Surface-reacted calcium carbonate and its use in waste water treatment

Abstract

The present invention relates to a process for the purification of water, wherein a surface-reacted natural calcium carbonate is brought into contact with the water to be purified, the surface-reacted natural calcium carbonate being the reaction product of a natural calcium carbonate with an acid and carbon dioxide, which is formed in situ by the acid treatment and/or supplied externally.

Claims

1. A composite material comprising surface-treated natural calcium carbonate and at least one impurity selected from a heavy metal impurity, an organic impurity, a microorganism, a polycyclic compound, cholesterol, and/or an endocrine disrupting compound, adsorbed or absorbed from water comprising the impurity, wherein the composite material is obtained by (i) contacting surface-treated natural calcium carbonate with water comprising at least one impurity selected from a heavy metal impurity, an organic impurity, a microorganism, a polycyclic compound, cholesterol, and/or an endocrine disrupting compound, so that the at least one impurity is adsorbed or absorbed by the surface-treated natural calcium carbonate, and (ii) separating the surface-treated natural calcium carbonate with the adsorbed or absorbed at least one impurity from water to obtain the composite material, wherein the surface-treated natural calcium carbonate is natural calcium carbonate from a natural source that is not saturated with heavy metals, that was treated with an acid and carbon dioxide, formed in situ or applied from an external source, in water to obtain the surface-treated natural calcium carbonate, wherein the surface-treated natural calcium carbonate has a specific surface area of from 5-200 m.sup.2/g as measured using nitrogen and BET method.

2. The composite material according to claim 1, wherein the natural calcium carbonate is marble, calcite, chalk, dolomite, limestone, or mixtures thereof.

3. The composite material according to claim 1, wherein the acid has a pK.sub.a at 25° C. of 2.5 or less.

4. The composite material according to claim 1, wherein the acid has a pKa at 25° C. of 0 or less.

5. The composite material according to claim 1, wherein the acid is sulphuric acid, hydrochloric acid, or mixtures thereof.

6. The composite material according to claim 1, wherein the acid has a pK.sub.a at 25° C. of from 0 to 2.5.

7. The composite material according to claim 1, wherein the acid is H.sub.2SO.sub.3, HSO.sub.4.sup.−, H.sub.3PO.sub.4, oxalic acid, or mixtures thereof.

8. The composite material according to claim 1, wherein the acid is H.sub.3PO.sub.4.

9. The composite material according to claim 1, wherein the surface-treated natural calcium carbonate has a mean grain diameter of from 0.1 to 50 μm, measured according to the sedimentation method.

10. The composite material according to claim 1, wherein the surface-treated natural calcium carbonate has an intra-particle porosity within the range of 20% vol to 40% vol, measured by mercury porosimetry.

11. The composite material according to claim 1, wherein the surface-treated natural calcium carbonate comprises a dispersant.

12. The composite material according to claim 1, wherein the surface-treated natural calcium carbonate is stabilized with a cationic dispersant, and wherein the surface-treated natural calcium carbonate has been prepared from marble in the presence of at least one silicate.

13. The composite material according to claim 1, wherein the surface-treated natural calcium carbonate is in powder form and/or in the form of granules.

14. The composite material according to claim 1, further comprising a polymeric flocculant and/or activated carbon, wherein the polymeric flocculant is an anionic, cationic, or polyacrylamide flocculant.

15. The composite material according to claim 14, wherein the polymeric flocculant is anionic.

16. The composite material according to claim 14, wherein the polymeric flocculant is cationic.

17. The composite material according to claim 14, wherein the polymeric flocculant is polyacrylamide.

18. The composite material according to claim 17, wherein the polyacrylamide has a weight average molecular weight M.sub.w in the range of 100,000 g/mole to 10,000,000 g/mole.

19. The composite material according to claim 17, wherein the polyacrylamide has a negative overall charge and comprises comonomer units derived from (meth)acrylic acid.

20. The composite material according to claim 17, wherein the polyacrylamide has a positive overall charge and comprises comonomer units derived from aminoalkyl(meth) acrylates.

