FORMED BODY BASED ON MAGNESIUM OXIDE AND CALCIUM CARBONATE AND METHOD FOR ITS PREPARATION

Abstract

A method for producing a formed body containing magnesium oxide and calcium carbonate is shown and described, comprising the steps: a) Providing the following components: 1) A magnesium oxide component which has the following properties, in each case based on the total weight of the magnesium oxide component: i) Content of magnesium oxide in the dry substance of more than 70% by weight, ii) Ignition loss of less than 25% by weight, iii) Free calcium oxide content of less than 5% by weight, 2) a calcium carbonate component, the components as a whole having a free calcium oxide content of less than 2% by weight, based on the total weight of the components; b) Mixing components 1) and 2) to obtain a mixture; c) Forming at least one formed body from the mixture obtained in b) with the addition of water.

Claims

1. A method for producing at least one formed body comprising magnesium oxide and calcium carbonate comprising the steps of: a) Providing the following components: 1) A magnesium oxide component which has the following properties, in each case based on the total weight of the magnesium oxide component: i) Content of magnesium oxide in the dry substance of more than 70% by weight, ii) Ignition loss of less than 25% by weight, and iii) Free calcium oxide content of less than 5% by weight; 2) A calcium carbonate component, wherein the components as a whole have a free calcium oxide content of less than 2% by weight, based on the total weight of the components; b) Mixing the magnesium oxide component with the calcium carbonate component to obtain a first dry mixture; and c) Forming at least one formed bod) from the first dry mixture obtained in step b) by adding water to the first dry mixture.

2. The method according to claim 1, characterized in that the magnesium oxide component has a reactivity such that, in a citric acid activity test with 100 ml of 4N solution of citric acid after addition of 2 g of the magnesium oxide component to the solution of citric acid, a color change of a phenolphthalein indicator from colorless to pink occurs within 90 to 230 seconds.

3. The method according to claim 1, characterized in that step c) further comprises adding 1% to 30% of water by weight, based on the total amount of magnesium oxide component, the calcium carbonate component, and water.

4. The method according to claim 1, characterized in that the magnesium oxide component has a d50 value of less than 100 μm.

5. The method according to claim 1, characterized in that the calcium carbonate component has a d50 value of less than 100 μm.

6. The method according to claim 1, characterized in that the provided amount of magnesium oxide component is 20% to 50% by weight, based on the amount of magnesium oxide component and calcium carbonate component.

7. The method according to claim 1, characterized in that the provided amount of calcium carbonate component is 50% to 80% by weight, based on the amount of magnesium oxide component and calcium carbonate component.

8. The method according to claim 1, characterized in that step b) further comprises mixing the magnesium oxide component and the calcium carbonate component in a mixer and/or step c) further comprises forming the at least one formed body on a dish granulator.

9. The method according to claim 1, characterized in that step b) further comprises mixing the magnesium oxide component and the calcium carbonate component to obtain the first dry mixture wherein the first dry mixture is homogeneous and/or step c) further comprises spraying water on the first dry mixture.

10. The method according to claim 1, characterized in that the magnesium oxide component and the calcium carbonate component are mixed in step b) for a period of 5 to 60 minutes, and/or the mixture is formed in step c) 10 to 240 minutes into at least one formed body.

11. A formed body comprising magnesium oxide and calcium carbonate, wherein the formed body has a content of magnesium oxide of at least 23% by weight, a content of calcium carbonate of at least 40% by weight, and a content of free calcium oxide of less than 2% by weight, each based on the total weight of the formed body.

12. The formed body according to claim 11, characterized in that the formed body has a volume-equivalent spherical diameter of 0.1 to 4 mm.

13. The formed body according to claim 11, characterized in that the formed body has a BET surface area of 1 to 10 m2/g and/or wherein the formed body exhibits such a reactivity, that a raw water is treated, by treatment with the formed body within an Empty Bed Contact Time value of less than 20 minutes, to the extent that the water subsequently has a calcite dissolving capacity of less than 5 mg/l.

14. The formed body according to claim 11, characterized in that the formed body can be obtained or prepared according to a method according to claim 1.

