WO2020161230A1

WO2020161230A1 - Composition for dust control

Info

Publication number: WO2020161230A1
Application number: PCT/EP2020/052975
Authority: WO
Inventors: Zoran Popovic; Johannes ÖHRLEIN; Frank Hellmers; Alexander PAASCHE; Patrik Stenner; Jessica ANTONI
Original assignee: Evonik Operations Gmbh
Priority date: 2019-02-08
Filing date: 2020-02-06
Publication date: 2020-08-13

Abstract

The present invention relates to adust controlling composition comprising water and a mixture of carboxymethylcellulose (CMC) and silica, wherein the CMC and silica have a solid weight ratio of 50:1-20:1.

Description

COMPOSITION FOR DUST CONTROL

FIELD OF THE INVENTION

The present invention relates to a composition and method that are used to control dust generation. In particular, the composition comprises water and a composition of

carboxymethylcellulose (CMC) and silica and this composition is applied to a dust generating surface to prevent dust production.

BACKGROUND OF THE INVENTION

Dust occurs in open-pit mines and unpaved rural roads and poses a major health risk especially in dry seasons. In particular, dry conditions and even light winds can carry away exposed portions of the soil to create airborne dust that contributes to atmospheric pollution.

A simple dust suppression method is to cover the exposed soil with a plastic sheet. This method has several drawbacks, including the cost of materials and the labor involved in covering and uncovering the soil with the sheet. Further, sheets are especially impractical for covering large areas of exposed soil typically created by road construction and also for covering soil that is being actively worked on during construction.

Another common practice in reducing dust occurrence is spraying the surface with water. This practice however must be repeated as soon as the surface becomes dry. Water thus only acts as a temporary binder that holds together loose soil aggregates that may otherwise become airborne as water can quickly leave the exposed dirt surface through a combination of soil absorption and surface evaporation. In hot and dry environments, using only water to reduce dust occurrence may result in the dust surface being continuously wetted to prevent dust production.

In order to thus reduce frequency of water spraying dust control agents can be added to spraying water. Dust control agents typically include at least one chemical, or a mixture of chemicals selected from the group of inorganic salts, polyacrylates, polyacrylamides and surfactants. By dosing dust control products in the range of 0.5-10% (by weight) the frequency of spraying can be reduced. This leads to saving water and time. However, the main drawback of these currently used dust control agents is their low biodegradability and high consumption (dosing).

Accordingly, there is a need in the art for an economic and more efficient method of controlling dust generation and/or dispersion. DESCRIPTION OF THE INVENTION

The present invention attempts to solve the problems above by providing a dust controlling composition that is efficient in controlling dust generation and/or dispersion and that is economic to prepare and use. The dust controlling composition according to any aspect of the present invention may also be biodegradable and since only a small amount of the composition may be needed to control dust, this makes the composition not only economically efficient to use but also reduces the environment impact left by the

composition.

According to one aspect of the present invention, there is provided a dust controlling composition comprising water and a mixture of carboxymethylcellulose (CMC) and silica, wherein the CMC and silica have a solid weight ratio of 50:1 -20:1 .

The CMC dispersed according to any aspect of the present invention is anionic and water- soluble. It is important that the CMC is water-soluble so that the aqueous solutions of CMC have a suitable viscosity to enable them to be easily distributed on the dusty surface. All anionic water-soluble carboxymethylcellulose salts can be used according to any aspect of the present invention. In one example, sodium carboxymethylcellulose may be used. In particular, the polymers (i.e. different CMCs) used according to any aspect of the present invention may have a carboxymethyl degree of substitution (number of carboxymethyl groups per anhydroglucose unit) of about 0.4 to about 1 .2.

When added to aqueous systems, water-soluble CMC tends to agglomerate or form clumps. Agglomeration can be reduced in many cases by adding the polymer to the aqueous system slowly with agitation. In particular, the CMC particles may be made to get wet separately and then added to the aqueous system. In one example, CMC may be added to the vortex of vigorously agitated water. The rate of addition must be slow enough to permit the particles to separate and their surfaces to become individually wetted, but it should be fast enough to minimize viscosity buildup of the aqueous phase while the CMC is being added. In another example, the CMC powder may first be wetted with a water-miscible liquid such as alcohol, glycol, or glycerol that will not cause the CMC to swell. Two to three parts of liquid per part of CMC should be sufficient. The wetted CMC may then be added to the aqueous system. In another method, a dry-blend of CMC with any dry, non-polymeric material may be used in the formulation. The CMC may be less than 20% of the total blend. In yet another example, a water educator may be used to wet the CMC polymer particles rapidly. A polymer solution preparation system (PSP), may then be used in conjunction with a water educator. Any one of these methods may result in a stable, concentrated, aqueous water-soluble polymer carboxymethylcellulose suspension that can be used to incorporate water-soluble carboxymethylcellulose in aqueous solutions readily, without formation of agglomerates or clumps, and which may be handled without the problems associated with dry powder water- soluble carboxymethylcellulose polymers.