Description

EXAMPLES

(1) Measuring Methods

(2) Mean Grain Diameter (d50)

(3) Mean grain diameter and grain diameter distribution are determined via the sedimentation method, i.e. an analysis of sedimentation behaviour in a gravimetric field. The measurement is made with a Sedigraph™ 5100 of Microtronics. The method and the instrument are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurement is carried out in an aqueous solution of 0.1 wt % Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and supersonic.

(4) Specific Surface Area

(5) The specific surface area is measured via the BET method according to ISO 9277 using nitrogen.

(6) Dewatering According to the “Sieving Test Method”

(7) An aqueous sludge sample, e.g. from a municipal sewage plant, is treated with the flocculant(s) to be tested. Subsequent to the flocculation treatment, the sludge sample is filtered and dewatered on a metal sieve having a mesh size of 200 μm. The time needed for dewatering a given amount of filtrate and the clarity of the water running through the filter are determined. Values for clarity are provided on a scale from 0 to 46, wherein 46 indicates the highest level of clarity.

(8) Type and Amount of Impurities

(9) The type and amount of impurities which are present in the water samples before and after treatment according to the process of the present invention were determined using Optima 3200 XL ICP-OES instrumentation from Perkin-Elmer. The samples were directly analysed following treatment with SRCC.

(10) Turbidity

(11) Turbidity of the water samples was measures using a Hach 2100β Iso Turbidimeter.

(12) pH of the Suspension

(13) The pH of the aqueous suspension is measured using a standard pH-meter.

(14) Intra-Particle Porosity by Mercury Porosimetry

(15) Tablets were made from suspensions of the surface-reacted natural calcium carbonate. The tablets are formed by applying a constant pressure to the suspension/slurry for several hours such that water is released by filtration through a fine 0.025 μm filter membrane resulting in a compacted tablet of the pigment. The tablets are removed from the apparatus and dried in an oven at 80° C. for 24 hours.

(16) Once dried, single portions from each of the tablet blocks were characterised by mercury porosimetry for both porosity and pore size distribution using a Micromeritics Autopore IV mercury porosimeter. The maximum applied pressure of mercury was 414 MPa, equivalent to a Laplace throat diameter of 0.004 μm (i.e. ˜nm). The mercury intrusion measurements were corrected for the compression of mercury, expansion of the penetrometer and compressibility of the solid phase of the sample. Further details of the measuring method are described in Transport in Porous Media (2006) 63: 239-259.

Example 1

(17) In example 1, the adsorption capacity of the surface-reacted natural calcium carbonate with regard to different heavy metals is determined.

(18) 500 g of a heavy metal solution, containing 5 ppm each of cadmium, chromium, copper, mercury, nickel, and lead was stirred for 15 minutes with 3% (w/w %) surface-reacted natural calcium carbonate. The solution was left for 24 hours at pH 11.5 and the upper liquid phase was analysed with ion chromatography (Dionex DX 120 Ion-Chromatograph).

(19) The surface-reacted natural calcium carbonate was prepared as follows:

(20) A finely divided natural calcium carbonate originating from Omey, France, was suspended to achieve a suspension of approximately 16% by weight of dry matter. The slurry thus formed is then treated by slow addition of phosphoric acid at a temperature of approximately 55° C., sufficient to provide a product featuring a BET specific surface area of 35 m.sup.2/g according to ISO standard 92777, and an approximate number average diameter of 10 micrometers estimated from scanning electron microscope images obtained using a LEO 435 VPe scanning electron microscope.

(21) The results are summarised in Table 1.

(22) TABLE-US-00001 TABLE 1 Treatment of heavy metal ion solution with surface-reacted calcium carbonate Amount Amount Amount Amount Amount of of of of of Amount cadmium chromium copper mercury nickel of lead (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) Untreated 5.0 5.0 5.0 5.0 5.0 5.0 solution Solution <0.1 <0.1 <0.1 <0.1 0.5 <0.1 after treatment Sediment 2.6 2.5 3.2 2.1 3.7 2.6 obtained after treatment

(23) It is obvious that the surface-reacted natural calcium carbonate was able to reduce cadmium, chromium, copper, mercury, and lead very efficiently. From the originally dissolved 5 ppm, less than 0.1 ppm was recovered in the treated sample. For nickel, 90% of the starting amount of 5 ppm was adsorbed and thus removed from the solution.

