DE4403781A1 - Prodn. of highly pure beta-wollastonite - Google Patents

Abstract

Prodn. of highly pure beta -wollastonite comprises: (a) treating Si-rich material with aq. alkali soln., where such material is treated with aq. alkali soln., where such material is treated with amorphous SiO2 modification at 50-120 deg C and with crystalline SiO2 modification at 140-350 deg C; (b) isolating the alkali solns. formed and reacting with a lime component of high purity with molar CaO:SiO2 ratio of 1:05-2.0; and (c) converting the pptd. or crystallised Ca-silicate hydrate at 500-1100 deg C after solid/liq. sepn. into a highly pure wollastonite free of foreign phases and contg. less than 0.5 Na2O, Fe2O3, MgO and Al2O3, more than 95% white degree, having 2-5 mu m grain size for 90% of the particles and 2.8-2.9 g/cm<3> density.

Description

The invention relates to a process for the preparation of high-purity calcium silicate hydrates of the wollastonite type a silicon-rich feed, which is a silicon-rich Raw material or a residue from industrial or commercial can be application.

The preparation of calcium silicate hydrate of wollastonite Type is usually made of naturally degraded wollasto nit or by melting together of calcium oxide or calcium carbonate with silica; see for example DE-A-30 02 346.

Furthermore, a method is known from DE-A-33 02 729, Produce calcium silicate molded products by reacting in aqueous Phase a kalkhaltiger and a kieselhaltiger feed be reacted with heating to give a calcium silicate to arrive at a certain Molver CaO / SiO₂ and then with a filter press Forming procedure is performed.

Other patents are concerned with the manufacture special forms of wollastonite for specific application purposes (DE-C-29 36 169 or DE-C-29 53 525).

Starting point of the method for producing a bin demittels in DE-C-28 21 657 is a residue from the smoke gas desulphurization, in which a multiphase mixture is obtained, the finally ground up and with granulated slag up to a be If grinding fineness is mixed.

The invention has set itself the task of high purity  Produce β-wollastonite and thereby on silicon rich Ein substances, in particular residues, which represent industrial waste products.

According to the invention, this object is achieved by a method solved, at the

• (a) silicon-rich feedstocks of a selective treatment be subjected to aqueous alkali solution, with those with amorphous SiO₂ modifications at temperatures in the range of 50 to 120 ° C and those with crystalline SiO₂ modifications at temperatures ranging from 140 to 350 ° C who treated the;
• (b) isolating the alkali solutions formed and then with a lime component of high purity in a molar CaO: SiO₂ ratio of 1: 0.5 to 1: 2.0 are reacted;
• (C) the precipitated or crystallized calcium silicate hydrate is converted at 500 to 1100 ° C after the solid / liquid separation into a highly pure, foreign phase-free β-wollastonite with the following parameters sum of the contents Na₂O, Fe₂O₃, MgO and Al₂O₃ | <0.5 whiteness <95% Grain size of 90% of the particles 2 to 5 μm density 2.8 to 2.9 g / cc

It can for the complete processing of the use material used in the isolation of the alkali silicate solution and / or incurred in the digestion with the lime component process Reststoff either further treatment with aqueous Alkaline solution and subsequent treatment with a Kalkkom subjected to component with subsequent thermal treatment or he can only use one thermal treatment each be subjected to the conditions mentioned above thereby to a wollastonithaltigen product with more than 50% Wollastone share to get.

As a silicon-rich feedstock are especially before added quartz, sands, power plant ashes, rice ashes and dusts or their mixtures. Particularly preferred are power plant ashes  all types or dusts from filter systems. They can do this Starting materials directly as they are present in the invention can be used in accordance with appropriate methods, or they can before be classified to be used as a concentrate. Also a thermal pretreatment for the adjustment of certain SiO₂ Phases can be done beforehand.

The said selective treatment with alkali solution can in the amorphous SiO₂ modifications preferably in the temperature range from 70 to 100 ° C and the crystalline SiO₂ modifications preferably in the temperature range 200 to 280 ° C. In the alkali solution used is preferably Potassium hydroxide or sodium hydroxide, in particular sodium hydroxide with a Content of 60 to 300 g / l Na₂O. But there may be others Alkalisilikatlösungen be used, provided that the Production of high purity β-wollastonite not impaired becomes. A particularly preferred range of Na₂O content is at 100 to 200 g / l. When using other alkali solutions than NaOH, the concentration range should be selected accordingly.

The alkali silicate solution obtained can be replaced by a usual solid / liquid separation are separated.

Subsequently, the recovered alkali silicate solution with a lime component offset. This lime component can be However, it is preferred that it be the usual calcareous product Quicklime or hydrated lime with high purity, which is a molar CaO / SiO₂ ratio of 0.5 to 2.0, preferably 0.9 to 1.1. The temperature during the reaction can be 50 to 120 ° C, preferably 70 to 90 ° C. He then again follows a solid / liquid separation according to known Ver driving, with the high-purity precipitated or crystallized Calcium silicate hydrate is separated from the mother liquor. To The usual solid / liquid separation methods include Filtra with or without negative pressure, centrifuging, decanting etc. is advantageous z. B. a filtration process at normal pressure and ambient temperature.

