WO1997034848A1

WO1997034848A1 - Method of waste stabilization via chemically bonded phosphate ceramics, structural materials incorporating potassium phosphate ceramics

Info

Publication number: WO1997034848A1
Application number: PCT/US1997/004132
Authority: WO
Inventors: Arun S. Wagh; Dileep Singh; Seung-Young Jeong
Original assignee: The University Of Chicago
Priority date: 1996-03-18
Filing date: 1997-03-18
Publication date: 1997-09-25
Also published as: CN1214030A; AU2530897A

Abstract

A method for regulating the reaction temperature of a ceramic formulation process is provided comprising supplying a solution containing a monovalent alkali metal; mixing said solution with an oxide powder to create a binder; contacting said binder with bulk material to form a slurry; and allowing the slurry to cure. A highly crystalline waste form is also provided consisting of a binder containing potassium and waste substrate encapsulated by the binder. A structural product is provided comprising a phosphate-containing ceramic binder encapsulating bulk waste to confer strength and resistance against weathering and thermal and chemical attack.

Description

METHOD OF WASTE STABILIZATION VIA CHEMICALLY BONDED PHOSPHATE CERAMICS, STRUCTURAL MATERIALS INCORPORATING POTASSIUM PHOSPHATE CERAMICS

CONTRACTUAL ORIGIN OF THE INVENTION

The United States Government has rights in this invention pursuant to Contract No. W-31-109-ENG-38 between the U.S.

Department of Energy and the University of Chicago, representing Argonne National Laboratory

BACKGROUND OF THE INVENTION li Field of the invention

This invention relates to a method for stabilizing large volumes of waste and creating structural products from waste, and more specifically, this invention relates to a ceramic materi¬ al to stabilize large volumes of low-level radioactive and mixed wastes, to a method for using the ceramic material to produce structural products, and to a method for producing the ceramic material. J Background of the Invention

Low-level mixed wastes contain hazardous chemical and low-level radioactive materials. Generally, mixed waste streams contain aqueous liquids, heterogeneous debris, inorganic sludges and particulates, organic liquids and soils. The projected volume over the next five years of the mixed waste generated by the U.S. Department of Energy alone is estimated at approximate- ly 1.2 million cubic meters.

Stabilization of these mixed wastes requires that both phases of contaminants are stabilized effectively.

Typical approaches to stabilization and storage of these mixed wastes include vitrification. For example, one process (Crowe, U.S. Patent No. 5,302,565) requires firing temperatures of at least 1 ,850°C for at least 12 hours to produce ceramic containers. However, such processes, associated with high temperatures are costly. In addition, vitrification of waste streams often result in the lighting off of volatile components contained in the waste stream. This lighting off results in the unwanted generation of secondary waste streams.

One system for producing cements having ceramic type properties does not require high temperatures for final crystalli¬ zation (Sugama et al. U.S. Patent No. 4,436,555, assigned to the instant assignee). However, that process results in ammonia being liberated during processing and storage, which leads to container corrosion, and also explosive compositions if wastes contain nitrates.

The inventors also have developed ceramic fabrication methods to both stabilize and encapsulate waste. These methods offer a number of advantages over more typical Portland cement, grout-, polymer-, and ceramic-encapsulation techniques. Ceram¬ ic encapsulation systems are particularly attractive given that the bonds formed in these systems are either ionic or covalent, and hence stronger than the hydration bonds in portland cement. Since waste stabilization using ceramics is due to chemical stabilization as well as physical encapsulation, the leaching characteristics of these final waste forms are superior to the above-identified waste forms which are mainly dependent on physical encapsulation. Also, unlike prior vitrification require¬ ments, the exothermic ceramic formulation process needs no thermal treatment or heat input, resulting in waste stabilization being done economically on site and without capital intensive equipment and transportation procedures.

However, exothermic ceramic formulation processes are not suitable for the economic encapsulation of large amounts of waste. The inventors have found that the production of large amounts of heat during reaction causes the reacting solution to boil, leading to flaws (i.e. pores) in the final ceramic form, short workability time, and fast, uneven curing. While reaction temper¬ atures may be partially controlled by circulating cold water around the slurry container or mold in which the sample is setting, sufficient heat conduction is not present as sample sizes increase.

Another drawback to typical ceramic waste production processes is that such systems foster low pH conditions. For example, acid-base ceramic encapsulation reactions begin in severe acidic conditions, near pH 0. Such severe conditions destabilize HgS to a leachable form prior to its physical encapsu¬ lation. Low pH conditions also lead to CaCθ₃ decomposition. Aside from the mixed wastes discussed above, more common waste materials also pose disposal problems. For example, bulk materials such as lumber waste, styrofoam, cellulose fibers, tires, ashes, used carpet backing, mineral wastes and plastics exacerbate the problem of dwindling landfill space. Some of these materials, e.g. styrofoam, are flammable.

Previous attempts to convert many of these waste forms into usable products have failed. For example, using polymeric binders, comprising such organic compounds as formaldehyde, to encapsulate waste often results in flammability problems and fume out-gassing. Also, such polymeric applications are expen¬ sive. Housing applications are therefore limited.

Processes using ceramic binders to encapsulate bulk waste require high weight ratios of the binder to the waste material. High amounts of binder makes the process expensive, exothermic and as a result of the exothermicity, fast setting. As such, the use of ceramic binders to encapsulate bulk waste for use as insulation, building materials and composites also has been stymied.

A method for encapsulating waste using phosphate-contain- ing material is disclosed in U.S. Patent No. Re. 32,329. However, that process, relegated to sugar cane, is designed to facilitate rapid setting of the final product. As such, the desired flow- ability characteristics of envisioned products (e.g., blowable insulation) is not forthcoming A need exists in the art for a high volume waste stabiliza¬ tion and solidification method that does not generate high amounts of heat during the encapsulation process. The process must be operational at moderate pH conditions so as to facilitate stabilization of wastes which are unstable at low pH. The final product must exhibit low leachability and high durability in aqueous systems.

A need also exists in the art for a method to utilize or otherwise dispose of non-recyclable and non-biodegradable, benign waste without generating secondary waste streams. The method must be economical in providing structural materials for use in housing. A need also exists for an inexpensive structural product which is partially comprised of benign waste. SUMMARY OF THE INVENTION

An object of the present invention is to overcome many of the disadvantages of the prior art in the encapsulation and stabilization of low-level, radioactive, mixed and other wastes.

Another object of the present invention is to provide a temperature-controlled ceramics formation process to encapsu¬ late and stabilize wastes. A feature of the invention is the utilization of readily available compounds to regulate the acid- base reactions associated with the formation of ceramics waste forms. An advantage of the invention is maintaining a low temperature during the formation process.

Yet another object of the present invention is to provide a low temperature reaction liquor in a process to stabilize mixed waste using chemically bonded phosphate ceramics. A feature of the present invention is the moderation of the pH of the reaction liquor. An advantage of the present invention is that the lower reaction temperatures facilitate the formation of more dense waste forms. Another advantage is that certain waste materials, which decompose or destabilize in low-pH environs, are more completely stabilized.

