waste streams of metal-making processes, 
industrial or other processes. These waste materials may be combined with 
other waste materials recovered from furnace exhaust streams. Many 
processes produce an iron poor waste stream, such as reduction furnaces 
and iron and steel making processes. Many other processes produce an iron 
rich waste stream. Other processes remove iron rich materials prior to 
processing. The iron poor materials can be combined with a typical 
industrial waste stream which, after treatment, results in an iron rich 
material suitable for use as a feedstock to a steel mill. Iron rich 
materials also can be combined with the typical industrial waste stream 
and the iron poor waste stream. 
A typical industrial waste stream used is a flue gas where the charge 
contains galvanized steel, having the percent composition shown in Table 
I: 
TABLE I 
______________________________________ 
Analysis of Flue Dust 
Component Percent By Weight 
______________________________________ 
Zinc Oxide 30 
Iron Oxide 40 
Lead Oxide and Chloride 
6.48 
Inert Materials 9.10 
Sodium Oxide and Chloride 
5.00 
Calcium Oxide 2.80 
Potassium Oxide and 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 Materials 
0.22 
______________________________________ 
A second typical industrial waste stream used is a zinc rich fume from a 
rotary hearth furnace used in an iron-making or steel-making process, 
having the percent composition shown in Table II: 
TABLE II 
______________________________________ 
Analysis of Rotary Hearth Furnace Fume 
Component Percent By Weight 
______________________________________ 
Zinc Oxide 70 
Lead 6 
Sodium 3 
Potassium 3 
Chloride 11 
Insoluble 3 
Miscellaneous 4 
______________________________________ 
General Process Description 
Generally, the present process is a novel addition to a continuous method 
for the recovery of chemical and metal values from waste material streams. 
The basic process steps for recovering Group IA salts from such a method 
are shown as a flow chart in FIG. 2 and comprise: 
a. Heating a typical industrial process waste material stream comprising 
Group IA compounds such as from a metal or metal product process, in a 
reducing atmosphere to produce an exhaust stream (typically fumes); 
b. Treating the exhaust stream which may be a waste material combination 
comprising other waste streams, with an ammonium chloride solution at an 
elevated temperature to form a product solution and an undissolved 
precipitate comprising Group IA salts; 
c. Separating the product solution from the undissolved precipitate 
comprising the Group IA salts; 
d. Washing the undissolved precipitate to form a salt solution which 
comprises the Group IA salts and an undissolved solid; and 
e. Crystallizing out the Group IA salts from the salt solution by 
evaporative crystallization or spray drying. 
An alternative set of process steps for recovering Group IA salts from such 
a method are shown as a flow chart in FIG. 3 and comprise: 
a. Adding a fame from a rotary hearth furnace comprising Group IA salts to 
water to dissolve the Group IA salts; 
b. Filtering out the components of the fume which do not dissolve in the 
water as undissolved solids; and 
c. Crystallizing out the Group IA salts from the salt solution by 
evaporative crystallization or spray drying. 
The salt solution may be subjected to a cementation step to remove other 
compounds. The undissolved solids may be sent to a leaching solution to 
recover other chemical and/or metal values. 
Preferred Embodiment 
Referring to FIG. 1, a preferred embodiment of an overall waste stream 
recovery process is shown. Subprocess 100, the digestion and filtration 
steps, generally comprises the process disclosed and claimed in U.S. Pat. 
No. 5,464,596. Subprocess 200, the DRI production steps, generally 
comprises the process disclosed and claimed in U.S. applications Ser. Nos. 
08/348,446 and 08/665,043. Subprocess 300, the chemical values recovery 
steps, when combined with subprocess 100, generally comprises the process 
disclosed and claimed in U.S. Pat. No. 5,453,111. Subprocess 400, the 
enhanced DRI production steps, when combined with subprocess 200, 
generally comprises the process disclosed and claimed in U.S. Pat. No. 
5,571,306. Each of subprocesses 200, 300, and 400 may be added to the 
general process. The U.S. patents mentioned in this paragraph are 
incorporated herein by this reference. 
