WO2017072696A1

WO2017072696A1 - Stabilizaton of bodies of particulate material

Info

Publication number: WO2017072696A1
Application number: PCT/IB2016/056475
Authority: WO
Inventors: Michael Windsor Symons
Original assignee: Sappi Southern Africa Ltd
Priority date: 2015-10-27
Filing date: 2016-10-27
Publication date: 2017-05-04
Also published as: ZA201902823B; WO2017072689A1

Abstract

The invention provides a method of stabilizing a body of particulate material. The method includes applying to at least one of exposed surface particulate material and subsurface particulate material of a body of particulate material a liquid treatment composition comprising one or more alkali metal silicates, and spent soda liquor. The method may further include allowing or causing the liquid treatment composition to harden and thus bind at least some of the exposed surface particulate material and/or subsurface particulate material of the body of particulate material, thereby stabilizing the body of particulate material.

Description

STABILIZATION OF BODIES OF PARTICULATE MATERIAL

FIELD OF THE INVENTION

THIS INVENTION relates to the stabilization of bodies of particulate material. The invention provides methods of stabilizing a body of particulate material. The invention also provides compositions for stabilizing a body of particulate material. The invention further provides use of the compositions in stabilizing a body of particulate material.

BACKGROUND TO THE INVENTION

UNSTABLE BODIES OF PARTICULATE MATERIAL, such as unsealed bodies of in situ soil, unsealed heaps of particulate material (e.g. heaps of waste material), surfaces of bodies of compacted in situ soil which comprise loose particles, and the like, specifically as encountered at mining sites, are hazardous from various perspectives. For instance, loose particles can easily become airborne and can give rise to hazardous dust, often in copious quantities. In mining applications in particular, this dust may be siliceous, may contain manganese fines, chromite, and/or coal. Inhalation thereof can give rise to silicosis, manganosis, and other lung disorders. In addition, such dust can rapidly clog vehicle air filters and result in engine damage. Furthermore, in rainy weather, loose particles can give rise to creamy surfaces which can negatively affect vehicle handling and stability, adding to the danger that is already associated in mining applications with the size of the vehicles that are used. In addition, such unstable surfaces are readily eroded by natural elements such as wind and rain, negatively affecting their ability to support load, e.g. in the case of unsealed or unpaved roads.

Managing dust, on roadways in particular, conventionally involves the application of bitumen emulsions, typically of a penetration index in the range 40 to 70. Sodium or calcium ligno- sulphonates are also used, as are molasses and lime. Other natural polymers that are also suitable include starches, collagens, gelatins, dextrins and the like.

There are several difficulties with conventional treatments. Among them are included high cost, residual odour, and unpleasant colour. More significantly, and especially in the case of bitumen emulsions and ligno-sulphonates which are in liquid form, logistics play a major part in the treatment cost since large volumes of pre-prepared liquid treatment agent need to be transported to sites requiring treatment. A further difficulty is that in desert environments, the repeated application of water borne suppressants is very wasteful of water.

There is therefore a need for a method of dust suppression, particularly for unpaved and unsealed surfaces of bodies of material, in which binder systems can be transported in a dry form, in the interests of better logistics, and made up into liquid treatment agents close to the point of application.

In addition, it is advisable that whatever binder system is utilized, it can be converted from the liquid phase either to an insoluble phase, or to a gel, or to a semi-solid phase, and that after desiccation the binder material is either waterproof or selectively, to a controllable degree, water insoluble.

It is also important that the treatment method is environmentally friendly, and not dangerous to wildlife and that the dust that may be created on subsequent road usage is not hazardous.

It is furthermore desired that treatments of unstable bodies of particulate material not only manage dust formation, which focuses on treatment of exposed surfaces, but also stabilizes the underlying body of particulate material against erosion by improving its mechanical characteristics. The present invention seeks to provide a treatment that addresses, inter alia, the abovementioned challenges associated with unstable bodies of particulate material.

SUMMARY OF THE INVENTION IN ACCORDANCE WITH A FIRST ASPECT OF THE INVENTION IS PROVIDED a method of stabilizing a body of particulate material, the method including

applying to at least one of exposed surface particulate material and subsurface particulate material of a body of particulate material a liquid treatment composition comprising one or more alkali metal silicates, and

spent soda liquor; and

allowing or causing the liquid treatment composition to harden and thus bind at least some of the exposed surface particulate material and/or subsurface particulate material of the body of particulate material, thereby stabilizing the body of particulate material. "Stabilization" in the sense used in this specification is not limited to, but expressly includes dust suppression, typically by applying the liquid treatment composition, i.e. the one or more alkali silicates and the spent soda liquor separately or in admixture, to exposed surface particulate material of the body of particulate material and then obtaining the stabilized body of particulate material by geopolymerisation or desiccation of the one or more alkali silicates and polymerization of the spent soda liquor; and

layer stabilization, which includes applying the liquid composition, i.e. the one or more alkali silicates and the spent soda liquor separately or in admixture, to exposed surface particulate material and subsurface particulate material up to a desired depth, e.g. by blending, and then obtaining the stabilized body of particulate material by geopolymerisation or desiccation of the one or more alkali silicates and polymerization of the spent soda liquor.