Example 2

(24) In Example 2, the adsorption capacity of the surface-reacted natural calcium carbonate with regard to microorganisms is determined.

(25) A barm suspension of 100 ppm was used with a germ count of 6*10.sup.5 cfu/cm.sup.3. In a first experiment, the barm suspension was filtered through a blue band paper filter. In a second experiment, the suspension was filtered through a layer made of the surface-reacted natural calcium carbonate, the layer having a diameter of 90 mm and a thickness of 30 mm.

(26) The surface-reacted natural calcium carbonates was prepared as follows:

(27) Two samples were tested and provided the same results within 0.5%.

(28) First Surface-Reacted Natural Calcium Carbonate:

(29) A finely divided natural calcium carbonate originating from Omey, France, was suspended to achieve a suspension of approximately 16% by weight of dry matter. The slurry thus formed is then treated by slow addition of phosphoric acid at a temperature of approximately 55° C., sufficient to provide a product featuring a BET specific surface area of 35 m.sup.2/g according to ISO standard 92777, and an approximate number average diameter of 10 micrometers estimated from scanning electron microscope images obtained using a LEO 435 VPe scanning electron microscope.

(30) Second Surface-Reacted Natural Calcium Carbonate:

(31) A finely divided natural calcium carbonate originating from Molde, Norway, was suspended to achieve a suspension of approximately 16% by weight of dry matter. The slurry thus formed is then treated by slow addition of phosphoric acid at a temperature of approximately 55° C., sufficient to provide a product featuring a BET specific surface area of 50 m.sup.2/g according to ISO standard 92777, and an approximate number average diameter of 20 micrometers estimated from scanning electron microscope images obtained using a LEO 435 VPe scanning electron microscope.

(32) The results are shown in Table 2.

(33) TABLE-US-00002 TABLE 2 Filtration of barm suspension through different filter materials Germ count of suspension (cfu/ml) Untreated suspension 6 * 10.sup.5 Suspension after filtering through 6 * 10.sup.5 paper filter Suspension after filtering through 7 * 10.sup.3 filter layer made of surface-reacted calcium carbonate

(34) The results indicate that the use of the surface-reacted natural calcium carbonate reduced the germ count by a factor of 100.

Example 3

(35) In Example 3, river water was subjected to the purification method of the present invention. 100 ppm surface-reacted natural calcium carbonate and 4 ppm polyaluminium chloride were suspended in a river water sample. After two minutes, the flocculated solids were filtered off and the filtrate was analysed for its content of iron and manganese.

(36) The surface-reacted natural calcium carbonate used in Example 3 was prepared as follows:

(37) A finely divided natural calcium carbonate originating from Vermont, U.S.A, containing 800 ppm of magnesium oxide and 2500 ppm anionic polyacrylate dispersant per equivalent dry gram of calcium carbonate, was suspended to achieve a suspension of approximately 16% by weight of dry calcium carbonate. The slurry thus formed is then treated by slow addition of phosphoric acid at a temperature of approximately 55° C., sufficient to provide a product featuring a BET specific surface area of 68 m.sup.2/g according to ISO standard 92777, and a d50 of 10 micrometers measured by means of the Sedigraph™ 5100 from Micromeritics™.

(38) The results are summarized in Table 3.

(39) TABLE-US-00003 TABLE 3 Treatment of river water with surface-reacted calcium carbonate Amount of iron Amount of manganese (mg/l) (mg/l) River water sample before 2.03 0.88 treatment River water sample after 0.023 0.104 treatment

(40) The results clearly indicate that treatment with the surface-reacted natural calcium carbonate significantly reduces the amounts of heavy metal ions such as iron and manganese.

