HU187328B - Method for dewatering sludges of mineral origin - Google Patents

Abstract

In a method of dewatering minerals suspensions, tensides or a mixture containing tensides is added to the suspensions in an amount between 0.03% and 2%, wherein the tensides or mixture thereof has an HLB number falling within the range 8 to 12 or an H/L number falling within the range of 50% to 150% and thereafter the suspensions are dewatered.

Description

The present invention relates to a process for separating the solid phase of aqueous suspensions (sludges) containing mineral solids from the water forming the liquid phase, i.e. a process for dewatering mineral sludges. The process according to the invention relates in particular to the processing of fine sludges from the preparation of minerals, the ore enrichment and the processing of fine sludge, which is difficult to dewater, which is difficult to dehydrate by methods known hitherto, and which are difficult to dehydrate in soil excavation and sludge treatment. can be advantageously used.

A number of processes have already been proposed for solving the problems of processing or disposing of said fine sludge, which have been based mainly on flotation, flocculation, sedimentation, centrifugation or filtration operations, or combinations thereof. In particular, the addition of flocculating agents to the sludge has sought to improve the sedimentability of the sludge and the separation of the solid particles from the aqueous phase. However, since only very limited improvement can be achieved in this way, various methods have been proposed to increase the effect of flocculants. so the

No. 119,826 According to the German patent, the flocculant is added in two portions to the sludge first so that flocculation is just started, then the sedimented sludge is separated from the bulk of the aqueous phase and treated with another dose of flocculant prior to filtration.

No. 3,398,093. U.S. Pat. No. 5,198, first sludges the sludge without the addition of a chemical, and then transfers the slurry thus concentrated to a centrifuge after adding a flocculating agent.

It is also proposed to add flocculating agents, namely high molecular weight organic polyelectrolytes or iron (III) salts, to the sludge in several steps to improve the sedimentability of the sludge. Hungarian Patent Specification.

However, all these procedures, according to the data provided in the cited quotations, only result in a limited improvement in the sedimentability of the sludge; the filterability of the sludge is not significantly improved by the addition of flocculant alone, the hourly filtration capacity is generally between 10 kg / m ² and 60 kg / m ² , and only with a particularly favorable granulometric distribution sludge reaches about 150 kg / m ² . The residual moisture content of the filtered sludge is between 30% by weight and 50% by weight (although the desired value would be 20-30% by weight), but even the residual moisture content of 30-35% by weight can only be achieved with expensive machinery, many chemical additives, and (see, for example, Hungarian Patent Application No. 151,111).

Some authors also investigate the theoretical applications of various flocculants, such as J. Maibecs (Vodni Hospod - B 25 (10), 259-261 (1975)) as a cationic polyelectrolyte, as well as iron (III) chloride and aluminum sulfate in water. effect on the filterability of suspended impurities. P. Biddle and J. H. Miles (Nucl. Sci.

Abstr. 31 (12), 35667 (1975)) investigate the effect of polyacrylamide and sodium carboxymethylcellulose on the filtration of sludges. However, these authors do not recommend an industrially applicable procedure.

Soviet authors (Chem. Techn. (Leipzig), 23 (9), 528-531 (1971)) have already investigated the effect of surfactants on dehydrating filter cakes obtained from high dispersions of suspensions, but in their experiments they dealt only with dehydration of certain organic dye pigments. as a surfactant, a chemically unspecified wetting agent has the effect of enhancing the hydrophilic nature of the surface of organic particles. This effect reduced the tendency of the highly dispersed organic particles to aggregate, so that the water content of the high dispersion filter cake was reduced by a few percent with 4 atmospheres, but the zeta potential and filtration time increased. However, no inferences can be drawn from these data for completely different types of mineral sludge, not least because it is not desirable to increase the hydrophilic character during the dewatering of the latter.

The object of the present invention is to provide a new process which eliminates the known sludge dewatering processes and which allows dewatering of various sludges of mineral origin in a simple and economical way, i.e. separating the solid phase from the water forming the liquid phase with better energy efficiency. , without the use of special machinery and in a short operating time.

