Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ZEOLITE-~YDRAULIC CEMENT CONTAINMENT MEDIU~
R~rK¢RoUND OF THE INVENT~ON
1. Field of the Invention
The present invention generally relates to a
zeolite-hydraulic cement containment medium for
hazardous wastes. In particular, the invention relates
to a process for preparing a zeolite-portland cement
containment medium from a paste prepared by mixing
zeolite in amounts from 5-60 weight percent with
portland cement in amounts from 95-40 weight percent
until a blend is achieved. Thereafter, a chosen amount
of small particle size hazardous wastes material is
blended with zeolite to form a wastes-zeolite mixture,
which is mixed with portland cement. Water is added
with mixing to the waste zeolite/portland cement
mixture to produce a free flowing paste, and the paste
mass is poured into appropriate molds to form a cement
monolith after about 7 days.
The zeolite-hydraulic cement containment
medium of the invention is not encumbered by the
disadvantages attendant to the use of portland cement
per se, and is therefore able to contain: (1) high-
concentrations and high loading levels of arsenic in
the presence of high concentrations of other hazardous
elements; (2) high amounts of metal cations which
normally make soluble complexes with arsenic in the
presence of high arsenic and high metal concentrations;
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and (3) arsenic in the presence of cations with which
it normally makes soluble complexes, and the arsenic is
contained in higher concentrations than is usual in
portland cement monoliths.
2. Background of the Invention
Control of pollution is one the main concerns
in the environment today, and mining, mineral and
metallurgical processing wastes in the U.S. accumulate
at the rate of thousand of tons per day, and thereby
exposes the environment to great risks of pollution.
In the field of inorganic hazardous wastes from mining
and mineral processing industries, such as the copper
mining and processing industry, it has been found that
large amounts of oxy-anion wastes (such as arsenic)
cannot be disposed of economically. Further, the most
common way to solidify and stabilize mining and mineral
processing waste solids and waste sludges is
cementation using a hydraulic material.
However, cements and other hydraulic material
~o are the most common media for the solidification-
stabilization of hazardous waste, and these containment
materials after cementation and disposal (by ocean or
land) are accompanied by several disadvantageous
aspects in that - salts of manganese, tin, zinc, copper
and lead are active in reducing the physical strength
of these cements, and anions such as phosphate, iodate,
borate, and sulfide retard the setting of these
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cements, to the extent that, if sufficient quantities
of these anions are present, the cement never hardens.
In all of these cases, the ions to be contained leach
from the cement matrix to some extent.
There are a number of cement-based processes
that use various additives in substantial amounts to
aid portland cement in the containment of hazardous
substances. A general classification of these cement-
based processes is as follows: cement/lime,
1~ cement/clay, cement/sorbent, and cement/polymer.
In the cement/lime process, lime is used to
elevate the pH of the waste containment system to basic
values, typically 8-10 in order to form insoluable
oxides, insoluable hydroxides, or insoluable calcium
salts. Weaknesses of this system are: (1) Some
hazardous materials exist as anions which are soluble
as calcium salts; and (2) some hazardous cations form
hydroxides or complexes at basic pH ranges which are
soluble to some extent.
In the cement/clay process, clays are used to
absorb hazardous materials. Weaknesses of this system
are: (1) The loading capacities of clays vary with the
ion or material being attached (in some cases this
loading capacity is quite small); (2) Anions do not
adhere well on clays; and (3) The ions or materials are
adsorbed or absorbed on clays and not strongly bonded
chemically. This means the attached ions or materials
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may be washed off the clay under the proper conditions.
The clay can therefore act as a chromatography bed.
The cement/sorbent system is similar to the
cement/clay system, the difference being that the
material used to adsorb the hazardous substance is not
clay. Sawdust, for example has been used to adsorb
oils prior to encapsulation in concrete. The
disadvantages of the cement/sorbent systems are
essentially the same as the cement/clay system.
Additionally, biodegration of the sorbent may occur if
the sorbent is organic.
Cement/polymer systems usually consist of the
polymer acting as a permeation limiting device by
filling cement pores with hydrophobic materials, and by
microencapsulation of the waste material. Usually,
there is no direct reaction between the waste
constituents and the polymer, and the system does not
actually precipitate, adsorb, detoxify, or destroy the
hazardous constituents. Biodegration of the polymer
2d may occur. Leaching of exposed hazardous constituents
may occur if the cement monolith becomes cracked or
broken.
