WO1992006050A1

WO1992006050A1 - Method and material for treating solid and semi-solid waste materials containing reactive sulfides

Info

Publication number: WO1992006050A1
Application number: PCT/US1991/007363
Authority: WO
Inventors: Gerald R. Roehrig
Original assignee: Itex Enterprises, Inc.
Priority date: 1990-10-03
Filing date: 1991-10-02
Publication date: 1992-04-16
Also published as: AU8860691A

Abstract

A method and material is provided for treating solid and semi-solid waste materials containing reactive sulfides wherein from about 60 % to about 90 % of a solid or semi-solid waste material containing reactive sulfides is mixed with from about 5 % to about 40 % hydraulic cement, from about 5 % to about 40 % metal carbonate, and from about 0 % to about 15 % water. The mixture is allowed to cure and the resultant end product is a physically and chemically stable solid material with a reduced concentation of reactive sulfides. The reactive sulfides remaining in the material are permanently encapsulated in the monolithic mass.

Description

METHOD AND MATERIAL FOR TREATING SOLID AND SEMI-SOLID WASTE MATERIALS CONTAINING REACTIVE SULFIDES

This invention relates to a method and material for treating solid and semi-solid waste materials containing reactive sulfides.

Industries generate large quantities of liquid, semi-solid and solid waste materials on a daily basis. As a result of this industrial activity, large masses of such material exist which present a considerable hazard to the environment. These waste materials are often in the form of solids or highly viscous semi-solids containing hard lumps of solid material. Of particular concern are those waste materials containing reactive sulfides. Waste materials containing reactive sulfides have been defined as those sulfide-bearing wastes that generate toxic gases, presumed to be hydrogen sulfide (H₂S) , when exposed to a pH between about 2 and about 12.5, in a sufficient quantity to present a danger to human health and the environment. The United States Environmental Protection Agency ("EPA") has proposed a treatment standard for waste materials containing reactive sulfides of alkaline chlorination, chemical oxidation, or incineration followed by precipitation to insoluble sulfates. (Federal Register Volume 54, p. 48425). The EPA has also adopted an interim guideline for classifying materials within the reactive sulfides category of 500 mg. of H₂S generated per kilogram of waste. Thus, it has been proposed that waste materials that generate more than 500 mg. of H₂S per kilogram of waste, as measured by standard EPA test methods (SW 846, Method 7.3.4.2) must be treated by alkaline chlorination, chemical oxidation, or incineration followed by precipitation to insoluble sulfates. The foregoing methods of treatment are, however, in the case of large volumes of solid and semi-solid wastes materials, expensive and cumbersome. Thus there exists a need for an effective method of treating solid and semi-solid waste materials containing reactive sulfides that is economical.

It has been found that solid and semi-solid waste materials containing objectional amounts of reactive sulfides may be economically and effectively treated with a mixture of a metal carbonate, hydraulic cement and optionally water to produce a solid, stable and unobjectionable material. Surprisingly, it is has been discovered that not only does the treatment encapsulate the reactive sulfides within a monolithic mass, but also that the concentration of reactive sulfides in the treated waste material is greatly reduced. Thus, large volumes of solid and semi-solid waste materials containing objectional levels of reactive sulfides may be economically and efficiently treated through the use of the present invention.

Numerous other objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the following disclosure including the examples provided herein.

FIGURE 1 is a side view of an apparatus suitable for use in connection with the present invention;

FIGURE 2 is a cutaway side view of the separator and homogenizer units of the apparatus; Due to various industrial operations there exist in this country large volumes of solid and semi-solid waste materials that contain objectional levels of reactive sulfides. Volume 40 of the Code of Federal Regulations §261.23 identifies eight criteria for defining a waste as a reactive waste. One of the criteria identified is that the waste is a sulfide-bearing waste which, when exposed to pH concentrations between 2 and 12.5, can generate toxic 10 gases, vapors or fumes in a quantity sufficient to present a danger to human health or the environment. The toxic gas released by waste in the reactive sulfide category is presumed to be hydrogen sulfide (H₂S) . The United States Environmental Protection Agency has adopted an interim value of 500 mg. of H₂S generated per kilogram per waste for the purpose of classifying a given sulfide-bearing waste material a hazardous waste.

It has been proposed that waste materials containing reactive sulfides be treated by alkaline chlorination, chemical oxidation, or incineration followed by precipitation to insoluble sulfates. These techniques, however, when applied to large volumes of solid and semi- solid waste materials are expensive and cumbersome. Thus, there is a need for an inexpensive and efficient means of treating solid and semi-solid containing reactive sulfides.

