FI60548B - FOERFARANDE FOER FRAMSTAELLNING AV DIKALCIUMSILIKAT - Google Patents

Description

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jBjft IBJ <") utlAggningsskrift & u ^ 4 o vis? (45) '(51) Kv.ik? /int.ci.3 C 04 · B 7/38, C 01 P 7/22 ENGLISH I — FI N LAN D < M) P «t * ntclhak« mut - Patentanseknlng 793113 (22) H «k« mispllvl —An * ttknln («d« f 09-10.79 '' (23) Alkupllvl — Glltlghetsdag 09-10-79 (41) Translators for Public - Bllvlt off «mll | 10. OU.8l

Patent and Registration Office .... -.,.".. , , . .,, _. . (44) Nlhtivlkslptnon Is kuul.Julkalsun pvm. -

Patent and registration authorities Ansekui utiijd och uti.ikrifwn pubikerad 30.10.8l (32) (33) (31) Requested priority — B «glrd priority (71) Flovcon Oy, Valkeakoski, FI; Sperring, 02 ^ 00 Kirkkonummi,

The present invention relates to a process for the preparation of dicalcium silicate according to the preamble of claim 1. (72) Bengt Forss, Parainen, Finland-Finland (FI) (7 * 0 Seppo Laine (5 * 0 Process for the preparation of dicalcium silicate) .

The so-called Muller-Kuhne process, which is used to produce SO2 or sulfuric acid and cement from gypsum or anhydrite, is carried out according to the following formulas:

CaSO 2 + 2C = CaS + 2CO 2

CaS + 3CaS01 | = 4CaO + * JSC> 2 4CaO + (Al2O2, Fe2O4, SiO2, etc.) - cement clinker.

In the Muller-Kuhne method, carbon or coke is added to the combustible mass (gypsum + silicates) as a reducing agent, which facilitates the decomposition reactions of gypsum. The addition of carbon must be closely monitored for the process to work. Too little carbon addition causes the gypsum to melt and too much addition produces too much CaS, which causes agglomeration at higher temperatures.

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According to this method, the energy consumption in cement combustion is about 1800 kcal / kg of clinker and more, which is more than double the amount compared to modern cement production methods.

One downside is also the high combustion temperature required, which causes large heat losses. If the furnace feed contains alkalis, process disturbances often occur and dust from the electrostatic precipitators can only be returned to the furnace to a limited extent.

Attempts have been made in the past to produce sulfuric acid and cement clinker directly from gypsum and silicates. However, the gypsum only decomposes at such a high temperature that the mass melts and causes difficult, so far unresolved chemical and technical problems.

It has been found that various additions of Al 2 O 3 and Pe 2 O 2, and in particular the addition of kaolin (Al 2 O 2 * 2 SiO 2), substantially contribute to the gypsum decomposition reaction. The cause has not yet been determined today.

The raw material for the current production process is pure sulfur, which is burned in a suitable furnace, or sulphide ores, most often pyrite (FeS2), which is roasted. Most of the world's HgSO 4 production is used to dissolve apatite in the phosphoric acid and fertilizer industries. The function of the sulfuric acid is to bind the lime in Apatite (Ca With regard to the prior art, reference should also be made to GB Patent 1,203,950, which describes the processing of red slurry from aluminum production.

U.S. Pat. No. 2,426,147, which describes gypsum made from SO 2 and cement, and Al 2 O 2 and SiO 2 -containing materials with a small amount of sulfur added as a reducing agent, DE 4,117,172, which describes regeneration with alkaline silicates, DE 676,192, which describes the recovery of AlgO 2 from natural or technical alkali aluminosilicates, and 3,60548 DE 610,683, which relates to the decomposition of artificial natrolite (Na 2 O · 120 x 3 SiO 2) with a mineral acid.

The present invention aims to eliminate the above-mentioned disadvantages so that the CaO and SO 2 in the gypsum can be reused in their entirety and used to make useful products, lime cement, SO2 sulfuric acid and various valuable commercial products from the added silicates.

The process according to the invention is based on the advantageous effect of the addition of Al 2 O 3 and sulfur in the decomposition of gypsum and on the use of acid-soluble K-, Mg- and Al-rich technical or natural silicates as a co-raw material.

The invention is further based on e.g. the following ideas: natural gypsum, anhydrite, waste gypsum or the like is used as starting material, crushed, dried with combustion gases and ground, K-, Mg- and Al-rich, partially acid-soluble and possibly dolomite-containing silicate is used as silicate material. is extracted with mineral acids in one or more stages, the above-mentioned raw materials are fed together with any sulfur and Fe and / or Al components to a rotary kiln where they are incinerated at a temperature of 1150 ° C. The CaO / SiO 2 ratio of the feed is set between 2: 1 and 3: 1, depending on the clinker application.

sulfur or sulfur-containing materials are used as fuel, sulfur dioxide-containing fuel gases are used partly for drying gypsum, partly for extracting and decomposing dolomite from silicate material and mainly for producing sulfuric acid and acid soluble silicate components.

