ALUMINUM SULFATE SUSPENSIONS WITH REDUCED VISCOSITY

Abstract

The present invention relates to the use of a soluble magnesium compound for adjusting, in particular reducing, the viscosity of an aluminum sulfate suspension.

Claims

1. A method for adjusting a viscosity of an aluminum sulfate suspension, the method comprising providing a soluble magnesium compound to adjust the viscosity of the aluminum sulfate suspension.

2. The method as claimed in claim 1, wherein the aluminum sulfate suspension is at least one of a solidification accelerator and a hardening accelerator for a mineral binder.

3. The method as claimed in claim 1, wherein the magnesium compound is at least one selected from the group consisting of an oxide, a hydroxide, a carbonate, a nitrate, a sulfate, a phosphate, a halide, a formate, a citrate, and an acetate.

4. The method as claimed in claim 1, wherein the magnesium compound is at least one selected from the group consisting of magnesium carbonate, magnesium oxide, and magnesium hydroxide.

5. The method as claimed in claim 1, wherein an amount of the magnesium compound is chosen such that the magnesium atoms, based on a total weight of the aluminum sulfate suspension, have a proportion of 0.02-6.3% by weight.

6. The method as claimed in claim 1, wherein the aluminum sulfate suspension, based on a total weight of the aluminum sulfate suspension, has a proportion of sulfate (SO.sub.4.sup.−) of 19-40% by weight, and the aluminum sulfate suspension, based on the total weight of the aluminum sulfate suspension, has a proportion of aluminum (Al) of 3.5-10% by weight.

7. The method as claimed in claim 1, wherein the aluminum sulfate suspension, based on a total weight of the aluminum sulfate suspension, contains 22-46% by weight, of aluminum sulfate (Al.sub.2(SO.sub.4).sub.3).

8. The method as claimed in claim 1, wherein the aluminum sulfate suspension, based on a total weight of the aluminum sulfate suspension, contains 0.01-15% by weight of aluminum hydroxide.

9. The method as claimed in claim 1, wherein a molar ratio of aluminum to sulfate in the aluminum sulfate suspension is <0.7.

10. The method as claimed in claim 1, wherein the aluminum sulfate suspension, based on a total weight of the aluminum sulfate suspension, has a proportion of water of 30-80% by weight, including water of crystallization from components of the aluminum sulfate suspension.

11. The method as claimed in claim 16, wherein the magnesium compound reduces the viscosity in combination with a calcium compound.

12. The method as claimed in claim 11, wherein the calcium compound is at least one selected from the group consisting of an oxide, a hydroxide, a carbonate, a nitrate, a sulfate, a phosphate, a halide, a formate, an acetate, and a citrate.

13. The method as claimed in claim 11, wherein the calcium compound is at least one selected from the group consisting of calcium carbonate, calcium oxide, and calcium hydroxide.

14. The method as claimed in claim 11, wherein an amount of the calcium compound is chosen such that the calcium atoms, based on a total weight of the aluminum sulfate suspension, have a proportion of 0.001-4% by weight.

15. An accelerator being at least one of a solidification accelerator and a hardening accelerator for a mineral binder, the accelerator comprising: a) 22-46% by weight of aluminum sulfate (Al.sub.2(SO.sub.4).sub.3; b) optionally 0.01-15% by weight of aluminum hydroxide (AI(OH).sub.3); c) 0.035-10.4% by weight of magnesium oxide; d) optionally 0.001-5% by weight of calcium oxide; e) optionally 0.001-10% by weight of iron; f) optionally 0.001% to 5% by weight of silicon dioxide; g) optionally 0.001-20% by weight of at least one of an alkali metal aluminate and an alkaline earth metal aluminate; h) optionally 0.1-15% by weight of alkanolamine; i) optionally 0.01-10% by weight of fluoride; j) and a remainder being water.

16. The method as claimed in claim 1, wherein the soluble magnesium compound reduces the viscosity of the aluminum sulfate suspension.

17. The method as claimed in claim 1, wherein the aluminum sulfate suspension is a spray concrete accelerator.

18. The method as claimed in claim 1, wherein the molar ratio of aluminum to sulfate in the aluminum sulfate suspension is <2:3.

