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 decripitation tendency and the use of such material in the manufacture of glass.

Claims

1-15. (canceled)

16. A process for reducing the decrepitation propensity of a material; wherein said material comprises calcium carbonate and/or magnesium carbonate; and said material comprises particles having a primary particle size of more than 90 m and less than 1 mm; comprising, combining at least one additive(s) to said material as a surface treatment, and the treatment is conducted at temperatures below 60 C.; wherein said additive(s) are selected from one or a combination of two or more alkali metal compounds and/or acids and/or alkaline earth metal compounds, or any combination thereof; wherein the alkaline earth metal compounds have a solubility at 25 C. in water of at least 0.5%, and wherein the additive(s) are used in an amount of 0.05 to 5 wt. %, based on the amount of the material to be treated.

17. The process of claim 16, wherein said material is treated with said additive in an amount of 0.1 to 3 wt. %, based on the amount of the material to be treated.

18. The process of claim 17, wherein said material is treated with said additive in an amount of 0.5 to 1.5 wt. %, based on the amount of the material to be treated.

19. The process of claim 16, wherein said treatment with said additive is conducted at a temperature of less than 40 C.

20. The process of claim 16, wherein said material comprises more than 85 wt. % calcium- and/or magnesium carbonate.

21. The process of claim 20, wherein said material comprises more than 90 wt. % calcium carbonate and/or magnesium carbonate.

22. The process of claim 16, wherein said material comprising calcium carbonate and/or magnesium carbonate is dolomite or limestone or a combination thereof.

23. The process of claim 16, wherein said material comprising calcium carbonate and/or magnesium carbonate being surface-treated comprises 20 to 80 wt. % of particles having a primary particle size of more than 90 M and less than 1 mm.

24. The process of claim 16, wherein said material comprising calcium carbonate and/or magnesium carbonate is treated with a compound selected from any one or a combination of any of the following: sodium hydroxide (NaOH), sodium silicate (Na-silicate), sodium sulfate (Na.sub.2SO.sub.4), sodium carbonate (Na.sub.2CO.sub.3), potassium carbonate (K.sub.2CO.sub.3), magnesium sulfate (MgSO.sub.4).

25. The process of claim 16, wherein said material comprising calcium carbonate and/or magnesium carbonate is treated with a solution comprising the additive and a solvent.

26. The process of claim 25, wherein said solution comprises the alkali metal compound and/or the alkaline earth metal compound in an amount of 0.5 to 60 wt. %.

27. The process of claim 26, wherein said solution comprises the alkali metal compound and/or the alkaline earth metal compound in an amount of 5.0 to 60 wt. %.

28. The process of claim 27, wherein said solution comprises the alkali metal compound and/or the alkaline earth metal compound in an amount of 25 to 50 wt. %.

29. The process of claim 16, wherein said material comprising 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 comprising calcium- and/or magnesium carbonate.

30. The process of claim 16, wherein said decrepitation propensity of said material comprising calcium- and/or magnesium carbonate determined according to the following steps: a) a sample is dried at 100 C. to a constant weight; b) 9 grams of said sample are placed in a trough; c) a clean metal tray with lid are placed in a muffle furnace and heated to 1040 C. and left for 10 minutes to reach a steady temperature; d) the trough containing the dried sample is placed on the tray in the furnace and the tray is covered with the lid; e) any carbonate which can decrepitate out of the trough is trapped in the closed system by the lid, so that it falls on the tray; f) after 10 minutes of exposure in the furnace the apparatus is removed and allowed to cool; g) the weight of the material on the tray and remaining in the trough is measured; h) the percentage weight of the material remaining on the tray, is reduced by at least 10%.

31. The process of claim 30, wherein said decrepitation propensity of said material comprising calcium- and/or magnesium carbonate determined according to the following steps: a) a sample is dried at 100 C. to a constant weight; b) 9 grams of said sample are placed in a trough; c) a clean metal tray with lid are placed in a muffle furnace and heated to 1040 C. and left for 10 minutes to reach a steady temperature; d) the trough containing the dried sample is placed on the tray in the furnace and covered with the lid; e) any carbonate which can decrepitate out of the trough is trapped in the closed system by the lid, so that it falls on the tray; f) after 10 minutes of exposure in the furnace the apparatus is removed and allowed to cool; g) the weight of the material on the tray and remaining in the trough is measured; h) the percentage weight remaining on the tray, is reduced by 30% to 95%.