Still another object of the present invention is to provide a ceramic waste form high in potassium. A feature of the inven¬ tion is a high amount of crystalline phase in the final waste form. An advantage of the invention is a more dense, less porous waste form.

Another object of the present invention is to provide a method for producing a structural material. A feature of the invention is encapsulating benign waste using a nontoxic binder material. An advantage of the invention is utilizing the now encapsulated benign waste as safe insulative material and fire¬ proof material in housing and other structures. Another advan¬ tage of the invention is that the method does not emit noxious materials and therefore is safe for operators and end users. Yet another object of the present invention is to provide a method for producing light-weight structural materials. A feature of the invention is the room-temperature encapsulation of large amounts of widely available wastes with relatively smaller amounts of an inorganic binder. An advantage of the invention is that it is an inexpensive process to utilize non- recyclable waste material in blowable or pumpable preparations for ultimate use as housing materials.

Yet another object of the present invention is to provide a structural material partially comprised of benign waste. A feature of the invention is a high volume percent of waste to binder material. An advantage of the invention is the production of light weight, strong structural materials that can supplant traditional materials. Another advantage is that heretofore nonbiodegradable and sometimes-hazardous material is rendered usable, nonhazardous and nonflammable when incorporated into a structural form.

Another object of the present invention is to provide a method for producing a near-term containment material. A feature of the invention is using high weight ratios of the containment material to the invented binder. An advantage of the invented method is the ability to confine the near-term contain¬ ment material to desired mold shapes or structures until most activity is reduced or dissipated.

Briefly, the present invention provides for a method for regulating the reaction temperature of a ceramic formulation process comprising supplying a solution containing a monovalent alkali metal; mixing said solution with an oxide powder to create a binder; contacting said binder with bulk material to form a slurry; and allowing the slurry to cure.

A crystalline ceramic waste form is also provided compris¬ ing a potassium-containing ceramic binder and waste that is chemically stabilized and encapsulated with said binder. A method for stabilizing and encapsulating red mud is provided comprising supplying red mud in a predetermined configuration, combining the red mud with a solution containing a monovalent alkali metal to form a slurry, and allowing the slurry to cure. A method to produce structural products from benign waste is provided comprising preparing an inorganic oxide, contacting the prepared inorganic oxide with phosphoric acid to produce an acid solution, mixing the acid solution with waste particles to produce a slurry, and allowing the slurry to cure. A structural product is also provided comprising A structural material comprising waste particles, and an inorganic binder enveloping the waste particles. A nonflammable structural material is provided comprising styrofoam and an inorganic binder enveloping the styrofoam.

Also provided is a structural product or substrate compris¬ ing a potassium-containing ceramic binder and benign waste that is stabilized and encapsulated with said binder. BRIEF DESCRIPTION OF THE DRAWING

These and other objects and advantages of the present invention will become readily apparent upon consideration of the following detailed description and attached drawing, wherein:

FIG. 1 is a temperature graph showing the effects of the addition of a carbonate solution to the ceramic processing liquor, in accordance with the features of the present invention;

FIG. 2 is a graph showing the compression strength of an exemplary waste form, in accordance with the features of the present invention; FIG. 3 is a graph depicting the porosity of an exemplary ceramic form, in accordance with the features of the present invention; and

FIG. 4 is a schematic diagram of a method for producing structural forms from ceramic binder and benign material, in accordance with the features of the present invention.

DETAILED DESCRIPTION OF THE INVENTION This application provides a means for using ceramic materials to both encapsulate waste for safe disposal and also to produce structural products comprising waste. The waste- encapsulation for safe disposal process will be presented first:

Encapsulation for Disposal Disclosure

The encapsulation-for-disposal-teaching herein provides two processes for chemically controlling the reaction tempera¬ ture in ceramic formulation processes. These two processes allow for the formation of large final waste forms for a wide variety of waste streams, said waste streams containing ash, cement, silica, Bayer process wastes (red mud), potliner residue, pyrophorics, salt mixtures, volatiles, such as mercury, lead, cadmium, chromium, and nickel, and unstable compounds which cannot be treated by conventional high temperature techniques such as vitrification. The invention is also applicable to stabi¬ lize secondary waste streams resulting from thermal treatment processes, such as vitrification and plasma hearth processes.

Radioactive materials are also stabilized by this method, such materials including uranium, plutonium, thorium, americium, fission products, and any other radioactive isotopes. Irradiated lead, hazardous metals, flue-gas desuffurization residues are also stabilized and/or encapsulated by the invented method.

The invention also can be used to stabilize certain RCRA organics. The inventors have found that certain of these organics do not retard the setting of phosphate ceramics. In one scenario, organics such as naphthalene and dichlorobenzene are trapped in activated carbon which in turn is stabilized in the phosphate matrix by the method claimed herein. This method of stabiliza¬ tion can be utilized in situations wherein mixed waste contains trace amounts of organics such as polychlorinated biphenyls, dioxin, dichlorobenzene, naphthalene, among others. As such, the invented method is superior to encapsulation methods wherein cement is utilized, in that cement cannot stabilize in the pres¬ ence of organics. The method may also be used to stabilize and solidify wastes containing salts, such as chlorides, nitrates, nitrides, sulfites and sulfates. Conventional cement technology cannot stabilize these waste streams.

Ash waste may be consolidated by this process to 80 volume percent of its original volume. Experiments by the inventors show good reaction and bonding between amorphous and reactive silica from fly ash and bottom ash with phosphate matrix. Formation of hard silico-phosphate bonds via this reaction can be used for the stabilization of hazardous silica compounds such as asbestos. The invention also encapsulates and stabilizes silica based filter aids, such as vermiculites and perlites, which are used in the removal of contaminants from liquid waste streams.

The two invented temperature control processes yield superior-strength final forms having uniform high density throughout and improved microstructure compared to typical methods of ceramics formation.

A salient feature of the low-temperature ceramic-waste formulation processes is an acid-base reaction, such as that depicted in Equation 1 , below. Typically, the reaction produces phosphate of MgO (Newberyite).

MgO + H₃PO₄ + 2H₂0 - MgHP0₄- 3H₂0 Equation 1

The acid base reaction results in the reaction of the waste components with the acid or acid-phosphates. These reactions lead to chemical stabilization of the waste. In addition, encapsu¬ lation of the waste in the phosphate ceramics formed by the reaction products results in physical encapsulation of the waste components. This physical encapsulation of the waste is particu¬ larly noteworthy when structural forms (discussed supra) are being produced, inasmuch as product strength, and fire-, chemical- humidity- and weathering-resistance are also conferred to the final forms. As noted supra, a problem with the above-disclosed reac¬ tion sequence is the extremely low pH that exists in the reaction liquor as a result of the presence of the phosphoric acid. This low pH leads to destabilization of some waste materials during encapsulation, and higher reaction temperatures which ultimate- ly renders weak final waste forms.