Generally, in this specification, the "body" of particulate material need not be an independent body. It may be a part of a larger volume of particulate material, e.g. a part of a volume of soil. It may, in some cases, be necessary to stabilize only a part of such a larger volume of particulate material, e.g. a pre-formed unpaved road in a larger area of land comprising particulate material. Spent soda liquor is also referred to as black liquor and is a by-product produced from the soda wood pulping process in the pulp and paper industry.

The spent soda liquor may, in particular, be an unsulfonated spent soda liquid, as opposed to a lignosulphonate for example.

The one or more alkali metal silicates and the spent soda liquor may be applied to the exposed surface particulate material and/or the subsurface particulate material of the body of particulate material

separately and sequentially; or

separately and concurrently.

Alternatively, the one or more alkali metal silicates and the spent soda liquor may be applied to the exposed surface particulate material and/or the subsurface particulate material of the body of particulate material concurrently and jointly, i.e. as a mixture thereof.

The one or more alkali metal silicates and spent soda liquor are, separately or jointly, preferably applied to the exposed surface particulate material and/or subsurface particulate material of the body of particulate material in liquid form. "Liquid form" is regarded as including concentrates, dilutions, solutions, dispersions, colloids and emulsions. In the case of the one or more alkali metal silicates, the liquid form is typically a dispersion and in the case of spent soda liquor the liquid form is typically a concentrate. The one or more alkali metal silicates may be selected from sodium silicates, potassium silicates, and mixtures thereof.

The sodium silicate may have a silica to sodium oxide ratio of 2:1 to 3.3:1 .

The potassium silicate may have a silica to potassium oxide ratio of 1 .45:1 to 2.55:1 .

The sodium silicate may be sodium silicate in water, i.e. in liquid form, at a concentration in the range of from 1 to 40% solids by weight, based on the combined weight of sodium silicate and water. In other words, the "sodium silicate" of the liquid treatment composition may be "sodium silicate in water". Reference hereinafter to sodium silicate should therefore be regarded as including sodium silicate in water. Thus, when for example a weight or volume % is provided for sodium silicate, the weight or volume % evenly applies to a mixture of sodium silicate in water. For example, a mixture of 10% sodium silicate and 90% spent soda liquor by volume includes a mixture of 10% of a mixture of sodium silicate in water and 90% of soda liquor by volume.

The potassium silicate may be potassium silicate in water, i.e. in liquid form, at a concentration in the range of from 1 to 30% solids by weight, based on the combined weight of water and potassium silicate. In other words, the "potassium silicate" of the liquid treatment composition may be "potassium silicate in water". Reference hereinafter to potassium silicate should therefore be regarded as including potassium silicate in water. Thus, when for example a weight or volume % is provided for potassium silicate, the weight or volume % evenly applies to a mixture of potassium silicate in water. For example, a mixture of 10% potassium silicate and 90% spent soda liquor by volume includes a mixture of 10% of a mixture of potassium silicate in water and 90% of soda liquor by volume. The one or more alkali metal silicates may comprise sodium silicate and potassium silicate in a ratio of 3:1 by volume, separately or as a mixture. When the sodium silicate and potassium silicate are in water, the ratio of 3:1 would therefore comprise three parts of sodium silicate in water to one part of potassium silicate in water.

A dry form of sodium silicate may be used to form sodium silicate in water, for providing the liquid treatment composition. A typical suitable dry form is, e.g., SP33 or Britesil C335 by PQ Corporation with a ratio of Si0₂ to Na₂0 of 3.3:1 , 84% solids, 64.47% Si0₂ and 19.53% Na₂0. A pre-prepared wet form of sodium silicate, i.e. sodium silicate in water, is preferred. A typical suitable wet form is, e.g., code 3379 sodium silicate with a weight ratio of Si0₂ to Na₂0 of 3.3:1 , 37.88% solids, 29.07% Si0₂ and 8.81 % Na₂0.

The treatment composition may comprise the one or more alkali metal silicates, e.g. as sodium silicate in water, as potassium silicate in water, or as a 3:1 mixture of sodium silicate in water and potassium silicate in water, in the range of from 10 to 80% by volume, based on the joint volume of the one or more alkali metal silicates and the spent soda liquor.