The term“Suspension" and "dispersion" may be used interchangeably herein to refer to a system in which solid particles (water-soluble carboxymethylcellulose and/or silica) are dispersed in a liquid (water). It should also be understood that "solution" means a homogenous mixture of a solvent (e.g., water) with a soluble (e.g., dissolved silica, dissolved water-soluble soluble carboxymethylcellulose, etc.).

The silica used according to any aspect of the present invention may be considered a suspension stabilizer. Silica, also known as silicon dioxide, silicic acid or silicic acid anydride is an oxide of silicon with the chemical formula Si0₂, most commonly found in nature as quartz and in various living organisms. The silica used according to any aspect of the present invention may be obtained from fused quartz, fumed silica, silica gel, aerogels and the like.

According to any aspect of the present invention, the solid weight ratio of CMC to silica may be between 50:1 -20:1 . In particular, the solid weight ratio of CMC to silica may be about 50:1 , 45:1 , 40:1 , 35:1 , 30:1 , 25:1 , 20:1 and the like. More in particular, the solid weight ratio of CMC to silica may be 50:1 to 25:1 , 50:1 to 30:1 , 50:1 to 35:1 , 50:1 to 40:1 , 50:1 to 45:1 , 45:1 to 20:1 , 45:1 to 25:1 , 45:1 to 30:1 , 45:1 to 35:1 , 45:1 to 40:1 , 40:1 to 20:1 , 40:1 to 25:1 , 40:1 to 20:1 , 40:1 to 35:1 , 40:1 to 20:1 , 35:1 to 25:1 , 35:1 to 30:1 , 30:1 to 20:1 , or 30:1 to 25:1 . In one example, the dust controlling composition according to any aspect of the present invention may have a CMC and silica in a weight ratio of 30:1 to 20:1 . In particular, the CMC and silica according to any aspect of the present invention may have a weight ratio of about 25:1 .This specific solid weight ratio of CMC to silica according to any aspect of the present invention may result in a dust controlling composition that has an air particle count close to just background noise and a high water retention relative to CMC and silica alone.

The mixture of CMC and silica in the water according to any aspect of the present invention may have a solid weight content of about 2-20%, with the weight percentages referring to the total composition. In particular, the solid weight content of CMC and silica in the water may be in the range between 3-20, 4-20, 5-20, 6-20, 7-20, 8-20, 9-20, 10-20, 1 1 -20, 12-20, 13-20, 14-20, 15-20, 16-20, 17-20, 18-20, 19-20, 2-19, 3-19, 4-19, 5-19, 6-19, 7-19, 8-19, 9-19, I Q- 19, 1 1 -19, 12-19, 13-19, 14-19, 15-19, 16-19, 17-19, 18-19, 2-18, 3-18, 4-18, 5-18, 6-18, 7- 18, 8-18, 9-18, 10-18, 1 1 -18, 12-18, 13-18, 14-18, 15-18, 16-18, 17-18, 2-17, 3-17, 4-17, 5- 17, 6-17, 7-17, 8-17, 9-17, 10-17, 1 1 -17, 12-17, 13-17, 14-17, 15-17, 16-17, 2-16, 3-16, 4-16, 5-16, 6-16, 7-17, 8-16, 9-16, 10-16, 1 1 -16, 12-16, 13-16, 14-16, 15-16, 2-15, 3-15, 4-15, 5- 15, 6-15, 7-15, 8-15, 9-15, 10-15, 1 1 -15, 12-15, 13-15, 14-15, 2-14, 3-14, 4-14, 5-14, 6-14, 7-14, 8-14, 9-14, 10-14, 1 1 -14, 12-14, 13-14, 2-13, 3-13, 4-13, 5-13, 6-13, 7-13, 8-13, 9-13, 10-13, 11-13, 12-13, 2-12, 3-12, 4-12, 5-12, 6-12, 7-12, 8-12, 9-12, 10-12, 11-12, 2-11 , 3-11 , 4-11 , 5-11 , 6-11 , 7-11 , 8-11 , 9-11 , 10-11 , 2-10, 3-10, 4-10, 5-10, 6-10, 7-10, 8-10, 9-10 % and the like, with the weight percentages referring to the total composition.. More in particular, the composition of CMC and silica in the water is about 2, 3, 4, 5, 6, 7, 8, 9, 10,