Subprocess 200 comprises the leaching steps. Subprocess 500 comprises the 
feed process and includes the relevant step of heating the waste stream in 
a reducing atmosphere. Feed streams such as iron poor waste fume streams 
from electric arc furnaces 12 and other furnaces such as reduction 
furnaces or smelters 14 are filtered in a baghouse 16. Other feed streams 
such as iron rich DRI 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 are filtered in a baghouse 16. The constituents 
filtered out in baghouse 16 comprise the waste stream feed to subprocess 
100. 
In subprocess 500, the waste feed stream is heated in a reducing 
atmosphere, resulting in the reduction of the iron compounds into DRI. 
This heating typically occurs at between about 500.degree. C. and 
1315.degree. C., and preferably at between 980.degree. C. and 1260.degree. 
C. The DRI can be fed directly back into the industrial process, such as a 
steel making process. Exhausts from the heating step are recovered in a 
capture means, such as baghouse 16, and then subjected to the leaching and 
other chemical values recovery steps. 
In subprocess 100, the waste stream feed is leached in digester 18 with 
ammonium chloride, preferably at approximately 90.degree. C. and 
approximately 18-23% by weight concentration. Constituents soluble in 
ammonium chloride go into solution, while constituents insoluble in 
ammonium chloride, such as iron oxides, do not dissolve. At steady state 
the Group IA salts reach their saturation concentration in the solution 
and do not dissolve. The precipitates are filtered from the solution in 
filter 20. The filtered solution is sent to cementer 22, and subjected to 
subprocess 200 to recover other chemical values. The precipitate, which 
typically is a filter cake, is further treated to recover the Group IA 
salts and/or is sent to subprocess 300. 
If the precipitate is sent to subprocess 300 prior to or instead of 
recovering the Group IA salts, the precipitate is dried and crushed in 
dryer/crusher 24. Exhaust gases from dryer/crusher 24 may be sent to a 
baghouse such as baghouse 16, 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 crushed precipitates are compacted 
in compactor 28 and sent to a reduction furnace or smelter 14. In 
reduction furnace 14, the dried and crushed iron cake is heated at between 
980.degree. C. and 1315.degree. C., producing an enriched iron cake (EIC) 
which can comprise DRI and pig iron, which can be in liquid form. The EIC 
can be compacted in a second compactor 30, and then cooled by cooling 
water in a cooling conveyor 32, to produce the DRI. The DRI then can be 
used as the feed to a steel mill EAF, and the process cycle starts over. 
Exhaust fumes from the reduction furnace 14 are sent to scrubber 34, 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 flumes 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 one embodiment, the furnace 12, 14 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. If an ammonium 
chloride solution is used as the scrubbing liquid, it is preferred to 
maintain the solution at approximately 90.degree. C. and approximately 23% 
NH.sub.4 Cl. 
Heating In A Reducing Atmosphere 
The heating step can be carried out prior to the initial leaching step, and 
also optionally between a first and second leaching step. The waste stream 
is heated to temperatures greater than 500.degree. C., but typically no 
greater than 1315.degree. C. This temperature causes a reaction which 
causes a decomposition of the stable franklinite phase contained in the 
waste stream into zinc oxide and other components. 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 reduced using many conventional processes, 
such as, for example, direct or indirect heating and the passing of hot 
gases through the dust. For example, non-explosive mixtures of reducing 
gases, such as hydrogen gas and nitrogen or carbon dioxide, can be passed 
through the waste material. Hydrogen gas is not the only species that may 
be used for reductive decomposition of franklinite. It is possible to use 
carbon or simple carbon containing species, including carbon-containing 
reducing gases and elemental carbon. Heterogeneous gas phase reductions 
are faster than solid state reductions at lower temperatures and therefore 
suggest the use of carbon monoxide. The carbon monoxide can be generated 
in situ by mixing the franklinite powder with carbon and heating in the 
presence of oxygen at elevated temperatures. The oxygen concentration is 
controlled to optimize CO production. The carbon monoxide may be 
introduced as a separate source to more clearly separate the rate of 
carbon monoxide preparation from the rate of Franklinite decomposition. 
The prepared zinc oxide then can be removed by either ammonium chloride 
extraction or sublimation. 
Leaching Treatment 
The exhaust stream from the reducing step (typically fumes) and, optionally 
a portion of the waste material, is subjected to an ammonium chloride 
leach. An ammonium chloride solution in water is prepared in known 
quantities and concentrations. If the two-stage leaching process is used, 
the feed material, such as the exhaust stream and waste material flue dust 
described in Table I combined with any other feed material source which 
contains iron oxide, is added to the ammonium chloride solution. 