15. (canceled)

16. A filter material comprising a formed body according to claim 11.

17. (canceled)

Description

EXAMPLES

[0104] FIG. 1: pH values of water after neutralization with filter material P1 and CP at CO.sub.2 concentration of 0.4 mmol/dm.sup.3;

[0105] FIG. 2: pH values of water after neutralization with filter material P1 and CP at CO.sub.2 concentration of 0.7 mmol/dm.sup.3;

[0106] FIG. 3: pH values of water after neutralization with filter material P1 and CP at CO.sub.2 concentration of 1.0 mmol/dm.sup.3.

[0107] A mixture of 32% by weight of magnesium oxide (nedMag99, Nedmag BV; >97% by weight of magnesium oxide in the dry substance, 0.70% by weight of loss on ignition, 0.74% by weight of free calcium oxide, 0.2% by weight or less SiO.sub.2) and 68% by weight powdered limestone (0/60 my—T 756, August Hutter GmbH; >98% CaCO.sub.3, <0.8% by weight SiO.sub.2) was placed on a dish granulator and granulated with the addition of water. On the dish granulator, the granulation reaction then takes place without additional heat. The heat of reaction also leads to the drying of the formed granules.

[0108] Granules with the following particle size distribution were obtained:

TABLE-US-00001 Particle size Particle size Share group [mm] [weight %] Particle size <0.5 1.0 group 0 Particle size 0.5-2.5 80.3 group 1 Particle size 2.0-4.5 10.7 group 2 Particle size >4.5 8.0 group 3

[0109] The average hardness of the granules obtained from the method was 45 N.

[0110] The granules had a free calcium oxide content of 0.3% by weight. The content of free calcium oxide was determined according to DIN EN 12485:2017-10, item 6.8.

[0111] With the particle size group 1 of the granules thus obtained, a water having a water temperature of 8.6° C., a pH of 5.6, a conductivity of 120 μS/cm, a calcium content of 7 mg/l, a magnesium content of 2 mg/l, a base capacity up to pH 8.2 (K.sub.B 8.2) of 0.75 mmol/l and an acid capacity up to pH 4.3 (K.sub.S 4.3) of 0.2 mmol/l was freed of carbonic acid within an EBCT Value (Empty Bed Contact Time) of 5 to 6 minutes to the extent that a calcite dissolving capacity of less than 5 mg/I was present. For the same water, a comparative granulate with the same particle size based on semi-calcined dolomite which was obtained from dolomitic stone, required an EBCT value of 9 to 10 minutes for the same treatment result.

[0112] The calcite dissolving capacity was calculated according to the standard DIN 38404-10:2012-12 (Title: German standard methods for the examination of water, waste water and sludge—Physical and physical-chemical parameters (group C)—Part 10: Calculation of calcite saturation of a water (C 10)).

[0113] Hence, granules obtained according to the inventive method have improved water treatment properties over granules of semi-calcined dolomite which were obtained by conventional production methods.

[0114] In another example, a granulated product (P1) according to the invention was compared to a commercial product (CP) used for neutralization and remineralization of aggressive water, i.e. water that has some excess of carbon dioxide.

[0115] Product P1 is a granular material obtained from a mixture of 32 parts of a magnesium oxide component and 68 parts of a calcium carbonate component. The particle size of the granules after sieving was between 1.4 and 1.6 mm. The average composition of granular material P1 measured on 10 samples, by XRF and LOI on dry basis is presented below:

TABLE-US-00002 CaCO.sub.3 68.5% MgCO.sub.3 0.3% MgO 30.6% SiO.sub.2 0.1% Fe.sub.2O.sub.3 0.2% Al.sub.2O.sub.3 0.2% Mn.sub.2O.sub.3 0.1%

[0116] 0.3 dm.sup.3 of the product P1 was filled into a first column having a volume of 3 dm.sup.3 and a diameter of 0.1 m. Columns were preliminary backwashed during 2 min using tap water at a flowrate of 8 dm.sup.3/min. To characterize the system, the empty bed contact time (EBCT) was used. In this case, the system was operating at 20° C., the water to be treated had an initial concentration of CO.sub.2 between 0.4 and 0.7 mmol/L and initial concentrations of Ca.sup.2+ and Mg.sup.2+ of 11 mg/L and 5.0 mg/L, respectively. EBCT from 2 to 4 minutes were applied. The pilot unit was operated at a flow rate of 6 dm.sup.3/h for 5 days without interruptions.