11 , 12, 13, 14, 15, 16, 17, 18, 19 or 20 % solid weight content, with the weight percentages referring to the total composition.. Even more in particular, the solid weight content of CMC and silica in the water according to any aspect of the present invention is about 5%, with the weight percentages referring to the total composition.. Weight ratios of CMC and silica in the dust controlling composition according to any aspect of the present invention may be maintained at such a ratio as mentioned above such that the solution viscosity is 0.5-1.5 mPas. If the ratio in CMC and silica in water according to any aspect of the present invention is increased any further, then the aqueous solution viscosities will become extremely high or they form a gel. For reasons of this very high viscosity, these polymers cannot normally be pumped or handled (dissolved) in aqueous media when their concentrations exceeds 5-10 weight percent. This is one of the many reasons that the ratio of silica and CMC to water in the dust controlling composition according to any aspect of the present invention is very delicate and must be controlled to result in an efficient and easy to use dust controlling composition according to any aspect of the present invention.

The viscosity of the dust controlling composition according to any aspect of the present invention may be 0.5-1.5, 0.5-1.0, or 1.0-1.5 mPas. In particular, the viscosity may be about 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1 , 1.2, 1.3, 1.4 or 1.5 mPas. The viscosity is especially important to ensure that the dust controlling composition according to any aspect of the present invention is easy to be dispersed in the soil. The viscosity of the composition according to any aspect of the present invention are relatively independent of the molecular weight (or solution viscosity) of the CMC in suspension. Instead, viscosity is proportional to the quantity of CMC present. Further, the suspension viscosity is inversely proportional to the amount of water present. Consequently, to suspend larger amounts of CMC it is necessary to use larger amounts of water.

The viscosity is measured at 20 °C with a spindle CP50-1 49469 at a shear rate of 1- 1000rpm/s on a Modular Compact Rheometer MCR 302 (Anton Paar).

The term "stable" used herein refers to a state where in the dispersed phase (water-soluble carboxymethylcellulose) and aqueous phase do not separate for some minimum time after preparation, or if separation does occur the CMC may be readily redispersed with a minor amount of agitation. Stability is a function of the type of carboxymethylcellulose used, as well as the concentration of carboxymethylcellulose, salt, etc. The suspensions according to any aspect of the present invention are stable as made. They should be stable for at least three hours after preparation. In one example, the dispersion according to any aspect of the present invention may be stable for at least one day after preparation, and particularly stable for at least one month after preparation. The stability of the dispersions according to any aspect of the present invention can be further improved by mixing the dispersion in a

vacuum, so as to remove entrained air. The prolonged stability of the suspensions of this invention permits their preparation at one location and transportation to another location where they are to be used.

The water used according to any aspect of the present invention may be tap water,

deionized water, mineral water and the like. In one example, the water used according to any aspect of the present invention may be a salt solution. In particular, the salt solution may comprise 30 to 60, 40 to 60, or 40 to 50%, by weight of the total salt and water. In one

example, the salt used may be potassium carbonate. The desired concentration of salt in water may vary with the CMC type and quantity.

In one example, other additives may be present in the dust controlling composition according to any aspect of the present invention. In particular, the additive may be selected from the group consisting of pigments, dispersants, surfactants, glycols and thickening agents. These are generally used in amounts up to 10%, or 0.5% to 2%, based on the weight of the total suspension.

As used herein, the term "about", refers to a range of values that are similar to the stated reference value for that condition. In certain examples, the term "about" refers to a range of values that fall within 25, 20, 19, 18, 17, 16, 15, 14, 13, 12, 1 1 , 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 percent or less of the stated reference value for that condition. For example, a weight ratio employed during the composition according to any aspect of the present invention when modified by“about” includes the variation and degree of care typically employed in measuring in an experimental condition in production plant or lab. For example, the weight ratio when modified by“about” includes the variation between batches in multiple experiments in the plant or lab and the variation inherent in the analytical method. Whether or not modified by“about,” the amounts include equivalents to those amounts. Any value stated herein and modified by“about” can also be employed in the present invention as the amount not modified by“about.”