It is known that this disadvantageous property of poorly filtered or difficult to dewatered sludge is mainly due to the tendency of the sludge to thixotropy, the high zeta potential between the sludge solids and the liquid medium (water). Such sludges develop a capillary system, leading to an increase in structural viscosity. As a result, a large amount of structural water is trapped in the sludge, which can only be removed with difficulty, with high energy input and over a long period of time.

Water is present in the sludge in several states: first as a dispersion medium, then as capillary water between aggregate, colloidal fluff particles of the sludge, and as a solvate layer on the surface of the solid particles and finally as structural water embedded in the sludge solids.

Capillary water and solvate water can only be hardly or not at all removed by mechanical energy alone. Structural water (water in the body of bacteria or crystal water) can only be removed by heat transfer, and in some cases only by vigorous chemical intervention. Thus, increasing the efficiency of sludge dewatering depends primarily on the ability to facilitate removal of capillary water and solvate water.

The present invention is based on the discovery that facilitating the removal of capillary water and solvate water by the action of certain surfactants, surfactants, commonly referred to as wetting agents,

It can be solved by adding 187 328 sludges. It has been found that by adding relatively small amounts of suitable surfactants to the sludge, the tendency of the sludge to thixotropy is eliminated or reduced, the zeta potential between the solids and the water is reduced, the solvate water bound between the solids on the surface of the solids capillaries disintegrate or do not form and thus the water trapped therein can be easily removed. All these experimentally verifiable effects result in the solids dispersed in the slurry being easily separated from the liquid medium and separated easily and with good efficiency by sedimentation, filtration or other known methods.

This new discovery underpinning the invention is particularly surprising, since the surfactants generally have a wetting, dispersing effect on the particles suspended in the aqueous medium, and it would have been expected that the addition of the surfactants to the slurry would have the opposite effect of solid particles binding to the liquid medium. will have a magnifying effect. It is known that the molecules of surfactants have two opposite ends at the two ends of the carbon chain: a hydrophilic and a hydrophobic end group, and the wetting, dispersing action of the surfactant is based on the lipophilic (hydrophobic) end of the surfactant molecules the surfaces of the hydrophobic particles per se, while their hydrophilic ends are turned outward to form a hydrophilic layer on the surface of the particle, whereby the whole particle becomes hydrophilic. However, if the quality and quantity of the surfactant is appropriately selected, this process may be reversed: The hydrophilic ends of the surfactant molecules will bind to the solid particles of the mineral sludge, thereby losing the hydrophobic nature of the particle, the conditions for the formation of the capillary system, the capillary water is also released and the solid particles tend to separate from the liquid medium.

Because the two opposite end portions of the surfactant molecules may exhibit different degrees of hydrophilic and lipophilic activity, depending on the chemical nature of the surfactant, the hydrophilic-lipophilic balance of the different surfactants may vary. To precisely determine this equilibrium, the term "hydrophilic-lipophilic balance" (HLB), which expresses the hydrophilic-lipophilic balance of each surfactant and is clearly representative of that surfactant, has been introduced and is capable of exerting the effect described above underpinning the present invention. can also be used to characterize surfactants.

It has been found that certain surfactants have the surprising property of being able to bind to mineral particles suspended in an aqueous medium by their hydrophilic end-part, not at all a common phenomenon among surfactants, but only with surfactants having a hydrophilic and lipophilic character. that is, having an HLB of about 10, that is, between 8 and 12, preferably between 9 and 11.

Examples of such HLBs having an HLB of 8 to 12 and thus useful in the process of the present invention include polyethylene glycol fatty acid esters, in particular polyethylene glycol laurate (HLB: 9.2) and polyethylene glycol myristinate (HLB: 11.9), octylmaleinate (HBL: 11.6), hexaethylene glycol monooleate (HLB: 9.8), polyoxyethylene sorbitan monooleate (HLB: 10), polyoxyethylene sorbitan trioleate (HLB) : 11) and the like, and mixtures thereof.