It has been found that solid and semi-solid waste materials containing reactive sulfides can be stabilized by treatment with hydraulic cement and a metal carbonate to produce a solid end product. The concentration of reactive sulfides in the solid end product is greatly reduced and whatever reactive sulfides remain are permanently encapsulated in the material. Thus, the material and method of the present invention provide a relatively inexpensive and efficient means of treating solid and semi-solid waste materials containing reactive sulfides.

A hydraulic cement suitable for use in connection with the practice of the present invention in Portland type I cement. This cement is identified and defined in ASTM Standard C150-89, which is incorporated herein by reference. Although Portland I is known to be suitable for use in connection with the present invention, it is anticipated that other hydraulic cements, including ASTM Types II-V and variations thereon may be suitable for use in the practice of the present invention.

The amount of hydraulic cement, metal carbonate and water to be used in the treatment of solid and semi-solid waste materials containing reactive sulfides varies depending upon many factors, including the chemical composition of the waste materials and the amount of water present in the waste material. Preferably, from about 60% to about 90% of the waste material is mixed with from about 5% to about 40% Portland cement, from about 5% to about 40% calcium carbonate and an effective amount of water. More preferably, from about 75% to about 90% of the waste material is mixed with from about 5% to about 20% Portland cement, from about 5% to about 20% calcium carbonate and water as necessary. In some cases, the moisture content of the waste material will be sufficient and the addition of water will not be necessary.

The metal carbonate used in connection with the present invention is preferably a dry, finely ground material. Although it is known that calcium carbonate is suitable for use in the present invention it is contemplated that other carbonate compounds containing magnesium, potassium or sodium may be suitable for use in connection with the present invention. Bicarbonates and sesquicarbonates may also be suitable for use in connection with the present invention.

In order to clearly illustrate the present invention the following examples are given. Although the examples are presented to illustrate certain specific embodiments of the invention, they are not to be construed as to be restrictive of the scope and spirit thereof.

EXAMPLE 1

A sample of a typical sulfide-containing refinery sludge was analyzed for reactive sulfide content. Triplicate analysis of the sludge indicated that the reactive sulfide content of the material was 2,800 mg./Kg. The sludge was mixed with Portland Type I cement, calcium carbonate and water in the proportions set forth in Table 1 below. All percentages herein are on a weight basis unless otherwise indicated.

TABLE 1 MATERIAL WEIGHT

Sludge 79.6%

Portland Cement 10%

Calcium Carbonate 5.1%

H₂0 5.3% Total 100%

After solidification the material was allowed to cure for one week and was then tested according to EPA method 7.3.4.2 as found in the Third Edition of SW 846 (detection tube method) . The EPA method was modified to the extent that a higher concentration sulfuric acid was used as set forth below.

A 4.0 gram sample of the solidified material was slurried in 100 ml. deionized water and titrated with 1.00 N sulfuric acid to a pH below 2. EPA method 7.3.4.2 specifies 0.005 M, or 0.010 N, which is weaker by a factor of 100, for the titration. The results of the titration are set forth in Table 2 below:

It was noted that upon addition of the acid to the sample slurry, the pH immediately dropped and then began to rise slowly. It is assumed that this is the result of the buffering action of the calcium carbonate as well as other salts and weak acids in the material. It was determined that a fifteen minute time interval between the addition of acid and testing the pH of the system was adequate to allow the system to reach equilibrium.

Significantly, there was no detected release of hydrogen sulfide even though the slurry was titrated to a pH below 2.0. EXAMPLE 2 A second sample slurry was prepared with 4.0 grams of the solidified material of Example 1 and 100 ml. of deionized water. The sample slurry was titrated with 1.0 N sulfuric acid and the pH was measured. The results of the titration are set forth below:

As in the case of Example 1, no evolution of H₂S was detected at any time. (Detection limit 2.5ppm).

EXAMPLE 3

A sulfide-containing refinery sludge was analyzed for reactive sulfide using the procedure outlined in EPA method 7.3.4.2, as found in the Third Edition of SW 846 (scrubber method) . The method was modified to the extent that l.ON sulfuric acid was used rather than 0.005M, or 0.010N acid. Two scrubbers, connected in series, were used to collect the hydrogen sulfide released during the titration. The results of the analysis of the sludge are set forth below:

A sample of the sludge was mixed with calcium carbonate, Portland Type I cement and water in the proportions set forth below:

TABLE 5

After solidification, the material was allowed to cure for one week and was then analyzed for reactive sulfides as set forth above. The results of the analysis are set forth in Table 6 below:

TABLE 6

The foregoing examples illustrate that the concentration of reactive sulfides in solid and semi-solid waste materials treated in accordance with the present invention are greatly reduced. Moreover, any reactive sulfides remaining after treatment are permanently encapsulated in a monolithic mass and thereby rendered innocuous even when exposed to highly acidic conditions. The practice of the present invention on a commercial scale requires a method whereby solid or highly viscous semi-solid waste materials containing hard lumps may be economically and effectively mixed with Portland cement and calcium carbonate to produce a chemically and physically stable end product. Thus, the present invention also provides a method for mixing portland cement and calcium carbonate with waste materials containing reactive sulfides to produce a homogeneous end product in which any remaining reactive sulfides are permanently encapsulated.

