WO2002016659A1

WO2002016659A1 - Ferrous metal particle briquettes and method of making and using them

Info

Publication number: WO2002016659A1
Application number: PCT/US2001/026358
Authority: WO
Inventors: Thomas A. Cobett
Original assignee: Solvent Systems International
Priority date: 2000-08-23
Filing date: 2001-08-23
Publication date: 2002-02-28
Also published as: AU2001285236A1

Abstract

Ferrous metal briquettes made from ferrous metal particles and an alkaline metal silicate, for adding to ferrous metal melts to recycle the particles.

Description

5543-00002

FERROUS METAL PARTICLE BRIQUETTES AND METHOD OF MAKING AND USING THEM

This application is a continuation of U.S. Patent Application Serial No.

09/575,226 filed May 22, 2000 and entitled BRIQUETTING OF FERROUS METAL

PARTICLES WITH AN ALKALI METAL SILICATE FOR RECOVERY BY MELTING.

BACKGROUND OF THE INVENTION

Many methods of processing ferrous metal materials (iron and steel), such as

crushing, grinding, cutting, polishing, machining, screening and melting ferrous metal

parts, produce large amounts of fine ferrous metal particles. It is desirable to recover and

reprocess these particles. The ferrous metal has significant value if it can be re-melted by

a foundry, smelter or steel making operation. It is also environmentally preferable to melt

existing metal scrap instead of extracting new metal from the earth as ore.

Unfortunately, particles of ferrous metals will oxidize (rust) rapidly at ambient

temperature, particularly in humid weather. When such ferrous particles are added

to a hot melting furnace, they are likely to be oxidized so rapidly that they will burn

before melting. Additionally, fine, light particles of ferrous metal are often blown out

of the melt bath and into the atmosphere by heat convection or by the air blast from

a cupola furnace. Finally, the iron in such iron oxide particles that do not burn and

are not blown away are nevertheless difficult or inefficient to recover by melting, and

often end up being lost into the slag produced as a byproduct of the melting

process. Thus, most of the ferrous metal particles produced in ferrous metal

processing are so problematic to recycle, that they are regarded as practically non- recyclable. They therefore are often placed in landfills and lost forever. A method of

forming these fine ferrous metal particles into compacted masses or briquettes that

resist oxidation and can be simply and efficiently re-melted in foundries, smelters or

steel making operations, would constitute an important improvement in the current

state of the art.

SUMMARY OF THE INVENTION

The present invention is directed to ferrous metal masses or briquettes

bonded by a glassy binder coating and to a method of making those masses and

using them in recycling ferrous metal particles.

The ferrous metal masses (iron and steel) comprise a mixture of at least 80%

by weight ferrous metal particles and preferably over 90% by weight ferrous metal

particles. They also include an alkali metal silicate. Forming the particles into

briquettes makes it possible to conveniently and efficiently recycle the particles by

adding them to a ferrous metal melt.

DETAILED DESCRIPTION OF THE INVENTION

In carrying out the method of the present invention, ferrous metal particles

and an alkali metal silicate solution liquid alkaline metal silicate are mixed together in

any convenient manner, and shaped into masses or briquettes, preferably

compacted, and caused to cure or harden by gelation and/or dehydration. After

curing, the mixture should be at least 80%, and preferably at least 90%, 80% by

weight of ferrous metal with the balance being an alkali alkaline metal silicate and other inorganic impurities, such as silica sand.

The ferrous metal particles are recovered from ferrous metal processing,

including crushing, grinding, cutting, polishing, and machining operations. The

particles may range in size from fine powders to coarse, grains. Particles in the

range of about 100 mesh to about 10 mesh are preferred. However, larger and smaller

particles can also be utilized. It is desirable to ensure that the ferrous metal particles

are kept free from rust prior to being combined with the silicate. Various liquid alkaline

alkali metal silicates may be used in the practice of the invention, including sodium

silicate, potassium silicate, and lithium silicate. Among these, sodium silicate is

preferred. Additionally, one or more silicates may be combined in the mixture. The

silicate should be used in the form of an aqueous solution containing from about 20%

to 50% by weight solids preferably 35% to 45% by weight solids, and most preferably

about 38% by weight solids, with the balance water. Where the ferrous metal particles

are provided in a form which already includes water, the alkali metal silicate may be

provided, in whole or in part, in dry form so that the already present water supplies

some or all of the water in the alkali metal solution.

