GB2098194A - Method for dewatering mineral suspensions - 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

SPECIFICATION Method for dewatering mineral suspensions FIELD OF THE INVENTION The invention relates to a method for dewatering mineral suspensions. More particularly, this invention concerns such a method with which the fine slurry or suspension produced in great quantity by mineral and ore dressing or concentration or with coal washings/coal sludge/, by sewage purification or by silting in earthwork, can be dewatered.

BACKGROUND OF THE INVENTION The dewatering and filtering process of these slurries or suspensions as mentioned above for satisfying the laws and constraints of storage and enviromental pollution, involves an ever increasing expenditure, wasting in time and energy. Various continuous and discontinuous methods combined with flotation and flocculation are known with which frame filters, discfilters, band and drum filters, vacuum filters, filter presses as well as centrifuges are used.

Furthermore, precipitation with calcium or magnesium-hydroxide finds application, too. Sometimes, filtrate additives such as sand is given to the material to be filtered and its index of pH is changed, too. For ion-ore filtration, sulphonised organic compounds known from the textile industry are used as well.

These methods and apparatuses for the realisation of them are disclosed in detail in e.g.

German Patent Specifications No. 26 14 260, 11 19 826 and in US Patent Specifications No.

3 398 093, 3 408 293 and 2 266 954.

However, these solutions do not fulfil the requirements set nowadays in connection with dewatering methods. Also, they are relatively disadvantageous either in the great amount of energy or in the rather complicated and sophisticated apparatuses needed for dewatering according to these known processes. Thus, the operational costs are relatively elevated. The filter capacity of the known solutions is about 10 to 60 kg/m2/hour, which can be increased in the case of optimal composition and granulometric distribution to about 150 kg/m2/hour.

OBJECTS OF THE INVENTION It is therefore an object of this invention to eliminate the aforesaid defficiencies of the previously known solutions and to provide a method for dewatering with which-on the first place the energy consumption can be considerably decreased.

Another object is to provide the possibility of applying the previously known and relatively simple filtering methods with this invention and, thus, to reduce the operational costs.

SUMMARY OF THE INVENTION In the course of our efforts for attaining these objects, we found that the difficulties in filtering slurries or suspensions have their reason in the susceptibility of the slurry or suspension to thixotropy, to structural viscosity resulting from this thixotropy as well as to the great Zetapotential between the suspended substance and the solvent agent. These are the reasons for the relatively high moisture content which can only be removed with a great amount of energy and expenditure.

The susceptibility to thixotropy and the high Zeta-potential can be minimized or even eliminated by changing the interface proprieties of the suspended substance. This changing decreases both the structural and solvate water content of the suspension. For this purpose, the suspended particles in the slurry should be treated with compounds covering or coating the interface of them and, thus, preventing the forming of the slurry structure. Namely, this slurry structure holds the capillary water. After the treatment, the suspended particle content of the slurry will be much more nonhygroscopic or moisture-repellent than before and, obviously, this greatly decreases the power and energy requirement of the dewatering process.

The ability of the various combinations to reduce the hygroscopic nature of the suspended particles can be established by measuring the CST number/Cappillar Suction Time/of the slurry. This procedure is disclosed in detail in the book of R. S. Galle: Optimizing the Use of Pretreatment Chemicals/Solid Liquid Separation Equipment Scale Up, page 40 to 82; Upland Press Ltd. Croydon England, 1976/. For characterising the agent used for promoting the dewatering process, a so called HLB number/Hydrophil-Lypophil Balance/ or an H/L number/ relation of hydrophilic portion to lypophilic portion/are introduced. The latter gives the ratio in per cent of the two portions of of molecules having different character. These numbers can either be measured or calculated from the rate or groups of molecules.A more detailed definition of these terms is to be found in the following references: Griffin, W.C.:I.Soc. Cosmetic Chemists 1.311/1949/ Griffin, W.C.:l.Soc. Cosmetic Chemists 5.249/1954/ Moore, C.; Bell, M.: Soap Perphumery and Cosmetics 29.893/1956/ Davis, l.T.: Proceedings of 2nd International Congress on Surface Activity Juhász, É.; Lelkesné, Eros, M.: Feliiletaktiv anyagok zsebk6nyve/Publisher:: Müszaki Könyvkia- dó, Budapest,/1979/ Accordingly, the invention is, in the first place, concerned with a method for dewatering mineral suspensions containing the steps of adding tensides or a mixture of tensides to the suspension in a quantity of 0,03 to 2 per cent depending on the suspended particle content and the molecular structure of the suspension, the tensides or the mixture of tensides having an HLB number of 8 to 12 or an H/L number of 50 per cent to 150 per cent, and of dewatering the suspension after the above said treatment in one of the manners known per se.The importance of this solution is in that the tendency of the suspended particles to thixotropy and to the forming slurry structure as well as their Zeta-potential are considerably lessened, nearly eliminated by treatment with the compounds having the specific HLB or H/L numbers given in this invention. By this, the moisture adsorbing ability of the suspended particles and, thus, of the slurry itself is reduced which has an obviously beneficial effect on the power and energy demand of the dewatering procedure.