Referring to FIGURE 1, there is shown an apparatus for processing waste material, into an environmentally acceptable end product. Waste material to be treated enters the apparatus for processing by means of a sludge unloading hopper 10 positioned at one end of a separator 12 that includes two pair of rotating chopper augers 14, each driven by an electrically actuated power unit 22. The separator 12 is supported on a foundation 24 by means of conventional support structure.

Depending on the consistency of the waste material to be processed, water is available at the hopper 10 by means of a feed line (not shown) . Water, if needed, is added to the waste to control the consistency thereof for improved operation of the treatment process and to facilitate removal of foreign objects. Also provided for removal of foreign objects of magnetic material is a plurality of magnets 28 supported at the bottom of the separator 12.

Such magnets are of a conventional design and are powered from an available source.

Each of the chopper augers 14 are rotatively driven by individual power units 22 and controlled to circulate the waste material within the separator 12 until foreign objects are removed and large pieces of sludge are broken up as desired.

For this initial processing step of breaking up the waste material and removing foreign objects, the augers 14 are driven in pairs in a clockwise or counter-clockwise direction to achieve the desired movement of waste within the separator 12. When an operator observes that the waste material within the separator 12 has been properly broken up, the direction of rotation of the augers 14 is set to cause a movement of the waste from right to left as illustrated in FIGURE 1 and shown by the arrows 21 of FIGURE 2.

The waste processed in the separator 12 passes over a dam 30 positioned between the separator 12 and the homogenizer 32. Rotatably mounted within the homogenizer 32 are pin mixers 34 each rotatively driven by separate electrically powered drive units 42.

Each of the pin mixers comprises a plurality of individual pin units where each pin unit comprises four (4) pins radially extending from a shaft.

Each pin mixer 34 comprises a shaft 44 with radially extending pins 46. It is to be noted that each pin 46 is mounted to the shaft 44 at an angle to promote the movement of waste in the homogenizer 32 in accordance with direction of rotation of the pin mixers. Again, the operator controls the direction of rotation of the pin mixers 34 to create a pattern of waste movement within the homogenizer 32 as illustrated by the arrows 33.

As the waste material passes over the dam 30 and enters the homogenizer 32, it is further treated to develop a substantially uniform mass of small particles. The waste is processed in the homogenizer 32 until the desired consistency and homogeneity of the material is achieved. At the completion of the processing step within the homogenizer 32, a plurality of gate valves 60 are opened and the pin mixers 34 are caused to rotate in a direction to deliver the waste to the now open gate valves.

As best illustrated in FIGURE 2 the gate valves 60 are operated by electrically powered actuators 68.

With the gate valves of the homogenizer open, the now substantially homogenized waste is dropped into a storage tank 70 (FIGURE 1) supported on a foundation 72 within a pit 74. The waste material which has now been treated in two steps is of a pumpable consistency. Mounted within the storage tank 70 are two slurry pumps 76, only one shown in FIGURE 1, each having an outlet pipe 78 connected to a blender unit 80.

With reference to the blender unit 80, it is supported within a frame 82 mounted on a foundation 84. The height of the blender unit 80 above the foundation 84 is sufficient to permit a truck to be positioned under the blender unit to accept the processed waste material for delivery to a waste storage site. Typically, the blender unit may be a conventional mixer usually employed for concrete mixing such as marketed by BHS/Ross and known as a "Compulsory Mixer".

Positioned above the blender unit 80 are one or more additive hoppers 86 (only one shown in FIGURE l) for storing additive materials such as Portland cement, calcium carbonate or mixtures thereof to be blended in the unit 80 with the waste material pumped from the storage tank 70. Each of the one or more additive hoppers 86 is equipped with a dust collector 88 and is connected to the blender unit 80 by means of a butterfly valve 90. Additives to be blended with the waste material in the unit 80 are delivered into the additive hoppers by means of a filler pipe 94. Also connected to the blender unit 80 is an air scrubber 92 of conventional design and operation.