The two processes for minimizing the exothermicity of the acid-base reactions are disclosed as follows: Process #1 deals with pretreating phosphoric acid with a carbonate, bicarbonate or hydroxide of a monovalent metal prior to mixing with an oxide or hydroxide powder so as to buffer the acid. An exemplary reaction for process #1 is illustrated in Equation 2, below:

H3PO4 + M2CO3 + M'Oxide — MΗPO4 Equation 2 whereby M is a monovalent metal which can be selected from the group consisting of potassium, sodium, lithium. M'oxide desig- nates the oxide powder, whereby M' is a metal which can be selected from the group consisting of Mg, Al, Ca, and Fe. As noted above, M' also can be supplied as an hydroxide.

Process #2 discloses a method for bypassing the use of acid altogether and mixing the oxide powder with a dihydrogen phosphate to form a ceramic at a higher pH. Illustrations of process #2 are Equations 3-5, below:

MgO + LiH₂P0₄ + nH₂0 - MgLiP0₄ ^• (n+1 )H₂0 Equation 3 MgO + NaH₂P0₄ + nH₂0 → MgNaP0₄ ^• (n+1 )H₂0 Equation 4

MgO + KH₂P0₄ + 5H₂0 → MgKP0₄ ^• 6H₂0 Equation 5

Solid Waste Preparation Detail

Solid wastes first can be manipulated in powder form by grinding the waste to an average, preferable approximate parti- cle size of 8 to 10 micrometers (μm). However, particles can range in size from between approximately 4 μm to several m il limeters.

Ash and cement wastes can be first mixed with the starter oxide or hydroxide powders using a vibratory shaker, or any conventional agitator. Weight percentages of the mixture varies at this juncture, but can range from between approximately 15 percent oxide to 50 percent oxide. Typically, an even weight percent (50:50) of oxide to solid waste is sought. However, the inventors have successfully encapsulated and stabilized single- component fly ash at weight percents as high as 85 percent ash to 15 percent MgO powder, which makes this technique particular¬ ly attractive for utilities where single-component fly ash is a major land-filling problem.

The above mixture of powders is then added to pretreated phosphoric acid solution (process #1) or to the dihydrogen phosphate solution (process #2) to form a reaction slurry. The slurry is mixed using a mixer for 10 minutes to 30 minutes during which it forms a viscous paste. The paste sets in a few hours once poured into a mold. Typically, no pressure is applied to the now-molded slurry. The slurry gains full strength in approximately one day.

Mold shapes can vary, depending on the configuration of the ultimate deposition site, and can be selected from a myriad of geometrical shapes including cuboid, pyramidal, spherical, planar, conical, cylindrical, trapezoidal, rectangular, and the like.

Generally, molds having the shape and size of a typical 55 gallon drum are used for waste management applications. Liquid Waste Processing Detail

In dealing with liquid waste, the invented temperature regulated encapsulation method provides a simplified approach for an end user compared to more typical encapsulation methods.

For example, acid phosphates systems are made by adding said phosphate to the liquid on site, a process similar to that prac¬ ticed in the cement industry. As such, liquid wastes, such as tritiated water, are easily and economically encapsulated with this procedure.

Either process #1 or process #2 can be used if solely liquid is being encapsulated and stabilized. In process #1 , the waste liquid is first combined with acid to form a pH modified solution. This modified solution is then mixed with oxide powder. Alterna¬ tively, the waste liquid can be added to oxide powder, to form a slurry, and then mix the slurry with acid. In process #2, the liquid waste is mixed with dihydrogen phosphate solution. Then, oxide powder is added. As above, an alternative procedure is to first combine the liquid waste with oxide powder and then add the dihydrogen solution. The inventors have found that the ratio of acid to water, selected from a range of between approximately 37:63 to 50:50, produces good results. An acid:water ratio of 50:50 is most preferred. If the liquid waste contains more than the required amount of water, then correspondingly less water is added to the acid to bring the water weight percent of the liquid waste-acid mixture up to 50 percent.

In situations involving liquid-solid waste streams, the liquid fraction of the waste stream can be prepared as outlined directly above. The resulting liquid waste-acid mixture is then mixed with a mixture of solid waste and oxide powder in weight percent ranges similar to those outlined above for solid waste processing. When using powder mixtures containing MgO and dibasic phosphate, weight percent ratios of the oxide to the phosphate selected from the range of approximately 87:13 to

77:23 produce good results.

Phosphate and Oxide Reactant Detail

Several phosphate systems can be used for the stabiliza¬ tion of the target chemical, radioactive and mixed waste streams. Some final phosphate-ceramic forms include, but are not limited to phosphates of Mg, Mg-Na, Mg-K, Al, Zn and Fe, whereby the metals are derived from starter oxide powders and hydroxide powders (such as in process #1 ). In process #2, the metals in the final phosphate ceramic forms are derived from both the starter powders and the dihydrogen phosphates. Exem¬ plary dihydrogen phosphates used in process #2 include, but are not limited to, phosphates of potassium, sodium and lithium. The acid component may be concentrated or dilute phosphoric acid or acid phosphate solutions such as dibasic or tribasic sodium or potassium, or aluminum phosphates. The setting times for the pastes formed by the reaction ranges from a few hours to a week. The phosphates attain their full strength in approximately three weeks.

Oxide powders can be pretreated for better reactions with the acids. One technique includes calcining the powders to a typical temperature of between approximately 1 ,200°C and 1 ,500°C and more typically 1 ,300°C. The inventors have found that the calcining process modifies the surface of oxide parti¬ cles in a myriad of ways to facilitate ceramic formation. Calcining causes particles to stick together and also form crystals; this leads to the slower reaction rates that foster ceramic formation. Fast reactions tend to form undesired powdery precipitates.

Another reaction enhancement technique is washing the powders with dilute nitric acid and then water.

A myriad of oxide and hydroxide powders can be utilized to produce the ceramic system, including but not limited to MgO, AI(OH)₃, CaO, FeO, Fe₂θ3, and Fe₃0 .

MgO and AI(OH)3 powders are available through any commer¬ cial supply house, such as Baxter Scientific Products, McGaw Park, Illinois.

The myriad iron oxides enumerated above could actually be supplied as part of some waste streams such as those generated in conjunction with soil and also in low-temperature oxidation systems which destroy organics using iron compounds. Process #1 — pH Modification of Acid Solution

Surprisingly and unexpectedly, the inventors have found that when carbonate, bicarbonate, or hydroxides of monovalent metals (such as K, Na, Li, and Rb) are used to pretreat the acid prior to the acid-base reaction, a decrease in reaction tempera¬ ture results. Also unexpectedly, the inventors have found that the addition of potassium containing alkali compounds (such as K₂Cθ₃) result in a more crystalline waste form that is impervi- ous to weathering, compressive forces and leaching.

Furthermore, and as can be determined in FIGS. 1-3, the higher the concentration of potassium containing compounds (such as K₂C0₃, KHCO₃, and KOH) in the pre-reaction mixture, the more crystalline the final product. This high crystallinity correlates to higher compression strength and lower porosity.

The carbonate in the prβtreatment process decomposes into hydroxide, with an evolution of C0₂. This results in a partial neutralization of the acid, which in turn reduces the rate of reaction and the rate of heat evolution. Typically, pH of the reaction slurry is raised from zero to between approximately 0.4 and 1.

Overheating of the slurry is thus avoided by this pH adjust¬ ment mechanism. Second, and as more thoroughly disclosed infra, the use of potassium carbonate generates more crystalline, and therefore more stable, phosphate complexes.

