BACKGROUND

1. The Field of the Invention

The present invention is related to a novel method for 5 recycling glass and to novel uses for such recycled glass. More particularly, the present invention is related to a method of processing scrap glass to produce uncontaminated glass particu¬ lates having rounded edges and to the use of such glass particu¬ lates as a substitute for natural sand.

° 2. Technical Background

Because the raw materials from which glass is made are indigenous to most areas of the world and are generally inexpen¬ sive, glass has become an important material for a variety of applications. Even with the proliferation of plastics, glass continues to be the material of choice for use in making many types of containers and windows. Indeed, millions of tons of glass are produced annually.

Although the unique properties of glass render it suitable for use in a variety of applications, disposal of glass following its intended use presents some significant problems.

Indeed, approximately eight percent of all municipal solid waste in the United States consists of glass. As environmental efforts to promote recycling increase, the amount of glass which is recovered from the solid waste stream will also continue to increase. In the United States alone, over one million tons of glass are recovered annually for recycling. One factor limiting the amount of recycling which is done is the lack of effective and convenient recycling opportunities in many areas.

The principal use of broken or refuse glass, generally called "cullet," is by glass container manufacturers. Although it is possible to manufacture some glass products using 50 per¬ cent cullet or more, most glass containers are manufactured using 20 to 30 percent cullet.

To meet strict manufacturing specifications, however, all cullet must be sorted by color, crushed to a size suitable for the furnace, and separated from bits of aluminum and other con¬ taminants. These requirements, combined with the relative high

cost of transporting cullet, make it difficult to produce high- quality cullet at a price which is affordable.

Because of the limited options for recycling glass, most scrap glass is disposed of merely by discarding it. As it becomes more difficult to utilize landfills as an alternative to recycling, increased emphasis has been placed on identifying effective and viable recycling options for glass.

Attempts have been made to grind scrap glass into small particles and to find uses for such ground glass. Because of glass's molecular structure, however, it easily fractures, pro¬ ducing particles having extremely sharp edges. The existence of such sharp edges render the use of ground glass impractical for most applications because of the obvious danger to those handling the ground glass. Methods have been proposed whereby glass is ground in a rotating drum with the aid of grinding compounds, thereby pro¬ ducing glass granules having roughened surfaces and rounded edges. However, producing glass granules by such methods is expensive and results in a product which is contaminated by the grinding compound. Removal of the grinding compound, if poss¬ ible, increases the cost of the final product, rendering it economically impractical for most uses.

Because no viable method of recycling glass presently exists, large quantities of waste glass are generated annually which contribute to the filling of landfills.

From the foregoing, it will be appreciated that it would be an advancement in the art to provide a method of recycling glass by which waste glass could be quickly and inexpensively processed into a form which could be safely handled. It would be a further advancement in the art if such a method could produce a glass free from contaminants such as grinding compounds.

It would be an additional advancement in the art if novel uses could be identified for waste glass, thereby providing viable recycling options for glass.

Such methods and uses are disclosed and claimed herein.

BRIEF SUMMARY AND OBJECTS OF THE INVENTION The present invention is directed to novel methods for pro¬ cessing scrap glass to produce uncontaminated glass particulates having rounded edges. As used herein, the term "glass" encom- passes all inorganic products which have cooled to a rigid solid without undergoing crystallization. The term "glass" is also intended to include other glassy materials including ceramic materials such as porcelain.

The method of the present invention is accomplished by obtaining a quantity of waste glass and introducing the glass into a mill having a grinding chamber. In a presently preferred embodiment, the grinding chamber is substantially cylindrical and is configured with a driver positioned for rotation within the grinding chamber. The driver is configured such that, upon rotation within the grinding chamber, the driver urges the glass to roll around the grinding chamber, thereby rounding any sharp edges of the glass without requiring the use of grinding com¬ pounds which contaminate the resulting glass particulates. Hence, as used herein, "uncontaminated" means that the glass particulates are substantially free of non-glass solids such as grinding compounds.

The driver includes a pair of weighted members flexibly connected to opposite sides of a rotor. The rotor is fixed to a rotatable shaft which extends within the grinding chamber. A motor is connected to the shaft to rotate the shaft. The weighted members preferably comprise at least two hammers which are .respectively connected to opposite sides of the rotor by chain links.

The shaft and rotor are rotated at a rotational velocity sufficient to move the hammers at a speed of less than about 15 meters per second and preferably at a speed of about 10 meters per second. Within the grinding chamber, the hammers urge the glass to roll within the grinding chamber, thereby rounding any sharp edges of the glass and simultaneously reducing the mean particle size of the glass particulates.