This beneficial effect can be increased according to the invention by adding an ionic linear polymer polyelectrolyte or a non-ionic linear polymer polyelectrolyte with cationic character to the suspension before dewatering. wherein the polyelectrolyte has in both cases a molecular weight of 500 000 or greater.

The method in this invention makes possible to add the tensides to or to mix the tensides into the suspension with the aid of a simple mixer or of a centrifugal pump as well as by atomization or by fiim-iike contacting.

The polyelectrolyte can be added to the suspension treated with the tensides on a slide by sprinkling.

After this, the actual dewatering can be fulfilled with on of the methods known per se, in a filter chamber or in a settling tank or in a cone shaped agglomerating container having a preferable cone angle of 30ç.

In the case of another preferable realization of the method in this invention, the suspension treated with the tensides and, eventually, with the polyelectrolyte and concentrated can be forwarded to and dewatered on a settling vale and a filter having a vibrating or rotating cylinder and being connected to the settling vale.

SPECIFIC DESCRIPTION OF THE INVENTION The suspension or slurry produced in the course of the technological process and which has to be filtered is forwarded to a container, wherein the tensides are added to it by intensive mixing or by atomization. In one case, the suspension or slurry treated with the tensides is brought from the tank to a centrifuge or to a vacuum filter and is dewatered there. In other case, the slurry or suspension treated accordingly is brought from the tank onto a slide whereon the polyelectrolyte is mixed to it by e. 9. film-like contacting. The suspension coming from the slide flows into the tank of a vacuum filter and gets dewatered there.

The slurry or suspension coming from the slide and treated with the tensides and the polyelectrolyte can be forwarded into a settling vale, too. The water, i.e. the filtrate is sucked up at the end of the vale opposite to the entry of slurry or suspension and fed back into the system.

The settled substance is brought away from the bottom of the vale to a rotation filter and from there, to a storage place.

Further objects and features of the method in our invention will be described in conjunction with the following examples.

Example I Raw material: Slurry produced in the process of phosphate ore dressing from Jordan Composition: some per cent of raw phosphate kaolin, halloysite, illite, clay mineral containing montmorillonite Granulometric composition: below 0,07 mm - 48 per cent by weight 0,07 to 0,1 mm - 18 per cent by weight 0,1 to 0,125 mm - 34 per cent by weight Concentration of the slurry: 700g/litre Tenside used: mixture of an ester formed with polyethylene glycol ether and lauric acid and of an ester formed with octanole and maleine acid Quantity: 10 kg/ton dry substance Polyelectrolyte with cationic character: methyleted polyacryle amide with a molecular weight of 2 to 5 million Quantity: 0,25 kg/ton dry substance The additives are used in aqueous solution.

The slurry produced in the process of phosphate ore dressing is forwarded to a tank wherein the tenside is added by atomization or by intensive mixing. Afterwards, the slurry is brought on a slide, whereon the polyelectrolyte having cationic character is added by film-like contacting.

Thereafter, the slurry coming from the slide is brought into the tank of a vacuum filter. The vacuum used here is i\Pmax = 0,9 bar. Without additives the performance of the filter is 302 kg/m2/hour dry substance.

The CST number of the slurry is 52 seconds without treatment. After treatment, with the tensides and the polyelectrolyte having cationic character the CST number of the slurry is 4 seconds and the performance of the filter is 2487 kg/m2/hour. The thickness of the filter cake is 20 mm.

The filtrant coming out of the filter is removed with a belt conveyor and the water is fed back.

Applying the same filter, the performance is 270 kg/m2/hour without treatment and cake thickness is 10 mm, while after treatment with the tenside and the polyelectrolyte of cationic character, the performance is 2790 kg/m2/hour.

These results obviously prove, that the performance of the filter is 8 to 10 times greater after the treatment with tensides and polyelectrolyte, also in the case of various cake thicknesses.

Example 2 The same slurry as in Example 1, treated in the same way as in Example 1, is brought into a settling centrifuge. RPM of the settling centrifuge is 1000, the centrifugal force is 67 g. The result: with a slurry without treatment, the water cannot be separated from the suspended particles not even after 10 seconds. The treated slurry will be concentrated to 60 per cent after operating the centrifuge for 2 seconds. This concentration does not change even at the end of the 10th second. The concentrated slurry is discharged onto a belt conveyor and the water is fed back into the system.

Example 3 Raw material: slurry produced by processing of a waste dump of a coal mine in Yugoslavia Composition: 5 per cent coal 95 per cent loam Granulometric composition: below 0,07 mm - 4 per cent by weight 0,07 to 0,1 mm - 9 per cent by weight 0,1 to 0,1 25 mm - 23 per cent by weight 0,125 mm to 0,351 mm - 64 per cent by weight Concentration of the slurry: 430 g/litre Tenside used: ester of polyethylene glycol ether formed with mixed fatty-acids produced by decomposition of vegetable oils Quantity: 8 kg/ton dry substance Polyelectrolyte used: polyacryleamide having a molecular weight of 2 to 5 million.

