Dry preparation of kaolin in the production of HPA

Abstract

A method for preparing raw kaolin (R) uses a milling and separating device (1) which has a milling section (13) and a first separating section (16). The raw kaolin (R) is a material mixture of at least kaolin as a first fraction (F1) and a second fraction (F2) which comprises at least quartz. The raw kaolin (R) is supplied to the milling section (13), in which the first fraction (F1) is at least partly removed from the raw kaolin (R) by means of a grinding process, and the first fraction (F1) is then separated from the second fraction (F2) in the first separating section (16).

Claims

1.-10. (canceled)

11. A method for preparation of raw kaolin (R) in a milling and separating device (1) which has a milling section (13) and a first separating section (16), comprising: providing the raw kaolin (R) as a material mixture comprising a first fraction (F1) including kaolin as and a second fraction (F2) including quartz; feeding the raw kaolin (R) to the milling section (13), in which the first fraction (F1) is extracted at least in part from the raw kaolin (R) by pulverizing; and subsequently separating the first fraction (F1) from the second fraction (F2) in the first separating section (16), wherein the preparation is carried out without production of a suspension of the raw kaolin (R).

12. The method according to claim 11, wherein the separation in the first separating section (16) is carried out by a gas flow which has a component opposite to the direction of gravitational force and is so arranged that particles of the first fraction (F1) are carried away at least in part by the gas flow whilst particles of the second fraction (F2) drop down against or out of the gas flow.

13. The method according to claim 11, wherein the milling section (13) comprises a rotatable grinding table (14) with a grinding table surface (14a) and at least one similarly rotatable, cylindrical grinding roll (15) with a roll grinding surface (15a), which faces the grinding table (14) and is spaced from the grinding table surface (14a) by a gap (D).

14. The method according to claim 13, wherein the gap (D) is adjustable.

15. The method according to claim 13, wherein positions and/or locations of the grinding rolls (15) relative to the grinding table (14) and/or a contact pressure of the grinding rolls (15) on the grinding table (14) are adjustable.

16. The method according to claim 13, wherein the raw kaolin (R) is delivered to the table grinding surface (14a), is transported outwardly due to the rotation of the grinding table (14) and subsequently enters the gap (D) between the table grinding surface (14a) and the roll grinding surface (15a), whereby the raw kaolin (R) is pulverised and the first fraction (F1) is extracted at least in part from the raw kaolin (R).

17. The method according to claim 16, wherein the table grinding surface (14a) and the roll grinding surface (15a) rotate in opposite directions.

18. The method according to claim 11, wherein the milling and separating device (1) has a second separating section (17), in which a selection of the first fraction (F1) according to particle size takes place.

19. The method according to claim 18, wherein the second separating section (17) comprises one or more deflecting plates (18) and a sifter (19), wherein the sifter has a collecting chamber (19a) and one or more sieve-like outer wall sections (19b) with a plurality of openings through which a part of the particles of the first fraction (F1) can pass so as to enter the collecting chamber (19a), whilst another part of the particles of the first fraction (F1) is deflected by the outer wall sections (19b) of the sifter (19) as well as the deflecting plates (18) and conducted back into the milling section (13).

20. The method according to claim 19, wherein the sifter (19) is preferably a rod basket sifter.

21. The method according to claim 19, wherein the separation in the first separating section (16) is carried out by a gas flow which is directed towards the sifter (19).

22. The method according to claim 19, wherein the sifter (19) is rotatable.

23. The method according to claim 19, wherein the sifter (19) is rotatable at an adjustable rotational speed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a schematic illustration of a milling and separating device for the dry preparation of kaolin.

DETAILED DESCRIPTION

[0026] In the following, preferred embodiments are described on the basis of the FIGURE.

[0027] FIG. 1 is a schematic illustration of a milling and separating device 1 for the dry preparation of kaolin.

[0028] The milling and separating device 1 has an interior defined by an enclosure 11 and a feed section 12, via which the raw kaolin R, which is preferably a mixture of at least kaolin and quartz, is fed to the interior. In the example of FIG. 1, the milling and separating device 1 has an approximately axially symmetrical construction, wherein the feed section 12 is located centrally in the upper region of the device, such that the raw kaolin R is transported into the interior of the milling and separating device 1 substantially centrally in the direction of gravitational force. However, the feed section 12 can also be arranged laterally or in some other manner, as long as the raw kaolin R enters the interior and can be fed for further processing.