Otherwise, the feed material first is heated in a reducing atmosphere. The 
majority of the waste mixture, 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. At steady state, the Group IA salts reach their 
saturation concentration in the solution and do not dissolve. 
It has been found that an 18-23% by weight ammonium chloride solution in 
water at a temperature of at least 90.degree. C. provides the best 
solubility for such a waste mixture. Concentrations of ammonium chloride 
below this range do not dissolve the maximum amount of zinc oxide from the 
waste mixture, and concentrations of ammonium chloride above about this 
range tend to precipitate out ammonium chloride along with the zinc oxide 
when the solution is cooled. Therefore, 18-23% has been chosen as the 
preferred ammonium chloride solution concentration. The iron oxide and 
inert materials such as silicates will not dissolve in the preferred 
solution. 
Ammonium sulfate may be added to the leaching solution to reduce and/or 
remove excess calcium build-up during the process. The ammonium sulfate 
can be added to the leach tank prior to charging with dust. The calcium 
sulfate which forms will be filtered out with the iron cake and returned 
to the steel making furnace. The calcium will calcine to calcium oxide 
when it is heated during the steel making process. This method can also be 
used in using a rotary hearth furnace in the first step. The enriched dust 
in this process contains small amounts of calcium so that treatment will 
still be necessary on a smaller scale. The precipitated calcium sulfate 
along with unleashed solids will be returned to the rotary hearth furnace. 
The calcium sulfate will form calcium oxide and return with the iron units 
to the steel making. 
The zinc oxide, as well as smaller concentrations of lead or cadmium oxide, 
are removed from the waste mixture by the dissolution in the ammonium 
chloride solution. The solid remaining after this leaching step contains 
Group IA salts, iron oxides and some impurities including zinc, lead, 
cadmium, and possibly some other impurities. By subjecting the leachate to 
evaporation, the leachate can be concentrated, thus precipitating out 
Group IA salts. As the ammonium chloride concentration rises, the Group IA 
salt solubility falls, causing additional precipitation. 
Recovery of Group IA Salts 
When processing these EAF dusts, zinc-containing wastes and fumes from 
rotary hearth furnaces, upon reaching steady state, the filter cake 
obtained after the first leaching step contains sodium chloride and 
potassium chloride since these have reached their saturation concentration 
in the ammonium chloride solution. The filter cake comprises true 
insolubles, which are mainly silicates, and water soluble salts, which are 
mainly sodium chloride and potassium chloride. The salts can be recovered 
by: 
1. Washing the filter cake with water, dissolving all water soluble salts; 
2. Optionally cementing out heavy metals such as lead using powdered zinc; 
and 
3. Crystallizing out sodium chloride and potassium chloride salts either 
singly or mixed by selective evaporative crystallization or spray drying. 
These steps preferably are carried out in combination with a complete waste 
stream recycling operation as disclosed herein. If the optional 
cementation step is carried out, the heavy metals cemented out are 
filtered from the aqueous solution and sent on to a mixed metals 
separation step, such as Subprocess 300. 
The production of Group IA salts can be carried out to continuously remove 
the sodium chloride and potassium chloride salts during each cycle of an 
overall waste stream recycling process, such as that disclosed herein, so 
that the filter cake would not contain any significant amount of these 
salts. This can be done by taking the recycle stream going to the 
evaporator condenser and evaporating the stream to an ammonium chloride 
concentration which results in the precipitation of the sodium chloride 
and potassium chloride, since the salts solubility goes down as the 
ammonium chloride concentration goes up. The precipitated solid salts then 
can be filtered from the solution, dried and bagged. The salts then can be 
subjected to further separation into specific salts by another 
crystallization step. 