32. The process of claim 31, wherein said decrepitation propensity of said material comprising calcium- and/or magnesium carbonate determined according to the following steps: a) a sample is dried at 100 C. to a constant weight; b) 9 grams of said sample are placed in a trough; c) a clean metal tray with lid are placed in a muffle furnace and heated to 1040 C. and left for 10 minutes to reach a steady temperature; d) the trough containing the dried sample is placed on the tray in the furnace and the tray is covered with the lid; e) any carbonate which can decrepitate out of the trough is trapped in the closed system by the lid, so that it falls on the tray; f) after 10 minutes of exposure in the furnace the apparatus is removed and allowed to cool; ce Action, with regards to new claims 19, 23 and 26 ning in the trough is measured; h) the percentage weight remaining on the tray, is reduced by 40% to 90%.

33. The process of claim 32, wherein said decrepitation propensity of said material comprising calcium- and/or magnesium carbonate determined according to the following steps: a) a sample is dried at 100 C. to a constant weight; b) 9 grams of said sample are placed in a trough; c) a clean metal tray with lid are placed in a muffle furnace and heated to 1040 C. and left for 10 minutes to reach a steady temperature; d) the trough containing the dried sample is placed on the tray in the furnace and the tray is covered with the lid; e) any carbonate which can decrepitate out of the trough is trapped in the closed system by the lid, so that it falls on the tray; f) after 10 minutes of exposure in the furnace the apparatus is removed and allowed to cool; g) the weight of the material on the tray and remaining in the trough is measured; h) the percentage weight remaining on the tray, is reduced by 50% to 80%.

34. A product made from a process according to claim 16 wherein the process is treating a material comprising calcium carbonate and/or magnesium carbonate; comprising combining at least one additive(s) to said material, as a surface treatment; wherein said additive(s) are selected from one or a combination of two or more alkali metal compounds and/or alkaline earth metal compounds, or any combination thereof; wherein the alkaline earth metal compounds have a solubility at 25 C. in water of at least 0.5%; and wherein the additive(s) are used in an amount of 0.05 to 5 wt. %, based on the amount of the material to be treated.

35. A product of claim 34, made from said material comprising 20 wt. % to 80 wt. % of particles having a primary particle size selected from particles that are: more than 90 m, more than 150 m, less than 1 mm, and less than 500 m.

36. A product of claim 34, wherein said material comprising calcium carbonate and/or magnesium carbonate, comprises sulfur in amounts selected from 0.07 to 3.0 wt. %, 0.1 to 2.5 wt. %, 0.15 to 2.0 wt. %, and 0.2 to 1.7 wt. %, and/or sodium in amounts selected from 0.04 to 4.5 wt. %, 0.05 to 4.0 wt. %, 0.08 to 3.5 wt. %, and 0.1 to 2.9 wt. %, and/or potassium in amounts selected from 0.08 to 5.0 wt. %, 0.1 to 4.5 wt. %, 0.15 to 4.0 wt. %, and 0.2 to 3.5 wt. %, based on the material comprising calcium- and/or magnesium carbonate.

Description

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

1.1 General Procedure

[0053] In Examples 1 to 13 the following operating procedure is used.

[0054] 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.

[0055] 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.

[0056] 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.

1.2 Test Results

[0057] 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 in Decrepitation Example Treating agent (%) 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.2CO3 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%

[0058] Column 3 of Table 1 shows the decrepitation value of Examples 1 to 13 determined using the Pilkington test.

[0059] Example 1 indicates the decrepitation value of raw dolomite not treated in the process according to the invention. Example 1 is used as reference to compute the decrepitation reduction shown in column 4.

[0060] 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.

[0061] 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.

[0062] 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

2.1 General Procedure

[0063] 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.

2.2 Test Results

[0064]

TABLE-US-00002 TABLE 2 Decrepitation tests on dolomite (0-2 mm) 10 wt % 10 wt % % of Dolomite NaOH Na.sub.2SiO.sub.2 additive Decrepitation 0-2 mm solution solution Additional relative Pilkington Decrepitation (g) (g) (g) water (g) to (%) reduction (%) 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

[0065] Example 17 is the reference (non-treated dolomite). By comparison, example 16 shows no influence of water alone.

[0066] 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

[0067] 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.

[0068] 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 amount Production of treated NaOH ratio NaOH NaOH rate of 0-3 mm to the raw solution solution 0-3 mm Trial dolomite dolomite concen- flow dolomite duration produced mass tration rate ~42 12 hours ~500 tons 1 wt % 50 wt % ~850 kg/ tons/hour hour

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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

[0073] 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.2 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 B.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