WO1992010439A1

WO1992010439A1 - Process for producing concrete and mortars

Info

Publication number: WO1992010439A1
Application number: PCT/CA1991/000440
Authority: WO
Inventors: Daniel A. Mackie; Richard A. Kuntze
Original assignee: Mackie Daniel A; Kuntze Richard A
Priority date: 1990-12-10
Filing date: 1991-12-10
Publication date: 1992-06-25
Also published as: AU9064691A; GB9026779D0

Abstract

A process is disclosed for rendering toxic heavy metals in neutralized sludges substantially inert in a mortar or concrete mass by substituting said aqueous neutralized sludges for a cement or pozzolanic material in an effective amount up to 80 % by volume of said cement or pozzolanic material in a mortar or concrete mix, mixing with an effective amount of water of hydration, and allowing the resulting mixture to cure to a solid mortar or concrete mass. The mass of hydration can be replaced by said aqueous neutralized sludge in an effective amount of up to 100 % by volume of the water of hydration.

Description

PROCESS FOR PRODUCING CONCRETE AND MORTARS

FIELD OF THE INVENTION

This invention relates to a process for producing cementitious mixes such as concretes and mortar and, more particularly, relates to a process for producing concretes and mortars using sludges containing heavy metals from acidic waste neutralization.

BACKGROUND OF THE INVENTION

It is common practice to treat runoff from mines, tailings ponds, and other areas where exposure to the environment has created acidic water and wastes containing toxic metals by adding alkalines, such as limestone, calcined limestone, calcium hydroxides, or caustic soda to increase the pH of the water to levels that are not harmful to the environment. Such treatment creates gelatinous precipitates which are primarily gypsum or gypsum-like compounds and hydroxides of metals such as iron, nickel, copper, zinc and the like. These precipitates settle to the bottom of water reservoirs, ponds and lakes as an aqueous suspension containing 2 - 5% solids by volume and eventually must be disposed of or rendered harmless to the environment to avoid contamination by the soluble, possibly toxic metals.

Dewatering of the sludges is a very costly process, involving large settling ponds, thickeners, filters and dryers. Also, the product formed consists of very fine, dusty gypsums, which if placed into the environment, create dust problems. Further, the gypsums often contain toxic metals as metal hydroxides, which if allowed to leach into the environment, can cause metal levels in the water table that are harmful to plant, animal, and human health.

Sludges which settle naturally can contain up to 98% water, requiring huge storage areas. Dewatering without heat addition can be accomplished with thickeners, filters and other means to about 30% to 45% solids by volume. This reduces the storage volume requirements in basins or ponds enormously, but the cost of building dams and the like is still substantial. The mining industry, in particular, has been searching for.a means of further dewatering, disposing of this material, and rendering it harmless to the environment. Canadian Patent No. 1,024,277 for example discloses a process for solidification of sludges. This method forms soils or weak stones through the formation of complex silicates. Other methods tried are bitumen addition, mixing with spils, and many other stabilization techniques, none of which has commercial applications.

It is known to combine neutralized sludges with clay and to calcine or sinter the resulting mixture to fuse the metal hydroxides into inert silicates or expanded ceramics, such as disclosed in U.S. Patents

Nos. 4,872,993 and 4,882,067. These processes are costly in that considerable energy must be expended to heat the waste materials to high temperatures to form inert aggregates.

Gypsum is added in rock form to cement clinkers during grinding in the commercial manufacture of Portland cements for concrete and mortar as a retarder of the initial setting of the concrete or mortar. Excessive quantities of gypsum added to cement, however, have been found to weaken the resulting concrete or mortar. Fixation of toxic chemicals in concrete is generally known as a means to prevent or limit leaching of toxic chemicals from natural rainfall and ground waters. The use of the toxic chemicals themselves, such as in heavy metal hydroxides found in neutralization sludges, in place of and substitute for Portland cement, slags, or other pozzolanic materials in conjunction with the gypsums in the sludges, has not been practiced.