The grinding chamber is preferably configured with a screening chute for use in removing glass particulates which have achieved a predetermined particle size. During the processing of the scrap glass, glass particulates exit the

grinding chamber and pass through the screening chute where they are passed over a screen. Those particulates larger than a predetermined size, as determined by the mesh size of the screen, do not pass through the screen and are directed to re- enter the grinding chamber for further processing. Those glass particulates which do pass through the screen exit the mill through an exit port.

As the particulates exit the mill, the discharge stream is sprayed with water to entrain any lighter-than-air particles, thereby reducing the amount of dust which is discharged into the ambient air. The glass particulates may then be dried to remove the water.

The resulting product is inorganic, uncontaminated glass particulates, or "cultured sand," having rounded edges which may be used as a substitute for sand in accordance with the inven¬ tive methods of use described herein. As used herein, "cultured sand" refers to glass particulates having rounded edges obtained by recycling glass, such as that made in accordance with the method of the present invention. Grinding glass according to known prior-art methods pro¬ duces glass particulates having extremely sharp edges, rendering it unsuitable for use in most applications. Advantageously, however, the cultured sand produced in accordance with the method of the present invention does not have sharp edges. Cul- tured sand therefor is similar to natural beach sand. Unlike natural beach sand, however, cultured sand does not include organic contaminants. And, because grinding compounds are not required to be used in its processing, uncontaminated cultured sand may be made. The present invention also includes the use of cultured sand as a substitute for natural sand. The color of cultured sand is, of course, dictated by the color of the glass which is recycled to obtain the cultured sand. By using only clear glass, cultured sand having the appearance of highly pure silica sand is obtained. Such "clear" cultured sand is aesthetically comparable to the sand found on the most popular white sand beaches.

Thus, cultured sand produced in accordance with the method of the present invention may be used in a variety of decorative

and landscaping applications. Such applications include in aquariums and as ground cover for landscaping. Other, similar applications include the use of cultured sand as a substitute for natural sand used in playgrounds and in golf course sand bunkers. Such uses of cultured sand are greatly enhanced by the ability to obtain various colors of cultured sand merely by sorting by color the glass to be ground in making the cultured sand.

Cultured sand may also be effectively used as a top dress- ing for golf course greens. Similar applications include the use of cultured sand as a soil conditioner and as a potting soil.

Because of its highly reflective quality, cultured sand may also be utilized as a replacement for sand in concrete aggregate and in other mixtures intended for ground coverings. One par¬ ticularly useful application is in concrete used for airport run¬ ways, thereby providing a ground covering that is highly reflec¬ tive and providing increased visibility to airplane pilots.

The cultured sand produced by the method of the present in- vention resists compaction. Thus, it may be advantageously used in spawning beds for fish. Because of its resistivity to com¬ paction, cultured sand is quite porous and can be used as a fil¬ tering media, such as for use in filtering solids out of water. One such filtering application is in sewage processing. The cultured sand of the present invention exhibits good load bearing capabilities. Cultured sand is therefore an ideal candidate for use as a propant, or filler sand, for use in the hydraulic fracturing in oil wells, which sand is sometimes refer¬ red to as "fracking sand." Thus, it is an object of the present invention to provide a method for recycling glass by which waste glass may be quickly and inexpensively processed into a form which may be safely handled.

It is a further object of the present invention to provide such a method which produces glass particulates which are free from contaminants such as grinding compounds.

It is an additional object of the present invention to identify novel uses for waste glass, thereby providing viable recycling options for glass.

These and other objects and advantages of the present in¬ vention will become more fully apparent by examination of the following description of the preferred embodiments and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more particular description of the invention briefly des¬ cribed above will be rendered by reference to the appended draw¬ ings. Understanding that these drawings only provide informa¬ tion concerning typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which:

Figure 1 is a perspective view of a grinding mill employed in a presently preferred method of the present invention; Figure 2 is a cross-section taken along line 2-2 of Figure 1; and

Figure 3 is perspective view of one embodiment of a driver utilized in the grinding mill of Figure 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is directed to novel methods for recycling glass. In particular, the present invention includes methods for processing scrap glass to produce uncontaminated glass particulates having rounded edges, generally referred to herein as "cultured sand." The method of the present invention thus provides a means of recycling glass into a form which can be widely used, thereby providing a use for the substantial quantities of available scrap glass. Additionally, the cultured sand produced by the method of the present invention may be used as a substitute for natural sand. Indeed, for many applica- tions, the cultured sand of the present invention is more suit¬ able for use than natural sand.

