DE1912183B2 - PROCESS FOR MANUFACTURING LOW FLUORINE CEMENT CLINKER FROM PHOSPHORIC ACID BY-PRODUCT PLASTER - Google Patents

Description

The invention relates to a method of manufacturing Development of low-fluorine cement clinker made from phosphoric acid by-product gypsum, which in itself contains too much fluorine Contains, according to the gypsum-sulfuric acid process.

In the production of phosphoric acid from rock phosphate and sulfuric acid fall as a by-product large amounts of impure calcium sulfate in the form of dihydrate, hemihydrate or anhydrite. Below are these types of calcium sulfate regardless of their actual degree of hydration simply by-product plaster of paris or just plaster of paris.

In general, the by-product gypsum in phosphoric acid plants is an annoying waste material, ilen one throws on the dump. In addition to the transport and property costs, you often have to high costs of securing groundwater from contamination by those present in gypsum Harmful compounds such as phosphates and fluorides are used.

In recent times many efforts have been made to reduce the by-product gypsum in the so-called To use clips sulfuric acid process and to process on zeinent and sulfuric acid.

Such a use would be particularly advantageous because it would contain almost all of the sulfuric acid the phosphoric acid used in the manufacture of animal products would be recovered. The sulfuric acid would thus be practically in a cycle, while the lime component of the Rock phosphate would be converted into cement clinker.

However, this use of the by-product gypsum is also due to the impurities of phosphates and fluorides. Thus, under certain circumstances, by-product gypsum with 1 "/ o P2O5 or no more clinker can be produced that leads to a Portland cement that conforms to standards can be processed, as this relatively high P2Os ratio in particular could adversely affect the wedge winding in the initial stage of cement setting. On the other hand, for lower P2Os contents due to detailed: Investigations z. B. according to silica technology / 7. Year 17, 1956. P. 316, a cheaper, d. H. Activity-increasing influence demonstrable.

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Also in the case of the fluorine content in the waste gypsum, practice shows both, depending on the concentration a favorable as well as an unfavorable inflow. Small fluorine contents of up to about 0.15 »/ o can be used make clinker firing considerably easier. In fact, however, the fluorine content in the waste gypsum was significant higher ζ B. by 1 ° / (C and endanger from concentrations from Z. B. 0.5 ° / c in continuous operation also that Oven lining of the rotary kiln, as its softening point due to its well-known strong flux effect Reduce the material in the sintering zone. In addition, they undesirably increase the setting time of cement.

Various processes are now known for producing purer waste phosphoric acid gypsum Thus, in Belgian patents 6 96 523 and 7 00 367 there are methods of reducing it the phosphate content, which is described with a transition of the gypsum from a hydration state work in another. However, a reduction in the fluorine content is not the subject of this invention Processes which remove fluorine and phosphate impurities are also state of the art have to the subject. Such a method is e.g. B. in the Belgian patent 6 60 216 described, whereby extensive cleaning is not necessary in a complex apparatus only from phosphate and fluoride, but also from other impurities such as magnesium oxide and Alkali compounds is carried out. This procedure is then inexpedient, too cumbersome and too expensive if z. B. only the fluorine content reduced in the waste gypsum, but the Phosphalgehali can be retained. The same applies to a procedure by the applicant according to Belgian patent 7 13 349, the subject of which is also the Removal of both fluorine and phosphate from waste gypsum is. This procedure is based on it. that the fluorine compounds present by relatively brief heating in a period of 3 to 30 minutes with the stoichiometric amounts of silica and sulfuric acid to 200 to 400 ° C to form volatile compounds converts and through this heat treatment at the same time the waste gypsum present as dihydrate converted into anhydrite. As a result, the educated gaseous fluorine compounds volatilized and the phosphate in an easily washable state convicted. In this process, the waste gypsum is calcined twice, namely once before and once after washing out. This is why this process is too complex or even too complex not useful if only the fluorine content is undesirably high, but the phosphorus content is unchanged can or must be retained.

Processes have also become known. which only reduce the fluorine content in the waste gypsum For example, there is a method in DL patent specification 47 180 for the defluorination of phosphogypsum from the phosphoric acid wet process, characterized in that that in the filtration of the waste gypsum through appropriate Amounts of sulfuric acid in the washing liquid in the gypsum filter cake have a sulfuric acid content is set, which is sufficient to in the following Calcination process to decompose and volatilize the solid fluorine compounds present. According to the example, the calcination takes place at 400 C. The occurrence of sulfuric acid vapors, moreover bci "calcinicrlcmpcr; itures of about W Γ. Must be im

Continuous operation leads to significant signs of corrosion to lead. In British Patent 11 04 738 of the same group of applicants will refer to this fact in the statement on the state of the art also pointed out and stated that the addition of sulfuric acid at the required calcination temperature of 400 ° C leads to serious corrosion problems. Actual subject of the latter Patent specification is a process for the defluorination of phosphoric acid waste gypsum according to the after the addition of silicon dioxide, which should be distributed as little as possible, in a stream of superheated Water vapor between 200 and 400 C is alkali metal.