The separated calcium silicate hydrate is replaced by a thermal aftertreatment in the temperature range from 500 to  1100 ° C, preferably 600 to 1000 ° C, in particular 850 to 1050 ° C in wollastonite, preferably β-wollastonite, umgewan delt. This temperature treatment takes place until one a high purity wollastonite without foreign phases, a whiteness of <95%, a grain size of 90% in the range of 2 to 5 microns and a density in the range of 2.7 to 2.9 g / cm³. The Time is usually 2 to 12 hours, preferably 4 to 8 hours.

Surprisingly, obtained by the inventive Process also from heavily polluted residues a high white wollastonite, naturally degraded and purified wollastonite, both in terms of whiteness and is superior in terms of its phase purity.

The manufactured β-wollastonite may be outstanding because of its outstanding whiteness as a filler in the plastic, paint, Color and paper industry are used, but also as Asbestos replacement for sealing and friction elements and in ceramics Industry. Furthermore, the use of wollastonithal possible products as aggregate in the construction industry as well as welding and casting powder for metallurgical processes.

The invention also relates to a method for Aufberei tion of silicon-rich residues, which characterized is that

• (a) the silicon-rich residues of a selective treatment be subjected to aqueous alkali solution, with those with amorphous SiO₂ modifications at temperatures in the range of 50 to 120 ° C and those with crystalline SiO₂ modifications at temperatures ranging from 140 to 350 ° C who treated the;
• (b) isolating the alkali solutions formed and then with a lime component of high purity in a molar CaO: SiO₂ ratio of 1: 0.5 to 1: 2.0 are reacted;
• (C) the precipitated or crystallized calcium silicate hydrate is converted at 500 to 1100 ° C after the solid / liquid separation into a highly pure, foreign phase-free β-wollastonite with the following parameters sum of the contents Na₂O, Fe₂O₃, MgO and Al₂O₃ | <0.5 whiteness <95% Grain size of 90% of the particles 2 to 5 μm density 2.8 to 2.9 g / cc; and
• (d) optionally, in the isolation of Alkalisilikatlö solution and / or obtained by digestion with the lime component Process residue either a further treatment with aq riger alkali solution and subsequent treatment with a Lime component with subsequent thermal treatment or only one thermal treatment in each case under the above subject to conditions to become a wollasto nithaltigen product with <50% Wollastonitanteil to arrive.

With the help of this method it is possible to use silicon-free completely work-up solids without substantial Residues remain. In addition, according to the Steps (a) to (c) resulting mother solutions and / or washing After complete concentration adjustment, complete the water dig returned to the overall process.

The term "residues" means products those used in industrial or commercial processes as By-products or waste products incurred. Under the term "Process residue" becomes that in the present process resulting by-product understood.

The invention will be explained in more detail by examples be explained.

example 1

As a feedstock for the production of β-wollastonite served Lignite filter ash of the following composition (GV = Glüh loss):

The brown coal filter ash is classified in the Grain areas <100 microns, 100 to 315 microns and <315 microns subjected. The ash of the grain range 100 to 315 microns with a SiO Ge Now holding 84.6% is with a 17% sodium hydroxide in  a solid / liquid ratio of 1: (3-5) mixed and over stirred intensively for four to five hours at 200 ° C. The sustain sodium silicate solution with a composition in molar Ratio Na₂O / SiO₂ of 1: (1-2) is abge from the solid separates and as starting solution the precipitation of calcium silicates used thydrate. After adding quicklime under Be taking into account a molar ratio CaO / SiO₂ of 1.0 is included over a period of four to six hours a temperature of 80 ° C with vigorous stirring the Her position of calcium silicate hydrate. This will follow separated from the mother liquor. The washed calcium silicic acid Thyrrate is given over a period of four to six hours converted to β-wollastonite at a temperature of 900 ° C. The product obtained consists exclusively of β-wollasto nit. The properties achieved are summarized in Table 1 caught.

The washed pulping residue with a chemical Composition of

is used directly as an aggregate in the building materials industry puts. He can also through a thermal aftertreatment, such as described above, to a wollastonithaltigem product which is used in the ceramics industry. The properties of wollastonite-containing product are in Table 1 is also shown.

The ash of the grain area <315 μm is more than 90% coal and returned to the combustion process leads.

The ash of the grain area <100 microns with a chemical Composition of

is used directly in the building materials industry as an aggregate or used for water purification.  

Example 2

Feedstock for the production of high-purity β-wolla stonit is quartz sand with the composition:

The quartz sand is used for the production of Alkalisilikatlö an alkaline hydrothermal digest with a 17 % sodium hydroxide solution and a solid / liquid ratio of 1: (3-5) over 90 minutes at a temperature of 250 ° C below worfen. From the resulting sodium silicate solution with a Composition in molar ratio Na₂O / SiO₂ of 1: (1-2) is precipitated as in Example 1, the calcium silicate hydrate and converted to a single-phase wollastonite, whose egg properties are shown in Table 1. At the processing tion of quartz sand, no pulping residue is formed.