The method of the present invention includes introducing a supply of scrap glass into a grinding chamber. The glass is caused to roll within the grinding chamber, thereby rounding any sharp edges of the glass and simultaneously reducing the par¬ ticle size of the glass to a particle size corresponding to

sand. Importantly, the glass may be processed within the grinding chamber without the use of grinding compounds.

The glass particulates are then removed from the grinding chamber and screened whereupon all glass particulates larger than a predetermined size are reintroduced into the grinding chamber for further processing. Glass particulates smaller than the predetermined size may be further screened and mixed to produce a cultured sand having a desired distribution of par¬ ticle size, or "gradation profile." The method of the present invention is preferably accom¬ plished by utilizing the grinding mill illustrated in Figure 1 and designated generally as 10. The grinding mill 10 includes an inlet chute 12, a grinding chamber 14, and a screening chute 16. A motor 18 provides a source of power for operating the grinding mill 10. Motor 18 may include any conventionally known motor which may be adapted for rotating a drive shaft. For many applications, however, it will be preferred to utilize a vari¬ able speed motor, thereby permitting the operator of the mill to easily adjust the speed at which the mill is operated.

As illustrated in Figure 2, the inlet chute 12 includes an opening 20 through which glass may be introduced into the grind¬ ing mill 10. The inlet chute 12 is configured with a transverse internal passageway to keep materials within the grinding cham- ber from exiting the mill through the inlet chute 12 and to shield those operating the mill from the internal workings of the grinding chamber 14. An injection port 22 is provided in the inlet chute 12 through which water or other substances may be introduced into the grinding chamber. The grinding chamber 14 is substantially cylindrical and includes a housing 24 with a removable cover 26 (Figure 1) . Within the housing 24, a liner 28 is removably attached within the grinding chamber 14. The liner 28 is preferably made of a hardened steel, such as any of those hardened steels known for use as liners in rock grinders and crushers.

The grinding chamber 14 is further configured with a driver 30 positioned for rotation within the grinding chamber 14. As viewed in Figure 2, the driver 30 is configured to rotate in a clockwise direction, as indicated by Arrow A. The driver 30 in-

eludes a pair of weighted members flexibly connected to opposite sides of a rotor 32. The rotor 32 is fixed to a rotatable shaft 34 which extends within the grinding chamber 14. The motor 18 (Figure 1) is connected to the shaft 34 by any of those methods known to those of skill in the art.

In this preferred embodiment, as best illustrated in Fig¬ ures 2 and 3, the weighted members comprise hammers 40 which are connected to opposite sides of the rotor 32 by chain links 42. Unlike many grinding mills, such as those used in ore process- ing, the mill 10 used in accordance with the method of the pre¬ sent invention includes no anvil. As will be appreciated by those of skill in the art, other shapes and configurations of weighted members may also be employed.

The hammers 40 are configured with flanges 44 through which a bolt 46 may be placed to flexibly attach each hammer 40 to the rotor 32 via its respective chain link 42. Similarly, the rotor 32 is configured with flanges 48 having transverse bolt holes through which attachment bolts 50 may be inserted.

Referring to Figure 2, the screening chute 16 includes a door 54 which is pivotally mounted to the mill at 56. The door 54 includes an exit port 58 through which materials may exit the mill 10. A screen 60 having a rubber perimeter fits over the opening of the door 54. Thus, when the door 54 is closed, the rubber perimeter of the screen acts as a seal. A closure mech- anism, such as an over-center clamp 62, is provided to lock the door 54 in the closed position.

As will be appreciated by one of skill in the art, screen 60 may include any of those screens conventionally known for use in particle separation. The mesh size of the screen 60 is selected according to the maximum particle size desired of the cultured sand. Of course, much of the cultured sand which is generated will be smaller than the maximum particle size. In a presently preferred embodiment, the mesh size of the screen 60 is eight mesh. An injection port 64 is also provided in the screening chute 16 thereby providing an additional inlet through which to introduce water or other substances into the mill 10.

The screening chute 16 is partially defined by an interior wall 66 positioned to partially partition the grinding chamber

14 from the screening chute 16. Thus, particles must pass over the top portion 68 of the interior wall 66 to reach the screen 60.

Cultured sand is produced according to the method of the present invention by initially obtaining a quantity of scrap glass to be recycled. Advantageously, the method of the present invention may be utilized to produce cultured sand having a pre¬ determined color. This is done by selecting for recycling only glass having the color desired in the cultured sand. For some applications, such as for use as ground cover and in golf course sand bunkers, sand having a particular color is generally desired. For many applications, of course, the color of the sand is immaterial to its effectiveness.