More specifically, the method according to the invention is mainly characterized by what is set forth in the characterizing part of claim 1.

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In the case where the raw material consists of waste gypsum and a silicate containing acid-soluble alkali, alkaline earth and Pe and Al compounds, it is advantageous from the point of view of the process that these components are removed by a suitable extraction method before the combustion step of the process. If the silicate containing carbonates in addition, it is preferable to first remove these components e.g. transforming them into soluble bisulfite SO ^ -pitoisten flue gases, whereby the process end side of the steps are simplified.

If the raw materials are "cleaned" in this way before incineration, the load on the rotary kiln and the energy consumption will be reduced and it will not be necessary to remove time aluminates from the clinker obtained as in other known methods.

The process diagram is shown in the attached drawing.

In this case, the starting materials are gypsum as well as tailings containing phlogopite (72%), dolomite (22%) and insoluble silicates (5%).

According to the method, the gypsum is dried to anhydrite after crushing, ground to a fineness of 0.1 mm and fed to a rotary kiln with a different treatment of the "purified" silicate component and the sulfur or sulfur component.

The silicate component is treated as follows:

The alkaline earth carbonates are dissolved from the finely ground tailings by means of the combustion gases from the gypsum drying. The Mg and Ca oxides obtained after roasting can be separated from one another in ways known per se. For example, CaO can be precipitated as CaCO2 by means of CCl4 gases. The rest of the SOg-containing combustion gases are used for the production of H2SO4 in a manner already known.

The carbonate-free silicate residue is treated with a strong mineral acid such as HNO 2, H 2 SO 4, etc. The nitric acid extract contains the alkali, alkaline earth, and Pe and Al components as nitrates. When this extract is neutralized to pH, the Al and Pe components precipitate as hydroxides and can be further separated in a manner known per se. Mg (NO 2) 2 is extracted from the remaining solution. KN0 ^ remains in the solution, which after evaporation can be used e.g. as a fertilizer.

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After the above-mentioned mineral acid treatment, fairly pure SiO 2 remains insoluble, as well as insoluble silicates which are fed to the rotary kiln with gypsum and other additives.

To promote sintering and decomposition of the gypsum, sesquioxide components can be added up to 20% of the total feed. Too large an increase affects the removal of SOg from the combustion process.

The amount of sulfur component added to the feed for gypsum reduction should be 3.5 - 5% ·

If sulfur or a sulfur-containing substance is used as fuel, the SOg content of the combustion gases can be substantially increased and the amount of H 2 SO 4 produced can also be increased.

A mixture of (HNO ^ + Η-, δΟ ^) can also be used in the mineral acid treatment of the silicate component. The amount of i ^ SO ^ rn must then be proportional so that upon evaporation of the solution, after extraction, the Al component precipitates in the form of alum (KA1 (SO2) 2 · 12 ϊ ^ Ο). In this case too, the recovery of Mg (NO2) 2 and KNO2 takes place as previously described.

Claims (3)

6 60548 A process for the preparation of dicalcium silicate ("CgS") starting from a CaSO 4 and SiO 2 -containing mineral, wherein alkali and alkaline earth metals, such as Mg, Na and K, which are harmful to the preparation of the SiO 2 -containing mineral as a binder, are dissolved in one or SO 2 -containing flue gases from water production in several steps "with HgSO 4 and water with the formation of HgSO 4 and in the following steps with stronger acids, such as HNO 2 or H 2 SO 4, characterized in that harmful alkaline earth metals, bisulphites and sulphites the compounds MgtHSO 4, MgSO 4, Ca 2 SO 4 and CaSO 4 are roasted to release SO 2 after separation from the less soluble phlogopite and silicate components and that the SO 2 thus obtained is reused for the leaching of said alkaline earth metals. Process according to Claim 1, characterized in that the SC 2 released during roasting is used for the production of H 2 SO 4. Process according to Claim 1, characterized in that the ratio of HgSO 4 to HNO 2 corresponds to the ratios of K to Mg and Al in the original SiO 2 -containing mineral, so that part of the amount of K is obtained remain in solution as KNO 2 and the others are precipitated as KA1 sulphates. * 1. Process according to Claim 1, characterized in that the phlogopite is treated with HNO 2 --Ha, whereby the resulting KNO 2 - (MglNO 2 - g and AlO 2 N 2 O 3) remain in solution and SiO 2 - insoluble is used in the combustion process with CaSO 4 to produce "C 8 S" .