Example 1

K^CO^ Buffer

5, 10 and 15 weight percent of potassium carbonate K₂CO₃ was added to a 50 weight percent dilute solution of phosphoric acid. The resulting solution was allowed to equilibrate for several hours. In the equilibration process, the pH of the solution raised from near zero to 0.4, 0.6 and 0.9, respectively. After equilibration, 100 grams of the solution was mixed with 50 grams of an oxide powder. The oxide powder was a combination of calcined MgO and boric acid in a 85 weight percent MgO to 15 weight percent boric acid ratio.

While adding the MgO and boric acid mixture to the acid solution, the temperature of the slurry, for phosphate concentra- tions ranging from 0 to 10 weight percent, was monitored. FIG. 1 depicts the temperature rise in each case. System A was a simulation of a process wherein no K₂CO3 was added. The maxi¬ mum temperature reached in this system was 45 °C in a 50 cc volume sample. For samples B and C made with 5 and 10 weight percent of K₂Cθ3, the temperature rise was 8 °C and 2 °C, respec¬ tively. No temperature increase was noted when 15 weight percent of K₂C03 was added to the acid prior to reaction.

X-ray diffraction analysis of the samples showed high crystallinity with samples made with 15 weight percent of K₂C03. Samples made with 5 and 10 weight percent of K₂00₃ were more glassy. As can be noted in Table 1 , below, the X-ray diffraction studies of the samples identified unique mineral phases that are responsible for the desired low solubility prod¬ uct constant of the final product. This superior final product, a chemically bonded composite ceramic, is designated hereafter as MKHP. Table 1 : Mineral composition of Ceramic Developed Via K^COT Addition

Magnesium potassium phosphate MgKPO₄-6H₂0 52

Lϋnebergite Mg₃B₂(PO₄)₂(OH)₆-6H₂0 24

Newberyite MgHPO₄-3H^0 14

Residual Magnesium Oxide MgO 10

Surprisingly and unexpectedly, magnesium potassium phosphate (MKP) is a new component in the material that formed exclusively by the addition of K2CO3. MKP represents a superior phase for waste form matrix materials, given its solubility constant of 10- ^{1 1} , which is five magnitudes lower than that of newberyite which is 10- 6. All of the phases depicted in Table 1 have very low solubilities in ground water, and lϋnebergite and newberyite are natural minerals which are hence stable in ground water environments.

Porosity characteristics of the samples varied widely. In the K₂CO3 5- and 10-weight percent samples, the glass phase of the samples was abundant, with a concomitant higher amount of cracking and therefore porosity. By comparison, the K2CO3 15 weight percent samples showed an open porosity of approximate¬ ly 6.1 percent. Density was 1.77 g/cc, and closed porosity was 10.2 volume percent. Compression strength was approximately 3,700 psi. Example 2

K₂CD₁ Buffer + Flv Ash

The matrix material disclosed in Example 1 was used in

Example 2. Starter powder composition was 70 weight percent fly ash, 25.5 weight percent calcined MgO, and 4.5 weight percent boric acid. The solution used was a 50 weight percent diluted H₃P0 buffered with K₂CO₃. The solution was poured into a mixer, such as a cement mixer, and the powder was slowly added until all the powder was mixed with the solution in approximate¬ ly 48 minutes. A cylindrical sample of 1 ,000 ml was made. The maximum temperature during mixing and setting ranged from between approximately 50 °C and 60 °C. These tempera¬ tures did not increase, even when smaller weight percents of K₂CO₃ were used. For example, when 10 weight percent of K₂CO₃ was used, even at higher volumes (1 ,200 cc), maximum tempera- tures attained were between 56 °C and 58 °C.

The inventors have found that in the absence of K₂CO₃, the concentration of MgO in the final product is high, with Newberyite as the main crystalline phase in the material.

Data on compression strength and porosity of the materials made in Example 2 are shown in FIGS. 2 and 3. These figures show that as the content of K₂CO₃ increases, the strength increas¬ es and the porosity drops. When K₂CO₃ is 15 weight percent in the solution, the compression strength is 8,750 psi (which is more than twice that of portland cement) while porosity is reduced to 7.5 percent.

Example 3

Sodium Carbonate

5, 10, and 15 weight percent of sodium carbonate (Na₂θθ₃) was added to 50 weight percent of a dilute solution of phosphoric acid and the resulting solution was allowed to equilibrate for several hours. The pH of the solution was raised in the process from near zero to approximately 2.3. 100 grams of this solution was reacted with 30 grams of a mixture of calcined MgO and boric acid (85 weight percent MgO and 15 weight percent boric acid) and 70 grams of fly ash.

The properties of the 5 weight percent Na₂C0₃ sample were measured. Density was 1.7 g/cc and its open porosity was 8.6 volume percent. Microstructural analysis of the samples re¬ vealed that the sample was primarily glassy except for the fly ash particles. This process shows that completely glassy phase material can be made by the process described above.

Example 4 Hazardous Material + MKHP

Two different hazardous material waste streams were treated. An iron oxide-iron chloride waste stream (95 weight percent Fe₂θ₃ + 5 weight percent FeCk) was spiked with 0.5 weight percent of Ce3+ and Ce*+ as surrogates of U3+.4+ and Pu3+.4+, incorporated as oxide. Also added was 0.5 weight percent of Ce*⁺ as a surrogate of U ⁺ and Pu ⁺, incorporated as oxide.

The second waste stream was iron phosphate waste stream (FeP0 ) spiked with 0.5 weight percent of Pb to represent hazard- ous component, introduced as soluble nitrates.

Both waste streams were stabilized via the carbonate modification method of Process #1. Containment of Ce3⁺, Ce⁴⁺ and Pb was 8.7 ppm, <0.09 ppm and <0.2 ppm, respectively. In as much as the 5 ppm regulatory limit on Pb is due to be revised downward to 0.37 ppm, the results show that the invented encapsulation procedure provides an acceptable method of containment. Process #2--Dihvdrogen Phosphate

Instead of adding carbonate to reactants to reduce reaction temperatures, the inventors have devised a simplified method to achieve the same results. This second process reacts dihydrogen phosphates of potassium, sodium, lithium, or any other monova¬ lent alkali metal with an oxide to form a phosphate ceramic. This method forms a ceramic at higher pH while minimizing heat generation. An exemplary ceramic formed via this process is magnesium potassium phosphate hexahydrate (MKP), which is formed via the reaction mechanism depicted in Equation 5, above. The inventors found that with the avoidance of acid in the initial reaction slurry, initial pH values are approximately 6.2. Consistent with the fact that the dissolution of KH₂P0₄ is an endothermic process, the inventors found that at initial mixing, the temperature of the slurry slightly decreases. As the dissolu¬ tion and reaction of MgO progresses, however, slurry tempera¬ tures increase to approximately 30 °C.

Example 5

MKP Ceramic Fabrication One mole of calcined and ground MgO was mixed with one mole of ground potassium dihydrophosphate (KH₂P0₄) crystals.

The mixture was slowly added to 5 moles of water to form a paste. When the paste was well mixed, it was poured into cylindrical molds, of 1 cm in diameter and 20 cc volume. Hard ceramic forms developed in approximately 1 hour.

X-ray diffraction analysis revealed that all major peaks were MKP. No peaks of the potassium dihydrophosphate were noted, indicating that it all reacted. Open porosity, measured by the water intrusion method, was calculated as 2.87 volume percent. Density was 1.73 g/cc.

Given a theoretical density of 1.88 g/cc, the total porosity is calculated to be 8.19 volume percent. Thus, closed porosity (i.e., that porosity that is not accessible from outside the sample) was 5.33 g/cc. These values show that MKP is much denser than

Mg-phosphate ceramic, wherein total porosity is approximately

30 percent.

Example 6 MKP + Flv Ash

MKP ceramic synthesized in Example 5 was used to develop waste forms of fly ash. Samples were made using three differ¬ ent powders which are mixtures of calcined MgO and KH₂P0₄ in mole ratios of 1 :1 , 1.5:1 and 2:1. These powders were mixed with fly ash in equal weight proportions using a hopper and feeder mechanism. The final mixtures of the powders were combined at a slow but constant rate with 5 moles of water in a cement mixer to form a slurry.

The slurry was poured into 1.5 gallon molds as well as 1 liter molds. Smaller samples were made by stirring the powders in water and using 1 cm diameter, 20 cc cylindrical molds. All samples set in about 1 hour and hardened fully after one week.

Unlike the material described in Examples 1 and 2, the temperature of the slurry does not rise during mixing, but only during setting. This eliminates the prior art problem of evapora¬ tion of contaminants that occurs as a result of heat generation during the mixing stage. The inventors found that temperatures of the slurry before setting generally do not exceed 30 °C. As such, no evaporation of either the water fraction or the compo¬ nents of the waste occur. Once the slurry starts setting, the temperature rises. However, maximum temperatures (approxi¬ mately 75 °C) are reached after the sample sets into a hard monolith, thereby not resulting in any detrimental effect on the final waste form. Furthermore, the inventors have found that the temperature rise is not proportional to the size of specimens but in fact tapers off as the specimen size is increased. This facili¬ tates the target waste encapsulation sizes of 55 gallons. The invented process utilizing MKP generates superior final ceramic forms. Open porosity values of the waste forms was found to be approximately 4.18 volume percent. Measured density was 1 .8 g/cc. Given the estimated theoretical density of 2.05 g/cc, the total porosity is 8.9 volume percent, which is much lower than Mg-phosphate ceramic found in the prior art. Closed porosity was calculated as 4.72 volume percent. Compression strength of the sample was 6,734 psi, which is more than 50 percent stronger than portland cement concrete.

Example 7 Boric Acid + MKP + Ash

Samples of fly ash waste forms were made with MKP matrix and calcined MgO powder in which from 0-5 weight percent boric acid was added. The addition of boric acid delayed the temperature rise of the reacting slurry. Therefore, the addition of boric acid facilitates the large scale processing of waste streams where more time is needed to mix and pour the slurry. Example 8

CaCX Stabilization

As noted supra, CaCθ₃ decomposes in low pH environs. As a result, if waste streams contain this compound, carbon dioxide is produced which bubbles from the reaction slurry. Such bubbling makes the set product porous and hence permeable to ground water. Strength is also compromised.

Cement sludge, typical of cement-containing waste streams was prepared. The composition of the waste stream is depicted in Table 2, below:

Table 2: Cement Waste Stream Composition

Component Weight Percent

Activated Carbon 10

Fly Ash 10 Water 10

Concrete 50

Plaster of Paris 10 Haematite (Fe2O3) 3

Alumina 3 Perlite 1.5

Samples were made by two methods. In the first method, slurry was formed with H₃P0₄ as the reacting acid and waste forms containing approximately 30 volume percent of waste were fabricated. During this first process, the slurry formed tiny bubbles of C0₂, which made the samples porous.

When samples were made with the MKP process disclosed in Examples 5 and 6, supra, wherein KH₂P0₄ was used as the acid phosphate, no evolution of C0₂ occurred. Comparison of the sample values are presented in Table 3, below.

Table 3 shows that the waste forms generated via the MKP process are denser and contain relatively small amounts of open porosity, thereby illustrating the superiority of the invented process compared to processes whereby large amounts of acid are utilized.

Table 3: Physical properties of chemically bonded waste forms.

Parameter HjPOj. Stabilization KF^POa Stabilization pH of acid soln. 0.2 4

Open porosity

(volume percent) 28-33 6.2

Density 1.2-1.3 1.77

Example 9 Red Mud + MKP

The refining of bauxite to produce aluminum oxides results in the production of large amounts of residue, known as red mud. Red mud consists of 50 percent inorganic oxides, other compounds and hazardous metals. Tremendous amounts of red mud are generated annually.

Large volumes of red mud are easily stabilized when combined with the invented phosphate ceramic binder. If the reaction slurry, loaded with red mud, is poured as a barrier layer, it not only bonds with the substrate soil but also enters fissures in the soil and quickly hardens to form a nonporous ceramic layer. For example, red mud ceramics produced by the invented process exhibit low porosities ("2 volume percent) and high compression strengths (4,944 psi). The materials display a low porosity and high durability in a range of acid and basic environ¬ ments, thereby making them ideal for mining industry applica¬ tions, pond liners, tailing liners, waste pond dikes, and quick- setting grouts. A myriad of red mud waste can be utilized in producing final structural forms. Red mud waste used by the inventors was produced from gibbsitic bauxite. Essentially, it was dry mud collected from the periphery of a red mud waste pond. Its contents were *50 weight percent iron oxide (Fe₂03), «16.5 weight percent alumina

~3 weight percent silica (Si0₂) , *5.7 weight percent calcium oxide (CaO), and *6.8 weight percent titania (Ti0₂). X-ray diffraction analysis identified haematite

(α-Fe₂03), goethite (α-FeOOH), calcite (CaC0₃), boehmite (y- AIOOH), anatase (Ti0₂), and bayerite (β-AIOOH) as the major crystalline phases. Surprisingly and unexpectedly, the inventors have learned that the hydrated phases, i.e., boehmite, bayerite and goethite, facilitate the development of phosphate bonds in the binding process.

The amorphous characteristics of the alumina and silica components of red mud, which is discussed above, plays a major role in the ceramic bonding mechanisms. The inventors have found that it is the characteristically smaller particles of amorphous material that readily participates in the acid-base reaction and therefore facilitates the setting reaction during ceramic formation. As discussed supra, MgO, when reacted with phosphoric acid or an acid phosphate solution, forms magnesium phosphate precipitate in an exothermic reaction. This reaction can be controlled by use of calcined MgO and also by adjusting the feed rate of the solid phase (i.e., the red mud powder + oxide + boric acid) to the solution.

In one embodiment, calcined MgO first is mixed with red mud powder in a specific weight percent, disclosed in Table 4, below. Crushed dry red mud is a super-fine material with more than 60 weight percent of the particles finer than 10 mm. Particle sizes ranging from between 1 and 5 mm provide good results, so that grinding of the mud may not always be necessary prior to combining with the MgO.

The dry mixture is then reacted with the phosphoric acid or an acid phosphate solution via constant stirring. This results in a low-viscosity paste which thickens as the reaction proceeds. The paste is then poured into cylindrical molds of 1.9 cm in diameter. Dense ceramics form in approximately 15 minutes, with complete hardening occurring in 2 to 24 hours. Prior to testing, the samples were stored for three weeks. Table 4: Physical Properties of Red Mud Ceramics

Waste Maximum Open Compression loading particle size Density Porosity Strength

(wt%) (mm) (g/cπώ) (%) (psi) 40 5 2.19 0.82 4944

40 1 2.1 1.09 4294

50 5 2.26 2.98 2698

55 5 2.29 1.94 2310

Density was measured by weighing the samples and measur¬ ing the dimensions and determining the volume. Open porosity was determined by water immersion in which the pre-weighed samples were immersed in water at 70 °C for 2 hours. The samples were then cooled in the water and then removed from the water. Excess water was wiped from the surface of the samples and the samples were weighed again to determine the amount of water that filled the open pores. This higher weight (compared to pre-immersion weights) yielded the volume of the open pores in the samples, thereby allowing for calculation of the open porosity.

Compression strength was measured with an Instron™ machine used in compression mode. Waste loadings of the samples ranged from 40 to 55 weight percent. As an example, a 40 weight percent waste loading means that 40 grams of a sample is red mud and 60 grams is both binder and water. Densities of samples with red mud are slightly higher than that of pure matrix (binder) material, which is 1.73 g m/cm3. Red mud density is approximately 3.3 g/cm3.

As can be determined in Table 2, the open porosity of the red-mud-loaded samples was low compared to the ^«20 percent value seen in cement. Furthermore, the compression strength of the samples with 40 weight percent loading was found to be higher than the 4,000 psi value for portland cement concrete.

Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analyses of a fractured red-mud sample revealed a glassy region and a granular region. Both of these regions are well bonded. The glassy phase was cracked everywhere while the granular phase displayed only those cracks emanating from the glassy phase. Table 5, below, provides the general elemental composition of each phase. The values contained therein are averages of three measurements taken at three different loca¬ tions of each phase. The granular phase is attributable to the red mud and the glassy phase is mostly the phosphate matrix. As shown, the granular phase was found rich in red-mud elements such as Fe and Al, while the glassy phase is rich in Mg phosphate elements 97/34848 PC17US97/04132

29

such as Mg and P.

Table 5 : Elemental distributions of glassy and granular phases of red-mud ceramics

Phase Elements

_Fe_ Al Mg P Other

Glassy 5.78 4.7 23.53 34.23 31.76 Granular 23.66 18.6 5.3 16.2 36.2

That significant amounts of phosphate and some magne¬ sium are also in the granular phase indicates that phosphate binding occurred here with Fe and Al as the cations.

The relatively few cracks seen in the granular phase (red mud) portion of the samples indicates that the strength of the invented material is due to this phase. Improving the strength of the ceramic therefore entails reducing the amount of the glassy phase or reinforcing the glassy phase with particulates. One method for such reinforcement is to incorporate finer red mud in the starter powder so as to facilitate more consistent distribu¬ tion and better particle reinforcement. Grinding the red mud prior to mixing with the oxide powder is one way to obtain this finer red mud material.

Structural Products via Bulk Substrate Encapsulation

Unlike previous attempts to produce stable structural materials from bulk waste, the instant process produces an amorphous, more flowable material by utilizing lower volume percents of binder to formulate the final forms. The resulting ceramic formulation is sufficiently amorphous and low in crystal¬ line properties to insure good flow of the material and extended work time. The amorphous phase mimics polymeric formulations by facilitating the encapsulation of waste particles with binder during formation of the final slurry.

Many of the details associated with solid and liquid waste preparation disclosed above for the waste disposition process are applicable in producing structural products from benign waste. Generally, waste that can be used for structural compo¬ nent manufacture includes, but is not limited to, ash, potliner residue, wood, plastic, rubber, cellulose, textile products (such as carpet backing), styrofoam, and combinations thereof. Prod¬ ucts produced from the structural component manufacture method include blowable insulation, particle board, packaging materials, bricks, tiles, wall-forms, and engineered barrier and shield systems.

A generic embodiment of the invented method is depicted in FIG. 3 as numeral 10. First, a supply of oxide 12 is subjected to either or both a calcining pretreatment step 14 and a boric acid addition step 16. Both steps serve to slow down the reaction mechanism.

The resulting dry mixture 18 is then mixed with between approximately 50 to 60 weight percent dilute phosphoric acid 20 to form an acid solution or binder 22. A preferable weight percent is at or below 55 percent, i.e., 55 grams of dry mixture to 45 grams of 50 percent dilute phosphoric acid, so as to facilitate flowability of the resulting solution. Concentrated acid tends to make the reaction more intense. This results in a thick slurry developing which is not conducive to coating the particles.

Waste particles, 24, which may be subjected to a pretreat¬ ment sizing process 23, are then thoroughly mixed with the binder. The mixing step 26 ensures that the waste particles are completely encapsulated or coated with binder.

The resulting slurry is molded into desired shapes 28 under no pressure or under small pressure (approximately 1 ,000 pounds per square inch), depending on the waste material being bonded, under no pressure or under small pressure (approximately 1 ,000 psi), depending on the waste material being bonded. For example, processes for encapsulating wood waste often requires the aid of pressurization, primarily because wood surfaces participate less in the ceramic formation reaction. Bonding in such cases is primarily from the phosphate phase encapsulating the wood particles. When using high-water content wastes, such as sludges and benign wastes, to produce structural products, concomitant modification of the acid:water ratio is required. The inventors have found that the volume of the loading of the wastes in the final product can range from between approxi¬ mately 50-90 volume percent. For insulation and building reinforcement applications, the composition of the mixture is adjusted to convert it into a pumpable slurry (50 volume percent waste) or a blowable particle mixture (80-90 volume percent waste) so as to facilitate the filling of cavities.

Slurries which comprise the above-identified benign wastes are molded into desired shapes. The acid-base reaction between the oxide and phosphoric acid results in the formation of phosphates on the surface of the particles thereby encapsulating individual particles with a thin layer of impermeable phosphate binder. This results in a structural product in which particles of the waste are protected by the binder to provide not only product strength but also confers resistance to fire, chemical attack, humidity and other weathering conditions.

Several advantages of the resulting embodiment exist over commercially available polymer-based binders. Unlike polymer binders, phosphate binders are nonflammable. Also, several polymer ingredients are occupational hazards, whereas inorganic phosphate binders are comparatively safe. No toxic chemicals or vapors are released during production of phosphate bonded products. Lastly, phosphate based binder improves the rigidity and long-term stability to the structural product, compared to currently used organic binders.

Boric Acid/Oxide Preparation Detail

Generally, the boric acid is incorporated when a slower reaction is required, for example when extended workability of the material is desired. The inventors have found that the boric acid forms a glassy phase that coats the oxide particles so that the oxide cannot as readily react with phosphoric acid.