Once the desired quantity of scrap glass has been obtained, a screen 60 having a mesh size corresponding to the maximum par¬ ticle size desired in the cultured sand is selected and placed in the screening chute. By closing the door 54 and fastening the over-center clamp 62, the screen 60 is held securely in place. Of course, one of skill in the art will appreciate that the screen size selected may vary widely depending on the appli¬ cation for which the cultured sand is to be used.

The motor 18 is then started and the rotor 32 is brought to a rotational velocity such that the curvilinear velocity of the hammers 40 is less than about 15 meters per second. In one pre- sently preferred embodiment in which the radius from the center of the drive shaft 34 to the tip of each hammer 40 is about 13 centimeters, this hammer velocity corresponds to a rate of rota¬ tion of the- rotor 32 of less than about 1,000 revolutions per minute. It is presently preferred, however, that a hammer velo- city of about 10 meters per second be utilized for processing glass (corresponding to a rotational velocity of about 700 revolutions per minute in the described embodiment) .

As the hammer velocity increases, the mean particle size of the glass particulates generated in the mill decreases. If the hammer velocity is too high, the glass will be ground into silt. Thus, the hammer velocity should be carefully controlled accord¬ ing to the desired particle size to be generated.

With the rotor rotating at the desired rate, waste glass may be introduced into the grinding chamber 14 by feeding it

through the opening 20 of the inlet chute 12 and permitting it to fall into the grinding chamber 14 under the force of gravity. In one embodiment, an inert liquid, such as water, is also introduced into the grinding chamber 14. The water may be introduced into the grinding chamber by injecting it through ports 22 and 64, by feeding a stream directly into opening 20 of the inlet chute 12, or by dampening the waste glass initially and introducing the waste glass into the inlet chute 12 in dam¬ pened form. During- the grinding process, a substantial amount of fine particulate matter is generated. Thus, the primary purpose of adding water (or other inert liquid) into the grinding chamber is to entrain much (if not all) of the fine particulate matter in the water. Because many lighter-than-air particles may be generated, the addition of a liquid into the grinding chamber reduces the amount of such particles which become suspended in the ambient air. It is preferable, however, to reduce to a minimum the amount of liquid added into the grinding chamber. Thus, in accordance with a presently preferred embodiment, the glass is ground dry and water is added to the ground glass upon exit from the mill, as will be explained below.

Importantly, the addition of a grinding compound into the grinding chamber is not required. It will be appreciated by one of skill in the art that cultured glass which is "contaminated" by grinding compounds may be effectively used for some applica¬ tions. Thus, for such applications, it will, of course, be acceptable to add contaminants such as grinding compounds to the glass being ground. It should be understood, however, that the use of such non-glass solids is not required to process glass in accordance with the teachings of the present invention.

Within the grinding chamber, the hammers 40 or other drivers urge the glass to roll along the liner 28. Because of the substantial speed at which the hammers 40 are traveling, the glass is forced to roll rapidly around the interior of the grinding chamber. It is presently believed that the hammers 40, traveling at such a rapid velocity within the grinding chamber, induce substantial aerodynamic forces within the grinding cham¬ ber which cause the glass to roll around the grinding chamber.

As the glass particles roll, their size is reduced and any rough or sharp edges are quickly rounded smooth.

As best illustrated in Figure 2, the centrifugal forces acting upon the glass particles as they roll around the grinding chamber cause them to pass over the top portion 68 of the wall 66, at which point they enter the screening chute 16 and pass over the screen 60. The particles which have been ground to a particle size sufficiently small to fall through the screen 60 will pass through the screen 60 and exit the mill through exit port 58. The remaining particles pass along the screen 60, below the wall 66, and are reintroduced into the grinding cham¬ ber 14 where they are subjected to additional grinding.

Upon exit of the mill 10 through exit port 58, the exit stream of particles is preferably sprayed with a fine mist of water or other inert liquid to entrain any fine particulate matter in the water and thereby reduce the amount of dust which is introduced into the ambient air.

The glass particles may be washed and further screened to isolate glass particles having a particular size. The particles may then be dried according to conventionally known techniques to remove the liquid in which they were slurried and/or washed. Glass particles of various sizes may then be mixed together to produce a sand having a desired gradation profile. The result¬ ing cultured sand is then ready for use in accordance with the methods of use of the present invention.