The amount of surfactant to be used depends primarily on the concentration of sludge to be dewatered, i.e., the amount of solid particles per unit volume of sludge; Thus, the preferred amount of surfactant (sufficient to form a surface layer on the solid particles), depending on the amount and granulometric distribution of the slurry suspended in the slurry, may be between 0.03% and 2% by weight based on the solids content of the slurry. Within this range, the optimum amount may be determined experimentally. The use of a much greater amount of the surfactant than that given above is not advisable because the excess surfactant can no longer be bound to the solid particles of the sludge as described above and may even be dispersible; that is, it may have the opposite effect.

Since the surface of the slurry solids is generally non-homogeneous and therefore the surface zeta potential may vary, in most cases two or more surfactants with slightly different HLB values, such as an HLB below 10 and above 10, may be desirable. surfactant mixture.

The surfactant, or. the effect of adding the surfactant mixture to the sludge can be further enhanced by adding a water-soluble flocculant to the sludge after mixing the surfactant with the sludge and preferably conditioning the sludge so treated.

The known effect of the flocculant is primarily to accelerate sedimentation. Non-ionic, anionic or cationic organic polymers (polyelectrolytes) or, optionally, precipitating inorganic salts are suitable as flocculating agents.

By adding the surfactants selected as described above and optionally flocculants to the sludge to be dewatered, the sludge filtration (i.e., the relative filtration power of untreated sludge) can be increased by 10 to 10% and the dewatering efficiency by 50-100%.

Accordingly, the present invention provides a novel process for dewatering sludges of mineral origin by the addition of a surfactant and optionally a flocculating agent, characterized in that the sludge to be dewatered has a HLB value of 8 to 12, preferably 9 to 11, or a mixture thereof. per sludge solids of ,, an amount between 2 weight% and 0.03 weight ^0, then - preferably after the reaction mixture Kondića onálása with stirring - optionally the sludge solids

A water-soluble anionic, cationic and / or nonionic polymeric or copolymer flocculant of greater than 500,000, preferably 2 to 5 million molecular weight, based on 187,328 content of 0.17 kg / t, is added to the system with slow agitation, and then the system solids are sedimented. , centrifugation, filtration or other known means to separate it from the aqueous medium.

As a surfactant with an HLB of between 2 and 8 - just like this. as mentioned above, in particular polyethylene glycol esters of fatty acids, esters or ethers of fatty alcohols, ethylene oxide adducts of polyhydric alcohols and fatty acid esters and the like. These surfactants are usually added in the form of an aqueous solution, in particular in the form of a dilute aqueous solution, preferably 0.5 to 5% by weight, to ensure good mixing with the sludge, preferably with vigorous stirring of the sludge. After mixing the surfactant with the slurry, the slurry is suitably conditioned by further mixing for a few minutes. It is also advantageous to settle or centrifuge or to improve the sedimentation of the sludge and thereby further increase the efficiency of dewatering. add a water soluble flocculant to the sludge prior to filtration. The flocculant is preferably an anionic, cationic or nonionic polymer or copolymer based air of less than 500,000 flocculants, preferably polyacrylamide, or polyacrylic acid derivative polyelectrolytes, preferably based on the solids content of the slurry. In quantities of 1-1 kg / t. Preferably, the flocculant is added to the slurry in a dilute aqueous solution of 0.1 to 1% by weight with gentle agitation of the slurry. Particularly good effect is obtained by adding the flocculating agent solution after sludge settling and decanting, under conditions ensuring film-like contact of the flocculating agent with the solid particles of the sludge, preferably by spraying onto a slurry of compacted sludge or by sludge.

Sludge solids treated with surfactants and optionally flocculant as described above can be separated from the liquid phase by methods known per se, such as sedimentation, centrifugation, vacuum filtration, or pressure filtration, or possibly flotation. Separation of the solids, i.e., the actual dewatering of the sludge, is much easier, faster and multiplied by treatment with surfactants having an HLB value of 8-12 HLB and optionally a flocculant.

The process according to the invention is suitable for the filtration and / or the sludge filtration. such a large effect on dewatering performance can be experimentally demonstrated by determining the CST (Capillary Suction Time) characteristic of these sludge properties (see RS Gallé: Optimizing the use of anti-creasing chemicals in solids: Upland Press Ltd., Croydon, England, 1976. pp. 40-82). Experimental data presented in the Examples illustrating the process of the invention show that the CST value of the sludge is reduced to 4-5 and even less than one tenth of the original value as a result of the treatment according to the invention. The water content of the sludge decreased by 10-15% by weight.