Example 3

As a feedstock for the production of high-purity β- Wollastonite becomes silicon dusts of ferrosilicon production used, have the following composition.

The silicon dust containing amorphous silicon is mixed with a 17% sodium hydroxide solution in a solid / liquid ratio of 1: (3-5) and stirred at 100 ° C for 90 minutes leaches. The resulting sodium silicate solution is as under Example 1 described to calcium silicate hydrate and β-wollasto nit processed. The properties of single-phase wol lastonits are shown in Table 1. That means GV = loss on ignition.  

Table 1

Properties of the wollastonites prepared in Examples 1 to 3

Claims (11)

1. A process for the preparation of high purity β-wollastonite, characterized in that

• (A) silicon-rich starting materials are subjected to a selective treatment with aqueous alkali solution, wherein those treated with amorphous SiO₂ modifications at temperatures ranging from 50 to 120 ° C and those with crystalline SiO₂ modifications at temperatures in the range of 140 to 350 ° C who the;
• (B) the alkali solutions formed are isolated and then reacted with a lime component of high purity at a molar CaO: SiO₂ ratio of 1: 0.5 to 1: 2.0;
• (c) the precipitated or crystallized calcium silicate hydrate is converted at 500 to 1100 ° C after solid / liquid separation into a high purity, foreign phase free wollastonite having the following parameters: sum of contents Na₂O, Fe₂O₃, MgO and Al₂O₃ | <0.5 whiteness <95% Grain size of 90% of the particles 2 to 5 μm density 2.8 to 2.9 g / cc.

2. The method according to claim 1, characterized in that the in the isolation of the alkali silicate solution and / or on conclusion ent with the lime component accumulating process residue ent neither further treatment with aqueous alkali solution and subsequent treatment with a lime component with after following thermal treatment or only a thermal one Treatment under the conditions mentioned in claim 1 is subjected to a wollastonite-containing product to arrive with <50% wollastone content.   3. The method according to claim 1, characterized in that the silicon-rich feedstock is selected from the group made of quartz, sands, power plant ashes, rice ashes and Dust or mixtures thereof, preferably from strength factory bags and dusts. 4. The method according to any one of claims 1 to 3, characterized marked records that the feedstock directly or after previous Classification as silicon concentrate or after thermal pre treatment is used to set certain phases. 5. The method according to any one of claims 1 to 4, characterized marked characterized in that the selective treatment with alkali solution of amorphous SiO₂ modifications are carried out at 70 to 100 ° C and the of crystalline SiO 2 modifications at 200 to 280 ° C. 6. The method according to any one of claims 1 to 5, characterized gekenn characterized in that the molar ratio CaO: SiO₂ 1: 0.9 to 1: 1.2 is. 7. The method according to claim 1, characterized in that the Concentration of the aqueous alkali solution in the range of 60 to 300 g / l Na₂O is. 8. The method according to claim 1, characterized in that the after the stages a) to c) accumulating mother solutions and / or Washing waters after concentration adjustment of the aqueous Alka lilösung to a range of 60 to 300 g / l Na₂O completely be returned to the overall process. 9. The method according to claim 1, characterized in that the Conversion according to c) in the temperature range 850 ° C to 1050 ° C. he follows.   10. A process for the treatment of silicon-rich residues, characterized in that

• (A) the silicon-rich residues are subjected to a selective treatment with aqueous alkali solution of concentration 60 to 300 g / l Na₂O, wherein those with amorphous SiO₂ Modifi cations at temperatures ranging from 50 to 120 ° C and those with crystalline SiO₂ modifications at Temperatures in the range of 140 to 350 ° C are treated;
• (B) the alkali solutions formed are isolated and then reacted with a lime component of high purity at a CaO: SiO₂ ratio of 1: 0.5 to 1: 2.0;
• (c) the precipitated or crystallized calcium silicate hydrate is converted at 500 to 1100 ° C after solid / liquid separation into a high purity, foreign phase free wollastonite having the following parameters: sum of contents Na₂O, Fe₂O₃, MgO and Al₂O₃ | <0.5 whiteness <95% Grain size of 90% of the particles 2 to 5 μm density 2.8 to 2.9 g / cc; and
• (d) optionally the solution obtained in the isolation of the Alkalisilikatlö and / or digestion with the lime component process either a further treatment with aq alkaline solution and subsequent treatment with a lime component followed by thermal treatment or only a thermal treatment respectively under the above ge called Conditions to obtain a wollasto Nithaltigen product with <50% Wollastonitanteil.

11. The method according to claim 10, characterized in that the mother solutions resulting from steps a) to c) and / or or wash water after appropriate concentration adjustment the alkali solution according to (a) completely back to the overall process be supplied.