Claims
- 1. A process for immobilizing a hazardous waste containing a heavy metal comprising the steps of:
- adding a sulfide to said hazardous waste so as to generate a sulfide of said heavy metal;
- mixing a chemical reagent with the hazardous waste containing the generated sulfide of said heavy metal, said chemical reagent containing a mixture of a retarder and an accelerator, said accelerator comprising calcium chloride, said retarder selected from the group consisting of: glycerine and polyethylene glycol; and
- blending the mixture of said chemical reagent and said hazardous waste containing the generated sulfide of said heavy metal with a pozzolanic material.
- 2. The process of claim 1, further comprising the step of:
- mixing a neutralizing agent with said hazardous waste so as to cause said hazardous waste to have a pH between 5 and 14.
- 3. The process of claim 2, said neutralizing agent added so as to cause said hazardous waste to have a pH between 7 and 11.
- 4. The process of claim 2, said neutralizing agent being a chemical selected from the group consisting of: lime, hydrate lime and calcium hydroxide.
- 5. The process of claim 1, said sulfide being a chemical selected from the group consisting of: sodium hydrosulfide and sodium sulfide.
- 6. The process of claim 5, said sulfide being a 5 weight percent to the saturated solution of sodium hydrosulfide.
- 7. The process of claim 1, further comprising the step of:
- separating the hazardous waste containing the generated sulfide of said heavy metal from the supernatant portion of said hazardous waste prior to the step of mixing said chemical reagent.
- 8. The process of claim 7, said step of separating:
- decanting said supernatant from the hazardous waste containing the generated sulfide of said heavy metal.
- 9. A process for immobilizing a hazardous waste containing a heavy metal comprising the steps of:
- neutralizing said hazardous waste such that said hazardous waste has a pH of between 5 and 14;
- adding a sulfide to the neutralized hazardous waste so as to generate a sulfide of said heavy metal from said hazardous waste;
- separating the waste containing the generated sulfide of said heavy metal from the supernatant of said hazardous waste; and
- solidifying said waste containing the generated sulfide of said heavy metal said step of solidifying comprising:
- mixing a chemical reagent with the hazardous waste containing the generated sulfide of said heavy metal, said chemical reagent containing the mixture of a retarder and an accelerator, said retarder being a chemical selected from the group consisting of: glycerine and polyethylene glycol, said accelerator comprising calcium chloride.
- 10. The process of claim 9, said step of neutralizing comprising:
- adding a neutralizing agent to said hazardous waste in such a quantity as to cause said hazardous waste to have a pH of between 7 and 11.
- 11. The process of claim 10, said neutralizing agent being a chemical selected from the group consisting of:
- lime, hydrated lime, and calcium hydroxide.
- 12. The process of claim 9, said sulfide being a chemical selected from the group consisting of:
- sodium hydrosulfide and sodium sulfide.
- 13. The process of claim 12, said sulfide being a 5 weight percent to the saturated solution of sodium hydrosulfide.
- 14. The process of claim 9, said step of separating comprising:
- decanting said supernatant from the hazardous waste containing the generated sulfide of said heavy metal.
- 15. The process of claim 9, said step of separating comprising:
- removing said supernatant from said hazardous waste containing the generated sulfide of said heavy metal by centrifuging.
- 16. The process of claim 9, said step of separating comprising:
- removing said supernatant from said hazardous waste containing the generated sulfide of heavy metal by filtering.
RELATED APPLICATIONS
The present application is a continuation-in-part of U.S. patent application Ser. No. 177,613, filed on Apr. 5, 1988 and entitled "Chemical Reagent and Process for the Disposal of Waste", now abandoned. U.S. patent application Ser. No. 177,613 was a continuation of U.S. patent application Ser. No. 883,360, filed on July 8, 1986, now abandoned.
The present invention relates to the field of disposal of inorganic and organic waste including chemical waste and low-level and medium-level nuclear waste and, more particularly, to the field of disposal of waste via microencapsulation or solidification. Still more particularly, the present invention relates to the field of disposal of waste in which the heavy metals within the waste are insolubilized so as to allow such heavy metals to be reacted with a chemical reagent in pozzolanic material to form a solid suitable for safe storage of disposal.
One of the biggest problems facing the industrial world is the disposal of waste that has been generated and is presently being generated by the various industries. Several techniques were developed in the past to solve the problem. One method involved the use of landfills where the waste is transported for disposal. The disadvantage of that method is that it requires the transportation of the waste to the landfill from areas that are very distant from such landfills, thereby making such disposal uneconomical and often times hazardous to the populated areas through which the waste is transported. Another disadvantage is that, in the landfill, the waste is merely covered and permanently contained whereby the problem is passed on to future generations. Waste being disposed in landfills may seep through the ground to subterranean water streams and the waste could be returned to populated areas through the natural waste streams. The Environmental Protection Agency has issued regulations prohibiting the prior practice of disposing of liquid waste in landfills and regulating the types of solid waste and solidified waste which can be disposed in certain landfills. Such regulations have made many prior art practices obsolete.