The treatment composition may comprise the spent soda liquor in the range of from 20 to 90% by volume, based on the joint volume of the one or more alkali metal silicates and the spent soda liquor.

The spent soda liquor may have a pH in the range of from 1 1 to 13, more preferably 12 to 13. The spent soda liquor may have a dissolved alkali soluble lignin content in the range of from 6 to 9% by weight.

The spent soda liquor may have a solids content of from 17 to 25% by weight. The spent soda liquor may be used in solid form to provide spent soda liquor in liquid form, e.g. as a solution or suspension. For example, the spent soda liquor may be in powder form. Such a powder form may have been obtained by spray-drying concentrated spent soda liquor.

The particulate material of the body of particulate material may be compacted or loose.

The body of particulate material, as referred to in this specification generally, may, for example, be an area of land, e.g. bare land or a bed of a forest, a body or bed of in situ soil, a heap or bed of dumped particulate material, e.g. waste material from a mining operation or mine tailings, a pre-formed unpaved road, sand, etc.

The method may include applying to exposed surface particulate material and/or subsurface particulate material of the body of particulate material a gelling, or hardening, agent for the one or more alkali metal silicates. The use of spent soda liquor in some cases obviates the requirement to use a gelling agent, and the use of a gelling agent is therefore optional. Whether or not use of a gelling agent is preferred depends on the characteristics of the spent soda liquor, specifically if these characteristics fall outside of the ranges defined above for the spent soda liquor, and the characteristics of the body of particulate material, e.g. its acidity.

The gelling agent may be selected from calcium oxide, calcium chloride, aluminum and magnesium salts, bicarbonates and other acid salts, zincates and acidic gases.

The gelling agent may be applied separately from the one or more alkali metal silicates, or in admixture with the one or more alkali metal silicates. When in admixture with the one or more alkali metal silicates, quantitfication of the gelling agent may be selected such that the mixture does not gel within a predetermined time period, e.g. 4 hours, thereby to allow time for application of the mixture of the one or more alkali metal silicates and the gelling agent to the body of particulate material before gelling of the one or more alkali metal silicates, for gelling to occur after application to the body of particulate material.

The coherence and gelling time of the one or more alkali metal silicates can be varied within wide ranges, depending on the grade of the one or more alkali metal silicates or gelling agent that is used. Therefore, for example, the gelling agent can be applied first and the one or more alkali metal silicates second, or the one or more alkali metal silicates can be applied first and the gelling agent second, or, as a further alternative, delayed action gelling agents or precursors thereof can be added to the one or more alkali metal silicates for gelling thereof to be delayed for a sufficient length of time prior to application.

The method may also include applying a thermoplastic polymer to exposed surface particulate material and/or subsurface particulate material of the body of particulate material, separately of and sequentially with, or separately of and concurrently with, or jointly and concurrently with, i.e. in admixture with, the liquid treatment composition, that is the one or more alkali metal silicates and/or the spent soda liquor.

The thermoplastic polymer may be in solution in water, in dispersion in water, or may be an emulsion. Such dispersion may comprise from 40 to 70%, more preferably 50 to 65% of the thermoplastic polymer by weight.

Examples of thermoplastic polymers are vinyl polymers and polymers of acrylates and methacrylates. Several monomers are used in the manufacture of these vinyl polymers, particularly the acrylates and methacrylates, but styrene and vinyl acetates and vinyl chloride can also be used. Co-polymers or any two or more of these polymers can then be employed.

Styrene butadiene copolymer latexes, such as Synthomer 29Y40, can for example also be used, or a styrene butadiene rubber as such. The method may include applying the treatment composition to exposed surface particulate material and/or subsurface particulate material of the body of particulate material such that, on a dry basis, the one or more alkali silicates and dry material content of the spent soda liquor of the liquid treatment composition that is applied to the exposed surface particulate material and/or subsurface particulate material of the body of particulate material is in a quantity of 0.5 to 2% of the weight of the exposed surface particulate material and/or subsurface particulate material of the body of particulate material to be treated. Application of the liquid treatment composition, the gelling agent and the thermoplastic polymer, respectively or jointly, to the exposed surface particulate material of the body of particulate material may be by surface spraying liquid forms of one or a blend thereof. Application of the liquid treatment composition, the gelling agent and the thermoplastic polymer, respectively, to the subsurface particulate material of the body of particulate material may be by blending to a predetermined depth, e.g. 200mm, liquid forms of one or a blend thereof with the subsurface particulate material.

Application, and particularly blending of the liquid treatment composition or any of the other adjunct agents with a layer of subsurface particulate material of the body of particulate material may require a prior step of loosening the subsurface particulate material, e.g. by scarifying.