Example 4

(41) The example concerns the process of treating water coming from sludge samples which were provided from a municipal sewage plant. To these samples the following compositions were added in varying amounts: (a) a cationic polyacrylamide having cationic acrylic acid monomer units, the polyacrylamide being commercialised under the trade name Praestol™ 857 BS, (b) the polyacrylamide mentioned under (a) in combination with iron(III) chloride. FeCl.sub.3 was provided as an 10 vol % aqueous solution, (c) the polyacrylamide mentioned under (a) in combination with the surface-reacted natural calcium carbonate

(42) The surface-reacted natural calcium carbonate was prepared as follows:

(43) Finely divided natural calcium carbonate originating from Vermont, U.S.A, containing 800 ppm of magnesium oxide and 2500 ppm anionic polyacrylate dispersant per equivalent dry gram of calcium carbonate, was suspended to achieve a suspension of approximately 16% by weight of dry calcium carbonate. The slurry thus formed is then treated by slow addition of phosphoric acid at a temperature of approximately 55° C., sufficient to provide a product featuring a BET specific surface area of 68 m.sup.2/g according to ISO standard 92777, and a d50 of 10 micrometers measured by means of the Sedigraph™ 5100 from Micromeritics™.

(44) The product was spray dried using a Mobil Minor spray dryer from Niro A/S.

(45) Each sample was subjected to the Sieving Test Method described above and time for dewatering the filtrate as well as clarity of the water running through the filter were determined.

(46) The results are summarized in Table 4.

(47) TABLE-US-00004 TABLE 4 Dewatering according to Sieving Test Method Dewatering Dewatering Dewatering Dewatering time [sec] Clarity time [sec] Clarity time [sec] Clarity time [sec] Clarity with added with added with added with added amount of PAA of amount of PAA of amount of PAA of amount of PAA of 4.5 kg/t dry matter 4.8 kg/t dry matter 5.2 kg/t dry matter 5.5 kg/t dry matter Polyacryl-amide, 83 6 38 10 25 19 17 34 no pretreatment PAA with 1 kg 16 46 12 46 11 46 10 46 FeCl.sub.3/m.sup.3 sludge PAA with 1 kg 26 5 22 16 18 26 17 46 surface-reacted CC/m.sup.3 sludge PAA with 2 kg 18 46 14 46 12 46 9 46 FeCl.sub.3/m.sup.3 sludge PAA with 2 kg 22 46 18 46 17 46 14 46 surface-reacted CC/m.sup.3 sludge

(48) The results indicate that the surface-reacted natural calcium carbonate in combination with a polymeric flocculant such as polyacrylamide is an efficient flocculation system, comparable to flocculation systems commonly used such as iron(III) chloride in combination with polyacrylamide.

Example 5

(49) The example concerns the process of treating water coming from sludge samples which were provided from a municipal sewage plant. To these samples the following compositions were added in varying amounts: (a) a cationic polyacrylamide having cationic acrylic acid monomer units, the polyacrylamide being commercialised under the trade name Praestol™ 853 BC, (b) the polyacrylamide mentioned under (a) in combination with iron(III) chloride. FeCl.sub.3 was provided as an 10 vol % aqueous solution, (c) the polyacrylamide mentioned under (a) in combination with the surface-reacted natural calcium carbonate.

(50) The surface-reacted natural calcium carbonate was prepared as indicated above in Example 4.

(51) Each sample was subjected to the Sieving Test Method described above and time for dewatering the filtrate as well as clarity of the water running through the filter were determined.

(52) The results are summarized in Table 5.

(53) TABLE-US-00005 TABLE 5 Dewatering according to Sieving Test Method Dewatering Dewatering Dewatering time [sec] Clarity time [sec] Clarity time [sec] Clarity with added amount with added amount with added amount of PAA of 4.8 kg/t of PAA of 5.2 kg/t of PAA of 5.5 kg/t dry matter dry matter dry matter Polyacryl-amide, 40 16 25 21 17 26 no pretreatment PAA with 0.5 kg 31 20 18 27 16 32 FeCl.sub.3/m.sup.3 sludge PAA with 0.5 kg 32 18 23 22 20 26 surface-reacted CC/m.sup.3 sludge PAA with 2 kg 10 46 9 46 8 46 FeCl.sub.3/m.sup.3 sludge PAA with 2 kg 24 28 19 33 14 46 surface-reacted CC/m.sup.3 sludge

(54) The results indicate that the surface-reacted natural calcium carbonate in combination with a polymeric flocculant such as polyacrylamide is an efficient flocculation system, comparable to flocculation systems commonly used such as iron(III) chloride in combination with polyacrylamide.