Another method used in the past for the disposal of waste has been chemical treatment. One disadvantage of such treatment is that it is not effective because most of the compounds presently in waste, and especially hazardous waste, do not react chemically with other compounds to form non-hazardous compounds. Furthermore, even if the conversion to harmless compounds is possible, such a process is uneconomical.
Incineration has also been and is used as a means for the disposal of waste. Incineration, however, is not effective in numerous applications; in fact, it is totally ineffective for wastes containing heavy metals and their compounds. Furthermore, incineration processes result in the formation of other undesirable chemicals in the form of ash or gases emitted to the environment. Furthermore, incineration is a very costly process that requires highly sophisticated incineration equipment and requires the transportation of the waste to special locations for the incineration to be performed.
Another method that has been used in the past for the disposal of waste has been the process of solidifying the waste by mixing it with sawdust, various pozzolanic materials and polymeric substances. One disadvantage of such methods is their inability to adequately solidify liquid or sludge-type waste. Another disadvantage is that several pozzolanic materials used in the past have not been shown to be effective because of their physical or chemical properties. Attempts in the past, for example, to solidify waste with Portland cement produced a solid product which was very permeable, porous, subject to leaching and deficient in mechanical strength. The use of the other pozzolanic materials having better physical properties for promoting the interaction of various compounds, such as fly ash, was also ineffective because such materials possessed undesirable properties such as quick setting before the waste could be uniformly dispersed in such material. Although used as a bonding agent, polymers have not been shown to have successfully bonded most wastes and, to be successful, large quantities of the polymer are required. Furthermore, the use of polymeric compounds to promote the solidification is also undesirable because many polymeric compounds themselves are complex and hazardous, the resulting waste compound is toxic, and chemical attack, such as sulfate attack, is prompted by such polymers. Also, the resultant waste compound degenerates over time when polymers are used. Thus, such disposal is often not permanent.
Numerous wastes, in various forms, liquid, solid and slurry, can be made non-hazardous by immobilizing them through solidification processes. Nevertheless, many wastes contain heavy metals, such as arsenic, cadmium, chromium, copper, nickel, mercury, lead, and zinc, or their compounds. While their solubilities are often relatively small, their toxicity limits are extremely small. Thus, it is highly desirable or sometimes even essential that the solubilities of heavy metals and their compounds be substantially reduced in the course of waste solidification.
It is an object of the present invention to provide a solidification process that immobilizes the hazardous waste.
It is another object of the present invention to provide a process that reduces the solubility of heavy metals and their compounds.
It is another object of the present invention to provide a waste disposal process that reduces the solubilities of heavy metals in an inexpensive, safe, and simple manner.
It is still a further object of the present invention to provide a process for the disposal of waste that makes such waste easily transportable and easily disposable in landfills or in readily available natural disposal sites, such as salt domes and the like.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.
The present invention is a process for immobilizing a hazardous waste containing heavy metals. The process comprises the steps of: (1) pretreating the hazardous waste by adding a sulfide to the waste so as to generate in situ the sulfides of the heavy metals on the surface and inside of the waste's solid particles or to generate the precipitate of the sulfides of the heavy metals from the liquid portion of the waste: (2) mixing a chemical reagent with the waste containing the generated sulfides of the heavy metals; and (3) blending the resultant mixture with a pozzolanic material. This process further includes the step of mixing a neutralizing agent with the hazardous waste so as to cause the hazardous waste to have a pH of between 5 and 14 and, preferably, between 7 and 11. The neutralizing agent is an alkaline material, preferably lime, hydrated lime, or calcium hydroxide. The sulfide is either sodium hydrosulfide or sodium sulfide. This process further includes the step of separating the waste containing the generated sulfides of the heavy metals from the supernatant portion of the hazardous waste prior to the step of mixing the hazardous waste with the chemical reagent.
The chemical reagent includes a retarder, which could be glycerine or other viscosity-altering reagent, and an accelerator, namely calcium chloride. The retarder prevents the flash setting of the pozzolanic material and slows the setting process, whereas the accelerator promotes the solidification activity. The retarder further acts as a lubricant and improves the viscosity. The pozzolanic material may be not only pozzolanic material specifically manufactured for cementing operations, such as Portland cement, but also waste material produced in several industrial applications, such as fly ash, kiln dust, and steel or lead baghouse dust. The solid waste materials, containing the heavy metals, which are thusly formed may thereafter be stored or disposed in natural storage places without affecting or harming the environment.
US Referenced Citations (10)
Foreign Referenced Citations (5)
| Number |
Date |
Country |
| 81403 |
Jun 1983 |
EPX |
| 124966 |
Nov 1984 |
EPX |
| 2614848 |
Oct 1977 |
DEX |
| 2717656 |
Oct 1978 |
DEX |
| 1458501 |
Nov 1966 |
FRX |
Continuations (1)
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Number |
Date |
Country |
| Parent |
883360 |
Jul 1986 |
|
Continuation in Parts (1)
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Number |
Date |
Country |
| Parent |
177613 |
Apr 1988 |
|
Patent Grant
5049285