According to a further aspect of the present invention, there is provided a method of

controlling dust dispersion, the method comprising applying the dust controlling composition according to any aspect of the present invention to a dust generating surface. The

composition according to any aspect of the present invention may be sprayed onto the surface or poured onto the surface and is absorbed into the surface where it has been found to bind surface particles to form a relatively hard surface thereby reducing dust production and/or dispersion. The composition used according to any aspect of the present invention may be biodegradable and effective at extreme low dosing for example at 0.02% which is below dosing of the well-known and commonly used commercial products. The dust generating surface may comprise soil. In particular, the dust generating surface may be an unpaved roadway or sport surfaces such as tennis courts. More in particular, the dust generating surface may be an unpaved roadway.

The dust controlling composition according to any aspect of the present invention may be a concentrated version. Before the dust controlling composition is used or applied to the relevant surface, the composition may first be diluted. The dilution factor according to any aspect of the present invention may be anything between 10-5000. In particular the dilution factor may be I Q- 4500, 10-4000, 10-3500, 10-3000, 10-2500, 10-2000, 10-1500, 10-1000, 10-600, 10-550, 10-500, 10-450, 10-400, 10-350, 10-300, 10-250, 10-200, 10-150, 10-100, 100-5000, 100-4500, 100-4000, 100-3500, 100-3000, 100-2500, 100-2000, 100-1500, 100-1000, 100-900, 100-800, 100-700, 100- 600, 100-500, 100-400, 100-300, 100-200, 200-5000, 200-4500, 200-4000, 200-3500, 200-3000, 200-2500, 200-2000, 200-1500, 200-1000, 200-900, 200-800, 200-700, 200-600, 200-500, 200- 400, 200-300, 300-5000, 300-4500, 300-4000, 300-3500, 300-3000, 300-2500, 300-2000, 300- 1500, 300-1000, 300-900, 300-800, 300-700, 300-600, 300-500, 300-400, 400-5000, 400-4500, 400-4000, 400-3500, 400-3000, 400-2500, 400-2000, 400-1500, 400-1000, 400-900, 400-800, 400- 700, 400-600, 400-500, 500-5000, 500-4500, 500-4000, 500-3500, 500-3000, 500-2500, 500-2000, 500-1500, 500-1000, 500-900, 500-800, 500-700, 500-600, 600-5000, 600-4500, 600-4000, 600- 3500, 600-3000, 600-2500, 600-2000, 600-1500, 600-1000, 600-900, 600-800, 600-700, 700-5000, 700-4500, 700-4000, 700-3500, 700-3000, 700-2500, 700-2000, 700-1500, 700-1000, 700-900, 700-800, 800-5000, 800-4500, 800-4000, 800-3500, 800-3000, 800-2500, 800-2000, 800-1500, 800-1000, 800-900, 900-5000, 900-4500, 900-4000, 900-3500, 900-3000, 900-2500, 900-2000, 900-1500, 900-1000, 1000-5000, 1000-4500, 1000-4000, 1000-3500, 1000-3000, 1000-2500, 1000-2000, 1000-1500, 2000-5000, 2000-4500, 2000-4000, 2000-3500, 2000-3000, 2000-2500, 3000-5000, 3000-4500, 3000-4000, 3000-3500, 2500-5000, 2500-4500, 2500-4000, 2500-3500, 2500-3000, 3000-5000, 3000-4500, 3000-4000, 3000-3500, 3500-5000, 3500-4500, 3500-4000, 4000-5000, 4000-4500, and the like. In particular, the dilution factor may be about 5000 resulting in at least a 0.02% dilution of the concentrated version of the composition according to any aspect of the present invention. The diluted dust controlling composition according to any aspect of the present invention may then be applied to the dust generating surface at a coverage level of 0.25- 0.75 liters per square meter of soil surface. In particular, the dust controlling composition is applied to the dust generating surface at a coverage level of about 0.5 liters per square meter of soil surface.

According to another aspect of the present invention, there is provided a use of the dust controlling solution according to any aspect of the present invention to prevent dust generation and/or dispersion.

BRIEF DESCRIPTION OF FIGURES Figure 1 is a graph showing the dust particle count of soils sprayed with different compositions and stored for 3 hours at 40°C.