Accordingly, in mining and mineral processing
industries, such as the copper mining and processing
industry, which produces large amounts of oxy-anion
wastes, such as arsenic, there is a need to devise
means whereby these oxy-anion wastes can be disposed of
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economically, as the present way of solidifying and
stabilizing mining and mineral processing wastes solids
and wastes sludges by cementation is uneconomical.
su~uRr OF THE INVENTION
One object of the invention is to provide a
method for producing a hydraulic containment medium for
mining and mineral processing wastes materials that is
effective for containment of transition metals, heavy
metals, and oxy-anions, such as arsenic.
Another object of the invention is to provide
a method for producing a hydraulic containment medium
for mineral processing wastes contA;ning arsenic from
the refining of copper, lead, cobalt and gold ores.
A yet further object of the invention is to
provide a method for producing a hydraulic containment
medium for solid wastes or sludges.
In general, the method of the invention
utilizes a zeolite-hydraulic cement containment medium
for hazardous wastes. The containment medium is
prepared by obtAining a zeolite-hydraulic cement paste
prepared by mixing from about 5 to 60 weight percent of
zeolite contAining the waste and 95 to 40 weight
percent of hydraulic cement until a blend is obtained.
The waste is in small particle sizes [Tyler Mesh No. 7
(i.e. 2.80 mm) or higher]. Thereafter, an amount of
water sufficient to produce a free flowing paste is
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added to waste-zeolite/hydraulic cement mixture with
mixing, and the paste mass i8 then poured into an
appropriate mold. After a sufficient period of time
from about 24 hours to 7 days, a cement monolith is
formed, and can be removed from the mold as a monolith
for disposal.
The amount of water added depends upon the
characteristics of the waste sample, but may vary
between about 20 to about 35% by weight of the combined
la portland cement plus waste-zeolite mixture. After the
paste is poured into the mold, good results are
obtained when the temperature is kept at about 25C -
45C during a 24 hour to 7 day time period in which the
monolith is formed.
DE'r~l Tr-rn n~z5cp rPTION OF THE INVENTION
Portland cement by itself has been used for
many years in Japan and elsewhere for solidification of
wastes having hazardous constituents before ocean
disposal; however, portland cement has several
disadvantages when considering cementation for land
disposal of hazardous wastes. For example, salts of
manganese, tin zinc, copper and lead are active in
reducing the physical strength of portland cement.
Further, the anions of phosphate, iodate, borate, and
sulfide retard the setting of portland cement, and if
sufficient quantities of these anions are present, the
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cement will never harden. (P.L. Bishop, Leaching of
Inorganic Hazardous Constituents from
Stabilized/Solidified Hazardous Wastes. Hazardous
Wastes Hazardous Mater., 5(2): 129-143, 1988; P. Cote,
Containment Leaching from Cement-Based Forms Under
Acidic Conditions. Ph.D. thesis, McMaster University,
Hamilton, Ontario, Canada, 1986; M.J. Cullinane et al.,
An As6essment of Materials that Interfere with
Stabilization/Solidification Processes. Proc. 13th
Annual Research Symposium, Cincinnati, OH pp. 64-71,
1987; and R.M. Kondo et al., Influence of inorganic
salts on the hydration of tricalcium silicate. J.
Appl. Chem. Biotechnol, 27:191, 1977).
The zeolite-hydraulic cement containment
medium of the invention is an excellent medium for
containment of materials having transition metals,
heavy metals and oxy-anions, especially oxy-anions or
arsenic. Oxy-anions are anions which contain oxygen as
one component of the moiety.
The zeolite-hydraulic cement containment
medium for wastes containing arsenic from the refining
of copper, lead, cobalt and gold ores - as well as
solid wastes or sludges is prepared by mixing from
about 5 to 60% zeolite containing waste with about 95
to 40 weight percent or portland cement until an
intimate blend is obtained. The hazardous waste is in
small particle sizes [Tyler Mesh 7 (i.e. 2.80 mm) or
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higher]. Thereafter, an amount of water sufficient to
produce a free flowing paste is added with mixing to
produce paste mass of zeolite-waste/portland cement.
The paste is poured into appropriate molds and kept
there until a cement monolith is formed.