Example 6

(55) The example concerns the process of treating water coming from clay suspensions. These clay suspension samples were treated with an iron(III) chloride flocculant, a surface-reacted calcium carbonate which has been prepared in the presence of a silicate and is stabilised by a cationic dispersant (abbreviated as CC1), and a surface-reacted calcium carbonate without dispersant (abbreviated as CC2), respectively. In some experiments, a polyacrylamide flocculant, either PAM or PAA2, was additionally used.

(56) For each sample, the following properties were measured: (i) turbidity of the solution after sedimentation, (ii) the time needed to achieve the final turbidity value, (iii) mass, volume, and density of the filter cake.

(57) The surface-reacted natural calcium carbonate CC1 was prepared as follows:

(58) A high solids slurry of finely divided natural calcium carbonate originating from Vermont, U.S.A, is diluted to achieve a suspension of approximately 20% by weight of dry matter. The slurry thus formed is then treated by slow simultaneous addition of phosphoric acid and sodium silicate at a temperature of approximately 55° C. A slurry of 19% by weight of dry matter of a product featuring a BET specific surface area of 55 m.sup.2/g, a d50 of 1.5 μm measured by means of the Sedigraph™ 5100 from Micromeritics™ is obtained.

(59) The slurry is then dewatered to 32% by weight of dry matter and subsequently dispersed using a cationic dispersant.

(60) The surface-reacted natural calcium carbonate CC2 was prepared as follows:

(61) Finely divided natural calcium carbonate originating from Omey, France, is suspended to achieve a suspension of approximately 20% by weight of dry matter. The slurry thus formed is then treated by slow addition of phosphoric acid at a temperature of approximately 55° C. A slurry of product featuring a BET specific surface area of 41 m.sup.2/g according to ISO standard 92777, a d50 of 1.5 μm measured by means of the Sedigraph™ 5100 from Micromeritics™ is obtained.

(62) Polyacrylamide PAA1 is a cationic flocculant, the positive charge being introduced by cationic acrylamide derivative units. PAA1 is available under its trade name PRAESTOL® 611.

(63) Polyacrylamide PAA2 is a medium anionic flocculant, available under its trade name PRAESTOL® 2540.

(64) The results are summarized in Table 6.

(65) TABLE-US-00006 TABLE 6 Treatment of clay suspensions Primary + CC1 CC2 FeCl3 PAA1 Secondary (kg/t (kg/t (kg/t (kg/t PAA2 Turbidity additives dry) dry) dry) dry) (ml) 1 2 3 4 1 0 437 431 419 413 2 CC1 67 24 22.2 22.2 21.7 3 CC1 + PAA1 67 0.008 13.3 12.2 12.2 11.4 4 CC1 + PAA1 67 0.042 7.5 8.71 7.74 7.81 5 PAA1 0.042 157 157 154 150 6 CC1 + PAA1 67 0.042 26.6 23.5 24.2 20.2 7 CC1 67 0.5 12.7 14.9 14.1 13.2 8 FeCl3 33 93.3 92.1 91.1 94.4 9 FeCl3 67 10 CC2 + PAA2 67 0.5 148 146 144 151 11 CC2 67 350 344 353 347 12 CC2 + PAA1 67 0.042 170 163 165 158 13 CC1 67 14.7 12.7 11.8 11.6 14 CC1 + PAA2 67 0.5 16 15.4 14.8 14.4 15 CC1 + PAA1 33 0.042 28.7 28.4 28.3 27.9 16 CC1 + PAA2 33 0.5 29.8 28.2 28.5 28.4 17 FeCl3 + PAA1 33 0.042 44 42.7 44.1 42 18 FeCl3 + PAA2 33 0.5 60.9 61.3 59.3 59.4 19 FeCl3 + PAA1 67 0.042 20 FeCl3 + PAA2 67 0.5 Primary to PAA2 secondary (kg/t additive Time (min:sec) mass vol dry) ratio Turbidity 150 ml 100 ml 50 ml (g) (ml) density 1 425 2 23 3 8000 12 4 1600 8 5 155 6 1600 24 7 0.042 1600 14 8 93 58 56 1.04 9 Too turbid to measure 10 0.042 1600 147 0:52 1:45 40 43 0.93 11 349 3:24 6:47 58 58 1.00 12 1600 164 0:55 2:13 11:10  50 47 1.06 13 13 0:49 2:30 65 62 1.05 14 0.042 1600 15 0:20 3:00 49 46 1.06 15 800 28 0:50 2:01 49 48 1.03 16 0.042 800 29 0:13 0:36 4:00 48 45 1.07 17 800 43 0:34 1:36 62 59 1.04 18 0.042 800 60 1:15 2:30 62 60 1.03 19 1600 Too turbid to measure 20 0.042 1600 Too turbid to measure CC1: Surface-reacted natural calcium carbonate which was prepared in the presence of a silicate and dispersed with a cationic dispersant CC2: Surface-reacted natural calcium carbonate without dispersant Primary additive (SRCC of FeCl3) was added as kg per m.sup.3 slurry (g/L slurry) Starting solids of clay was 3%. Density of solution taken as ~1 g/ml.