The method may also include consolidating and/or compacting the body of particulate material prior to and/or subsequent to application of the liquid treatment composition to the body of particulate material.

The liquid treatment composition is preferably a solution of the one or more alkali metal silicates and the spent soda liquor in water. In essence, it is an added benefit of the invention that water is preferred as carrier medium, since the components of the liquid treatment composition are miscible in water. Hence, the invention prefers "solutions" which operate at the molecular level rather than "dispersions" or "emulsions". Emulsions typically comprise dispersed particles. When it comes to binding or stabilising very small/fine particles - solutions which operate at the nano or molecular level are more effective at binding and stabilising compared with emulsions which operate in the larger dispersed particle phase.

IN ACCORDANCE WITH A SECOND ASPECT OF THE INVENTION IS PROVIDED a treatment composition for stabilizing a body of particulate material, the composition comprising one or more alkali metal silicates, and

spent soda liquor.

The composition may be a liquid composition, i.e. a mixture of the one or more alkali metal silicates in liquid form and the spent soda liquor in liquid form. These liquid forms may be as hereinbefore described in accordance with the method of the invention.

The one or more alkali metal silicates may be selected from sodium silicates, potassium silicates, and mixtures thereof.

The sodium silicate may have a silica to sodium oxide ratio of 2:1 to 3.3:1 .

The sodium silicate may be sodium silicate in water, i.e. in liquid form, at a concentration in the range of from 6 to 40% solids by weight, based on the combined weight of sodium silicate and water. In other words, the "sodium silicate" of the liquid treatment composition may be "sodium silicate in water". As in the method of the invention hereinbefore described, reference hereinafter to sodium silicate should therefore be regarded as including sodium silicate in water. Thus, when for example a weight or volume % is provided for sodium silicate, the weight or volume % evenly applies to a mixture of sodium silicate in water. For example, a mixture of 10% sodium silicate and 90% spent soda liquor by volume includes a mixture of 10% of a mixture of sodium silicate in water and 90% of soda liquor by volume. The potassium silicate may be potassium silicate in water, i.e. in liquid form, at a concentration in the range of from 6 to 30% solids by weight, based on the combined weight of potassium silicate and water. In other words, the "potassium silicate" of the liquid treatment composition may be "potassium silicate in water". Reference hereinafter to potassium silicate should therefore be regarded as including potassium silicate in water. Thus, when for example a weight or volume % is provided for potassium silicate, the weight or volume % evenly applies to a mixture of potassium silicate in water. For example, a mixture of 10% potassium silicate and 90% spent soda liquor by volume includes a mixture of 10% of a mixture of potassium silicate in water and 90% of soda liquor by volume. The one or more alkali metal silicates may comprise sodium silicate and potassium silicate in a ratio of 3:1 by volume, separately or as a mixture. When the sodium silicate and potassium silicate are in water, the ratio of 3:1 would therefore comprise three parts of the sodium silicate in water to one part of the potassium silicate in water. A dry form of sodium silicate may be used to form sodium silicate in water, for providing the treatment composition. A typical suitable dry form is, e.g., SP33 or Britesil C335 by PQ Corporation with a ratio of Si0₂ to Na₂0 of 3.3:1 , 84% solids, 64.47% Si0₂ and 19.53% Na₂0.

A pre-prepared wet form of sodium silicate, i.e. sodium silicate in water is preferred. A typical suitable wet form is, e.g., code 3379 sodium silicate with a weight ratio of Si0₂ to Na₂0 of 3.3:1 , 37.88% solids, 29.07% Si0₂ and 8.81 % Na₂0. The treatment composition may comprise the one or more alkali metal silicates, e.g. as sodium silicate in water, potassium silicate in water, or as a 3:1 mixture of sodium silicate in water and potassium silicate in water, in the range of from 10 to 80% by volume, based on the joint volume of the one or more alkali metal silicates and the spent soda liquor.

The treatment composition may comprise the spent soda liquor in the range of from 20 to 80% by volume, based on the joint volume of the one or more alkali metal silicates and the spent soda liquor. The spent soda liquor may have a pH in the range of from 1 1 to 13, more preferably 12 to 13.

The spent soda liquor may have a dissolved alkali soluble lignin content in the range of from 6 to 9% by weight. The spent soda liquor may have a solids content of from 17 to 25% by weight.

The spent soda liquor may be used in solid form to provide spent soda liquor in liquid form, e.g. as a solution or a suspension. For example, the spent soda liquor may be in powder form. Such a powder form may have been obtained by spray-drying concentrated spent soda liquor.

The body of particulate material may be as hereinbefore described in accordance with the method of the invention.