Curing of the briquettes is believed to proceed by causing the alkali metal

silicate solution to form a gel, which contracts and forces the water out of the

ferrous metal/silicate mixture, thusthereby hardening the final product. Thus, during

the curing of the briquettes, the moisture in the alkaline metal silicate solution is

given up to the atmosphere.

Also, it is preferred that the gelling of the silicate be accelerated by adding an

appropriate amount of an accelerant. For example, the following materials can be used as curing accelerants for this purpose: calcium silicate, aluminates such as

calcium aluminate, sodium aluminate, magnesium aluminate, potassium aluminate

and lithium aluminate; acetic acid esters such as ethylene glycol diacetate, ethylene

glycol monoacetate, glycerol triacetate, glycerol diacetate, and glycerol

monoacetate; carbonic acid esters such as ethylene carbonate and propylene

carbonate; formic acid esters such as methyl formate and ethyl formate; lactic acid

esters; adipic acid esters; glutaric acid esters and succinic acid esters. Injecting

carbon dioxide gas into the mixture is another method of accelerating the curing

process. Heating is yet another way to accelerate the curing, and may be used

either alone or in combination with any of the other accelerants. Indeed, any known

method used to cause the curing of the alkali metal silicates solutions may be

utilized to harden the ferrous metal particles fines into convenient shapes.

In the absence of the addition of accelerants or the use of heating, the

briquettes may be hardened by simply permitting them to dehydrate until hardened.

The mixture of ferrous metal particles and liquid alkaline alkali metal silicate

solution is compacted into appropriately sized forms corresponding to the size and

shape of the mass desired before allowing the mixture to cure, either slowly at ambient temperature, or more rapidly by adding accelerants as described above. The

briquettes may be of any practical size convenient for melting in the particular furnace

being used. For example, briquettes of about 2" x 2" x 2" up to 10" x 10" x 10" in size

have been made and used in accordance with the invention in induction furnaces and

in an iron foundry cupola. Briquettes less than about 2" x 2" x 2" in size are less

desirable because of the danger that they will be blown out of the melt bath. Surprisingly, although one would expect the exposed ferrous metal particles

to rust on the surface of the final briquette produced, this does not occur. Rather,

the silicate forms a glassy coating on the ferrous metal particles, preventing the

briquettes from rusting, even under humid conditions. Furthermore, porosity of the

briquette would also be expected which would produce rusting that works its way

through the briquette, weakening the briquette and reducing its reuse value. Again,

surprisingly, this is not found not to be the case.

The melting point of the metal particles fines is controlled by their chemistry.

When the briquettes are added to a hot melting furnace maintained at a

temperature sufficiently high to cause melting of the metal particles fines, the entire

briquette breaks up, releasing the iron into the melt, while the silicates float up to

the surface to become part of the slag. For example, it has been found that many

such briquettes will melt at a temperature of at least about 2400°F, and up to about

3000°F. This occurs with little or no loss of metal due to high temperature

oxidation, and certainly no blow out of fine metal particles. Indeed, it is believed

that the glassy coating of the ferrous metal particles by the silicate continues to

remain in place at the high melting temperatures, until after the ferrous metal

particles melt into the furnace bath, whereupon the sodium silicate becomes a part

of the slag floating on top of the molten metal.

The following examples are intended to be illustrative of the present invention

and to teach one of ordinary skill how to make and use the invention. These examples are not intended to limit the invention or its protection in any way. Example 1

A briquette in accordance with the present invention was prepared by

combining 90% by weight of ferrous metal particles produced by grinding iron

castings with 10% by weight of a solution of aqueous sodium silicate containing

42% by weight solids, which had a weight ratio of about 3.22 parts Si0 to about

1.0 part Na₂O. In other tests, it was found that a weight ratio of about 2.4 parts

Si0₂ to about 1.0 part Na₂O could be used and indeed, weight ratios of as low as 2.0

to 1.0, and as high as 4.0 to 1.0, will produce satisfactory briquettes. Acceptable

solids contents of the aqueous sodium silicate solutions ranged from as low as about

20% to as high as 50%.