(66) The results of Table 6 indicate that the use of the surface-reacted natural calcium carbonate, optionally in combination with a polyacrylamide flocculant, significantly reduces turbidity at high flocculation rate (i.e. quickly achieving final turbidity value). Furthermore, a low volume filter cake (i.e. improved compactness) can be obtained, thereby significantly reducing disposal costs.

Example 7

(67) The example concerns the process of treating water coming from cow manures. The cow manure samples were treated with an iron(III) chloride flocculant, a surface-reacted calcium carbonate which has been prepared in the presence of a silicate and is stabilised by a cationic dispersant (abbreviated as CC1), and a surface-reacted calcium carbonate without dispersant (abbreviated as CC2), respectively. In some experiments, a polyacrylamide flocculant, either PAA1 or PAA2, was additionally used.

(68) For each sample, the following properties were measured: (i) solids content, (ii) the time needed for settlement of the precipitated solids, (iii) mass and volume of the filter cake.

(69) The surface-reacted natural calcium carbonates CC1 and CC2 were prepared as described above in Example 6. The polyacrylamide flocculants correspond to those used in Example 6.

(70) The results are summarized in Table 7.

(71) TABLE-US-00007 TABLE 7 Treatment of manure Prim FeCl3 CCl CC2 Ratio Manure Additive Sec. (kg/t (kg/t (kg/t PAA1 PAA2 Prim/Sec Volume of Mass (g) Type Floc dry) dry) dry) (kg/t) (kg/t) Additive Solids cake (ml) Cake (g) Times 1 200 None n/a 200 nothing settled to the naked eye 2 200 FeCl3 n/a 56 0.51% 150 settled 50 ml in 13 minutes, 100 in 50 minutes 3 200 n/a Cationic 5 0.51% 40.5 40.3 full settlement in 4.5-5 minutes 4 200 CC1 n/a 111 0.69% 34 33.9 full settlement in 4.5-5 minutes 5 200 CC1 Cationic 111 5 22 0.46% 44 43.9 almost full settlement 25 sec. 6 200 CC1 Anionic 111 5 22 0.53% 37 36.7 almost full settlement 2 minutes 7 200 FeCl3 n/a 111 0.60% 162 163.4 in 15 minutes only settled about 20-30 ml 8 200 FeCl3 Cationic 111 5 22 0.68% 103 103.2 settled 50 ml in 5.5 minutes, 100 in 15 minutes 9 200 FeCl3 Cationic 56 5 11 0.38% 106 107 settled ~100 ml in 1-2 min but never changed after that 10 200 FeCl3 Cationic 28 5 6 0.34% 78 77.7 settled to final value in about 1 minutes 11 200 CC1 Cationic 111 5 22 0.38% 54 53.4 settled to near full value in 2 min 12 200 CC2 Cationic 111 5 22 0.41% 53 54.6 settled to near full value in 2 min 13 200 CC1 Cationic 56 5 11 0.49% 55 56.4 settled to near full value in 1 min 14 200 CC2 Cationic 56 5 11 0.47% 40 39.3 settled to near full value in 20 sec
Starting solids of the manure was 1.79%.
Added 3.6 g of 0.5% dispersant each time of the 200 g of 1.79% solids material
0.01
=3.6*.005/(200*.0.179)=0.0050 g/g=5 kg/t
The results indicate that the use of the surface-reacted natural calcium carbonate result in efficient flocculation at high rate of settlement. Furthermore, the volume of the filter cake can be decreased significantly.