GB2184036A - Separation - Google Patents

Abstract

Separation of solids from liquids or solids from solids is facilitated by applying a wide range of anionic or non-ionic surface active agents. Separation may involve filtering or settling of a suspension or wet or dry screening to classify solid particles. The agents are added in specific amounts to the suspension or dissolved in water and applied to the solids before screening. Solids may be coal, barium sulphate, calcium carbonate, quartz or ashes.

Description

SPECIFICATION Process of separating solid phases In order to obtain more applicable and more valuable products, minerals are pretreated in physico-chemical operations whereupon the solid phase of products is of increased homogenity and/or concentration.

Classification operation is carried out on the basis of differences -in grain size by screening, or -in grain size and mass, e.g. by table separation.

Classification can be dry (gas-solid) or wet (liquid-solid) process.

1. In wet processes the liquid applied is usually water. Different methods are used for separation of water and the solid phase, if the solid product is coarse-grained or if it is in a sludge: a.) Low residual water content can be easily attained if the solid is coarse-grained e.g. by using a storage vessel equipped with drainage system, a dewatering screen or a centrifuge.

b.) Sludges are usually dewatered in two steps. At first most of the water is separated from the solid particles sedimented on standing or concentrated in pulp thickener. Water content of the thick sludge obtained can be decreased further by centrifuging and, optionally, by heatdrying.

Continuous vacuum filtration is the usually applied preparatory operation, however, revolving filters or press filters are also often used. Water content of the filter cake is about 30-40% by weight.

Operations mentioned above are known and generally used in processes applied in preparatory plants for minerals, e.g. for handling waste water sludge, activated sludge, mud, dross in uranium ore processing, bauxite processing, coal dressing, coal firing, etc.

Present invention is based on the recognition that direct interaction between surfaces of solid particles is a factor which determines sedimentation properties of the solid dispersed in a liquid.

Strength of interaction depends on the areas of the interacting surfaces and on the nature of the layers adsorbed on the surfaces. Surface layer can consist of ions only (electrical double-layer in electrolytes) or molecules only (lyosphere) The most general case is when both ions and molecules are adsorbed in the surface layer. The layers adsorbed can enhance or diminish the strength of adhesion between particles.

Interaction of solid particles in a solid-liquid dispersion can be controlled by soluble additives.

Application of additives, such as anionic or non-ionic surface-active substances are preferred because they also decrease the surface tension of the liquid. In relation with separation of liquid and solid phase, lower surface tension is advantageous.

For granular materials the lower limit of water content which can be achieved by mechanical methods depends on the particle size distribution, primarily on the amount of particles smaller than 0.5 mm. Water adhered to surface and bound in capillaries is usually referred as coarse wetness. Amount of adhered water is proportional to the specific surface area. Capillaries which are smaller than a certain size retain water by capillary forces. Such pores can be formed where particles are in contact. Due to capillary rise part of the total pore volume is filled up with water.

If surface tension is smaller capillary rise is also smaller, and, as a result, pore volume filled up with water is proportionally smaller.

2. Dry processes are used in the absence of water or when it is disadvantageous to contact material and water, e.g. separation of water soluble crystals, classification of milled cement, etc.

It is difficult to separate fine-grained materials because they tend to stick and agglomerate. As described under point 1, present invention is based on the recognition that in a dispersion, the character of the interaction between particles can be influenced by ionic or non-ionic additives.

Efficiency of separation can be improved and energy consumption can be reduced applying the method invented.

According to our process dispersing agent is contacted with the surface of particles in aqueous solution. Amount of liquid (water) is 0.01-3% by weight related to the weight of the air-dry solid. The amount of the additive is 0.004-10% by weight related to the liquid (water).

Additives applied in our experiments were the sodium salts of alkylsulfates, alkyl benzenesulfonic acids, alkylsulfonic acids, alkyl naphthalenesulfonic acids, petroleum sulfonic acids, fattyacids, perfluoridated fatty-acids and ligninsulfonic acids; adducts of ethylene oxide; fatty-acid esters of polybasic alcohols.

Example 1 Wet screening Black stone coal of South Transdanubian origin consisting of. particles smaller than 2.5 mm was separated by wet screening. The screening was carried out in water and in an aqueous solution containing 0.05% by weight SAA, i.e. Evatriol R (EVM) which is a mixture of alkylsul phates, alkyl sulphonates and alkyl-aryl sulphonates.

Data obtained are shown as follows: Amount of fraction (% by weight) Particle size if the medium is mm water solution of SAA4 2.5-0.125 78.5 75.6 0.125-0.071 8.8 10.1 0.071 12.7 14.3 * SAA* is Evatriol R As it can be seen from the above results amount of size fraction containing particles smaller than 0.071 mm is larger using solution of a surface active material for wet screening in accordance with the present invention compared to the amount of fraction obtained by wet screening without surface active agent.

Example 2 Sedimentation Sedimentation of a barium sulfate was studied as a suspension in water and in aqueous solution containing surface active agent (SAA) in a concentration of 0.08% by weight, i.e.

TWEEN 60R (Atlas); chemically nonionic ethylene oxide adduct. When steady state was attained the volume of the deposit was 30% smaller in solution of SAA than in water, i.e. a solid phase of smaller water content can be separated.