The composition may include a gelling, or hardening, agent for the one or more alkali metal silicates. The inclusion of spent soda liquor in some cases obviates the requirement to add a gelling agent, however, and inclusion of the gelling agent is therefore optional. Whether or not inclusion of a gelling agent is preferred depends on the characteristics of the spent soda liquor, specifically if these characteristics fall outside of the ranges defined above for the spent soda liquor, and the characteristics of the body of particulate material, e.g. its acidity.

Quantification of the gelling agent in the composition may be such that the mixture does not gel within a predetermined time period, e.g. 4 hours, thereby to allow time for application of the mixture of the one or more alkali metal silicates and the gelling agent to the body of particulate material before gelling of the one or more alkali metal silicates, for gelling to occur after application to the body of particulate material. For example, delayed action gelling agents or precursors thereof can be included in the composition for gelling of the one or more alkali metal silicates to be delayed for a sufficient length of time prior to application. The composition may also include a thermoplastic polymer.

The thermoplastic polymer may be in dispersion in water. Such dispersion may comprise from 40 to 70%, more preferably 50 to 65% of the thermoplastic polymer by weight. Examples of thermoplastic polymers are vinyl polymers and polymers of acrylates and methacrylates. Several monomers are used in the manufacture of these vinyl polymers, particularly the acrylates and methacrylates, but styrene and vinyl acetates and vinyl chloride can also be used. Co-polymers or any two or more of these polymers can then be employed. Styrene butadiene copolymer latexes, such as Synthomer 29Y40, can for example also be used, or a styrene butadiene rubber as such. The liquid treatment composition is preferably a solution of the one or more alkali metal silicates and the spent soda liquor in water. In essence, it is an added benefit of the invention that water is preferred as carrier medium, since the components of the liquid treatment composition are miscible in water. Hence, the invention prefers "solutions" which operate at the molecular level rather than "dispersions" or "emulsions". Emulsions typically comprise dispersed particles. When it comes to binding or stabilising very small/fine particles - solutions which operate at the nano or molecular level are more effective at binding and stabilising compared with emulsions which operate in the larger dispersed particle phase. IN ACCORDANCE WITH A THIRD ASPECT OF THE INVENTION is provided use of a treatment composition of the second aspect of the invention in stabilizing at least one of exposed surface particulate material and subsurface particulate material of a body of particulate material. The use may occur in accordance with the method hereinbefore described.

IN ACCORDANCE WITH A FOURTH ASPECT OF THE INVENTION IS PROVIDED a method of stabilizing a body of particulate material, the method including applying to at least one of exposed surface particulate material and subsurface particulate material of a body of particulate material a liquid treatment composition comprising

a thermoplastic polymer, and

spent soda liquor; and

allowing or causing the liquid treatment composition to harden and thus bind at least some of the exposed surface particulate material and/or subsurface particulate material of the body of particulate material, thereby stabilizing the body of particulate material.

The thermoplastic polymer and the spent soda liquor may be as hereinbefore described in accordance with the first and second aspects of the invention. The thermoplastic polymer and the spent soda liquor may be applied to the exposed surface particulate material and/or the subsurface particulate material of the body of particulate material

separately and sequentially; or

separately and concurrently.

Alternatively, the thermoplastic polymer and the spent soda liquor may be applied to the exposed surface particulate material and/or the subsurface particulate material of the body of particulate material concurrently and jointly, i.e. as a mixture thereof.

IN ACCORDANCE WITH A FIFTH ASPECT OF THE INVENTION IS PROVIDED a liquid composition for stabilizing a body of particulate material, the composition comprising

a thermoplastic polymer, and

spent soda liquor.

The thermoplastic polymer and the spent soda liquor may be as hereinbefore described in accordance with the first and second aspects of the invention. IN ACCORDANCE WITH A SIXTH ASPECT OF THE INVENTION is provided use of a treatment composition of the fifth aspect of the invention in stabilizing at least one of exposed surface particulate material and subsurface particulate material of a body of particulate material. The use may occur in accordance with the method of the fourth aspect of the invention.

IN ACCORDANCE WITH A SEVENTH ASPECT OF THE INVENTION is provided a method of stabilizing a body of particulate material, the method including applying to at least one of exposed surface particulate material and subsurface particulate material of a body of particulate material, sequentially or concurrently, and separately, treatment agents in liquid form comprising

a lignosulphonate, and

a fully hydrolysed polyvinyl alcohol; and

allowing or causing the liquid treatment agents to harden and thus bind at least some of the exposed surface particulate material and/or subsurface particulate material of the body of particulate material, thereby stabilizing the body of particulate material. Preferably the separate applications of the treatment agents are sequential, wherein the lignosulphonate liquid treatment agent is applied first and the fully hydrolyzed polyvinyl alcohol liquid treatment is applied second.