[0117] The water was also treated under equivalent conditions in a column containing the commercial product CP as a comparative example, wherein the commercial product CP was sieved to have a grain size between 1.4 and 1.6 mm. The commercial product CP was obtained from semi-calcined dolomite. The composition of commercial product CP measured on 10 samples, by XRF and LOI on dry basis is presented below:

TABLE-US-00003 CaCO.sub.3 68.9% CaO 1.4% MgO 25.4% MgCO.sub.3 0.5% Fe.sub.2O.sub.3 0.5% Al.sub.2O.sub.3 0.2% SiO.sub.2 0.4% Water 2.7%

[0118] FIG. 1 shows pH-values of treated water at the outlet of the column using a column containing product P1 according to the invention compared with pH-values of treated water at the outlet of a column containing the commercial product CP as comparative example. The pH-values were obtained for various alkalinities with a CO.sub.2 concentration of 0.4 mmol/dm.sup.3. In all the cases, the pH-values are slightly higher for the inventive product P1 but the difference of pH obtained at the outlet with the two examples does not exceed 5%.

[0119] FIG. 2 shows pH-values of treated water at the outlet of the column using a column containing product P1 according to the invention compared with the pH-values of treated water at the outlet of a column containing the commercial product CP as comparative example. The pH-values were obtained for various alkalinities with a CO.sub.2 concentration of 0.7 mmol/dm.sup.3. In all the cases, the pH-values are slightly higher for the inventive product P1 but the difference of pH obtained at the outlet with the two examples does not exceed 5%.

[0120] FIG. 3 shows pH-values of treated water at the outlet of the column using a column containing product P1 according to the invention compared with pH-values of treated water at the outlet of a column containing the commercial product CP as comparative example. The pH-values were obtained for various alkalinities with a CO.sub.2 concentration of 1 mmol/dm.sup.3. In all the cases, the pH-values are slightly higher for the inventive product P1 but the difference of pH obtained at the outlet with the two examples does not exceed 5%.

[0121] Table 1 shows the final alkalinity of treated water that was filtered through either a filter containing product P1 according to the invention or a filter containing commercial product CP, for various water samples having particular initial alkalinities and a particular initial CO.sub.2 concentrations. The difference in final alkalinity between the water sample treated with P1 and the water sample treated with CP is shown in percent [%].

TABLE-US-00004 Initial Initial EBCT Final Alkalinity Alkalinity CO.sub.2 applied P1 CP % [mmol/L] [mmol/L] [min] [mmol/L] [mmol/L] difference 0.456 0.4 2.6 0.828 0.822 0.72 0.656 0.4 2.4 1.082 1.088 0.55 1.072 0.4 2.2 1.392 1.31 5.89 1.4 0.4 2.1 1.514 1.512 0.13 0.378 0.7 3.5 1.158 1.158 0 0.548 0.7 3.4 1.22 1.292 5.9 0.922 0.7 3.2 1.596 1.448 9.27 1.316 0.7 2.9 1.914 1.928 0.73 1.618 0.7 2.7 2.08 2.11 1.44 0.404 1 4 1.506 1.444 4.12 0.714 1 3.8 1.792 1.79 0.11 1.004 1 3.5 1.92 1.872 2.5 1.282 1 3.2 2.262 2.162 4.42 1.512 1 3.1 2.292 2.296 0.17

[0122] The difference of alkalinities of water treated with product P1 according to the invention compared to water treated with commercial product CP does not exceed 10%.

[0123] Thus, the inventive product P1 provides an excellent deacidification of aggressive water. The product of the invention represents an excellent alternative to commercial products based on semi-calcined dolomite.