Manufacture of a Material on the Basis of Calcium-and/or Magnesium-Carbonate Having a Reduced Decrepitation Tendency

Abstract

Process for the manufacture of a material on the basis of calcium- and/or magnesium carbonate having a reduced decrepitation tendency, wherein a material on the basis of calcium- and/or magnesium carbonate is treated with at least one additive selected among alkali metal compounds and/or acids and/or alkaline earth metal compounds in an amount of 0.05 to 5 wt. % based on the amount of the material on the basis of calcium- and/or magnesium carbonate. Also claimed are the material obtainable by the process and showing reduced decrepitation tendency and the use of such material in the manufacture of glass.

Claims

1. Process for the manufacture of a material on the basis of calcium- and/or magnesium carbonate having a reduced decrepitation tendency, characterized in that a material on the basis of calcium- and/or magnesium carbonate is treated with at least one additive selected among alkali metal compounds and/or acids and/or alkaline earth metal compounds in an amount of 0.05 to 5 wt. % based on the amount of the material on the basis of calcium- and/or magnesium carbonate.

2. Process according to claim 1, characterized in that the material is treated with the additive in an amount of 0.1 to 3 wt. % and in particular 0.5 to 1.5 wt. %, based on the amount of the material on the basis of calcium- and/or magnesium carbonate.

3. Process according to claim 1 or 2, characterized in that the treatment with the additive is conducted at a temperature of less than 100 C.

4. Process according to any of claims 1 to 3, characterized in that the material on the basis of calcium- and/or magnesium carbonate comprises more than 65 wt. %, preferably more than 90 wt. %, calcium- and/or magnesium carbonate.

5. Process according to any of claims 1 to 4, characterized in that dolomite and/or limestone is used as material on the basis of calcium- and/or magnesium carbonate.

6. Process according to any of claims 1 to 5, characterized in that a material on the basis of calcium- and/or magnesium carbonate comprising 20 to 80 wt. % of particles having a primary particle size of more than 90 m and less than 1 mm is treated.

7. Process according to any of claims 1 to 6, characterized in that the material on the basis of calcium- and/or magnesium carbonate is treated with sodium hydroxide (NaOH), sodium silicate (Na-silicate), sodium sulfate (Na.sub.2SO.sub.4), sodium carbonate (NaCO.sub.3), potassium carbonate (K.sub.2CO.sub.3), magnesium sulfate (MgSO.sub.4), or sulfuric acid (H.sub.2SO.sub.4).

8. Process according to any of claims 1 to 7, characterized in that the material on the basis of calcium- and/or magnesium carbonate is treated with a solution containing the additive and a solvent.

9. Process according to claim 8, characterized in that a solution containing the alkali metal compound and/or the alkaline earth metal compound in an amount of 0.5 to 60 wt. %, preferably 5 to 60 wt. %, most preferably 25 to 50 wt. % and/or the acid in an amount of 1 to 98 wt. %, preferably 5 to 95 wt. %, most preferred 30 to 90 wt. %, and most preferred 50 to 80 wt. % is used.

10. Process according to any of claims 1 to 9, characterized in that the material on the basis of calcium- and/or magnesium carbonate is treated in the presence of SiO.sub.2 in an amount of less than six times the amount of the material on the basis of calcium- and/or magnesium carbonate.

11. Process according to any of claims 1 to 10, characterized in that the decrepitation tendency of a material on the basis of calcium- and/or magnesium carbonate according to Pilkington is reduced by at least 10%, preferably by 30% to 95%, more preferably by 40% to 90% and most preferred by 50% to 80%.

12. Material on the basis of calcium- and/or magnesium carbonate having a reduced decrepitation tendency, manufacturable in a process according to any of claims 1 to 11.

13. Material according to claim 12, characterized in that the material comprises 20 wt. % to 80 wt. % of particles having a primary particle size of more than 90 m, preferably more than 150 m, and less than 1 mm, preferably less than 500 m.

14. Material according to claim 12 or 13 characterized in that the material on the basis of calcium- and/or magnesium carbonate comprises sulfur in an amount of 0.07 to 3 wt. %, preferably 0.1 to 2.5 wt. %, more preferably 0.15 to 2 wt. %, and in particular 0.2 to 1.7 wt. %, and/or sodium in an amount of 0.04 to 4.5 wt. %, preferably 0.05 to 4 wt. %, more preferably 0.08 to 3.5 wt. %, and in particular of 0.1 to 2.9 wt. %, and/or potassium in an amount of 0.08 to 5 wt. %, preferably 0.1 to 4.5 wt. %, more preferably 0.15 to 4 wt. %, and in particular 0.2 to 3.5 wt. %, based on the material of calcium- and/or magnesium carbonate.