[0029] The milling and separating device 1 also has a milling section 13, which in the embodiment of FIG. 1 comprises a rotatable grinding table 14 with a table grinding surface 14a and a plurality of similarly rotatable, cylindrical grinding rolls 15. The cylindrical grinding rolls 15 each have a beveled roll grinding surface 15a, which faces the grinding table 14 and is spaced from the table grinding surface 14a by a gap D. The grinding rolls 15 are located in the region of the outer circumference of the grinding table 14 and co-operate with the grinding table 14 as follows:

[0030] The raw kaolin R fed via the feed section 12 falls onto the grinding table 14 and is transported outwardly due to the rotation of the latter. The raw kaolin R goes into the gap D between the two grinding surfaces 14a and 15a, which preferably rotate in opposite sense. In this manner, the raw kaolin R is pulverized, resulting in separation into a first fraction F1, which is a fine or light fraction, and a second fraction F2, which is a heavy or coarse fraction relative to the first fraction F1. The second fraction F2 comprises at least quartz; the first fraction F1 consists substantially of the kaolin that is released.

[0031] The grinding rolls 15 are preferably individually adjustable. In particular, the gap D is preferably variable in order to be able to vary the contact pressure during the pulverizing. In addition, the speed of rotation, position and/or location of the grinding rolls 15 can be organized individually or in groups, and/or the speed of rotation, location and/or position of the grinding table 14 can be organized to be adjustable.

[0032] After the particles of the first and second fractions F1, F2 have outwardly departed from the gap D in the radial direction of the grinding table 14, they enter a gas flow, preferably an air flow, the flow parameters, such as volume flow, flow velocity or the like, of which are adjusted so that a separation of the first fraction F1 from the second fraction F2 takes place. The gas flow can be generated, for example, by a blower (not shown). Particles of the second fraction F2 fall down past the grinding table 14 and are discharged (not shown), and particles of the first fraction F1 are carried along upwards by the gas flow, as shown by arrows in FIG. 1. The separation of the first fraction F1 from the second fraction F2 takes place in a section which is referred to herein as the first separating section 16.

[0033] The milling and separating device 1 also has a second separating section 17, which can be used to adjust the fineness of the particles of the first fraction F1, that is, the fineness of the kaolin particles. For this purpose, the second separating section 17 comprises deflecting plates 18 and a rotatable sifter 19, which is preferably a rod basket sifter.

[0034] The rod basket sifter 19 is a cylindrical or hollow-cylindrical component, which has a collecting chamber 19a and one or more sieve-like outer wall sections 19b. The outer wall sections 19b are located at least in sections at the outer circumference of the rod basket sifter 19 and have several openings, slots or the like through which particles of a certain size can pass. The gas flow, which carries away the particles of the first fraction F1 in upward direction due to the low weight, is thus preferably directed towards the rod basket sifter 19. A part of the particles of the first fraction F1 passes through the sieve-like outer wall sections 19b into the collecting chamber 19a, from which the kaolin, which has been extracted and pulverized to the desired degree of comminution, can be discharged. Another part of the particles, essentially particles with too large a diameter, is “thrown back” by the outer wall sections 19b and falls down away from the main gas flow. The deflecting plates 18 are arranged in such a manner that the particles rejected by the rod basket sifter 19 fall back onto the grinding table 14 and mix with the feed material from the feed section 12. The fineness of the particles of the first fraction F1, i.e., the prepared kaolin, can be adjusted by means of the rotational speed of the sifter 18.

[0035] The dry breaking down or dry preparation of the raw kaolin with the assistance of the milling and separating device 1 completely dispenses with a costly wet phase. With the milling and separating device 1, the contact pressure of the grinding rolls 15 can be varied so that selective crushing can be achieved. This selective crushing makes it possible to separate kaolin and quartz by a subsequent sifting process. Moreover, by adjusting the process parameters, such as contact pressure of the grinding rolls 15, mass flow of the ground material, volume flow to the sifter 19, drying temperature, etc., an optimal classification or sieving of the kaolin can be achieved.

[0036] In the preparation of kaolin, up to the production of high-purity aluminum oxide, various process steps, such as filtration and calcination/drying of the product, can be omitted. This makes it possible to significantly simplify the preparation process. The process using the milling and separating device 1 saves energy and resources and can be carried out cost-effectively.

[0037] To the extent applicable, all individual features explained in the embodiments can be combined and/or exchanged.

LIST OF REFERENCE SIGNS

[0038] 1 milling and separating device [0039] 11 enclosure [0040] 12 feed section [0041] 13 milling section [0042] 14 grinding table [0043] 14a table grinding surface [0044] 15 grinding roll [0045] 15a roll grinding surface [0046] 16 first separating section [0047] 17 second separating section [0048] 18 deflecting plate [0049] 19 sifter [0050] 19a collecting chamber [0051] 19b outer wall section [0052] R raw kaolin [0053] D gap [0054] F1 first fraction [0055] F2 second fraction