The cultured sand produced by the methods of the present invention is free from sharp edges and may be used in a variety of applications. Because of the novel methods employed in pro¬ ducing the cultured sand of this invention, a cultured sand pro- duct may be produced which does not include contaminants which may affect how the cultured sand could be used. Thus, the pre¬ sent invention also includes the use of cultured sand produced in accordance with the method of the present invention as a sub¬ stitute for natural sand. One such substitute for natural sand includes the use of cultured sand for decorative purposes. Because the color of the cultured sand may be carefully controlled, the use of cultured sand for decorative purposes can be aesthetically more pleasing than the use of many natural sands. Examples of the use of cul-

tured sand for decorative purposes include using cultured sand as a ground cover or as a sand bed in aquariums. Use of cul¬ tured sand in aquariums is particularly advantageous because the cultured sand can be prepared to be entirely inorganic, thereby avoiding the introduction of organic materials into the tempera¬ mental ecosystem of the aquarium. Other uses which may be cat¬ egorized as at least partially decorative include use as play¬ ground sand.

The cultured sand of the present invention may also be used for "sports-turf" applications such as a substitute for sand used in golf course sand bunkers and as a top dressing for golf course greens. Because the color of the cultured sand may be preselected, the sand used in golf course sand bunkers may be selected to correspond to a particular color scheme appropriate to the golf course. One of the principal advantages of the cul¬ tured sand of the present invention is the ability to produce sand having a generally consistent particle size. Hence, a cul¬ tured sand having a predetermined gradation profile may be easily mixed. The ability to produce a sand having a particular gradation profile is especially advantageous when using cultured sand for sports-turf applications. For example, when using cultured sand as a top dressing on a golf course green, it is generally desir¬ able to match the gradation profile of the existing layer of sand upon which the green is built. When using cultured sand for sand bunkers, a gradation profile established by a rules committee or other organization may be easily matched.

Another use of the cultured sand of the present invention is as a soil conditioner. A problem often encountered by veget- able farmers is that the hardness of the soil restricts growth of the vegetables. By conditioning the soil with cultured sand having a generally uniform gradation profile, the treated soil compacts less readily, thereby facilitating plant growth and enhancing the harvest. Sewage sludge may be similarly condi- tioned with cultured sand to produce fertilizer.

Cultured sand may also be used as a potting soil, thereby providing an inorganic matrix in which nutrients and water may be introduced to carefully control the growth environment of young plants.

The cultured sand of the present invention may also be advantageously used as a complete or partial replacement for sand in concrete aggregate. Because of the luster and bril¬ liance of cultured sand, particularly that made of clear glass, cultured sand may be used as a concrete coating, applied over wet concrete to provide a sparkling, reflecting coating to the concrete. A different, and sometimes preferred sheen, may be obtained by using cultured sand made of other types of glass such as porcelain. The use of cultured sand as a concrete coating may also enhance the coefficient of friction on the concrete, thereby providing a surface with improved traction. One application where the combination of increased visibility due to the reflective nature of the cultured sand and the increased traction are particularly beneficial is in concrete used for airport runways.

Sand having a generally uniform gradation profile resists compaction. Because the cultured sand produced by the present invention may readily be produced with a uniform gradation pro¬ file, it is ideally suited for many purposes in which a sand having a uniform gradation profile is desired. One such example is as a spawning bed for fish. Many fish lay their eggs in sand. In order to bury the eggs in the sand, the sand must not be compacted to any significant degree. Cultured sand having a substantially uniform gradation profile is therefore an ideal sand for such an application.

One of the most significant uses of the cultured sand of the present invention is as a fluid filtering media. Because the gradation profile of the cultured sand may be precisely con¬ trolled, a cultured sand mixture having a predetermined porosity may be readily obtained. And, because cultured sand may be pro¬ duced to be inorganic, it may ideally be used to filter solids out of water. One such application is in the processing of sewage waste.

Another significant use of the cultured sand of the present invention is as a propant, or "fracking" sand, for use in the fracturing of strata in down hole mining applications. In order to increase oil flow through an oil well, the well may be sealed and pressurized sufficiently to fracture rock strata inside the well, thereby providing an opening to additional reservoirs of

oil. In order to keep the rock strata from healing and reseal- ing itself upon the release of the fluid pressure, a propant such as a liquid permeable sand is introduced into the well to provide a load bearing support for the rock strata. Such a sand is preferably inorganic, thereby avoiding the introduction of contaminants into the oil. Additionally, an ideal fracking sand will have a generally uniform gradation profile or be a mixture of two sands each of which has a uniform gradation profile, thereby maximizing pore size and porosity of the sand and enhancing the ability of the oil to flow through the sand. The cultured sand of the present invention provides a sand having these qualities. Indeed, cultured sand will have superior per¬ formance characteristics as a fracking sand than most natural sands which have been highly processed for this purpose. It should be appreciated that the methods of the present invention are capable of being incorporated in the form of a variety of embodiments, only a few of which have been illus¬ trated and described above. The invention may be embodied in other forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive and the scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

What is claimed and desired to be secured by patent is: