Reagent for Treating a Contaminated Waste Material and Method for Same

The present invention relates to a reagent material useful for converting a contaminated waste material, which is environmentally unacceptable, to a relatively harmless granular substance which is environmentally acceptable. The reagent material is comprised of an effective amount of alumina, silica, a hydroxide, or hydroxide precursor, of an alkali metal, calcium oxide, and a zeolitic material. The method involves blending an effective amount of said reagent material with said waste material and allowing it to dry without setting, thereby resulting in an environmentally acceptable particulate substance.

All industrial societies are faced with significant environmental problems associated with industrial waste materials, many of which are hazardous to both animal and plant life. Examples of such waste materials include sludges which settle as sedimentation layers at the bottom of the sea, lakes, and rivers; effluent sludges discharged from various industries including pharmaceutical, tanning, paper and pulp manufacturing, wool washing, fermenting, food processing, metal surface processing, plating, ore dressing, coal washing, and fume desulfurizing; as well as other wastes such as sewage sludges discharged from sewage processing stations, and those resulting from the refining of petroleum products. Such wastes are often contaminated with substances which can have an adverse effect on the ecological system. Contaminants found in such wastes often include unacceptable levels of heavy metals such as copper, lead, cadmium, arsenic, mercury, hexavalent chromium. Also found are other chronically toxic compounds such as PCB, PCP, DDT, 2-BHC, Dieldrin, Chlordecone, Mirex, Parathion, cyanic compounds, alkyl-mercury compounds, dioxins, furans; and the like. These waste materials are sometimes referred to herein as environmentally unacceptable.

The treatment and handling of such contaminated waste materials, many of which can be classified as hazardous, is strictly regulated by one or more governmental agencies because of their potential harm to the public welfare. As such, a great deal of work has been done in recent years in developing methods for safely handling these materials and for neutralizing their troublesome characteristics so they can be safely discarded.

Non-limiting examples of methods which have been developed and which have met with varying degrees of success, include sorption, adsorption, volatilization, biodegradation, chemisorption, passivation, ion-exchange, encapsulation, and embedment through solidification into a monolith structure, as well as stabilization of chemical constituents. Sorption involves adding a solid to the hazardous waste material to soak-up any liquid which is present. Non-biodegradable materials are typically used as the sorbent. Such materials include activated carbon, anhydrous sodium silicate, various forms of gypsum, celite, clays, bottom ash, fly ash, fly dust, kiln ash, and cement kiln dust. Biodegradable materials can also be used, such as peat moss, rice hulls, sawdust, and the like. These treatments primarily use biodegradation for reducing organic constituents of the waste material. The sorbent may interact chemically with the waste material, or it may simply be wetted by the liquid portion which is retained in the sorbent as a capillary liquid. Sorption generally cannot be used with many types of hazardous waste, such as those which contain potentially hazardous components, because they can often be easily leached from the sorbent. This is because sorption typically only requires that it be mixed with the waste. Further, as governmental regulations become ever stricter, sorption becomes less and less attractive for meeting such regulations.

Another method for treating hazardous waste involves the consolidation and solidification of the waste into a solid block of material that has relatively high structural integrity. The resulting block is often called a monolith. The monolith can be as small as the contents of a steel drum, or it can encompass the entire waste disposal site, called a monofill. The components of the monolith do not necessarily interact chemically with the reagents, but are usually mechanically locked within a solidified matrix, called microencapsulation. Contaminant loss is primarily limited by decreasing the surface area which is exposed to the environment and/or isolating the contaminants from environmental influences by encapsulating the waste particles. Wastes can also be microencapsulated. That is, bonded to, or surrounded by, an impervious coating.

While solidification can be very effective for treating some hazardous wastes, recently passed governmental regulations are placing greater demands on this technology. This is because of the ever stricter limitations relating to acceptable levels of leachates from the solidified block. Also, the block must withstand ever greater physical pressures without cracking and exposing contaminants to environmental influences.

Other methods of hazardous waste treatment include inorganic and organic stabilization. Unlike solidification processes which convert wastes into a solid mass, stabilization processes can reduce the solubility or chemical reactivity of the waste. Stabilization processes typically include adjusting pH, converting metals to hydroxides, and/or establishing oxidation-reduction conditions to prevent solubilization or leaching of contaminants into ground water. The most commonly used inorganic stabilization processes include mixing the waste product with inorganic materials such as fly ash, cement kiln dust, lime kiln dust, hydrated lime, Portland cement, or other pozzolanic materials. Stabilization processes, like solidification, are being pushed to meet the stricter governmental regulations.

A typical stabilization process is taught in U.S. Pat. Nos. 4,781,842 and 4,902,431 wherein a sewage sludge is stabilized and converted to fertilizer by mixing the sludge with an alkaline material which is sufficient to raise the pH to at least 12. The mixture is then allowed to dry for at least one day. The alkaline material is selected from cement, kiln dust, and lime dust, to achieve chemical stabilization. Bulking materials, such as slag fines, fly ash, gypsum, etc. may also be added. Such a process is primarily a drying process to eliminate offensive odors and pathogenic microorganisms. The process is not capable of generating a substantial amount of heat to destroy many of the contaminants.

Also, U.S. Pat. No. 4,859,367 teaches a waste solidification method wherein toxic mine tailings are incorporated into a cement mixture which contains a mineral binder selected from the class of alkali-activated silico-aluminate geopolymers which is stated to be related to natural and synthetic zeolites and feldspathoids.

Although a significant amount of work has already been done to treat contaminated waste materials, there is still a considerable need in the art for improved methods for treating and neutralizing such materials.

In accordance with the present invention, there is provided a reagent material for treating environmentally unacceptable waste materials, which reagent material, by weight, is comprised of:

(i) 1 part alumina; (ii) 1 to 3 parts of a silica having a surface area of at least about 10 m.sup.2 /g; (iii) 0.5 to 3 parts of a hydroxide, or hydroxide precursor, of an alkali metal; (iv) 2 to 5 parts of CaO; (v) 2 to 5 parts of a zeolitic material having a pore diameter equal to or greater than 4 .ANG., and an SiO.sub.2 to Al.sub.2 O.sub.3 ratio greater than or equal to 2.5.

Also in accordance with the present invention is an innocuous solid waste mixture which may be safely disposed of in a landfill comprising:

(a) a reagent material comprised of: (i) 1 part alumina; (ii) 1 to 3 parts of a silica having a surface area of at least about 10 m.sup.2 /g; (iii) 0.5 to 3 parts of a hydroxide, or hydroxide precursor of an alkali metal; (iv) 2 to 5 parts of CaO; and (v) 2 to 5 parts of a zeolitic material having a pore diameter equal to or greater than 4 .ANG., and an SiO.sub.2 to Al.sub.2 O.sub.3 ratio greater than or equal to 2.5; and

(b) a waste material, which prior to a reaction with said reagent material, contains unacceptable levels of one or more contaminants selected from the group consisting of heavy metals and organic components.

Also in accordance with the present invention, there is provided a method for treating an environmentally unacceptable contaminated waste material to convert it to an environmentally acceptable material, which method comprises mixing said contaminated waste material with an effective amount of a reagent material comprised of: (i) 1 part alumina; (ii) 1 to 3 parts of a silica having a surface area of at least about 10 m.sup.2 /g; (iii) 0.5 to 3 parts of a hydroxide, or hydroxide precursor, of an alkali metal; (iv) 2 to 5 parts of CaO; and (v) 2 to 5 parts of a zeolitic material having a pore diameter equal to or greater than 4 .ANG., and an SiO.sub.2 to Al.sub.2 O.sub.3 ratio greater than or equal to 2.5.

In a preferred embodiment of the present invention, the alkali metal hydroxide is NaOH, and the zeolite is a zeolite material which is iso-structural to a zeolite selected from clinoptilolite and chabazite.

In other preferred embodiments of the present invention, the reagent material is comprised of: (i) 1 part alumina; (ii) 1.5 to 2.5 parts of a silica having a surface area of at least about 10 m.sup.2 /g; (iii) 0.5 to 1.5 parts of a hydroxide of an alkali metal; (iv) 2.5 to 3.5 parts of CaO; and (v) 2.5 to 3.5 parts of a zeolitic material having a pore diameter equal to or greater than 4 .ANG., and an SiO.sub.2 to Al.sub.2 O.sub.3 ratio greater than or equal to 2.5.