19. The accelerator as claimed in claim 15, wherein the at least one of the solidification accelerator and the hardening accelerator is a spray concrete accelerator.

Description

WORKING EXAMPLES

[0156] 1. Production of Aluminum Sulfate Suspensions

[0157] A beaker was initially charged with a defined amount of water. While stirring (mechanical propeller stirrer at 850 revolutions), the respective powder mixture (Al.sub.2(SO.sub.4).sub.3.14.3H.sub.2O; MgO, MgCaO.sub.2, sepiolite) was then added in portions with the proportions according to table 1, and the suspension was heated up to 50° C. and stirred at that temperature for 1 h (the proportions of NaAlO.sub.2 are based on sodium aluminate as such, without the water of the solution. The latter is included under H.sub.2O). Subsequently, the heater was switched off and the mixture was stirred for a further 6 h.

TABLE-US-00001 TABLE 1 Aluminum sulfate suspensions prepared Example Substance ↓ 1 2 3 H.sub.2O [% by wt.] 28.8 28.3 27.3 Al.sub.2(SO.sub.4).sub.3•14.3 H.sub.2O [% by wt.] 68 68 68 MgO [% by wt.] 2.5 2 — MgCaO.sub.2 [% by wt.] — 1 4 Sepiolite.sup.1 [% by wt.] 0.7 0.7 0.7 .sup.1Pangel S9 from Tolsa Group

[0158] The aluminum sulfate suspensions thus prepared were found to be storage-stable over several months and have a viscosity suitable for practical applications as spray concrete accelerator in the region of <2000 mPa.Math.s. The viscosity was measured according to standard DIN EN ISO 2431:2011 with an ISO No. 6 cup at a temperature of 23° C.

[0159] 2. Effect of the Proportion of the Soluble Magnesium Compound

[0160] In a second set of experiments, the effect of the proportion of the soluble magnesium compound was examined. For this purpose, an aluminum sulfate suspension having a proportion of Al.sub.2(SO.sub.4).sub.3.14.3H.sub.2O of 62% by weight and different amounts of MgO (0-5% by weight) was prepared analogously to the method described in chapter 1, except that the samples were heated up to 60° C. and stirred at 650 revolutions per minute.

[0161] The viscosities were measured by the same method as described in chapter 1 after 6 h and after 24 h hours. Table 2 gives an overview of the results.

TABLE-US-00002 TABLE 2 Dependence of viscosity on the proportion of the soluble magnesium compound Proportion of MgO [% by wt.] 0 1 2 3 4 5 Viscosity after 6 h 495 515 490 141 150 90 [mPa .Math. s] Viscosity after 24 h 500 805 403 155 190 111 [mPa .Math. s]

[0162] As apparent from table 2, the viscosity of the aluminum sulfate suspension can be significantly reduced at a high aluminum sulfate content by the addition of 2% by weight or more of MgO. Accordingly, a soluble magnesium compound can be used to control the viscosity of an aluminum sulfate suspension after 6-24 hours.

[0163] In a third set of experiments, in place of magnesium oxide, magnesium hydroxide was tested as viscosity-reducing compound in an aluminum sulfate suspension with additional aluminum hydroxide.

[0164] For this purpose, aqueous aluminum sulfate suspensions comprising 63% by weight of Al.sub.2(SO.sub.4).sub.3.14.3H.sub.2O, 0.6% by weight of Al(OH).sub.3 (amorphous, containing 75% by weight of Al(OH).sub.3 with 25% by weight of water of crystallization), and water as the balance, were added to different amounts of Mg(OH).sub.2 (0-5% by weight; see table 3) analogously to the method described in chapter 1. But the samples were each heated up to 40° C. and stirred at 850 revolutions per minute.

[0165] The viscosities were measured by the same method as described in chapter 1 after 6 h, 24 h and 48 h hours. Table 3 gives an overview of the results.