This invention relates to the use of neutralization sludges by mixing the sludges with Portland cement, flyash, slags or other pozzolanic materials and with aggregates to form mortars and concrete. SUMMARY OF THE INVENTION

It has been found surprisingly that aqueous sludges from neutralization of acid wastes, when used in place of a portion of the cement and when used as a substitute for a portion of water of hydration for mixing concrete or mortars in quantities that would be considered excessive in terms of gypsum addition to produce a strong concrete or mortar, produce a concrete and mortar that is equal to or superior in strength to concrete and mortars made with ordinary cement and water. In addition, heavy metals present in the sludge are chemically and/or physically combined with the concrete or mortar to render the heavy metals chemically inert and to essentially prevent or at least reduce the rate at which the heavy metals can enter the environment.

In its broad aspect, the invention relates to a process for rendering heavy toxic metals in neutralized sludges substantially inert in a mortar or concrete mass comprising substituting said aqueous neutralized sludge containing heavy toxic metal for a cement or pozzolanic material in an effective amount up to 80% by volume of said cement or pozzolanic material, in a mortar or concrete mix, mixing with an effective amount of water of hydration, and allowing the resulting mixture to cure to a solid mortar or concrete mass..

In another aspect, the invention relates to a process in which said water of hydration is replaced by an effective amount of up to 100% by volume of aqueous neutralized sludge, preferably about 50% by volume of acgueous neutralized sludge. The invention contemplates and includes the use of acid neutralization sludges with any pozzolanic material such as flyash or slags for the purpose of forming concrete or mortar. Sludges produced by lime neutralization of acids from any of several processes can be used in the process of the invention and may be used in conjunction with waste from many processes as a means of capturing environmentally-hazardous materials and rendering them stable.

DESCRIPTION OF THE PROCESS AND PRODUCT OF THE INVENTION

Neutralized acid sludges and the like waste sludges containing heavy and toxic metals are produced from a variety of sources. For example, sludges are produced by neutralized mine waste run-off water, mine tailings and neutralized excess process water, neutralized solutions of run-off waters from exposed pyrite or other acid- producing surfaces at fresh road and construction sites, neutralized pickle liquors, plating waste, chemical plant waste, water treatment plant waste, wet scrubber effluent neutralization sludges and sludges from power plants using powdered limestone, calcined lime or hydrated lime for gaseous sulphur dioxide control.

The aqueous sludges, preferably dewatered to a range of 20 - 45% by volume solids, are substituted for up to 80%, preferably up to 30%, by volume of Portland cement or pozzolanic material such as flyash or slags used in the forming of concrete, or the like cementation mixes. The water content of the sludge provides the water necessary for hydration of the cement or the pozzolanic material. The resulting mixture can be mixed with an aggregate such as sand or sand and gravel in a conventional manner of, for example, 1 part cement or equivalent, 2 parts sand and 3 parts aggregate. It is has been found that a cementitious mix of, for example, 10 or 20% of a 35% solids by volume neutralized sludge mixed with Portland cement produces a compressive strength at the end of 28 days comparable to or better than a corresponding standard mix of Portland cement with water.

Large volumes of sludge substituted for Portland cement, for example, 60% to 80% substitutions of sludge for Portland cement, permit production of weak concretes that are suitable for making decorative stones or for solidifying tailings in a mine in order to prevent or limit runoff of metal hydroxides.

It .has also been found that by using sludges solely as a replacement or partial replacement of water of hydration, preferably in a ratio of about 1:1 by volume of sludge to water but using a standard portion of Portland cement, allows production of concrete that has a compressive strength at the end of 28 days comparable to or better than a corresponding standard mix of Portland cement with water. The process of the invention will now be described with reference to the following non-limitative examples. EXAMPLE 1

Tests were conducted on a standard concrete sample and on concrete samples made from cement - sludge compositions for evaluating compressive strengths in accordance with CSA Standard CAN3-A23.2-9C-M90 entitled "Compressive Strength of Cylindrical Concrete Specimens". The standard concrete sample tested consisted of 1 part cement (Type 10 Portland cement) , 2 1/4 parts sand and 3 parts 0.95 cm (3/8") aggregate by volume, mixed with water of hydration in a ratio of 250 ml of cement to 250 ml of water. The sludge was obtained from La Mine Doyon and was densified to 39% solids by weight. The samples were cylinders having a diameter of 5.87 cm (2 5/16") and a height of 14.29 cm (5 5/8") which were cured for 28 days.