15. Use of a material according to any of claims 12 to 14 in the manufacture of glass.

Description

1. EXAMPLES 1 TO 13: DETERMINATION OF THE DECREPITATION TENDENCY OF DOLOMITE SAMPLES

[0055] 1.1 General Procedure

[0056] In Examples 1 to 13 the following operating procedure is used.

[0057] Dolomite generally used in the glass industry is dried and separated to select the range of primary particle sizes between 90 m and 500 m. As explained above, dolomite having primary particle sizes between 90 m and 500 m are the most subject to decrepitation and are thus the fraction most sensitive for the Pilkington test.

[0058] The quantity of additive used is shown in column 2 of Table 1 (below) as weight percentage of dolomite to be treated. The additive is dispersed into 10 cm.sup.3 of water. The total amount of the solution thus formed is sprayed onto 100 g of dolomite (90/500 m), placed in a bowl of a blade laboratory mixer. Subsequently, the dolomite is homogenised by mixing for 30 seconds. The homogenised dolomite is then removed from the mixer, placed onto a drying plate and finally dried in a drying furnace at 105 C. for 3 hours.

[0059] The amount of water added to the dolomite together with the additive has been chosen to simultaneously allow homogeneous surface treatment and to limit the excess of liquid. In doing so the obtained product is not sticky.

[0060] 1.2 Test Results

[0061] The test results are summarized in Table 1 below.

TABLE-US-00001 TABLE 1 Decrepitation tests on Dolomite (90 to 500 m) 3 4 1 2 Decrepitation Decrepitation Example Treating agent in (%) reduction 1 21.9 Reference 2 0.5% MgSO.sub.4 19.7 10% 3 0.5% Na.sub.2SiO.sub.3 19.7 10% 4 0.5% H.sub.2SO.sub.4 19.5 11% 5 0.5% Na.sub.2SO.sub.4 18.4 16% 6 0.5% KOH 17.9 18% 7 0.5% NaOH 17.9 18% 8 0.5% Na.sub.2CO.sub.3 17.8 19% 9 0.5% K.sub.2CO.sub.3 17.5 20% 10 0.5% NaCl 17.8 19% 11 0.5% H.sub.3BO.sub.3 17.1 22% 12 0.5% KBr 14.9 32% 13 1.5% NaOH 14.2 35%

[0062] Column 3 of Table 1 shows the decrepitation value of Examples 1 to 13 determined using the Pilkington test.

[0063] Example 1 indicates the decrepitation value of raw dolomite not treated in the process according to the invention.

[0064] Example 1 is used as reference to compute the decrepitation reduction shown in column 4.

[0065] Examples 2 to 13 show the decrepitation value of raw dolomite treated in the process according to the invention. In examples 2 to 13 eleven different treating agents are used.

[0066] Except for example 13, the treating agent is added in an amount corresponding to 0.5 wt. % of the raw dolomite. The results (column 4) show that in all examples 2 to 13 the decrepitation tendency is reduced by at least 10% as compared to the reference.

[0067] In example 13, the amount of treating agent (NaOH) corresponds to 1.5 wt. % of the raw dolomite. Comparing examples 7 and 13 indicates the effect of increasing the amount of the treating agent used on the reduction of the decrepitation value (column 4).

2. EXAMPLES 14 TO 17: DETERMINATION OF THE DECREPITATION TENDENCY OF ENTIRE DOLOMITE SAMPLES

[0068] 2.1 General Procedure

[0069] Dolomite 0-2 mm sand usually used in the glass industry is separated in charges of 800 to 1200 g each assay by sample division and added to a laboratory mixer. Then, an additive solution containing 10 wt. % of an alkali metal compound is added drop-wise to the running mixer. Subsequently, the mixture is mixed for about five minutes at an average rotational speed. The humid sample is then removed from the mixer, placed onto a drying plate and dried at 105 C. in the drying furnace until the weight of the sample does no more change (about 12-24 h). The sample thereby obtained is tested for its decrepitation tendency using the Pilkington test (see above). Table 2 shows the decrepitation tendency of the different samples determined using the Pilkington test. In contrast to examples 1 to 13, the entire fraction 0 to 2 mm of raw dolomite is used.

[0070] 2.2 Test results

TABLE-US-00002 TABLE 2 Decrepitation tests on dolomite (0-2 mm) Dolo- 10 wt % 10 wt % Addi- % of Decrep- Decrep- mite NaOH Na.sub.2SiO.sub.3 tional additve itation itation 0-2 mm solution solution water relative Pilkington reduc- (g) (g) (g) (g) to (%) tion (%) 14 850 42.5 0.5 4.5 51 15 826 41.5 0.5 5.2 44 16 1229 55.0 9.0 2 17 1000 9.2

[0071] Example 17 is the reference (non-treated dolomite). By comparison, example 16 shows no influence of water alone.