A myriad of oxides, such as those enumerated supra, can be used in the invented method. Additional oxides, such as Fβ₃θ₄, Zr(OH)₄, ZrO, AND Ti0₂ are also suitable. Zr(OH)₄ is obtained through Atomergic Chemetals Corporation, Farmingdale, NY.

Any mixing of the oxide with the boric acid is strictly controlled to maintain an optimum weight percent of constitu¬ ents of the resulting dry mixture. This weight percent is select- ed from a range of between approximately 5 weight percent boric acid to the oxide to 25 percent boric acid to the oxide. A prefera¬ ble weight percent is 10 percent boric acid to oxide, e.g., 10 grams of boric acid for every 90 grams of oxide, to form the dry mixture.

Typically, the rate of powder addition to the acid solution should result in the reaction liquor being maintained at less than

100 °C. Typical times required for controlled mixing range from 30 minutes to 1 hour. Mixing times can be shortened if the heat from resulting exothermic reactions, associated with the above method, is dissipated via reaction vessel cooling. The inventors found that reaction vessel cooling is more likely to be necessary when the resulting oxide powder-solid waste mixture contains less than 50 weight percent of waste.

Example 10 Styrofoam Insulation

The inventors have found that utilizing the above-disclosed method, styrofoam particles are completely coated with a thin, impermeable layer of the phosphate binder phase. The uniform coating of the styrofoam particles not only provides structural stability but also confers resistance to fire, chemical attack, humidity and other weathering conditions. As shown in Table 1 , below, these characteristics are superior to more typical insula- tion materials.

As depicted in Table 6, the resulting binder-covered styrofoam material provided superior R values. For example, thermal conductivity measurements, utilizing a modified radial hot-wire technique (established by Anter Laboratories, Pitts- burgh, PA) showed that the thermal resistance of the material produced via the invented method was approximately 4.5 hour square foot degrees Fahrenheit per British Thermal Unit (h.ft.2°F/BTU, compared to 2-3 h.ft.2°F/BTU for fiber glass and 3- 3.5 h.ft.2°F/BTU for cellulose. This superior R value indicates that phosphate ceramic binder-covered styrofoam provides superior energy savings when used as an insulation product.

Insulation products often are susceptible to humidity and tend to sag, thereby loosing their structural integrity over time. The invented material was subjected to an aging test pursuant to ASTM D 2126 (ASTM = American Society for Testing and Materi¬ als), whereby the material is exposed to severe environments for extended periods of time with dimension changes of the material closely monitored. The material was exposed to 38 °C tempera¬ tures at 98 percent humidity for 3 weeks. Specimen volume change was shown to be approximately two percent after a two week period. This compares to 20 percent for cellulose insula¬ tion material and is also superior to that seen in fiberglass material.

Table 6: Comparison of ceramic-bonded Styrofoam insulation to Fiber Glass- and Cellulose-insulation

Kev Features Bonded Stvrofoam Fiberglass Cellulose Density (lb/fP) 2.0 0.4-1.0 2-3.5

R Values

(1 in. thicknesses) 4.5 2-3 3-3.5

Fire Resistance noncombustible noncombustible noncombustible

Water absorption <4% 1-2% 5-20%

Dimensional Stability -2% settling noted ^»20%

Health Hazards minimum high minimum

Material Costs Low blown or pumped high low

Generally, a wide range of waste particle sizes can be utilized when producing structural products using the invented method. When using styrofoam materials, optimal results are obtained when particle sizes ranging from 2 millimeters to 5 millimeters are used, and when the particles are mixed with binder in a weight ratio of 1 :2. Optimal weight loading of the styrofoam in the final product is approximately 7.5 weight percent, which corresponds to approximately 85 to 90 volume percent of the final product.

Example 11 Wood Waste The inventors have found that when wood waste is subject¬ ed to the invented method, particle board having superior flexural strength values is produced. For example, samples containing 50 weight percent of wood and 50 weight percent of binder display approximately 1 ,500 psi in flexural strength. Samples containing 60 weight percent and 70 weight percent of wood exhibit flexur¬ al strengths of 400 psi and 300 psi, respectively.

Generally, suitably sized wood particles range from be¬ tween approximately 1 and 5 millimeters (mm) long, 1 mm thick and 2 to 3 mm wide. In addition, once the wood and binder is thoroughly mixed, the samples are subjected to pressurized molding on the order of approximately 2650 psi, and for approximately 30 to 90 minutes. The disclosed process is not be construed as limited to the above examples. Also, aside from the myriad of wastes listed above for which this process can be used to encapsulate, other waste streams are also sufficiently stabilized herewith. For example, potliner residue, Bayer sands, ashes generated at plant sites and any other mining refuse can be stabilized by this process and utilized as structural components. Potliner residue, when combined with magnesium phosphate hexahydrate in a 50:50 weight proportion, yields a ceramic form having a density of 2.9 grams per cubic centimeter, a porosity of 2.17 percent and a compressive strength of 4,210 psi, the last of which is compara¬ ble to portland cement forms. Consistent with data disclosed supra, when higher proportions (60 weight percent) of waste material (in this instance potliner residue) is used, desired values degraded slightly from those values obtained when 50 weight percent loadings were used. Density decreased to 2.0 grams per cubic centimeter, porosity increased to 2.6 percent and compression strength decreased to 3,402 psi.

While the invention has been described with reference to details of the illustrated embodiment, these details are not intended to limit the scope of the invention as defined in the appended claims.

For example, in as much as process #2 of the waste encapsu¬ lation process utilizes KH₂P0₄, and in as much as KH₂P0₄ has components of common fertilizer, i.e. potash (K₂O) and phosphate (P_{2 5}), process #2 makes it possible to use high potash and high phosphate fertilizer to stabilize soils containing contaminants.

Also, given that red mud contains high concentrations of oxides, it is feasible to mix red mud with MKP to generate the stable waste forms otherwise generated using process #2. This modification precludes the need for supplying and pretreating oxides, such as MgO in red mud stabilization procedures.

Lastly, a hybrid structural product and a process for producing the hybrid structural product is obtainable by combin¬ ing the potassium-containing phosphates disclosed in the Waste- Encapsulation Detail portion of the DETAILED DESCRIPTION with the exemplary bulk material wastes used in the "Structural Products via Bulk Substrate Encapsulation " section herein. As discussed supra, the inventors have unexpectedly found that potassium-containing phosphates render highly crystalline forms that are more resistant to fracture compared to some other phosphates which are more glassy and brittle. The products produced from this hybrid method include, but are not limited to, blowable insulation, particle boards, packaging materials, bricks, tiles, wall-forms and engineered barrier and shield systems.

Claims

The embodiment of the invention in which an exclusive property or privilege is claimed is defined as follows:

1 . A method for regulating the reaction temperature of a ceramic formulation process comprising: a.) supplying a solution containing a monovalent alkali metal ; b.) mixing said solution with an oxide powder to create a binder; c.) contacting said binder with bulk material to form a slurry; and d.) allowing the slurry to cure.

2. The method as recited in claim 1 wherein the solution containing the monovalent alkali further comprises phosphoric acid and a compound selected from the group consisting of M- carbonate, M-bicarbonate, M-hydroxide, and combinations there- of, where M is a monovalent alkali metal.