Practical embodiments of the process of the invention are illustrated by the following examples.

Example 1

Starting material: sludge from the enrichment of phosphate ore of Jordanian origin.

Composition of solids:

CaO 20% by weight

MgO 3% by weight

A1 ₂ O ₃ 30% by weight

SiO ₂ 47% by weight

The crude phosphate content of the sludge, expressed as P ₂ O ₅ , was 3% by weight.

Distribution of granulometry:

Up to 0.070 mm 48% by weight

18% by weight between 0.07mm and 0.1mm

34% by weight between 0.1mm and 0.125mm

Slurry concentration: 700 g / l, CST value 52 sec.

Surfactant used: mixture of polyethylene glycol lurinate (HLB value: 9.2) and octyl maleinate (HLB value: 11.6)

The slurry was introduced into a tank where, with vigorous stirring, a 0.6% w / w aqueous solution of 10 kg of the above surfactant mixture per liter of solid was added, and after 10 minutes of further stirring, the resulting slurry was transferred from the tank to a slide. 0.25 kg of an aqueous solution of 0.25 kg of methylated polyacrylamide (molecular weight: 2-5 million) flocculant in a concentration of 0.6% was sprayed onto the slurry. The slurry from the slide was continuously transferred to the filter tank of a vacuum disk filter machine. Filtration was AP _max = 0.9 atm. vacuum.

The slurry treated with surfactant and flocculant had a CST value of 4 sec; With a thickness of 20 mm, the filtering power is 2487 kg / m ² solids per hour. With the same filtering device, a filtering capacity of 2790 kg / m ² per hour for a thickness of 10 mm was achieved. The sludge removed from the filter had a moisture content of 18.2 wt / y. In comparison, when the same slurry was applied to the same vacuum disk filter without treatment with surfactant and flocculant, the hourly filtration power was 302 kg / m ^{2 for the} same vacuum with a filter thickness of 20 mm and 270 kg / m ² for the filter thickness of 10 mm. and the water content of the sludge was 32% by weight.

So far, the same sludge has been dewatered by adding 600 to 800 g flocculant per tonne of dry matter and dewatering it by centrifuge; CST values were not measured, but the dewatered sludge had a moisture content of 35-50% by weight, was not molded and was stored in sludge ponds.

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187,328

Example 2

The slurry of the same quality as Example 1 was mixed with the surfactant and flocculant of Example 1 of the same quality and amount as described therein, and after 8 minutes of further stirring, the slurry treated was introduced into a centrifugal settling centrifuge at 1000 rpm. The sludge is concentrated in the centrifuge to a moisture content of 30% by weight, continuously transferred from the centrifuge to a conveyor belt, and the effluent can be recycled and reused.

In comparison, the same slurry was introduced into the centrifuge without the addition of a surfactant, under the same conditions, the water had not separated from the suspended solids within 10 seconds, while the treated slurry had already separated after 2 seconds.

Example 3

Starting material: sludge from the processing of the Yugoslav coal mine tailings pit.

Composition of solids: 5-6% by weight of carbonaceous clay mineral.

Granulometric distribution:

Below 0.07 mm 4% by weight

0.07-0.1 mm 9% by weight

23% by weight between 0.1 mm and 0.125 mm

64% by weight over 0.125 mm

Tail concentration: 430 g / l; CST value: 80 sec.

Surfactants used: Esters of polyethylene glycol with mixed fatty acids (HLB value 11.4).

The sludge from the carbon separation was fed to a tank, where 8 kg of surfactant per tonne of dry matter was added in vigorous stirring in an aqueous solution of 0.6 wt%, and after 10 minutes of further stirring, the treated sludge was transferred from the tank to a slide. An aqueous solution of 0.2 kg of poly (acrylamide) (molecular weight: 2-3 million) flocculant per 1 ton solids was sprayed onto the slurry slurry, which was then passed to a vacuum disk filter tank, where AP _max = 0, 9 atm vacuum sludge was filtered.