[0072] Example 14 concerning the treatment with sodium hydroxide shows a greater influence on decrepitation tendency than example 15, treated with sodium silicate.

3. EXAMPLE 18: INDUSTRIAL SCALE TREATMENT

[0073] At the laboratory scale, the experiments above show that the treatment of raw dolomite with at least one additive selected among alkali metal compounds, alkaline earth metal compounds and/or mineral acids according to the invention has a positive effect on lowering the decrepitation tendency of dolomite. In order to confirm this result, a test is performed in a continuous industrial scale process.

[0074] Dolomite usually used in the glass industry is treated by a sodium hydroxide solution (NaOH) during its crushing. At the entrance of the crushing line, the dolomite particle size ranges between 0 and 80 mm. At the outlet, the particle sizes are measured to range between 0 and 3 mm. The sodium hydroxide solution is sprayed through nozzles on the raw 0-80 mm dolomite when falling into the crusher. Thus, the crushing is used as a mixing step to guarantee the proper contact between the solid and the liquid phase. The experimental conditions used for this trial are summarised in table 3.

TABLE-US-00003 TABLE 3 Experimental conditions used during the industrial trial Total NaOH amount ratio Production of treated to the NaOH rate of 0-3 mm raw NaOH solution 0-3 mm Trial dolomite dolomite solution flow dolomite duration produced mass concentration rate ~42 12 hours ~500 tons 1 wt % 50 wt % ~850 tons/hour kg/hour

[0075] In contrast to examples 1 to 13, the entire fraction of crushed dolomite (0-3 mm samples) is treated and characterised (not only the 90-500 m fraction). All the raw (non treated) and treated samples are prepared in a specific way (see below) before the decrepitation measurements with the Pilkington test. This is done taking into account the tight link between the decrepitation rate of dolomite samples and the 90-500 m particle proportion contained.

[0076] Ten crushed dolomite blank samples (untreated dolomite) are analysed and their particle size distribution is determined by sieving with standard sieves (2 mm, 1 mm, 0.5 mm, 0.4 mm, 0.2 mm, 0.16 mm, 0.09 mm and 0.063 mm). For each blank sample, the proportion of the granulometric fraction (1-2 mm, 0.5-0.4 mm, is noted and an average particle size distribution is calculated using the values obtained for the blanks studied.

[0077] Subsequently, the granulometry of the NaOH-treated samples is recomposed according to the average particle size distribution obtained. This procedure allows for a comparison of the raw and the treated samples in order to focus on the influence of the NaOH treatment only, excluding any effect of the particle size distribution.

[0078] With the average particle size distribution, the considered raw dolomite samples (not treated) have a decrepitation rate close to 6%. With the same particle size distribution, the samples treated according to the invention with 1% NaOH solution have a decrepitation rate ranging between 1.5 and 2%. These values correspond to a decrease of the decrepitation rate close to 70%.

4. EXAMPLE 19: DETERMINATION OF THE AVERAGE COMPOSITION OF DOLOMITE TREATED ACCORDING TO THE INVENTION

[0079] The average composition of dolomite treated according to the invention is determined and compared to the average composition of untreated dolomite. The results are shown in Table 4.

TABLE-US-00004 TABLE 4 Average composition of dolomite treated in the process according to the invention. Dolomite Dolomite Dolomite Dolomite treated treated treated treated Dolomite with with with with untreated NaOH KOH Na.sub.2CO.sub.3 K.sub.2CO.sub.3 0.05% 5.00% 0.05% 5.00% 0.05% 5.00% 0.05% 5.00% Min % Max % Min % Max % Min % Max % Min % Max % Min % Max % Ca 20.0 24.3 Mg 10.9 14.1 S 0.004 0.06 Si 0.01 1.86 Na 0.01 0.03 0.03 2.87 0.02 2.17 K 0.01 0.07 0.03 3.48 0.03 2.75 Dolomite Dolomite Dolomite Dolomite treated treated treated treated with with with with Sodium Na.sub.2SO.sub.4 K.sub.2SO.sub.4 H.sub.2SO.sub.4 Silicate 0.05% 5.00% 0.05% 5.00% 0.05% 5.00% 0.05% 5.00% Min % Max % Min % Max % Min % Max % Min % Max % Ca Mg S 0.01 1.13 0.01 0.92 0.02 1.63 Si 0.01 1.15 Na 0.02 1.62 0.02 1.89 K 0.02 2.24