GB2083804A - A method of dewatering slurry - Google Patents

Abstract

A method of dewatering slurry in a centrifuge comprises adding to the slurry a rapidly hardening additive. The rapidly hardening additive is preferably cement.

Description

SF'tUlFlUA I IUN A method of dewatering slurry The invention relates to a method of dewatering slurry in a centrifuge, and is particularly suitable for dewatering a slurry which contains carbon.

The slurry, more particularly a slurry which contains carbon, is dewatered in a centrifuge in a manner known per se by adding flocking agents, in order to make it possible to separate very fine solid particles found in the slurry from the liquid. When it has been dewatered in this way the slurry is in the form of a doughy mass in most cases, which has to be subjected to a special subsequent treatment in order to enable it to be transported, stored or used in some other way. However, this involves high labour costs, capital costs and a large amount of time.

The invention therefore seeks to provide a method which will make it possible to dewater slurry, in a centrifuge while avoiding some or all of the above disadvantages and in which the solid end-product of the centrifuge is already in the form of a product which is easily transported and stored.

According to the invention, there is provided a method of dewatering slurry in a centrifuge, wherein a rapidly hardening additive is added to the slurry.

In this way the solids present in the slurry are consolidated during dewatering of the slurry in the centrifuge in an extremely advantageous manner and not only does this considerably assist the dewatering action but it also results in an end product which is in crumb form, as has been shown in practice, this end-product being very easily transported, stored or further processed without any subsequent treatment. Furthermore, in practical tests it was shown that the agglomerate-type product or crumb-like products, dewatered and extracted from the centrifuge, solidified noticeably after approximately two to three hours; but could be crushed easily. Samples of this dewatered product did not shown any tendency to dissolve in water either - even after several hours.

Cement, as the rapidly hardening additive, may be added to the slurry. The addition of cement to the slurry can be effected either in dry form or in the form of cement slurries, and this may be carried out independently of additions of flocking agent. As practical dewatering tests using slurry containing carbon have shown, in a solid sleeve screw centrifuge, particularly good results could be achieved when the quantity of cement added to the slurry as an additive was between 1 and 5%, more particularly 3%, by weight of the solids in the slurry. The solids extracted from the centrifuge during these tests had a relatively dry and crumb-like structure which could be easily loaded transported and stored. After approximately two to three hours of storage a distinct solidification of the crumb-like product was established.After storage for approximately 20 hours a further solidification of the crumb-like product was ascertained and the crumb-like product was very easily crushed; but did not show any signs of dissolving in water.

Because the slurry is dewatered by adding a rapidly hardening additive, the slurry can be transported, stored and/or utilized in a very advantageous manner immediately after dewatering without any special subsequent treatment. Therefore, in comparison to previously known methods, not only is there a substantial improvement in the dewatering action as a result of the present method but there is also an important reduction in labour and capital costs.

One embodiment of the invention will now be described in greater detail, by way of example: Flotation tailings with a solids concentration or with dry materials (TS), which make up 23 percent of the total, were dewatered in a solid sleeve screw centrifuge at 1450 revolutions of the drum per minute. Approximately 3% by weight PZ 35 (Portland Cement) i.e. 3% of the solids or the dry materials (TS), was then introduced into the centrifuge in dry form and mixed with the flotation tailings. At the same time a synthetic flocking agent, i.e. 2.5 kg per tonne of dry materials (TS), was added to the flotation tailings directly in the centrifuge inlet. The flotation tailings dewatered in this way in the solid sleeve screw centrifuge were crumb-like and clearly solidified after about 2 to 3 hours of storage.

Although these dewatered, crumb-like flotation tailings could be broken up and crushed very easily, there were, after storing the crumb-like flotation tailings for several days no signs of them dissolving in water.

The method according to the present invention is not restricted to this example. Apart from the slurries which contain carbon (such as flotation tailings) other types of slurry can also be dewatered profitably by the method according to the invention such as municipal slurry or sapropel. Furthermore, besides cement, ash can be used very profitably in accordance with the method of the invention, more particularly flue dust or flue dust combined with calcium hydroxide Ca (OH)2. Moreover, the additives such as cement or flue ash may be added to the slurry which is to be dewatered, directly before dewatering, in the centrifuge, either when dry or wet in the form of a sludge.

1. A method of dewatering slurry in a centrifuge, wherein a rapidly hardening additive is added to the slurry.

2. A method according to claim 1, wherein cement is added to the slurry as the rapidly hardening additive.

3. A method according to claim 1 or 2, wherein the quantity of additives added to the slurry is between 1 and 5% by weight of solid material in the slurry.