The materials were mixed for three minutes and compacted by hand into a

plastic form to increase the density of the briquette. The form was inverted onto a

plate and the resulting briquette carefully removed from the form. The briquette was

allowed to dehydrate for 72 hours.

Several of the briquettes were placed outdoors in an unprotected area. A

small pile of unbonded or free ferrous metal particles was placed next to the

briquettes. After 90 days of weathering, including rain, snow, ice and sunlight, the

briquettes exhibited no oxidation. The small pile of unbonded particles was

completely covered with bright orange rust. Example 2

Five pounds of briquettes prepared as explained in Example 1, were placed on

top of six pounds of liquid Class 30 gray iron that had been melted to a temperature

of 2700°F., in a small electric induction furnace. The briquettes, which floated on the surface, gradually melted into the existing molten iron. The floating of the

briquettes ensured insured that any moisture present in the glassy coating within the

interstices of the mass would evaporate and escape without entering the melt.

After removal of the slag on the surface of the molten metal, the iron was

poured into an ingot mold and permitted to cool. After cooling, the ingot was

weighed and found to be just slightly less than 11 pounds. This indicates nearly

complete recovery of metal from the 5 pounds of briquettes. Additionally, the

composition of the iron was verified as being acceptable Class 30 gray iron, which is

a standard iron composition with 30,000 p.s.i. tensile strength.

Example 3

A mixture of ferrous metal particles and sodium silicate solution was made as

explained in Example 1. This mixture was compacted into plastic forms and carbon

dioxide gas was injected at a pressure of 15 p.s.i., using a small lance. After 10

seconds of gassing, the partially cured mixture was easily removed from the form.

The partially cured shapes were allowed to dehydrate, forming briquettes in

accordance with the invention, and then were exposed to weather as in Example 1.

They were also melted in an iron bath, as in Example 2. In all cases, the results

were the same as in Examples 1 and 2.

Example 4

In this example, a mixture of 89.2% by weight of fine ferrous metal particles

generated by grinding iron castings, was combined with 10% by weight aqueous sodium

silicate and 0.8% by weight of an accelerant, ethylene glycol diacetate. The materials were

mixed for 3 minutes, and compacted by hand into a plastic form. After 15 minutes, a partially cured shape was easily removed from the form. The partially cured shape was

allowed to dehydrate to form briquettes in accordance with the present invention and

exposed to weather, as in Example 2. The shapes were also melted into an iron bath, as in

Example 1. The same results achieved in Examples 1 and 2 were achieved in this example.

Example 5

In this example, 10% by weight of the liquid sodium silicate was combined with

86% by weight of iron metal particles generated by grinding iron castings and 4.0% by

weight sodium aluminate, which was added as an accelerant. The materials were mixed

for 3 minutes and compacted by hand into a plastic form. After fifteen minutes, the

mixture was easily removed from the form. These partially cured shapes were allowed to

dehydrate, forming briquettes in accordance with the present invention. They were

exposed to weather and melted into an iron bath, as in Examples 1 and 2, producing

results commensurate with those Examples.

While the present invention is described above in connection with preferred or

illustrative embodiments, these embodiments are not intended to be exhaustive or

limiting of the invention. Rather, the invention is intended to cover all alternatives,

modifications, and equivalents included within its spirit and scope, as defined by the

appended claims.

Claims

CLAIMSWhat I claim is:

1. A method for making ferrous metal masses with a glassy coating comprising:

mixing ferrous metal fines particles and an aqueous alkali metal silicate

solution;

shaping the mixture into briquettes remove air pockets; and

permitting the briquettes to cure.

2. The method of claim 1 in which the briquettes are compacted to increase

their density.

3. The method of claim 1 in which the ferrous metal particles are supplied in an

amount sufficient to provide the cured briquettes with over 80% by weight ferrous

metal.