In yet other preferred embodiments of the present invention, the contaminated waste material is selected from the group consisting of sewage sludge; a biologic organic waste material; a non-biologic waste material; waste resulting from the drilling, production, and processing of petroleum, such as tanker bottoms; and waste contaminated with a naturally occurring radioactive material.

Any contaminated waste material may be treated in accordance with the present invention so long as it is a solid a liquid, or combination thereof. A typical waste stream which can be treated in accordance with the present invention is in the form of a sludge. The term "sludge" as used herein, means a material which is flowable at ordinary temperatures and at about atmospheric pressure, but which has a relatively high solids content, and which can typically be pumped by conventional pumping means. Non-limiting examples of such wastes included sludges which settle as sedimentation layers at the bottom of the sea, lakes, and rivers; effluent sludges discharged from various industries including pharmaceutical, tanning, paper and pulp manufacturing, wool washing, fermenting, food processing, metal surface processing, plating, ore dressing, coal washing, and fume desulfurizing; and still other wastes, such as sewage sludges discharged from sewage processing stations, and those resulting from the drilling, production, and processing of petroleum. Such wastes are often contaminated with substances which have an adverse affect on the ecological system. Non-limiting examples of such substances include heavy metals, such as copper, lead, cadmium, arsenic, mercury, hexavalent chromium; and other chronically toxic compounds such as PCB, PCP, DDT, 2-BHC, Dieldrin, Chlordecone, Mirex, Parathion, cyanic compounds, alkyl-mercury compounds, dioxins, furans; and the like. It is also within the scope of the present invention to treat a waste material which is contaminated with naturally occurring radioactive materials.

The term "contaminated waste" as used herein, means any waste material which is environmentally unacceptable. By "environmentally unacceptable" we mean those materials which governmental regulations define as being harmful, or potentially harmful, to the ecological system pertaining to the environment and which must be disposed of in accordance with governmental laws and/or regulations.

In accordance with the present invention, the contaminated waste material to be treated, will typically not meet environmental laws and/or regulations. After treatment, the waste is converted to a relatively innocuous granular substance. That is, a substance which will meet such regulations, and which will thus be environmentally acceptable. The resulting innocuous material is a granulated, or particulate substance, which when mixed with soil, will support the growth of vegetation. Furthermore, the method of the present invention can be performed on-site; thus, not requiring the transportation of contaminated substances which may be subject to even more restrictive regulations.

The waste material to be treated is placed into a containing means. Any suitable containing means may be used. Non-limiting examples of suitable containing means include earthen pits, barges, drums, as well as any relatively large metal container, such as those used to haul trash and soil. The particular containing means used will depend on such things as economics of the job, the waste to be treated, and the amount of waste to be treated.

An effective amount of reagent material is mixed with the waste to be treated. An effective amount will typically be that minimum amount needed to contact an effective amount of the waste material to an innocuous material. That is, enough which will contact at least that fraction of the waste material which must be treated to render the entire volume of treated waste material environmentally acceptable. Of course, it is most preferred to contact substantially all of the waste. For typical treatments and wastes, a preferred ratio of reagent material to waste material will range from about 10/1 to 1/10, more preferably from about 5/1 to 1/5, most preferably 2/1 to 1/2, particularly about 1/1. Of course, the level of contamination of the waste, the treating environment, and equipment used, will have an effect on the degree of mixing of reagent material and waste which can be achieved. It is especially preferred to achieve a substantially homogeneous mixture. Of course, water may be added to enhance mixing.