4. A method according to claim 3, wherein the quantity of additives is 3% of the solid material in the slurry.

5. A method according to any one of the preceding claims, wherein a flocking agent is also added to the slurry.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. SF'tUlFlUA I IUN A method of dewatering slurry The invention relates to a method of dewatering slurry in a centrifuge, and is particularly suitable for dewatering a slurry which contains carbon. The slurry, more particularly a slurry which contains carbon, is dewatered in a centrifuge in a manner known per se by adding flocking agents, in order to make it possible to separate very fine solid particles found in the slurry from the liquid. When it has been dewatered in this way the slurry is in the form of a doughy mass in most cases, which has to be subjected to a special subsequent treatment in order to enable it to be transported, stored or used in some other way. However, this involves high labour costs, capital costs and a large amount of time. The invention therefore seeks to provide a method which will make it possible to dewater slurry, in a centrifuge while avoiding some or all of the above disadvantages and in which the solid end-product of the centrifuge is already in the form of a product which is easily transported and stored. According to the invention, there is provided a method of dewatering slurry in a centrifuge, wherein a rapidly hardening additive is added to the slurry. In this way the solids present in the slurry are consolidated during dewatering of the slurry in the centrifuge in an extremely advantageous manner and not only does this considerably assist the dewatering action but it also results in an end product which is in crumb form, as has been shown in practice, this end-product being very easily transported, stored or further processed without any subsequent treatment. Furthermore, in practical tests it was shown that the agglomerate-type product or crumb-like products, dewatered and extracted from the centrifuge, solidified noticeably after approximately two to three hours; but could be crushed easily. Samples of this dewatered product did not shown any tendency to dissolve in water either - even after several hours. Cement, as the rapidly hardening additive, may be added to the slurry. The addition of cement to the slurry can be effected either in dry form or in the form of cement slurries, and this may be carried out independently of additions of flocking agent. As practical dewatering tests using slurry containing carbon have shown, in a solid sleeve screw centrifuge, particularly good results could be achieved when the quantity of cement added to the slurry as an additive was between 1 and 5%, more particularly 3%, by weight of the solids in the slurry. The solids extracted from the centrifuge during these tests had a relatively dry and crumb-like structure which could be easily loaded transported and stored. After approximately two to three hours of storage a distinct solidification of the crumb-like product was established.After storage for approximately 20 hours a further solidification of the crumb-like product was ascertained and the crumb-like product was very easily crushed; but did not show any signs of dissolving in water. Because the slurry is dewatered by adding a rapidly hardening additive, the slurry can be transported, stored and/or utilized in a very advantageous manner immediately after dewatering without any special subsequent treatment. Therefore, in comparison to previously known methods, not only is there a substantial improvement in the dewatering action as a result of the present method but there is also an important reduction in labour and capital costs. One embodiment of the invention will now be described in greater detail, by way of example: Flotation tailings with a solids concentration or with dry materials (TS), which make up 23 percent of the total, were dewatered in a solid sleeve screw centrifuge at 1450 revolutions of the drum per minute. Approximately 3% by weight PZ 35 (Portland Cement) i.e. 3% of the solids or the dry materials (TS), was then introduced into the centrifuge in dry form and mixed with the flotation tailings. At the same time a synthetic flocking agent, i.e. 2.5 kg per tonne of dry materials (TS), was added to the flotation tailings directly in the centrifuge inlet. The flotation tailings dewatered in this way in the solid sleeve screw centrifuge were crumb-like and clearly solidified after about 2 to 3 hours of storage. Although these dewatered, crumb-like flotation tailings could be broken up and crushed very easily, there were, after storing the crumb-like flotation tailings for several days no signs of them dissolving in water. The method according to the present invention is not restricted to this example. Apart from the slurries which contain carbon (such as flotation tailings) other types of slurry can also be dewatered profitably by the method according to the invention such as municipal slurry or sapropel. Furthermore, besides cement, ash can be used very profitably in accordance with the method of the invention, more particularly flue dust or flue dust combined with calcium hydroxide Ca (OH)2. Moreover, the additives such as cement or flue ash may be added to the slurry which is to be dewatered, directly before dewatering, in the centrifuge, either when dry or wet in the form of a sludge. CLAIMS

1. A method of dewatering slurry in a centrifuge, wherein a rapidly hardening additive is added to the slurry.

2. A method according to claim 1, wherein cement is added to the slurry as the rapidly hardening additive.

3. A method according to claim 1 or 2, wherein the quantity of additives added to the slurry is between 1 and 5% by weight of solid material in the slurry.

4. A method according to claim 3, wherein the quantity of additives is 3% of the solid material in the slurry.

5. A method according to any one of the preceding claims, wherein a flocking agent is also added to the slurry.

6. A method of dewatering slurry substantially as described herein.