Quantity: 0,2 kg/ton dry substance The slurry coming from the cyclone used for separation of the coal is forwarded into a tank wherein the tenside is added by atomization or intensive mixing. The slurry flowing out of the slurry tank is brought onto a slide and the polyelectrolyte with cationic character is added hereon by film-like contacting. The slurry flows from the slide into the filter tank of a vaccum filter and is dewatered there. The vacuum is Apm3x = 0,9 bar. The slurry has a CST number of 80 seconds without treatment and a CST of 5 seconds after treatment. Without treatment, the performance of the filter is 70 kg/m2/hour dry substance, after treatment 1400 kg/m2/hour of dry substance. The slurry coming out of the filter is taken away with a belt conveyor and the water is fed back. The thickness of the filter caks is 20 mm.

Example 4 Raw material: slurry produced by processing a waste dump of a coal mine in Austria Composition: 5 per cent lignite 95 per cent mixture of clay minerals used for fine ceramical products and earthenware Granulometric composition: below 0,07 mm 1 18 per cent by weight 0,07 to 0,1 mm - 25 per cent by weight 0,1 to 0,125 mm - 35 per cent by weight 0,125 to 0,315 mm - 22 per cent by weight Concentration of the siurry: 430 g/litre Tenside used: mixture of an ester formed with octanole and maleine acid and of an ester formed with lauric acid and polyethylene glycol ether Quantity: 9 kg/ton dry substance Polyelectrolyte used: methyleted polyacryle amide with a molecular weight of 2 to 5 million Quantity: 0,02 kg/ton dry substance The slurry has a CST number of 180 seconds without treatment, and a CST of 20 seconds after treatment.

The slurry is treated with the tenside and the polyelectrolyte in a manner described in the previous example and dewatered afterwards with a disc filter using the vacuum of Ap,,#, = 0,9 bar. Without treatment the capacity of the filter is 37 kg/m2/hour, after the treatment with only the tenside 185 kg/m2/hour and after treatment both with tenside and polyelectrolyte 250 kg/m2/hour. The filter cake has a thickness of 20 mm. The water is fed back and the dried material delivered onte 3 waste dump with the aid of a belt conveyor.

Example 5 The slurry of the previous example is treated with the tenside or with the tenside and the polyelectrolyte and afterwards, forwarded into a settling vale. The water is sucked up at the end of the vale being opposite to the entry of slurry and the settled substance, i.e. the concentrated slurry is brought from the bottom of the vale to a rotation filter. The dried material is forwarded from the filter to a waste dump with the help of a belt conveyor. The water is fed back into the system.

Example 6 Raw material: raw slurry for normal production of Portland-cement in Lábatlan, Hungary Composition: SiO2 - 20,31 per cent Awl203 - 5,41 per cent Fe2O3 - 3,08 per cent CaO - 68,12 per cent MgO - 2,66 per cent SO, - 0,29 per cent Granulometric composition: below 0.01 mm - 30 per cent by weight 0,01 to 0,065 mm - 60 per cent by weight 0,065 to 0,09 mm - 10 per cent by weight Concentration of the slurry: 1430 g/litre Tenside used: mixture of two esters as follows: ester of polyethylene glycole formed with myristic acid and hexaethylene glycole monooleate Quantity: 6 kg/ton dry substance Polyelectrolyte used: Polyacrylic acid Quantity: 0,2 kg/ton dry substance The output of the vacuum filter used here is 134 kg/m2/hour without treatment of the slurry and 555 kg/m2/hour with treated slurry. Applied vacuum: bp,,, = 0,8 bar.

Claims (8)

1. A method for dewatering mineral suspensions, wherein 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 a HLB number falling within the range 8 to 12 or an H/L number falling within the range of 50% to 150% and thereafter dewatering the suspensions.

2. A method according to Claim 1, wherein an ionic linear polymer polyelectrolyte or a nonionic linear polymer polyelectrolyte of cationic character is added to the suspension before dewatering, said polyelectrolytes having in both cases a molecular weight of 500,000 or greater.

3. A method as claimed in Claim 2, wherein said tensides or mixture of tensides is added to the suspension with a simple mixer, with a centrifugal pump, by atomization or by film-like contacting.

4. A method as claimed in Claim 3, wherein the suspension is forwarded after treatment with said tensides onto a slide and said polyelectrolyte is added by sprinkling on said slide.

5. A method as claimed in Claim 4, wherein the suspension is dewatered in a filter chamber or in a settling tank or in a cone shaped agglomerating container having a preferable cone angle of 30 .

6. A method as claimed in Claim 4 wherein the suspension treated with said tensides and eventually with said polyelectrolyte and concentrated is dewatered on a settling vale and a filter having vibrating or rotating cylinder and connected to said settling vale.

7. A method for dewatering mineral suspensions substantially as hereinbefore described and with reference to the accompanying examples.

8. Dewatering mineral suspensions when produced by the method as claimed in any preceding claim.