More particularly, the monolith formation is
formed as follows: (1) Arsenic waste is passed through
a sieve of Tyler mesh size 100 and intimately combined
with the desired amount of zeolite. (2) Dry hydraulic
cement is added to the waste-zeolite mixture in small
portions and intimately mixed until all the required
cement is incorporated. (3) Water is added with
constant stirring until a soft paste stage is reached.
The amount of water added will depend upon sample
characteristics, but can vary between about 20 to 35%
of the combined portland cement plus waste-zeolite
mixture. (4) The paste is poured into molds which are
kept at a constant humidity (88% relative humidity) and
temperature (40C) for 7 days at which time the
monoliths are removed from the molds.
However, the usefulness of the invention is
not confined to the percent relative humidity, curing
time, and temperature, or cementatious material or
zeolite class mentioned. Any relative humidity, curing
time, and temperature suitable for the cementation
process of a hydraulic cement and any zeolite will
suffice.
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A typical artificial zeolite-hydraulic cement
containment medium according to the invention is
monoliths of arsenic waste materials. The containment
medium consist of a hydrated Na (SiAlO2) type zeolite
(faujasite) with a cubic structure similar to sodalite,
and type 1 portland cement in volume ratios from 1:9 to
1:1 (zeolite to cement). The zeolite contained molar
ratios of Na2O:A12O3:SiO2 with variable amounts of
hydrated water present of 1:1:2.8+/-0.2 respectively.
However, the usefulness of the invention is not
confined to this group and/or structure or either
natural or artificial origin, as other zeolites will
perform the same function.
EXAMPLE 1
Containment of Copper Smelter Waste.
Table 1 contains the chemical analysis of a
copper smelter waste with typical high metal and high
arsenic contents. These high values make containment
of copper smelter waste difficult, and usually require
large dilution of the waste product. A containment
monolith of this material was made using the procedure
described above. The monolith contained 30% by volume
of the copper smelter waste. The copper smelter waste
in the novel zeolite-portland cement containment medium
successfully passed EPA's Toxicity Characteristic
Leaching Procedure (TCLP) requirements (see Table 2).
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Table 1
Copper smelter waste sample analysis
Element Concentration
Antimony....... mg/kg............. 8.87
Arsenic........ .pct.............. 10.7
Barium......... mg/kg............. 1400
Cadmium........ mg/kg............. 1200
Chromium....... mg/kg............. 7.7
Copper......... .pct.............. 7.9
Iron........... mg/kg............. 97.1
Lead........... mg/kg............. 65
Tin............ mg/kg............. 536
Table 2
Copper smelter waste TCLP analysis, mg/kg
Element Concentration Concentration
permitted by EPA Present
Arsenic 5.0 1.81
Barium 100 <1.00+
Cadmium 1.0 0.03
Chromium 5.0 0.07
Copper* 1.0 0.02
Iron* .4 <0.05
Lead 5.0 <0.05
Mercury .2 <0.002
Silver 5.0 <0.01
Tin* 5.0 <0.02
*Drinking water st~n~Ard.
*Element shown as "<" indicate below detection limit of
the analytical method used.
EXAMP~E 2
Containment of Arsenic Acid Production Wastes
Table 3 contains the chemical analysis of an
arsenic acid production waste with typical high iron
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11
and high arsenic contents. These high values usually
make containment of the waste difficult, because
arsenic forms a water soluble complex with ferric iron
and iron always disproportionates into ferrous and
ferric valence states.
Table 3
Crude arsenic acid production waste sample analysis
Element Concentration
Arsenic........ .pct................ 32
Barium......... mg/kg............... 308
Cadmium........ mg/kg............... 60
Chromium....... mg/kg............... 57
Copper......... .pct................ 84
Iron........... mg/kg............... 2.6
Lead........... mg/kg............... 399
Mercury........ mg/kg............... 79
Silver......... mg/kg............... 25
Zinc........... mg/kg............... 38
A containment monolith of this arsenic waste
material was made using the procedure described above.
The monolith contained the waste at a loading of 30% by
volume. The crude arsenic acid production waste in the
novel zeolite-hydraulic cement containment medium
successfully passed EPA's Toxicity Characteristic
Leaching Procedure ~TCLP) requirements (see Table 4).