Test results are shown in Table 1. Sample 1 was a standard concrete test for a standard value and Samples 2-9 were based on progressively increasing replacements of cement by the slurry densified to 39% solids by volume. TABLE 1

Sample Description Sludge Strength Percent psi by volume

1 Standard Concrete 0% 2710

2 Cement:Sludge 225 ml:25 ml 10% 3320

3 C:S 200:50 20% 2260

4 C:S 175:75 30% 2180

5 C:S 150:100 40% 1970

6 C:S 125:125 50% 1470

7 C:S 100:150 60% 1210

8 C:S 75:175 70% 750

9 C:S 50:200 80% 440

EXAMPLE 2

Comparative tests were conducted with the same materials under the same conditions as in Example 1 the quantity of 250 ml of cement was maintained constant and various amounts of aqueous neutralized slurry densified to 39% solids by volume were substituted for 30% to 100% by volume of the water hydration. Test results are shown in Table 2.

TABLE 2

Sample Description Sludge Strength Percent psi by volume

10 350 ml. sludge used 100% 1760 in place of water

11 125 ml. sludge 125 ml. water 50% 3330

12 175 ml. sludge 75 ml. water 70% 2840

13 75 ml. sludge 175 ml. water 30% 2340 Optimum results were obtained with a 50% by volume substitution of aqueous neutralized sludge for the water of hydration, a 70% by- volume substitution yielding a compressive strength superior to the strength of the standard sample No. 1.

The present invention provides a number of important advantages. A portion of cement in a mortar or concrete mix or of the water of hydration in said mix can be replaced by a neutralized acid slurry to produce a resulting mortar or concrete which not only has a compressive strength comparable, to that of a conventional mortar or concrete produced by the use of Portland cement but also the heavy toxic metals present in the neutralized sludge ^"has been rendered essentially inert and resistant to leaching by ground waters. The resulting concrete can be formed into end products such as walls, building structures, concrete blocks, sidewalks or roadways. Valuable energy otherwise needed to sinter or fuse the heavy toxic metals into a granular product is bypassed, the heavy toxic metals being directly converted into an inert form in a mortar or concrete mass.

Claims

1. - A process for rendering heavy toxic metals in neutralized sludges substantially inert in a mortar or concrete mass comprising substituting said aqueous neutralized sludge containing heavy toxic metal for a cement or pozzolanic material in an effective amount up to 80% by volume of said cement or pozzolanic material in a mortar or concrete mix, mixing with an effective amount of water of hydration, and allowing the resulting mixture to cure to a solid mortar or concrete mass.

2. A process as claimed in claim 1, in which up to 30% by volume of the aqueous neutralized sludge is substituted for the cement or pozzolanic material.

3. A process as claimed in claim 1, replacing said water of hydration with an effective amount of said aqueous neutralized sludge.

4. A process as claimed in claim 1 replacing said water of hydration with said aqueous neutralized sludge in an effective amount.up to 100% by volume of the water of hydration.

5. A process as claimed in claim 1, replacing about 50% by volume of said water of hydration with said aqueous neutralized sludge.

6. A process as claimed in any of the foregoing claims, in which said neutralized sludge is a densified neutralized acid sludge from at least one of neutralized mine waste run-off water, mine tailings and excess mine process water, neutralized run-off waters from pyrite deposits, neutralized pickle liquors, plating waste, chemical plant waste, water treatment plant waste, wet scrubber effluent and neutralized sludges from power plants.

7. A process as claimed in the foregoing claims in which the aqueous neutralized sludge has been dewatered to a range of 20-45% by volume solids.

8. A cementitious product produced by substituting a neutralized aqueous sludge containing heavy metals in an amount of up to 80% by volume of cement or pozzolanic material in a mortar concrete mix and allowing said mixture to cure to a solid mass.

9. A cementitious product produced by replacing up to 100% by volume of water of hydration in a cementitious mix with an aqueous neutralized sludge.

10. A cementitious product as claimed in claim 9 in which 50% by volume of water of hydration is replaced by an aqueous neutralized sludge.