Optional Carbon Addition Step 
The present process also can be operated to produce a high-quality 
iron-carbon cake as a residual product. The iron oxide contained in the 
waste stream does not go into solution in the ammonium chloride solution, 
but is filtered from the product solution as undissolved material. This 
iron oxide cake can be used as is as the feedstock to a steel mill; 
however, as previously discussed, it becomes more valuable if reduced by 
reaction with elemental carbon to produce an iron-carbon or direct-reduced 
iron product. One preferred method for producing such an iron-carbon or 
direct-reduced iron product from the waste material comprises the steps 
of, after first heating the waste stream in a reducing atmosphere: 
a. treating the waste material with an ammonium chloride solution at an 
elevated temperature to form a product solution which comprises dissolved 
zinc and dissolved zinc oxide whereby any iron oxide in the waste material 
will not go into solution and Group IA salts will precipitate out; 
b. adding carbon to the product solution whereby the carbon will not go 
into solution; 
c. separating the product solution from the undissolved materials present 
in the product solution including the Group IA salts, any of the iron 
oxide and the carbon; and 
d. washing the undissolved materials to dissolve and remove the Group IA 
salts for recovery, leaving the iron oxide and the carbon as an 
undissolved solid. 
A mixture of iron oxide and carbon is used by the steel industry as a 
feedstock for electric arc furnaces. The iron oxide cake which is removed 
as undissolved material from the leaching step is primarily iron oxide, 
being a mixture of Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4. The iron oxide 
cake can be made into the mixture of iron oxide and carbon by adding 
elemental carbon to the iron oxide cake in several manners. First, carbon 
can be added to the leaching tank at the end of the leaching step but 
before the undissolved materials are separated from the product solution. 
Since the carbon is not soluble in the ammonium chloride solution and will 
not react in an aqueous solution, the iron oxide cake and the carbon can 
be separated from the product solution and made into a hard cake. 
Different size carbon, such as dust, granules, or pellets, may be used 
depending on the desires of the steel makers. Second, the carbon can be 
added to the iron oxide after the iron oxide has been separated from the 
product solution. The dried iron oxide and the carbon can be ribbon 
blended in a separate process. Combining carbon and iron oxide in a 
reducing atmosphere and at an elevated temperature results in the 
reduction of the iron oxide, producing DRI. 
Generally the iron oxide and carbon product is pressed into a cake for ease 
of handling and use. The cake typically contains approximately 82% solids, 
but may range from 78% to 86% solids and be easily handled and used. 
Although cakes of less than 78% solids can be formed, the other 22%+of 
material would be product solution which, if the cake is used as a 
feedstock to a steel mill, would be reintroduced to the steel-making 
process, which is uneconomical. Likewise, drying the cake to have more 
than 86% solids can be uneconomical. 
The iron oxide cake can be treated in three manners. First, the iron 
oxide-carbon cake can go directly to the steel mill and, if it goes 
directly to the steel mill, then the reduction of the iron oxide would 
take place in the steel mill furnace. Second, the iron oxide-carbon cake 
can be pelletized and roasted in a reduction furnace to form direct 
reduced iron. The iron oxide precipitate, which typically contains around 
80% solids, is ground up with carbon and formed into pellets, briquettes 
or cubes and then heated. These pellets, briquettes or cubes then can be 
introduced to a steel making furnace. The difference in the material that 
would be introduced to the furnace from the first manner and the second 
manner is that in the second manner, direct reduced iron is introduced to 
the steel making furnace, while in the first manner, a combination of iron 
oxide and carbon is introduced to the steel making furnace. The iron oxide 
plus carbon can be supplied to the steel mill as is. When this carbon 
enriched iron oxide is melted, it forms a foamy slag, and a foamy slag is 
desirable in steel making. Third, the carbon can be added through a ribbon 
blender, and then the iron oxide-carbon cake can be introduced either 
directly into the furnace or, preferably roasted in a reduction furnace 
first to form direct reduced iron, which would be preferred for steel 
making. 
In order of preference, the first manner is the least preferable, that is 
adding the material itself as a mixture of carbon and iron oxide without 
any reducing agents mixed in with it. The second most preferable is the 
third manner, adding the material with carbon added to it either through 
the leaching step or through a ribbon blender and put directly into the 
furnace. The most preferable is the second manner, where carbon is added 
either though the leaching step or a ribbon blender, pelletizing or 
briquetting it, roasting it, and introducing it to the steel furnace. 
