Hazardous or toxic waste destruction or containment – Containment – Solidification – vitrification – or cementation
Reexamination Certificate
1999-08-26
2001-01-16
Green, Anthony (Department: 1755)
Hazardous or toxic waste destruction or containment
Containment
Solidification, vitrification, or cementation
C106S697000, C106S724000, C106S731000, C106S805000, C106S823000, C588S252000, C588S256000, C588S257000
Reexamination Certificate
active
06174275
ABSTRACT:
TECHNICAL FIELD
This invention relates to processes for immobilizing waste in solid or semi-solid matrices.
BACKGROUND
The processing of sugar cane milling or diffusing to make refined sugar and other products every year generates large amounts of a biomass byproduct commonly known as bagasse. Many have sought methods of disposing of or utilizing bagasse, in view of the millions of tons produced each year and the problems associated with disposal of large amounts of this particular organic byproduct. At the same time, the handling and disposal of many toxic or otherwise hazardous forms of waste produced by modem society have proven difficult and hazardous to those who handle or are in close proximity to such toxic waste. Various processes have been proposed to address the problem of hazardous waste disposal, including the use of various solidification and stabilization processes. Some of the proposed solidification and stabilization processes incorporate the use of cement for economic reasons. However, the amount of leaching prevalent in systems which rely heavily on cement alone has proven unsatisfactory. In addition, so far as is known, no previously developed process has successfully combined the features of a process which efficiently solidifies and stabilizes hazardous waste with a process for the efficient utilization of bagasse.
THE INVENTION
The present invention is deemed to provide at once both a highly effective and efficient method for properly solidifying and stabilizing hazardous waste, and a productive use for the major sugar cane processing byproduct, bagasse. In one aspect of this invention, a process for solidifying and stabilizing waste is provided. The process comprises (a) combining bagasse and a liquid medium having a pH below about 4 or above about 10 to form a mixture, (b) heating the mixture, (c) separating the mixture into solid matter and filtrate and washing the solid matter with a liquid in which sugar is soluble, (d) substituting the solid matter for the bagasse in (a) and repeating steps (a) through (c) until the filtrate is substantially colorless under ambient light conditions, thereby producing washed solid matter, (e) combining at least a portion of the washed solid matter with at least (1) the waste, (2) water, and (3) a cement, so as to form a cement slurry, and (f) curing the cement slurry. Preferably, this process further comprises the step of maintaining the mixture at least at one temperature in the range of about 80 to about 120° C. for a period of at least about 30 minutes, measured from the point in time at which the mixture reaches at least one temperature in the specified range, prior to separating the mixture into solid matter and filtrate. More preferably, the temperature(s) is/are in the range of about 90 to about 110° C., and the period of time during which the mixture is maintained at a temperature in the specified range is at least about 60 minutes, measured from the point in time at which the mixture reaches at least one temperature in the specified range. It also is preferred that, before combining the washed solid matter with at least the waste, water and the cement to form the cement slurry, at least the following additional steps are carried out:
(a) drying at least a portion of the washed solid matter, and
(b) pulverizing at least a portion of the washed solid matter so that the washed solid matter has an average particle size in the range of about 100 to about 500 microns, more preferably in the range of about 150 to 350 microns.
The step of combining the washed solid matter with at least the waste, water and cement to form the cement slurry in processes of this invention is preferably carried out by (a) mixing at least a portion of the washed solid matter with the waste and water to form a waste slurry, (b) maintaining at least a portion of the waste slurry in a substantially quiescent state for a period of at least 30 minutes, and more preferably for a period of at least 60 minutes, and (c) combining at least a portion of the waste slurry with the cement to form the cement slurry. Without being bound to theory, it is believed that either this procedure or the pulverization procedure described above, or both, enable particularly satisfactory binding between the waste molecules and the other slurry components to produce a particularly waste-stable cementitious solid product.
In another preferred embodiment of this invention, the process comprises:
(a) combining bagasse and a liquid medium having a pH below about 3 or above about 12 to form a mixture,
(b) heating the mixture and maintaining the mixture at least at one temperature in the range of about 90 to about 110° C. for a period of at least about 30 minutes,
(c) separating the mixture into solid matter and filtrate and washing the solid matter with a liquid in which sugar is soluble,
(d) substituting the solid matter for the bagasse in (a) and repeating steps (a) through (c) until the filtrate is substantially colorless under ambient light conditions, thereby producing washed solid matter,
(e) drying the washed solid matter,
(f) pulverizing at least a portion of the washed solid matter so that the washed solid matter has an average particle size in the range of about 100 to about 500 microns,
(g) mixing at least a portion of the washed solid matter with the waste and water to form a waste slurry,
(h) maintaining at least a portion of the waste slurry in a substantially quiescent state for a period of at least 30 minutes,
(i) combining at least a portion of the waste slurry with a cement to form a cement slurry, and
(j) curing the cement slurry at least at one temperature in the range of about 20 to about 30° C.
The invention also provides cementitious products formed by the practice of processes of this invention. The resulting solid cementitious products exhibit exceptional stabilization of waste, measured by low levels of waste leaching, as compared to controls which do not include material derived from bagasse. Such cementitious products can be useful as, for example, as fill material in a variety of products and settings in which solid cement is commonly employed.
These and other embodiments and features of this invention will be still further apparent from the ensuing description and appended claims.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The processes of this invention enable the effective use of components of bagasse, including lignin, to stabilize and trap hazardous waste within solidified cementitious matrices, thus putting to great use what heretofore has been an organic waste byproduct. Typical wastes for which processes of this invention may be utilized include, for example, wastes comprised of heavy metal compounds containing metals such as, e.g., arsenic, cadmium, chromium, and/or lead. However, the processes of this invention are not necessarily limited to use with heavy metal waste, but rather may be used for solidification/stabilization of any waste, as long as the process reduces the amount of waste which leaches from the solid cementitious product resulting from the process, as compared to the same process carried out without the use of bagasse. For ease of description only, the steps of the processes of this invention will be discussed hereafter in stages, the first stage being bagasse processing, and the second step being cement preparation and curing.
Bagasse Processing
The amount of bagasse material to be used in the processes of this invention can vary, depending upon the components present in the mixture and their relative amounts. Typically, the amount used will be in the range of about 1% to about 20% by weight to cement, and preferably about 10% by weight to cement.
In the step of combining bagasse and a liquid medium, the bagasse and liquid medium may be combined one into the other or concurrently. The liquid medium should have a pH which is below about 4 or above about 10, and more preferably which is below about 3 or above about 12. Typically, the liquid medium may be comprised of any acid or base which does not interfere with
Green Anthony
Nicholls State University
Sieberth & Patty L.L.C.
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