The lignosulphonate may be calcium lignosulphonate. Alternatively it may be sodium lignosulphonate.

The fully hydrolysed polyvinyl alcohol may be fully hydrolysed polyvinyl alcohol in water, typically in a concentration in the range of 1 to 20% by weight or, more preferably, 1 to 10% by weight.

The fully hydrolysed polyvinyl alcohol may have a degree of hydrolysis of from 97 to 99.5 mol%, a molecular weight in the range 100 000 to 170 000, a viscosity from 30 to 80 cP.s as a 4% solution in water at 20°C, and a degree of polymerisation of 2 700. Dissolution of the fully hydrolysed polyvinyl alcohol in water may be performed by first dispersing the fully hydrolysed polyvinyl alcohol in water at ambient temperature, and then raising the temperature of the water to a temperature in a range from 80 to 95^eC, thereby causing dissolution of the polyvinyl alcohol and obtaining an aqueous solution of a fully hydrolysed polyvinyl alcohol. The temperature of the solution need not be maintained in the range of 80 to 95°C after dissolution has taken place.

The fully hydrolysed polyvinyl alcohol may, for example be Mowiol 20/98 by Clariant or Goshenol N types NH18, NH20, NH300 by Nippon Goshei, with molecular weights in the range 125 000 to 160 000 g/mol and viscosities of 4% solution at 20^eC from 16 to 30 MPa.s with a degree of hydrolysis or saponification between 97 and 99.5 mol% and an ester value of 20 ± 5mgKOH/g. Molecular weights starting from 100 000 can be suitable, however, as indicated above. A most favorable grade is Poval 1 17 by Kuraray.

Allowing the treatment composition to harden may be by allowing desiccation of the fully hydrated polyvinyl alcohol, when applied as an aqueous solution.

Causing hardening of the treatment composition may include use of a polyvinyl alcohol gelling agent.

The gelling agent may be a gelling agent that increases the viscosity or causes the partial or complete gelling or precipitation of the fully hydrolysed polyvinyl alcohol. In this regard it is noted that the regularly arranged hydroxyl groups of the polyvinyl alcohol chain can form chemically more or less stable complex compounds or associations with certain substances. In addition, when the polyvinyl alcohol gels it loses all tack and becomes non-sticky. Furthermore, gelled polyvinyl alcohol envelopes loose particles as an integral part thereof, giving it considerable cohesive properties, which is advantageous when binding loose particles on a pre-formed unpaved road surface to obtain a stabilized road surface and allowing the road to be used in such a way that minimal breakage, friability, parting or fissures result. The classic complex formed from polyvinyl alcohol is its reaction with boric acid or one of the borates. Boric acid gives the monodiol complex, which in turn forms a poly-electrolyte and didiol complex. The gelation particularly suitable to the method is the precipitation of the polyvinyl alcohol by borax in solution which is Na2B₄05(OH)4.8l-l20 referred to as disodium tetraborate decahydrate. The pentahydrate is also satisfactory, as is lesser hydrated embodiments in cases in which delayed gelling is required, e.g. when the gelling agent is mixed with the aqueous solution of fully hydrolysed polyvinyl alcohol. Borax partially hydrolyses boric acid and this acts as a buffered gelling agent. In use, the borax is dissolved in water to give a solution concentration of between 1 - 8% by mass, more preferably in the range 2 - 5%.

Other possible gelling agents are elements of the sub-groups IV-VI on the periodic table, manganese, and certain other metal ions. Thermoplastic polymer dispersions in water can be added to the aqueous solution of a fully hydrolysed polyvinyl alcohol. These add desired properties including resistance to ultra-violet light and water, contribution to strength, impact resistance and toughness. Flexual strength is improved and the interfacial bond between the binder and the matrix improved. Some of these polymers have considerable coalesced flexibility. These polymer dispersions are characterized by solid percentage in water of from 40 to 70%, more preferably 50 to 65%. Examples are vinyl polymers and polymers of acrylates and methacrylates. Several monomers are used in the manufacture, particularly the acrylates and methacrylates, but styrene and vinyl acetates and vinyl chloride can also be used. Co-polymers or any two or more of these polymers can then be employed. Synthetic latex polymers have contributive properties such as styrene butadiene copolymer latexes, such as Synthomer 29Y40, an example of a SBR or a styrene butadiene rubber. The treatment agents in liquid form are preferably used as separate solutions of the lignosulphonates and the fully hydrolysed polyvinyl alcohol in water. In essence, it is an added benefit of the invention that water is preferred as carrier medium, since the components are miscible in water. Hence, the invention prefers "solutions" which operate at the molecular level rather than "dispersions" or "emulsions". Emulsions typically comprise dispersed particles. When it comes to binding or stabilising very small/fine particles - solutions which operate at the nano or molecular level are more effective at binding and stabilising compared with emulsions which operate in the larger dispersed particle phase. IN ACCORDANCE WITH AN EIGTH ASPECT OF THE INVENTION IS PROVIDED a method of stabilizing a body of particulate material, the method including applying to at least one of exposed surface particulate material and subsurface particulate material of a body of particulate material a liquid treatment composition comprising

