DE2506316B2 - Process for the comminution of rock phosphate - Google Patents

Description

The invention relates to a method for comminuting moist, pre-crushed rock phosphate in a rock phosphate with a grain size of 80% below 2 mm.

Rock phosphate is a solid, coarse-grained mineral. It will, inter alia. for the production of phosphoric acid by Reaction with sulfuric acid used. For this reaction it is necessary to add the rock phosphate to reduce at least 80% to a grain size of less than 2 mm.

For the comminution of the coarse-grained rock phosphate, two methods have so far proven to be applicable proven, namely dry grinding and wet grinding.

With dry grinding, the coarse-grained rock phosphate, which can have a moisture content of approx. 10% and more, is first subjected to drying to approx. 1 to 3% water content. This drying takes place in large heated drying drums. Since all rock phosphate, including the fine-grained part, is dried, a high heating energy consumption is inevitable. To reduce the natural moisture of z. B. 14% to a residual moisture of approx. 3% around 50 kg of heating oil / t P ₂ O _{5 are} required. The dried rock phosphate is ground in mills with an energy requirement of around 70 kWh / t P2O5. Air sifting was used to separate the material to be screened into fine and oversized particles.

When wet grinding the rock phosphate in a ball or rod mill, it is necessary to check the moisture content to increase to over 50%. If the moisture content is below 50%, the grinding media and The grinding surfaces are encrusted and stuck together with the rock phosphate, preventing the grinding.

The ground rock phosphate with a water content of over 50% must then be used for the Further processing can be dewatered again. This drainage creates difficulties, since filter cloths with large pore diameters only an insufficient separation of the fine fraction of the rock phosphate from the Bring liquid and plug filter cloths with small pore diameters.

A combination of grinding and sieving is used in the grinding of crystals, in the rock phosphate grinding was previously only a dry grinding with .Sichting through an air stream State of the art, since all types of sieves only have to be caked with the coarse grain and the fine grain poorly separated the coarse grain from the fine grain.

It should be noted that sieving a completely dry rock phosphate is entirely possible If the humidity is between 1 and about 5%, the grain is electrostatically charged, and it comes with the Sieving to form bridges, and the separation of the fine grain from the coarse grain is very poor Half of the fine grain present in the starting product can thus be carried away into the coarse grain.

The invention is based on the object of pit-damp Rock phosphate in a simple manner in terms of apparatus, without the use of heating energy and with avoidance the disadvantages of the known processes in a comminuted rock phosphate with a high fine grain content to convict.

According to the invention, this object is achieved in that the raw phosphate is at least twice as high Screen classification and the coarse grain resulting from the last classification in a roller burnishing mill is crushed to a grain size below 2 mm.

According to one embodiment of the invention, it has proven to be advantageous if the first sieve classification a sieve with a maximum grain size of 4 mm and the second sieve classification a sieve with a maximum grain size of 2 mm.

In order to get the coarse grain of the second classification, which has a grain size larger than 2 mm, trouble-free marry, according to a further embodiment of the Invention of the coarse grain of the last sieve classification at different speeds of the two smooth rollers of the roller burnishing mill. This measure is due to the existing in the nip Differential peripheral speed achieved a self-cleaning of the rollers. It doesn't come to that dreaded caking of ground phosphate on the rollers. The grain got between the rollers is caused by radial and tangential forces, the latter result from the differential peripheral speed, ■ '! grated.

The method according to the invention has the essential advantage of the direct processing of pit-moist rock phosphate. Neither an apparatus-related and energetically expensive drying with subsequent ■ '. Grinding at high output and an excessive increase in moisture to over 50% with their problem of effective filtration of the rock phosphate mash are required. The process according to the invention leads directly to a very fine-grained rock phosphate, the natural moisture content of which proves to be advantageous z. B. for further processing to phosphoric acid using sulfuric acid.

The following example gives numerical values for a comminution according to the invention of rock phosphate.

The method is not limited to these numerical values, but also includes those that are im approximate area.

1. Wet sieving on vibrating sieves
Moisture of the rock phosphate 13.8% Grain size Source material 63 mm
63-2 mm
2-1 mm
less than 1 mm 12.4%
14%
13.2%
60.4%

The sieving was carried out on two

ten seven.

Screen inclination 12 ° for both screens.

Mesh size Sieve 1 4 mm

Sieve 2 2 mm

Feed quantity sieve 1: 75 kg In the upper course as coarse grain: 19 kg Passage: 56 kg This "passage" served as a task for that

second sieve.

In the upper course as coarse grain: 4 kg Passage: 52 kg

About 3.5% of the grain under 1 mm still adheres to the upper grain of 19 or 4 kg.

2. Grinding in a roller burnishing mill. Peripheral speed: Ux = 11.1 m / s U ₂ = 13.4 m / s

Grain size of the feed material: upper reaches of the

Moisture of the feed material: bulk weight: Gap width of Finish rolling mill:

2 mm sieve from (l) 13.8% 1.0 t / ms

0.7 mm

The grist has the following fine grain content:

2-1 mm 18.18%

0.5-1mm 24.05%

0i-0iram 35.93%

below 0.2mm 21.84%

Specific energy requirement: 13.5 kWh / t P ₂ O ₅

Claims (3)

Patent claims: 1. Process for the comminution of moist, pre-broken rock phosphate into a rock phosphate with a grain size of 80% below 2 mm, characterized in that the rock phosphate subjected to at least two sieve classification and that with the last Classification of the coarse grain in a roller burnishing mill to a grain size below 2 mm is crushed. 2. The method according to claim 1, characterized in that the first sieve classification a Screening material with a maximum grain size of 4 mm and the second screening classification a screening material with a maximum grain size of 2 mm. 3. The method according to claim 1, characterized in that the coarse grain of the last sieve classification is crushed at different speeds of the two smooth rollers of the roller burnishing mill.