The SiCh: F ratio must be at least 2: 1. The disadvantage of this process is its disproportionately large quantities as a result of the necessary use Overtaking water vapor's obvious inefficiency.

Surprisingly, it was just! found that a very decisive reduction in the Fluorgelialts in Abiallgips can be achieved easily without any additional effort by this in a finely ground or fcinverteilem or free-flowing state in a suitable manner, for example in raw meal preheaters, z. B. Schwebegaswär.neauslauschern, in the furnace atmosphere containing SCh and at temperatures between 500 and 900 ^: C, especially those between 600 and 800 C for themselves, and not heated together with the raw meal aggregates as is usual. During this preheating, a large part of the volatile fluorine compounds get into the exhaust gas, from which they are known in ·. ·! Way can be removed by washing. The additives such as coke, sand etc. are then added in the almost oxygen-free SO: -containing atmosphere of the rotary kiln and / was immediately before it without any loss of heat.

In this connection it is known. Phosphorus gypsum at temperatures of 700 to 800 C outside to calcine the SO2-containing furnace atmosphere, whereby the calcination at such high temperatures makes special equipment measures necessary to reduce the detrimental dust movement and also through the necessary subsequent cooling for the purpose of admixing the aggregates, for example in Rohrniühlen and rewarming in the Rotary kiln is very uneconomical.

It is also known to preheat SO2-containing furnace meal, that is, the mixture of waste gypsum and aggregates in the furnace gases, to temperatures of 750 to SOO ' ¹ ° C. Up to now, however, it has not been known to couple the usual preheating under the influence of SO2-containing furnace gases in a very economical way with a fluorination of the preheated waste gypsum alone, whereby, depending on the type of gypsum material, often considerably lower temperatures than those previously known for preheating the raw mud sufficient.

The invention thus relates to a process for the production of low-fluorine cement clinker from pliosphorus waste gypsum according to the gypsum-sulfuric acid process by heating the gypsum to temperatures above 500 ° C before use in the rotary kiln, which is characterized in that this is by itself to temperatures of 500 to ¹ ) 00 C., preferably to temperatures of 6 (K) to 800 C in the de »SO .'- containing Ofonaimosphere and then admixing the additives known per se to the hot material without heat loss immediately before entering the furnace. The defluorization of the waste gypsum according to the invention can take place in various apparatuses. For example, the gypsum can be subjected to the heat treatment in the moist or predried state in a drum or a fluidized bed under the action of the SOi-containing furnace atmosphere. However, the multi-stage cyclone preheaters known for heating the oven meal can also be used very advantageously for the purpose according to the invention if it is ensured that the gypsum is in a free-flowing state by appropriate preliminary rocking. In this case, the additives are mixed in, depending on the treatment temperature, in one of the lower stages of the preheater or at the end of the same.

The treatment temperature is within the according to the invention, selected according to the gypsum zone, whereby the fluorine content or the type of fluorine compounds plays an essential role. Be: With low-fluorine grades, a temperature of 500 to 600 C. is sufficient for grades rich in fluorine or when they are present “Larger amounts of less harmful fluorine compounds it is recommended to use a correspondingly higher temperature in order to reduce the To achieve the fluorine content to the tolerated values.

For the success of the treatment according to the invention, the residence time is only important if than it has to be so great that the entire property is warmed up to the point of treatment is guaranteed. When preheating the cyclone vpu- ·.

which warm up within a few seconds occurs, a dwell time of this order of magnitude is sufficient the end. while with other devices that do not work according to the floating gas principle, the dwell time must be chosen accordingly larger.

Since the furnace atmosphere must have access to the entire reaction mixture in any case, it is recommended when using such devices as drums etc. dwell time and contact with the furnace atmosphere can be favorably influenced by low bulk and / or movement of the reaction material.

The following examples are intended to illustrate the invention Explain the procedure in more detail:

example 1

Secondary product gypsum from a phosphoric acid plant with an F-content of 0.8% was in an anhydrous state in an oven atmosphere with an SO: - Content of 8 percent by volume SO2 heated to 800 C. With a weight loss of 0.5%, the F content was 0.09% at the end of the test.

Example 2

the same conditions as in example 1 winch Abialigins with an F content of 0.33% F; '. Ui

500 C heated. The background noise was 0.14 ⁰ O searching for YYt.

After adding the gypsum-sulfuric acid

process common additives for heated, d. H. in the first case about 800. in the second case about 500 ° C waste gypsum was removed after the normal burning process get mcntklinker.

Claims (1)

19th Claim: Process for the production of low-fluorine cement clinker from phosphoric acid waste gypsum using the gypsum-sulfuric acid process by heating to temperatures? ^; Above 500 ° C before use in the calcining furnace, characterized in that this is heated by itself to temperatures of 500 to a maximum of 900 ° C, preferably to temperatures of 600 to 800 ° C, in the furnace atmosphere containing SCh, and then admixing which makes additives known per se to the hot material without heat loss immediately before entering the furnace.