The reagent material of the present invention is comprised of: (i) 1 part alumina; (ii) 1 to 3 parts, preferably 1.5 to 2.5 parts silica; (iii) 0.5 to 3 parts, preferably 1 to 2 parts of a hydroxide, or hydroxide precursor, of an alkali metal; (iv) 2 to 5 parts, preferably from about 2.5 to 3.5 parts of CaO; (v) and 2 to 5 parts, preferably from about 2.5 to 3.5 parts of a zeolitic material. It is also preferred that the silica material have a surface area of at least about 10 m.sup.2 /g, preferably at least about 50 m.sup.2 /g. The preferred hydroxide is NaOH. It is understood that hydroxide precursor materials may also be used. None limiting examples of NaOH precursors include Na.sub.2 O, NaAlO.sub.2, and Na.sub.2 O.(SiO.sub.2).sub.x. Preferred zeolitic materials are those having an average pore diameter equal to or greater than 4 .ANG., preferably equal to or greater than 5 .ANG.. The more preferred are zeolitic materials which are iso-structural to a zeolite selected from clinoptilolite and chabazite. It is also understood that precursors of both alumina and silica may be used. For example, bauxite, kaolin, NaAlO.sub.2, and Al.sub.2 O.sub.3.3H.sub.2 O are preferred materials for the alumina component of the reagent material of this invention. Preferred silica materials include: silica gel, silica smoke, volcanic ash, kaolin, and sodium silicate (water glass).

The reagent material of the present invention, which will typically be in particulate or granular form, is used by mixing an effective amount of it with the waste material. As previously stated, it is preferred that the two be mixed as homogeneously as possible. The mixture of waste material and particulate reagent material will need to reach an effective temperature in order to initiate a chemical reaction between the reagent mixture and some of the contaminants in the waste material. An effective temperature can often be reached by merely mixing the reagent material with the waste material, particularly if the waste material contains water, thereby causing an exothermic reaction. If necessary, the mixture can be heated by an external heating means to achieve the effective temperature. It will be understood that the temperature of the mixture should not be allowed to reach a temperature at which undesirable, or toxic, gases evolve. Acceptable temperatures for most waste materials will range from about 50.degree. C. to about 250.degree. C., preferably from about 100.degree. C. to about 200.degree. C.

After the desired temperature is reached, and held there for an effective amount of time, the mixture is allowed to dry without setting. This ensures that a granular, or particulate, product is produced. Such a product can be mixed with soil and used to support the growth of vegetation.

The following examples are presently for illustrative purposes only and should not be taken as limiting the present invention in any way.

A sample (236 gm) of a soil/sludge from a contaminated site near Manvel, Tex., was treated with 236 gm of a reagent mixture of the present invention having the composition set forth in Table I below. Mixing was conducted by use of a mortar and pestle and the resulting mixture was held at 175.degree. C. in an oven for 24 hours. After this treatment, the resulting dry sample was found to have lost 58 gm, which was assumed to be water because neither odor nor smoke was observed during heating. The texture of the treated material was observed to be a fine powder containing a few friable lumps. Analyses of the treated and untreated materials are given in Table II below.

A sample (200 gm) of a soil/tar from a contaminated site near Mayfield, Tex., was treated with 200 gm of the same reagent material which was used in Example 1 above. Mixing was again achieved by use of a mortar and pestle and the resulting mixture was heated at 175.degree. C. in an oven for 24 hours. After this treatment, the dried sample was found to have lost 151 gm, which was assumed to have been water because neither odor nor smoke was observed during heating. The texture of the treated material was also found to be a fine powder containing a few friable lumps. Analyses of the treated and untreated materials are set forth in Table II below.

A sample (100 gm) of contaminated soil from a site near Mexico City was mixed with 100 gm of the reagent material used in the previous two examples. The two were mixed with a spatula in a stainless steel bowl. Water (61 gm) was added and blended into the sample resulting in a relatively stiff mud-like substance. After treating the mixture for 24 hr. at 175.degree. C., the sample appeared to be powdery with only a few soft granules being present. There was no smoke or vapor evolution during heating, thus it was assumed that the weight loss was due to loss of water. The dry weight was found to be 174 gm. Analyses of the treated and untreated samples are given in Table III below.

A sample (100 gm) of contaminated soil from Chemical Pollution Control of New York, N.Y., was treated with 100 gm of the reagent material of Example 1 above. The waste and reagent material were mixed with a mortar and pestle and placed in a 175.degree. C. oven for 24 hr. The resulting dry sample appeared to be a powder and had a dry weight of 180 gm. The weight loss was assumed to be water because no odor or smoke was observed during heating. Analyses of the treated and untreated materials are given in Table IV below.