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Table 4
Crude arsenic acid production waste TCLP analysis,
mg/kg
Element Concentration Concentration
permitted by EPA Present
Arsenic 5.0 2.09
Barium 100 ~1.00
Cadmium 1.0 <0.02
Chromium 5.0 <0.05
Copper* 1.0 <0.02
Iron* .4 <0-05
Lead 5.0 <0-05
Mercury 0.2 <0.002
Silver 5.0 <0.01
Tin* 5.0 <0.02
*Drinking water stAn~Ard.
*Element shown as "<" indicate below detection limit of
the analytical method used.
EXAMPLE 3
Containment of Very High Level Artificial Waste
Table 5 contains the chemical analysis of an
artificial inorganic hazardous waste. The high ion
content for each element present, i.e., 5960 mg/kg of
mercury in the waste is not typical for hazardous waste
materials. These high values were used as a measure of
the potential effectiveness of the invention
containment medium for EPA listed inorganic hazardous
elements. A containment monolith of this material was
made using the procedure described above. The monolith
contained 30% by volume of the waste. This sample
successfully passed EPA's Toxicity Characteristic
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Leaching Procedure (TCLP) requirements (see Table 6~.
Mercury was contained to below detection limits.
Table 5
Artificial inorganic hazardous waste sample
analysis, mg/kg
Element Concentration
Arsenic 6310
Barium 6290
Cadmium 4600
Chromium 5670
Copper 5950
Iron 4930
Lead 5260
Mercury 5940
Silver 6040
Zinc 5530
Table 6
Artificial inorganic hazardous waste sample TCLP
analysis, mg/kg
Element Concentration Concentration
permitted by EPA Present
Arsenic 5.0 0.29
Barium 100 .09
Cadmium 1.0 .07
Chromium 5.0 .04
Copper* 1.0 <0.02
Iron* 0.4 .08
Lead 5.0 .51
Mercury 0.2 <0.002
Silver 5.0 .01
Tin* 5.0 .03
*Drinking water standard.
*Element shown as "<" indicate below detection limit of
the analytical method used.
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Before the advent of the present artificial
zeolite-hydraulic cement containment medium, hydraulic
cementation has not been very effective with wastes
containing oxy-anions, such as arsenate, selenate,
etc., or with soluble oxides or hydroxides.
The containment of oxy-anions in the zeolite
need not be limited to the direct accessibility of the
anion to normal zeolite binding sites. Any form of
faujasite zeolite is usable to contain oxy-anions.
Further, any zeolite that contains exchangeable mono-
valent cations are usable in the context of the
invention. Further still, any zeolite that contains
divalent or trivalent cations is usable in the context
of the invention to bind arsenate or other oxy-anions.
The families of zeolites that are useful in
the context of the invention are: faujasite,
chabazite, zeolite A, zeolite Rho, zeolite ZK-5,
zeolite X, zeolite Y. wilhendersonite, gmelinite,
edingtonite, natrolite, tetranatrolite, paranatrolite,
mesolite, seolecite, thomsonite, gonnardite, analcime,
wairakite, gismondine amicite, garronite, gobbinsite,
zeolite NaP-1, laumonitite, merliontite, paulingite,
phillipsite, harmotome, yugawaralite, canerinite,
erionite, levynite, zeolite 1, zeolite losed, zeolite
omega, sodalite, offretite, mazzite, bikitaite,
dachiardite, epistilbite, ferricite, zeolite ZSM-5,
mordenite, brewsterite, heulandite, clinoptilolite,
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stibite, stellerite, barrerite, afghanite, liottite,
franzinite, sacrofanite, giuseppettite, svetlozarite,
doranite, chiarennite, hsianghualite, lovdarite,
wenkite, roggianite, partheite, perlialite, viseite,
keoheite, leucite, pollucite, herscheilite, phacolite,
leonhardite, wellsite, goosecreekite, cowlesite,
zeotypes based on aluminum phosphate, and any zeolites
made by modifications of these structures.
The foregoing description of the specific
embodiments will so fully reveal the general nature of
the invention that others can, by applying current
knowledge, readily modify and/or adapt for various
applications such specific embodiments without
departing from the generic concept, and, therefore,
such adaptations and modifications should and are
intended to be comprehended within the meaning and
range of equivalence of the disclosed embodiments. It
is to be understood that the phraseology or terminology
employed herein i5 for the purpose of description and
not of limitation.