Figure 2 is a graph showing the water retention in soils sprayed with different compositions and stored for 3 hours at 40°C.

EXAMPLES

The foregoing describes preferred embodiments, which, as will be understood by those skilled in the art, may be subject to variations or modifications in design, construction or operation without departing from the scope of the claims. These variations, for instance, are intended to be covered by the scope of the claims.

Example 1

5% water solution of sodium CMC from the company Mikro-Technik GmbH& Co. KG was

prepared by dissolving in water and tested. The sample had viscosity characteristics (2% solution, Brookfield): 400 - 13000 mPa-s and substitution grade 0,7-0.8. Silica sample was Aerodisp

VW520 N from Evonik. CMC and Silica were tested alone and in mixtures at 0.02% dosing. In mixtures the weight ratio of solid CMC and solid silica was varied from 1 :4 to 25:1 (CMC to Silica).

Mine soil from a gold mine was used as a test soil. The soil was placed in aluminum trays (200g soil) and sprayed with water solutions (13ml containing 0,02% of dust control agent: coverage: 0.5 liter per square meter of soil). The soil was finally stored at 40°C and 70% rel. humidity for 3 hours.

Two parameters were tested: 1) particle count in air and 2) water retention in soil. The tests used to measure these parameters are at least disclosed in:

- Huertas Jl et al, Environ Sci Pollut Res Int. 2011 ; 19(7):2784-94 and

- Ismet, Ozdemir. (2015). A Decision Support System and Cost-Performance Analysis for Dust

Control at Open-Pit Coal Mines. Retrieved from http://publications.rwth-aachen.de/record.

As reference dust control agent tap water was used. For particle count references, the particle count of the air (background noise) was measured and for negative control soil that was not sprayed was used. The ideal dust control agent should contribute to prolonged periods of no dust formation in the air and to prolonged water retention in soil.

The results of parameter 1 , the dust particle count is shown in Figure 1 and the results of

parameter 2, water retention in soil is presented in the Figure 2.

As can be seen from figure 1 , CMC alone or in mixture with silica (volume ratios: 10:1 and 100:1) yielded air particle count close to background noise. At the same time, when the amount of silica increased, the water retention of the composition also decreased (figure 2). The addition of silica in the volume ratio of 100:1 (CMC to Silica) yielded the highest water retention (better than of CMC and Silica alone) and the lowest particle count in air.

Dust control compositions comprising CMC (viscosity characteristics for 2% solution, Brookfield:

400 - 13000 mPa-s and substitution grade 0.7-0.8.) and silica mixture in the volume ratio 100:1

(5% CMC and 0,005% of Silica) yields the best dust control results when dosed at 0.02% in tap water and sprayed on mine soil.

Claims

1 . A dust controlling composition comprising water and a mixture of carboxymethylcellulose (CMC) and silica, wherein the CMC and silica have a solid weight ratio of 50:1 -20:1 .

2. The dust controlling composition according to claim 1 , wherein the CMC and silica have a weight ratio of 30:1 to 20:1 .

3. The dust controlling composition according to either claim 1 or 2, wherein the CMC and silica have a weight ratio of about 25:1 .

4. The dust controlling composition according to any one of the preceding claims, wherein the mixture of CMC and silica in the water has a 2-20% solid weight content.

5. The dust controlling composition according to any one of the preceding claims, wherein the solid weight content of CMC and silica in the water is about 5%.

6. The dust controlling composition according to any one of the preceding claims, wherein the viscosity is 0.5-1 .5 mPas.

7. The dust controlling composition according to any one of the preceding claims, wherein the viscosity is about 1 mPas.

8. A method of controlling dust dispersion, the method comprising applying the dust

controlling composition according to any one of claims 1 to 7 to a dust generating surface.

9. The method according to claim 8, wherein the dust generating surface comprises soil.

10. The method according to either claim 8 or 9, wherein the dust generating surface

comprises an unpaved roadway.

1 1 . The method according to any one of claims 8 to 10, wherein the dust controlling

composition is applied to the dust generating surface at a coverage level of 0.25-0.75 liters per square meter of soil surface.

12. The method according to any one of claims 8 to 10, wherein the dust controlling

composition is applied to the dust generating surface at a coverage level of about 0.5 liters per square meter of soil surface.

13. Use of the dust controlling solution according to any one of claims 1 -7 to prevent dust generation and/or dispersion.