In operation of the blender unit 80, waste material from the storage tank 70 is pumped by means of the slurry pumps 76 into the blender unit until the blender unit receives a full charge of waste material. The amount of waste material in the blender unit is known and the amount of additives to be blended with the waste material are delivered into the blender unit 80 from the additive hoppers 86 in the desired ratios. The blender unit 80 blends the additives with the waste material with water added as required. The result is a concrete-like mixture wherein the waste material has been processed and treated to meet presently set environmental standards. This concrete-like material is then delivered into trucks for transportation to a permanent waste material storage site. The entire process of breaking up the sludge and removing foreign particles in the separator 12 and the homogenizing mixing in the homogenizer 32 is continuously repeated to replenish the supply of waste material in the storage unit 70 for processing in the blender unit 80.

Although a preferred embodiment of the invention has been described with reference to the examples and the foregoing detailed description it will be understood that the invention is capable of numerous rearrangements, modifications and substitutions of parts and elements without departing from the spirit and scope of the invention.

Claims

1. A method for treating waste material containing reactive sulfides comprising the steps of:

mixing from about 60% to about 90% of the waste material with additives consisting essentially of:

from about 5% to about 40% hydraulic cement;

from about 5% to about 40% of a metal carbonate; and,

an effective amount of water,

to produce an end product wherein the concentration of reactive sulfides has been reduced and the remaining reactive sulfides are encapsulated.

2. The method of Claim 1 wherein the hydraulic cement is Portland cement.

3. The method of Claim 1 wherein the metal carbonate is calcium carbonate.

4. The method of Claim 1 wherein the ratio of calcium carbonate to Portland cement is from about 1:1 to about 1:4.

5. The method of Claim 1 wherein an effective amount of water is from about 0% to about 15%.

6. The method of Claim 1 wherein the waste material, when exposed to pH conditions between about 2 and about 12.5 generates a toxic gas.

7. The method of Claim 6 wherein the toxic gas is hydrogen sulfide.

8. The method of Claim 7 wherein more than 500 mg. of hydrogen sulfide is generated per kilogram of waste.

9. A method of processing solid or semi-solid waste material containing reactive sulfides comprising the steps of:

breaking up the received material into a desired consistency;

homogenizing the material;

mixing from about 60% to about 90% of the homogenized material with additives consisting essentially of from about 5% to about 40% hydraulic cement, from about 5% to about 40% metal carbonate and from about 0% to about 15% water to produce a material wherein the concentration of reactive sulfides has been reduced and the remaining reactive sulfides have been encapsulated.

10. The method of Claim 9 wherein the hydraulic cement is Portland cement.

11. The method of Claim 9 wherein the metal carbonate is calcium carbonate.

12. The method of Claim 9 wherein the ratio of metal carbonate to hydraulic cement is from about 1:1 to about 1:4.

13. The method of Claim 9 wherein the waste material, when exposed to pH conditions between about 2 and about 12.5, generates a toxic gas.

14. The method of Claim 13 wherein the toxic gas is hydrogen sulfide.

15. The method of Claim 14 wherein more than 500 mg. of hydrogen sulfide is generated per kilogram of waste.

16. The method of Claim 9 further comprising the step of separating foreign objects from the waste material.

17. The method of Claim 9 further comprising the step of pumping the homogenized material with a slurry pump from the homogenizer to a mixer.

18. The method of Claim 9 further comprising the step of selectively retaining the homogenized material in a mixer with the hydraulic cement and metal carbonate for a predetermined period of time to obtain the desired degree of mixing.

19. A stabilized waste material, wherein reactive sulfides in the waste material have been stabilized by a process comprising the steps of:

from about 5% to about 40% hydraulic cement;

from about 5% to about 40% metal carbonate; and

an effective amount of water to produce a stabilized waste material wherein the concentration of reactive sulfides has been reduced and the remaining reactive sulfides are encapsulated.

20. The material of Claim 19 wherein the hydraulic cement is Portland cement.

21. The material of Claim 19 wherein the metal carbonate is calcium carbonate.

22. The material of Claim 19 wherein the ratio of metal carbonate to hydraulic cement is from about 1:1 to about 1:4.

23. The material of Claim 19 wherein an effective amount of water is from about 0% to about 15%.

24. The material of Claim 19 wherein the untreated waste material, when exposed to pH conditions between about 2 and about 12.5 generates a toxic gas.

25. The material of Claim 24 wherein the toxic gas is hydrogen sulfide.

26. The material of Claim 25 wherein more than 500 g. of hydrogen sulfide is generated per kilogram of waste.

27. The material of Claim 19 wherein said process further comprises the steps of: separating foreign objects from the waste material; homogenizing the waste material with a homogenizer; pumping the homogenized material with a slurry pump from the homogenizer to a mixer; and selectively retaining the homogenized material in the mixer with the hydraulic cement and metal carbonate for a predetermined period of time to obtain the desired degree of mixing.