The CST value of the slurry mixed with the surfactant and flocculant is 5 sec. Filtration power was 1400 kg / m ² solid per hour; the sludge moisture from the filter is 23% by weight.

By way of comparison, the same slurry was applied to the same vacuum disk filter without treatment with a surfactant and flocculant, with a filtration capacity of 70 kg / m ² solids / hour, and the slurry removed from the filter had a moisture content of 35%. Experiments were carried out with the same sludge using surfactants of the same moiety based on the solids of the sludge, one having an HLB of 15 and the other having a HLB of 4.7. These were mixed separately with the sludge and the sludge treated in this manner was dewatered under the same conditions as the above vacuum filter. The CST value of the slurry treated with HLB 15 surfactant 15 was 28 sec, and the CST value of slurry treated with HLB 4.7 was 22 sec. The moisture content of the sludge was nearly the same in both cases, 30% by weight, and the achieved power was 600 kg / m ² for 22 sec CST and 500 kg / m ² for 28 sec CST.

Until now, the same sludge in Yugoslavia has been dewatered by adding 600-1000 grams of flocculant per tonne of dry matter and thus being introduced into the centrifuge; the moisture content of the dewatered sludge from the centrifuge is such that it has to be taken to and stored in sludge ponds.

Example 4

Starting material: sludge from the processing of Austrian coal mines.

The solids composition is a mixture of material minerals for the production of fine ceramic and tile products and 5-6% lignite.

Granulometric distribution:

18% by weight below 0.07mm

25% by weight between 0.07mm and 0.1mm

35% by weight between 0.1mm and 0.125mm

22% by weight between 0.125mm and 0.315mm

Tail concentration: 450 g / l; CST value: 180 sec.

A surfactant used is a mixture of octyl rnaleinate (HLB: 11.6) and polyethylene glycol laurate (HBL: 9.2).

a) The slurry is mixed with a 0.7% w / w aqueous solution of 9 kg / t surfactant per solid, as described in Example 3, and after further 10 minutes of slurry, 0.2 kg / t methylated PCL (acrylamide) ( Molecular weight: 2-5 million) An aqueous solution of flocculant at a concentration of 0.6% is sprayed onto the slurry. The slurry was filtered through a vacuum disk filter under the same conditions as in Example 3. The slurry treated with the surfactant and flocculant has a CST of 20 sec and a filtration capacity of 250 kg / m ² solids per hour. The sludge removed from the filter has a moisture content of 27% by weight.

b) The same slurry is treated with the specified amount of surfactant as described above, then passed directly to the vacuum disk filter without spray application of flocculant and filtered under the same conditions. Hourly filtration power 185 kg / m ² solids; the sludge removed from the filter had a moisture content of 27% by weight.

For comparison, the same slurry is applied to the same vacuum disk filter without treatment with surfactant and flocculant. Under the same conditions, the hourly output is 37 kg / m ² ; the moisture content of the sludge removed from the filter is 35% by weight.

Example 5

The slurry of Example 4 is treated with a surfactant followed by a flocculating agent as described there, then the slurry thus treated is introduced into trough settling tanks. At the opposite end of the trough, the water is continuously aspirated, while the bottom of the trough is compacted with a near-shaped sediment5

-5187 328 with two conveyors mounted on the bottom of the trough, and the dewatered sludge from the end of the trough is conveyed to the storage site by conveyor odor.

Moisture content of dewatered sludge 30 weight ⁰ /. Without the addition of a surfactant, under the same conditions, only a loose, non-stable sediment is obtained with a water content of 55-60% by weight.

Example 6

Starting material: raw sludge used in the production of cement for the production of footless cement.

Composition of solids:

SiO ₂ : 20.31%; Al ₂ O ₃ : 5.41%;

Fe ₂ O ₃ : 3.08%; CaO: 68.12%;

MgO: 2.66%; SO ₃ : 0.29%.

Granulometric distribution:

30% by weight below 0.01 mm

60% by weight between 0.01-0.065 mm

10% by weight between 0.065-0.09 mm

Tail concentration: 1430 g / l.