a thermoplastic polymer, and

a lignosulponate; and

The thermoplastic polymer and the lignosulponate may be as hereinbefore described accordance with the first, second and seventh aspects of the invention.

The thermoplastic polymer and the lignosulponate may be applied to the exposed surface particulate material and/or the subsurface particulate material of the body of particulate material

separately and sequentially; or

separately and concurrently. Alternatively, the thermoplastic polymer and the lignosulponate may be applied to the exposed surface particulate material and/or the subsurface particulate material of the body of particulate material concurrently and jointly, i.e. as a mixture thereof. IN ACCORDANCE WITH A NINTH ASPECT OF THE INVENTION IS PROVIDED a liquid composition for stabilizing a body of particulate material, the composition comprising

a thermoplastic polymer, and

a lignosulponate. The thermoplastic polymer and the lignosulponate may be as hereinbefore described in accordance with the first, second and seventh aspects of the invention.

IN ACCORDANCE WITH A TENTH ASPECT OF THE INVENTION is provided use of a treatment composition of the ninth aspect of the invention in stabilizing at least one of exposed surface particulate material and subsurface particulate material of a body of particulate material.

The use may occur in accordance with the method of the eighth aspect of the invention. EXAMPLES

Example 1

The following is one example of a treatment composition in liquid form according to the second aspect of the invention:

Sodium silicate 3379 ratio Si0₂ to Na₂0 30:9, 38% solids 300 cc

Potassium silicate 2550 ratio Si0₂ to K₂0 20:8, 29% solids 100 cc

Water 300 cc Spent soda liquor at pH 13 600 cc

Reference below to "Blend A" is to this composition, absent the spent soda liquor, i.e. 300cc of the sodium silicate in liquid form, 100cc of the potassium silicate in liquid form, and 300cc of water.

Example 2

The following sample preparations of the composition of the second aspect of the invention were prepared, using pH 13 spent soda liquor.

All the samples were found to be in stable liquid form.

Adjustment of the ratios of spent soda liquor and Blend A from Sample 1 to Sample 4 is based on the structural and chemical specifications of the substrate being treated.

Generally speaking, where greater enhancement of geotechnical characteristics of a body of particulate material is required, e.g. where the geotechnical characteristics of the body of particulate material are particularly weak, the proportion of Blend A (alkali metal silicates) would be increased.

Alkali metal silicates, and particularly sodium and potassium silicate, geopolymerize under suitable conditions, e.g. low pH such as that which is associated with bodies of particulate material such as soil and the like. Such geopolymerization has been found to impart superior geotechnical stability on bodies of particulate material.

Example 3 - Forest ln-situ Soil Stabilisation with Blend A and Spent Soda Liquor

This example aims to illustrate the stabilising effect and enhancement of the geotechnical properties of in-situ soil obtained from a forestry gravel road in South Africa's KwaZulu Natal province, by applying the liquid treatment composition of the invention to the soil.

Soil samples were mixed with different ratios of Blend A and spent soda liquor and the resulting properties tested according to the standard soaked California Bearing Ratio (CBR) test.

Table 1 (attached) presents the various compositions and relative ratios of soil, Blend A and spent soda liquor that were subjected to testing, as well as the CBR test results, and Figure 1 illustrates the comparative CBR test results.

As can be seen from the CBR test results, samples treated with the liquid treatment composition of the invention exhibited superior geotechnical properties compared to samples treated with water only and samples treated with spent soda liquor only.

Geopolymerization of alkali metal silicates has been found by the applicant to impart hydrophobicity on or to polymerised spent soda liquor, which is otherwise water soluble.

The combined use of alkali metal silicates and spent soda liquor in accordance with the invention therefore provides more permanency to stabilization of bodies of particulate material using spent soda liquor, thus beneficiating spent soda liquor for this purpose. Spent soda liquor would otherwise have been subjected to chemical recovery processing.

Claims

1 . A method of stabilizing a body of particulate material, the method including applying to at least one of exposed surface particulate material and subsurface particulate material of a body of particulate material, a liquid treatment composition comprising one or more alkali metal silicates, and

spent soda liquor; and

2. The method of claim 1 , wherein the one or more alkali metal silicates and the spent soda liquor are applied to the exposed surface particulate material and/or the subsurface particulate material of the body of particulate material

separately and sequentially; or

separately and concurrently.