In any manner, the fumes exhausting from the steel mill furnace and the 
reduction furnace typically are iron poor, but comprise Group IA salt 
constituents and other valuable components. The furnace exhaust fumes are 
an excellent source of iron poor waste materials useful for recovery in 
the present process. The exhaust fumes may be filtered in a baghouse, with 
the resulting filtrate being added to the waste stream feed of the present 
process, or with the resulting filtrate being the primary waste stream 
feed of the present process. The exhaust fumes also may be scrubbed in a 
wet scrubber, with the resulting loaded scrubbing solution being added to 
the ammonium chloride leachant of the present process. If an ammonium 
chloride scrubbing solution is used instead of water, the loaded ammonium 
chloride scrubbing solution may be used as the primary leachant of the 
present process. 
Optional Recovery of Zinc Oxide From Product Solution 
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.degree. 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. 
Powdered zinc metal alone may be added to the zinc oxide and ammonium 
chloride solution in order to remove the solid lead and cadmium. However, 
the zinc powder typically aggregates to form large clumps in the solution 
which sink to the bottom of the vessel. Rapid agitation typically will not 
prevent this aggregation from occurring; however mixing with high shear 
forces typically will. Alternatively, to keep the zinc powder suspended in 
the zinc oxide and ammonium chloride solution, any one of a number of 
water soluble polymers which act as antiflocculants or dispersants may be 
used. In addition, a number of surface active materials also will act to 
keep the zinc powder suspended, as will many compounds used in scale 
control. These materials only need be present in concentrations of 10-1000 
ppm. Various suitable materials include water soluble polymer dispersants, 
scale controllers, and surfactants, such as lignosulfonates, 
polyphosphates, polyacrylates, polymethacrylates, maleic anhydride 
copolymers, polymaleic anhydride, phosphate esters and phosponates. 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 comprising zinc compounds, and a 
precipitate of Group IA salts, lead, cadmium and other products. The 
filtrate and precipitate are separated, with the precipitate being further 
treated to capture the Group IA salts and other chemical values. The 
filtrate also may be cooled resulting in the crystallization and recovery 
of zinc oxide and/or subjected to electrolysis resulting in the generation 
and recovery of metallic zinc. 
The filtrate then can be treated to crystallize out the complex salt 
diamino zinc dichloride. This can be done in a conventional crystallizer 
by cooling the filtrate to the proper temperature, generally between about 
20.degree. C. and 60.degree. C. The crystallized diamino zinc dichloride 
then can be mixed with 25.degree. C.-100.degree. C. water to decompose the 
diamino zinc dichloride into zinc oxide and ammonium chloride. Particle 
size may be controlled as described in related specifications. 
The zinc oxide then can be dried using a ring dryer or other drying means. 
Iron By-Product Recycle 
Iron-rich by-products produced during the recovery process can be processed 
further to obtain an end product which can be recycled back into the 
leaching step of the recovery process of the present invention. The 
iron-rich by-products preferably are reduced to DRI in a reduction 
furnace. During the reduction process, exhausts fumes which consists 
primarily of zinc, lead and cadmium are produced in the reduction furnace. 
In accordance with a first embodiment, the DRI is sent to a steel mill 
where it is used in the production of steel. The steel production process 
results in exhaust fumes which are processed through the baghouse or/and a 
wet scrubber, either or both of which can be located at the steel mill. 
Fumes processed through the baghouse are filtered, and the captured solid 
residuum, along with an added amount of EAF dust, is recycled back into 
the waste materials stream whereby it is returned to the leaching step of 
the recovery process. Fumes processed through the wet scrubber are 
scrubbed in a liquid stream and the residual impurities obtained from the 
scrubbing process are discharged from the wet scrubber directly into the 
ammonium chloride solution of the leaching step. 
In accordance with a second embodiment, the fumes exhausted from the 
reduction furnace used to produce the DRI are processed through the 
baghouse or/and the wet scrubber. Fumes processed through the baghouse are 
filtered, and the captured solid residuum is recycled back into the waste 
material stream, whereby it is returned to the ammonium chloride solution 
of the leaching step. In this embodiment, no EAF dust need be added in 
with the solid residuum. Fumes processed through the wet scrubber are 
scrubbed in a liquid stream and the residual impurities obtained from the 
filtering process are discharged from the wet scrubber directly into the 
ammonium chloride solution of the leaching step. 
The above detailed description of a preferred embodiment is for 
illustrative purposes only and is not intended to limit the spirit or 
scope of the invention, or its equivalents, as defined in the appended 
claims.