3. The method as recited in claim 2 wherein the weight ratio of the compound to the phosphoric acid is selected from between approximately 5:95 and 15:85.

4. The method as recited in claim 1 wherein the monova- lent alkali metal is selected from the group consisting of lithi- urn, sodium, potassium, and combinations thereof.

5. The method as recited in claim 1 wherein the oxide is selected from the group consisting of calcined MgO, crushed dibasic Na phosphate crystals mixed with calcined MgO, Mg(OH)₂, AI(OH)₃, FeO, Fe₂θ3, Fe₃0₄ CaO, or combinations thereof.

6. The method as recited in claim 1 wherein the binder and the solid waste is combined at a predetermined weight percent ratio of oxide powder to solid waste of from between approximately 15:85 and 50:50.

7. The method as recited in claim 1 wherein the solution containing a monovalent alkali metal is a dihydrogen phosphate.

8. The method as recited in claim 7 wherein the dihydrogen phosphate is mixed with the oxide powder in a molar ratio selected from a range of between approximately 1 :1 and 2.5:1.

9. The method as recited in claim 1 wherein the monova- lent alkali metal is selected from the group consisting of Li, Na, and K.

10. The method as recited in claim 1 wherein the bulk material is ground to a particle diameter selected from the range of between approximately 4 microns and 75 microns.

1 1 . The method as recited in claim 2 wherein the phospho- ric acid is 10 percent to 50 percent diluted.

12. The method as recited in claim 1 wherein the bulk material is selected from the group consisting of ash, cement, silica, red mud, pot liner residue, radioactive isotopes, irradiat- ed lead, hazardous metals, flue-gas desulfurization residue and combinations thereof.

13. A crystalline ceramic waste form comprising: a.) a potassium-containing ceramic binder; and b.) waste that is chemically stabilized and encapsu- lated with said binder.

14. The ceramic waste form recited in claim 13 wherein the binder has a chemical composition comprised of magnesium potassium phosphate, lϋnebergite, newberyite, and magnesium oxide.

15. The ceramic waste form recited in claim 13 wherein the waste exists as particles ranging in size from between approximately 5 microns and 5 millimeters.

16. The ceramic waste form as recited in claim 13 wherein the waste substrate is present in the waste form in a weight percent selected from a range of between approximately 10 weight percent and 85 weight percent.

17. The ceramic waste form as recited in claim 13 wherein the waste substrate is selected from the group consist- ing of ash, cement, silica, red mud, pot liner residue, radioactive isotopes, irradiated lead, hazardous metals, flue-gas desulfurization residue and combinations thereof.

18. A method for stabilizing and encapsulating red mud comprising: a.) supplying red mud in a predetermined configura- tion; b.) combining the red mud with a solution contain- ing a monovalent alkali metal to form a slurry; and c.) allowing the slurry to cure.

19. The method as recited in claim 18 wherein the solution containing the monovalent alkali further comprises phosphoric acid and a compound selected from the group consist- ing of M-carbonate, M-bicarbonate, M-hydroxide, and combina- tions thereof, where M is a monovalent alkali metal.

20. The method as recited in claim 18 wherein the solution containing a monovalent alkali metal is a dihydrogen phosphate.

21 . A method to produce structural products from benign waste comprising: a.) preparing an inorganic oxide; b.) contacting the prepared inorganic oxide with phosphoric acid to produce an acid solution; c.) mixing the acid solution with waste particles to produce a slurry; and d.) allowing the slurry to cure.

22. The method as recited in claim 21 wherein the inorganic oxide is selected from the group consisting of MgO, crushed dibasic sodium phosphate crystals mixed with MgO, AI(OH)₃, Zr(OH)₄, CaO, iron oxide, and combinations thereof.

23. The method as recited in claim 21 wherein the step of preparing an inorganic oxide further consists of calcining the oxide.

24. The method as recited in claim 21 wherein the step of preparing an inorganic oxide further consists of calcining the oxide and then mixing the calcined oxide with boric acid to form a mixture having a weight ratio of oxide to the boric acid of between approximately 5:95 and 15:85.

25. The method as recited in claim 24 wherein the mixture is mixed with the phosphoric acid to form an acid solution in a mixture to phosphoric acid weight ratio of between approximately 50:50 and 60:40.

26. The method as recited in claim 24 wherein the mixture is mixed with the phosphoric acid to form an acid solution in a mixture to phosphoric acid weight ratio of approxi- mately 55:45.

27. The method as recited in claim 21 wherein the acid solution in the slurry is present in a weight ratio to the waste particles in the slurry of between approximately 2.5:97.5 and 15:85.

28. The method as recited in claim 21 wherein the acid solution in the slurry is present in a weight ratio to the waste particles in the slurry of approximately 15:85.

29. A structural material comprising: a.) waste particles; and b.) an inorganic binder enveloping the waste particles.

30. The structural material as recited in claim 29 wherein the waste particles are sized to between approximately 4 and 75μm.

31 . The structural material as recited in claim 29 wherein the waste particles are bulk material selected from the group consisting of ash, potliner residue, wood, plastic, rubber, cellulose, textile products, styrofoam, and combinations thereof.

32. The structural material as recited in claim 29 wherein the inorganic binder is a phosphate ceramic.

33. The structural material as recited in claim 32 wherein the phosphate ceramic further contains an element selected from the group consisting of magnesium, sodium, aluminum, zirconium, and combinations thereof.

34. The structural material as recited in claim 32 wherein the phosphate ceramic is magnesium phosphate hexahydrate.

35. The structural material as recited in claim 29 wherein the waste comprises between 80 to 90 volume percent of the material.

36. The structural material as recited in claim 29 wherein the binder is present in a binder to waste weight ratio selected from between approximately 2.5 percent and 15 percent.

37. A nonflammable structural material comprising: a.) styrofoam particles; and b.) an inorganic binder enveloping the styrofoam.

38. The structural material as recited in claim 37 wherein the size of the particles are selected from a range of between approximately 2 millimeters and 5 millimeters.

39. The structural material as recited in claim 37 wherein the styrofoam is present at a weight percent of approxi- mately 7.5 of the structural material, and a volume percent of approximately 80 to 90 percent of the structural material.

40. The structural material as recited in claim 37 wherein the structural material is insulation having an R value greater than 4 for a 1" thickness.

41 . A structural product comprising: a.) a potassium-containing ceramic binder; and b.) waste that is chemically stabilized and encapsu- lated with said binder.

42. The structural product as recited in claim 41 wherein the binder has a chemical composition selected from the group consisting of magnesium potassium phosphate, lϋnebergite, newberyite, and magnesium oxide.

43. The structural product recited in claim 41 wherein the waste exists as particles ranging in size from between approximately 4 microns and 5 millimeters.

44. The structural product as recited in claim 41 wherein the waste is present in the structural form in a weight percent selected from a range of between approximately 10 weight percent and 85 weight percent.

45. The structural product as recited in claim 41 wherein the waste is bulk material selected from the group consisting of ash, potliner residue, wood, plastic, rubber, cellulose, textile products, styrofoam, and combinations thereof.