The surfactant used is a mixture of polyethylene glycol myristinate (HLB: 11.9) and octyl maleinate (HBL: 11.6).

a) The slurry is mixed with a 0.8% w / w solution of 6 kg surfactant in 0.8% w / w solution of polyacrylic acid / 0.6% w / w in a slow, gentle manner as described in the previous example. while stirring, to the slurry, which after 10 minutes of further stirring is passed to a disk vacuum filter. AP _max = 0.8 atm. vacuum filtration has a filtration capacity of 550 kg / m ² . The product has a moisture content of 15.5% by weight.

For comparison, the same slurry was applied to the disk filter without treatment with surfactant and flocculant. Under the same conditions, the filtration power was 134 kg / m ² / hour and the moisture content of the product was 32% by weight.

b) Work as described above, except that the flocculant polyacrylic acid is added to the surfactant mixture in the above proportions, and the mixture is added in the form of an aqueous solution to the slurry with gentle stirring, which is then stirred for 10 minutes. then applied to the disc filter. In this way, essentially the same result as in Example a) is obtained.

Example 7

Carbon sludge dewatering Sludge concentration: 223.2 g / l Granulometric distribution of the particles:

Below 0.045 mm, 85.7 g / l

Between 0.045 and 0.5 mm at 98.2 g / L

Between 0.5 and 1 mm, 33.4 g / l greater than 7.6 g / l

The surfactant used is a mixture of polyethylene sorbinate monooleate (HLB value: 11) and a 2-hydroxyethyl ester of a C 6 unsaturated carboxylic acid.

Flocculant: copolymer of acrylic acid and acrylamide (molecular weight: 2-3 million).

0.3 kg of flocculant is added to 7 kg of surfactant per tonne of dry solids and this mixture is added to the slurry as a gentle stirring in 0.5% w / w aqueous solution. The slurry is then transferred to a settler and the sludge settled further into a pneumatic suction filter. The filtration capacity was 1507 kg / m ² per hour; _g of final product moisture content of 15.3% by weight. The same carbon sludge without the addition of a surfactant and flocculant, if dewatered in a pneumatic press filter in the same manner as described above, has a filtration capacity of 430 kg / m ² per hour; moisture content of the final product is 29.7% by weight

Claims (6)

1. A process for mineral slurries derived dewatering by adding ⁵ surfactant and possibly flocculant, characterized in that the dewatering sludge of between 8 and 12 - preferably having an HLB of surfactant or these surfactants was between 9 and 11 are given calculated on the slurry dry matter content of ³⁰ to 0, A flocculant consisting of anionic, cationic and / or nonionic polymer ³⁵ or copolymer having a water-soluble content of more than 500,000, preferably 2-5 million, preferably water, is added at or about 3 to 2% by weight, optionally after conditioning the mixture. the slurry is separated from the aqueous medium by sedimentation, centrifugation, filtration or any other known method. Process according to claim 1, characterized in that the surfactant is a mixture of two different surfactants, preferably an HLB of between 8 and 10 and a HLB of between 10 and 12. 3. A process according to claim 1, wherein the surfactant or the surfactant is used. The surfactant mixture is mixed with the slurry in the form of a 0.5 to 2% by weight aqueous solution. 4. A process according to claim 1, characterized in that the aqueous flocculant dat ol ⁵⁰ as a 0.5 to 1% by weight - have been added to the blended slurry tenside - preferably by spraying or mixing. 5. A method according to any one of the preceding claims, characterized in that the treated polymeric flocculant surfactant, and optionally the slurry of solids ⁵⁵ settling and / or filtering - was isolated from the aqueous phase by means of - preferably vacuum filtration, press filtration or centrifugation. 6. A process according to any one of claims 1 to 3, characterized in that the flocculant is added together with the surfactant or surfactant mixture to the dewatering sludge with mixing. Without illustration Published by the National Office of Inventions Responsible for publishing: Zoltán Himer, Head of Department, Collected by the Printing Husbandry Plant (87 ⁷ 360/09) 88-0645 - Dabasi Printing House, Budapest - Dabas Chief executive: Csaba Uá'int