Example 3 Filtration Separation of water and quarz was studied with and without addition of SAA, i.e. Fluowet R (Hoechst); chemically sodium salt of perfluoridated fatty-acids). After the same period of time residual water content of the quarz was 11% by weight and 4.5% by weight in the experiments without and with SAA, respectively. Data show that applying the process of the present invention a solid phase of smaller water content can be obtained.

Example 4 Sedimentation Sedimentation of ash obtained from a thermal power station was examined in water and in an aqueous solution containing 0.08% by weight SAA, I.E. Ufapast 62 R (Unger); chemically alkylbenzene sulfonate. When steady state was attained volume of the deposit was 25% smaller in the solution of SAA than in water, i.e. a solid phase of smaller water content can be separated.

Example 5 Dry screening Black stone coal from South Transdanubian origin consisting of particles smaller than 2.5 mm was separated by screening. The coal was stored at ambient conditions for two months, then divided into two parts. One of the parts was screened (known method); and an aqueous solution containing 3.3% by weight Evatriol R (EVM)-chemically mixture of alkyl sulphates, alkyl sulphonates and alkyl-aryl sulphonates-was sprayed on the other part in an amount of 1.5% by weight related to the air-dry coal. 24 hours after spraying the sample was screened. Data obtained are as follows.

Particle size, Amount of fraction, % by weight mm air-dry coal air-dry coal+1.5% by weight water+0.05% by weight SAA* 2.5-0.125 74.1 69.6 0.25-0.071 8.1 9.2 < :0.071 17.8 21.20 * SAA is Evatriol R Results demonstrate that the amount of the size fraction smaller than 0.071 mm obtained is larger using the invented process (21.2% by weight) than that obtained by screening the air-dry sample (17.8% by weight.

Example 6 Dry screening Barium sulfate consisting of particles smaller than 1.0 mm was separated by screening. The barium sulfate was stored at ambient conditions for two months than divided into two parts.

One of the parts was screened (known method); and an aqueous solution containing 33% by weight TWEEN 60 R (Atlas)-chemically nonionic ethylene oxide adduct-was sprayed on the other part in an amount of 1.5% by weight related to the air-dry barium sulfate. 24 hours after spraying the sample was screened.

Data obtained are as follows: Particle size, Amount of fraction, % by weight mm air-dry BaSO4 air-dry BaSO4+1.5% by weight water+ 0.05% by weight SAA* 1.0-0.125 56.2 43.6 0.125-0.071 28.4 30.2 < :0.071 15.4 27.2 * SAA is TWEEN 60R Results demonstrate that the amount of the size fraction smaller than 0.071 mm obtained is larger using the invented process (27.2% by weight) than that obtained by screening the air-dry sample (15.4% by weight).

Example 7 Dry screening Ash from a thermal power station consisting of particles smaller than 0.8 mm was separated by screening. The ash was stored at ambient conditions for two months then divided into two parts. One of the parts was screened (known method); and an aqueous solution containing 3.3% by weight Fluovet R (Hoechst), chemically-sodium salt of perfluoridated fatty-acids-was sprayed on the other part in an amount of 1.5% by weight related to the air-dry ash. 24 hours after spraying the sample was screened.

Data obtained are as follows: Particle size Amount of fraction, % by weight mm air-dry ash air-dry ash+ 1.5% by weight water+0.05% by weight SAA* 0.8-0.125 44.3 34.80 0.125-0.071 15.5 18.50 < :0.071 40.2 46.20 * SAA is Fluovet R Results demonstrate that the amount of the size fraction smaller than 0.071 mm obtained is larger using the invented process (46.2% by weight) than that obtained by screening the air-dry sample (40.2% by weight).

Example 8 Dry screening Calcium carbonate consisting of particles smaller than 0.8 mm was separated by screening.

The calcium carbonate was stored at ambient conditions for two months than divided into two parts. One of the parts was screened (known method) and an aqueous solution containing 3.3% by weight Ufapast 62 R (Unger), chemically-alkyl benzene-sulfonate-was sprayed on the other part in an amount of 1.5% by weight related to the air-dry calcium carbonate. 24 hours after spraying the sample was screened.

Data obtained are as follows: Particle size, Amount of fraction, % by weight mm air-dry CaCO3 air-dry CaC03+ 1.5% by weight water +0.05% SAA* 0.8-0.125 57.3 48.4 0.125-0.071 23.3 27.4 < :0.071 19.4 24.2 * SAA is Ufapast 62 R Results demonstrate that the amount of the size fraction smaller than 0.071 mm obtained is larger using the invented process (24.2% by weight) than that obtained by screening the air-dry sample (19.4% by weight).

Claims (2)

1. A process for intensifying preparatory operations applied for separation and/or classification of minerals of natural origin or artifical products of mineral character which comprises adding at least one compound selected from sodium salts of alkylsulfates, alkylsulfonic acids, alkyl benzenesulfonic acids, alkyl naphthalenesulfonic acids, petroleum sulfonic acids, fatty-acids, perfluoridated fatty-acids and ligninsulfonic acids; adducts of ethylene oxide; fatty-acid esters of polybasic alcohols (a) in an amount of 0.03-5% by weight, related to the weight of the liquid phase in wet type separation processes, or (b) dissolved in water in dry type separation processes, wherein the amount of the additive is 0.004-10% by weight related to the liquid (water), and the amount of water added to the material by the solution is 0.01-3% by weight related to the weight of the air-dry material.

2. A process as claimed in claim 1, substantially as hereinbefore described in any one of Examples 1 to 8.