3. The method of claim 1 , wherein the one or more alkali metal silicates and the spent soda liquor are applied to the exposed surface particulate material and/or the subsurface particulate material of the body of particulate material concurrently and jointly, as a mixture thereof.

4. The method of any of claims 1 to 3, wherein the one or more alkali metal silicates are selected from sodium silicates, potassium silicates, and mixtures thereof.

5. The method of claim 4, wherein the sodium silicate has a silica to sodium oxide ratio of 2:1 to 3.3:1 .

6. The method of claim 4 or claim 5, wherein the potassium silicate has a silica to potassium oxide ratio of 1 .45:1 to 2.55:1 .

7. The method of any of claims 4 to 6, wherein the sodium silicate is sodium silicate in water at a concentration in the range of from 6 to 40% solids by weight, based on the combined weight of sodium silicate and water.

8. The method of any of claims 4 to 7, wherein the potassium silicate is potassium silicate in water at a concentration in the range of from 6 to 30% solids by weight, based on the combined weight of potassium silicate and water.

9. The method of any of claims 1 to 8, wherein the one or more alkali metal silicates comprise sodium silicate and potassium silicate in a ratio of 3:1 by volume.

10. The method of any of claims 1 to 9, wherein the treatment composition comprises the one or more alkali metal silicates in the range of from 10 to 80% by volume, based on the joint volume of the one or more alkali metal silicates and the spent soda liquor.

1 1 . The method of any of claims 1 to 10, wherein the treatment composition comprises black liquor in the range of from 20 to 90% by volume, based on the joint volume of the one or more alkali metal silicates and the spent soda liquor.

12. The method of any of claims 1 to 1 1 , wherein the spent soda liquor has a pH in the range of from 1 1 to 13.

13. The method of any of claims 1 to 12, wherein the spent soda liquor has a dissolved alkali soluble lignin content in the range of from 6 to 9% by weight.

14. The method of any of claims 1 to 13, wherein the spent soda liquor has a solids content of from 17 to 25% by weight.

15. The method of any of claims 1 to 14, wherein the body of particulate material is any one of a body of bed of in situ soil, a heap or bed of dumped particulate material, a preformed unpaved road, and sand.

16. A composition for stabilizing a body of particulate material, the composition comprising

one or more alkali metal silicates and;

spent soda liquor.

17. The composition of claim 16, wherein the one or more alkali metal silicates are selected from sodium silicates, potassium silicates, and mixtures thereof.

18. The composition of claim 17, wherein the sodium silicate has a silica to sodium oxide ratio of 2:1 to 3.3:1 .

19. The composition of claim 17 or claim 18, wherein the potassium silicate has a silica to potassium oxide ratio of 1 .45:1 to 2.55:1 .

20. The composition of any of claims 17 to 19, wherein the sodium silicate is sodium silicate in water at a concentration in the range of from 6 to 40% solids by weight, based on the combined weight of the water and the sodium silicate.

21 . The composition of any of claims 17 to 20, wherein the potassium silicate is potassium silicate in water at a concentration in the range of from 6 to 30% solids by weight, based on the combined weight of the water and the potassium silicate.

22. The composition of any of claims 16 to 21 , wherein the one or more alkali metal silicates comprise sodium silicate and potassium silicate in a ratio of 3:1 by volume.

23. The composition of any of claims 16 to 22, wherein the treatment composition comprises the one or more alkali metal silicates in the range of from 10% to 80% by volume, based on the joint volume of the one or more alkali metal silicates and the spent soda liquor.

24. The composition of any of claims 16 to 23, wherein the treatment composition comprises spent soda liquor in the range of from 20% to 90% by volume, based on the joint volume of the one or more alkali metal silicates and the spent soda liquor.

25. The composition of any of claims 16 to 24, wherein the spent soda liquor has a pH in the range of from 1 1 to 13.

26. The composition of any of claims 16 to 25, wherein the spent soda liquor has a dissolved alkali soluble lignin content in the range of from 6 to 9% by weight.

27. The composition of any of claims 16 to 26, wherein the spent soda liquor has a solids content of from 17 to 25% by weight.

28. The composition of any of claims 16 to 27, wherein the body of particulate material is any one of a body of bed of in situ soil, a heap or bed of dumped particulate material, a pre-formed unpaved road, and sand.

29. Use of a composition of any of claims 16 to 28 in stabilizing a body of particulate material.

30. The method of any of claims 1 to 15 or the composition or any of claims 16 to

28, wherein the spend soda liquor is an unsulfonated spent soda liquor.