TABLE-US-00003 TABLE 3 Dependence of viscosity on the proportion of the soluble magnesium compound Proportion of Mg(OH).sub.2 [% by wt.] 0 1 2 3 4 5 Viscosity after 6 h 536 752 745 497 462 — [mPa .Math. s] Viscosity after 24 h 387 420 273 166 225 275 [mPa .Math. s] Viscosity after 48 h 260 272 289 160 130 208 [mPa .Math. s]

[0166] As apparent from table 3, the viscosity of the aluminum sulfate suspensions comprising aluminum hydroxide can be significantly reduced at a high aluminum sulfate content by the addition of 2% by weight or more of Mg(OH).sub.2. Accordingly, it is possible to use Mg(OH).sub.2 as soluble magnesium compound to control the viscosity of an aluminum sulfate suspension after 6-48 hours and in particular after 24-48 h.

[0167] In addition, it has been found that the viscosities of the aluminum sulfate suspension thus produced can be maintained over 3 months without significant change.

[0168] The above-described aluminum sulfate suspensions have been found to be suitable accelerators for spray concrete and spray mortar.

[0169] 3. Effect of Magnesium Silicates (Comparative Experiments)

[0170] For comparative purposes, the effect of sepiolite (magnesium silicate) on the viscosity of an aluminum sulfate suspension was examined. For this purpose, an aluminum sulfate suspension having a proportion of Al.sub.2(SO.sub.4).sub.3.14.3H.sub.2O of 62% by weight and different amounts of sepiolite (0-5% by weight) was prepared analogously to the method described in chapter 1, except that the samples were heated up to 60° C. and stirred at 650 revolutions per minute.

[0171] The viscosities were measured by the same method as described in chapter 1 after 6 h, 24 h and 48 h hours. Table 4 gives an overview of the results.

TABLE-US-00004 TABLE 4 Dependence of viscosity on the proportion of the soluble magnesium compound Proportion of sepiolite.sup.1 [% by wt.] 0 1 Viscosity after 6 h 452 1186 [mPa .Math. s] Viscosity after 24 h 518 1275 [mPa .Math. s] Viscosity after 48 h 396 1066 [mPa .Math. s] .sup.1Pangel S9 from Tolsa Group

[0172] In the case of more than 1% by weight of sepiolite, the viscosity was so high that it was no longer measurable by the aforementioned method.

[0173] The results make it clear that sepiolite cannot be used to reduce the viscosity of an aluminum sulfate suspension, by contrast with the soluble magnesium compounds, within the period up to 48 hours after preparation. On the contrary, the viscosity of the aluminum sulfate suspension is significantly increased on account of the addition.

[0174] 4. Effect of Additional Organic Acid (Comparative Experiments)

[0175] For comparative purposes, the effect of citric acid and formic acid on the viscosity of an aluminum sulfate suspension was examined. For this purpose, the amount of magnesium hydroxide specified in table 5 was converted to a slurry in the specified amount of water, and 0.5 g of citric acid and 0.2 g of ascorbic acid were added in each case. Thereafter, 37 g of Al.sub.2(SO.sub.4).sub.3.14H.sub.2O and 15.6 g of amorphous Al(OH).sub.3 were added in each case and dissolved at elevated temperature. Stirring of the solution was continued until the temperature had dropped to 40° C. The viscosities of the solutions thus prepared, comprising proportions of finely dispersed solids, were measured by the same method as described in chapter 1 after 24 h hours. Table 5 gives an overview of the results.

TABLE-US-00005 TABLE 5 Influence of organic acid on the viscosity of Mg(OH).sub.2-containing aluminum sulfate suspensions Test 4-1 4-2 4-3 4-4 Water [g] 46.7 45.7 43.7 41.7 Mg(OH).sub.2 [g] 0 1 3 5 Viscosity after 24 h 28 34 434 n.m. [mPa .Math. s] n.m.: not measurable - solid

[0176] As apparent from table 5, aluminum sulfate suspensions having a relatively low aluminum sulfate content and a proportion of organic acid have relatively low viscosities. Addition of Mg(OH).sub.2 in amounts of 3% by weight or more leads to a distinct increase in viscosity or even to solidification of the suspension. Accordingly, it becomes clear that the viscosities of aluminum sulfate suspensions cannot be reduced by the addition of Mg(OH).sub.2 as soluble magnesium compound when a proportion of organic acid is present.

[0177] Although the above-described embodiments of the invention are preferred, it will be apparent that the invention is not limited to these embodiments and can be modified as desired within the scope of the disclosure.