4. The method of claim 1 in which the ferrous metal particles are supplied in an

amount sufficient to provide the cured briquettes with at least 90% by weight ferrous

metal.

5. The method of claim 1 in which the ferrous metal particles range in size from fine to coarse.

6. The method of claim 1 in which the ferrous metal particles are from about 10

to about 100 mesh in size.

7. The method of claim 1 in which the ferrous metal particles are recovered from

a ferrous metal processing operation chosen from the group consisting of crushing, grinding, cutting, polishing and machining.

8. The method of claim 1 in which the ferrous metal particles are free from rust

before being mixed with the alkali metal silicate solution.

9. The method of claim 1 in which the alkali metal silicate is chosen from the

group consisting of sodium silicate, potassium silicate, and lithium silicate.

10. The method of claim 9 in which the alkali metal silicate is sodium silicate.

11. The method of claim 10 in which the sodium silicate is in the form of an

aqueous solution having SiO₂ and Na₂O in a ratio from about 2.0 to 1.0 to about 4.0

to 2.0.

12. The method of claim 10 in which the sodium silicate is in the form of an

aqueous solution having SiO₂ and Na₂O in a weight ratio of about 3.22 to 1.0.

13. The method of claim 10 in which the sodium silicate is in the form of an

aqueous solution having SiO₂ and Na₂O in a weight ratio of about 2.4 to 1.0.

14. The method of claim 1 in which the alkali metal silicate is supplied in the form

of an aqueous solution having from about 20% to about 50% by weight solids.

15. The method of claim 1 in which the alkali metal silicate is supplied in the form

of an aqueous solution having about 38% by weight solids.

16. The method of claim 1 in which the gelling of the alkali metal silicate is

accelerated by adding an appropriate amount of a curing accelerant.

17. The method of claim 16 in which the curing accelerant is chosen from the

group consisting of calcium silicate, aluminates, acetic acid esters, carbonic acid

esters, formic acid esters, lactic acid esters, adipic acid esters, succinic acid esters,

glutaric acid esters and acidic gases.

18. The method of claim 17 where the aluminates include calcium aluminate,

sodium aluminate, magnesium aluminate, potassium aluminate or lithium aluminate;

the acetic acid esters include ethylene glycol monoacetate, glycerol triacetate,

glycerol diacetate, or glycerol monoacetate; the carbonic acid esters include ethylene

carbonate or propylene carbonate; the formic acid esters include methyl formate and

ethyl formate, and the acidic gases include carbon dioxide.

19. The method of claim 1 in which the curing of the briquettes is accelerated by

heating.

20. The method of claim 1 in which the briquettes range in size from 2" x 2" x 2"

to about 10" x 10" x 10" in size.

21. The method of claim 1 in which the briquettes are at least about 2" x 2" x 2" in size.

22. A method of recycling ferrous metal particles by first making ferrous metal

masses with a glassy coating by mixing ferrous metal particles and an alkali metal

silicate solution, shaping the mixture into briquettes, permitting the briquettes to cure,

storing the briquettes as desired, and then adding the briquettes to a ferrous metal

melt maintained at a temperature sufficiently high to melt the ferrous metal particles.

23. The method of claim 22 in which the ferrous metal melt is maintained at a

temperature of about 2400°F to about 3000°F.

24. The method of claim 22 in which the briquettes have at least 80% by weight ferrous metal.

25. The method of claim 22 in which the ferrous metal particles range in size from about 10 to about 100 mesh in size.

26. The method of claim 22 in which the alkali metal silicate is chosen from the

group consisting of sodium silicate, potassium silicate, and lithium silicate.

27. The method of claim 1 in which the ferrous metal particles are recovered from

a ferrous metal processing operation chosen from the group consisting of crushing,

grinding, cutting, polishing, machining, screening and melting.

28. A ferrous metal briquette made by mixing ferrous metal particles and an alkali

metal silicate solution, shaping the mixture into briquettes, and permitting the

briquette to cure.

29. The method of claim 1 where the ferrous metal particles are provided in a

form which already includes water, and the alkali metal silicate is provided, in whole

or in part, in dry form so that the already present water supplies some or all of the

water in the alkali metal silicate solution.