Process for the purification of water

1. A process for the purification of water comprising (a) contacting the water to be purified with (i) surface-treated natural calcium carbonate or (ii) an aqueous suspension comprising surface-treated natural calcium carbonate having a pH of greater than 6.0 measured at 20° C., so that the surface-treated natural calcium carbonate absorbs impurities in the water, wherein the surface-treated natural calcium carbonate is formed by treating a natural calcium carbonate with carbon dioxide and one or more acids, and (b) separating the surface-treated natural calcium carbonate with absorbed impurities from the water.

2. The process according to claim 1 , wherein the surface-treated natural calcium carbonate is prepared as an aqueous suspension having a pH of greater than 6.5, measured at 20° C.

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

4. The process according to claim 1 , wherein the acid has a pK a at 25° of 2.5 or less.

5. The process according to claim 4 , wherein the acid is hydrochloric acid, sulphuric acid, sulphurous acid, hydrosulphate, phosphoric acid, oxalic acid or mixtures thereof.

6. The process according to claim 1 , wherein the natural calcium carbonate is treated with the acid and the carbon dioxide in the presence of at least one silicate and/or silica, aluminium hydroxide, earth alkali metal aluminate, magnesium oxide, or mixtures thereof.

7. The process according to claim 6 , wherein the at least one silicate is an aluminium silicate, a calcium silicate, or an alkali metal silicate.

8. The process according to claim 1 , wherein the surface-treated natural calcium carbonate has a specific surface area of from 5 m 2 /g to 200 m 2 /g, measured using nitrogen and the BET method according to ISO 9277.

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

10. The process according to claim 1 , wherein the aqueous suspension comprising surface-treated natural calcium carbonate is stabilized with one or more dispersants.

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

12. The process according to claim 1 , wherein the surface-treated natural calcium carbonate is added in an amount of 10 ppm-1 wt.-%, based on the weight of the water to be treated.

13. The process according to claim 1 , wherein the pH of the water to be purified is adjusted to a value of >6.5, before being brought into contact with the surface-treated natural calcium carbonate.

14. The process according to claim 1 , wherein the water to be purified is selected from the group comprising industrial waste water, drinking water, urban waste water, waste water from breweries or other beverage industries, water in the paper industry and agricultural waste-water.

15. The process according to claim 1 , wherein the water to be purified contains heavy metal impurities.

16. The process according to claim 1 , wherein the water to be purified contains microorganisms as impurities.

17. The process according to claim 1 , wherein the water to be purified contains an endocrine disrupting compound (EDC) impurity selected from the group comprising an endogenous hormone, 17β-estradiol (E2), estrone (E1), estriol (E3), testosterone, dihydro testosterone, a phyto hormone, a myco hormone β-sitosterol, genistein, daidzein, zeraleon, a drug, 17α-ethinylestradiol (EE2), mestranol (ME), diethylstilbestrol (DES), an industrial chemical, 4-nonyl phenol (NP), 4-tert-octyl phenol (OP), bisphenol A (BPA), tributyltin (TBT), methylmercury, a phthalate, PAK or PCB.

18. The process according to claim 1 , wherein the water to be purified contains activated carbon impurities.

19. The process according to claim 18 , wherein the activated carbon impurities have further impurities adsorbed onto their surface.

20. The process according to claim 1 , wherein the water to be purified is brought into contact with the surface-treated natural calcium carbonate by surface filtration, depth filtration and/or alluvium filtration.

21. The process according to claim 1 , wherein the surface-treated natural calcium carbonate is prepared as an aqueous suspension having a pH of greater than 7.0, measured at 20° C.

22. The process according to claim 1 , wherein the surface-treated natural calcium carbonate is prepared as an aqueous suspension having a pH of greater than 7.5, measured at 20° C.

23. The process according to claim 4 , wherein the acid is phosphoric acid.

24. The process according to claim 1 , wherein the surface-treated natural calcium carbonate has a specific surface area of from 20 m 2 /g to 80 m 2 /g, measured using nitrogen and the BET method according to ISO 9277.

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

26. The process according to claim 1 , wherein the surface-treated natural calcium carbonate is added in an amount of 100 ppm-0.5 wt.-%, based on the weight of the water to be treated.

27. The process according to claim 1 , wherein the surface-treated natural calcium carbonate is added in an amount of 400 ppm-2000 ppm, based on the weight of the water to be treated.

28. The process according to claim 1 , wherein the pH of the water to be purified is adjusted to a value of >7 before being brought into contact with the surface-treated natural calcium carbonate.

29. The process according to claim 1 , wherein the surface-treated natural calcium carbonate with absorbed impurities is separated from the water by sedimentation or filtration.

30. The process according to claim 1 , wherein the surface-treated natural calcium carbonate with absorbed impurities is separated from the water by surface filtration, depth filtration and/or alluvium filtration.

31. The process according to claim 1 , wherein the water to be purified is brought into contact with the surface-treated natural calcium carbonate and the surface-treated natural calcium carbonate with absorbed impurities is separated from the water by surface filtration, depth filtration and/or alluvium filtration.

32. The process according to claim 1 , wherein the carbon dioxide is formed in situ by acid treatment.

33. The process according to claim 1 , wherein the carbon dioxide is supplied from an external source.