Method for processing and utilizing bypass dusts obtained during the production of cement

1. A method for processing and utilizing bypass dusts obtained during the production of cement, comprising the steps of

a) contacting the bypass dust with an aqueous phase and mixing the bypass dust with the aqueous phase to obtain a homogenous slurry, with water-soluble components of the bypass dust being dissolved in the aqueous phase,

b) carrying out a solid-liquid separation to separate solids contained in the slurry, with a brine remaining,

c) separating heavy metals present in the brine and precipitating calcium to obtain a processed brine, and

d) subjecting the processed brine to a fractional crystallization.

2. A method according to claim 1 , wherein the ratio of bypass dust to aqueous phase in step a) is 1:1 to 1:2.

3. A method according to claim 1 , wherein HCl is added in step a).

4. A method according to claim 1 , wherein a first separation step is performed according to step b) to obtain a first brine, which is fed to step c), and that the solids separated in the first separation step are slurried using an aqueous medium, wherein the water-soluble components of the solids are dissolved in the aqueous phase and the thus obtained slurry is subjected to at least a further separation step in which the solids contained in the slurry are separated and a second brine remains.

5. A method according to claim 4 , wherein the first and/or the at least one further separation step comprises filtration.

6. A method according to claim 5 , wherein said filtration is performed using a filter press.

7. A method according to claim 1 , wherein the solid-liquid separation according to step b) is performed by a continuous separation process, wherein the slurry and an aqueous phase are conducted in counter-flow, and contacted, in a continuously operating separation device.

8. A method according to claim 7 , wherein a second brine is withdrawn upon passage through a first section of the separation device, and a first brine is withdrawn upon passage through a further section of the separation device.

9. A method according to claim 4 or 8 , wherein the second brine remaining after the second and/or the at least one further separation step, or withdrawn from the separation device, is used for slurrying the bypass dust in step a), and/or for washing out or slurrying the filter cake resulting from the first or the at least one further separation step.

10. A method according to claim 1 , wherein the separated solids, after optionally being dried, are returned into the cement production process.

11. A method according to claim 1 , wherein in step c) a precipitant is added to the brine for precipitating calcium salts.

12. A method according to claim 11 , wherein CO 2 -containing exhaust gas is withdrawn from a kiln and used as precipitant in step c).

13. A method according to claim 1 , wherein calcium salt precipitated in step c) is added to the slurry in step a) and separated as a solid in step b).

14. A method according to claim 1 , wherein the separation of heavy metals is performed by sulfide precipitation.

15. A method according to claim 14 , wherein Na 2 S is used as precipitant for the sulfide precipitation.

16. A method according to claim 1 , wherein the precipitation of calcium salts takes place after the precipitation of the heavy metals.

17. A method according to claim 16 , wherein the precipitation of Ca is performed after the heavy-metal precipitation without previous solid-liquid separation of the precipitated heavy metals, and that a formed suspension is then separated into a liquid and a solid phase by a co-sedimentation of heavy metals and calcium salts.

18. A method according to claim 1 , wherein step c) further comprises precipitation of lithium as Li 2 CO 3 , wherein carbonates having a higher solubility than Li 2 CO 3 are used as precipitants.

19. A method according to claim 14 , wherein step c) after the precipitation of heavy metals, and optionally after the precipitation of calcium, further comprises the addition or preparation of an oxidant to remove sulfide anions (S 2− ).

20. A method according to claim 19 , wherein the addition or preparation of the oxidant is performed after a precipitation of sulfides and prior to the precipitation of calcium.

21. A method according to claim 1 , wherein an acid, is added at the end of step c) to lower the pH.

22. A method according to claim 1 , wherein waste heat from the cement production process is used in the fractional crystallization in step d) for evaporating the processed brine, and optionally for drying an obtained salt.

23. A method according to claim 22 , wherein the waste heat from the cement production process is supplied to vapor generation and the vapor is used for heating and evaporating the processed brine in step d), wherein evaporated water of the brine is at least partially supplied to said vapor generation.

24. A method according to claim 1 or 4 , wherein water evaporated in step d), of the brine is at least partially used for slurrying the bypass dusts and/or for slurrying or washing out the solids separated in the first and/or a further separation steps.

25. A method according to claim 1 , wherein the solid-liquid separation of step b) comprises a vacuum filtration or a filter press filtration.

26. A method according to claim 7 , wherein the separation device is a band filter or a vacuum band filter.

27. A method according to claim 11 , wherein the precipitant is comprised of CO 2 or carbonates.

28. A method according to claim 16 , wherein the calcium salts are CaCO 3 .

29. A method according to claim 21 , wherein the acid is HCl.

30. A method according to claim 22 , wherein waste heat from the preheater or the clinker cooler is used in the fractional crystallization in step d).

31. A method according to claim 23 , wherein the waste heat from the preheater or the cement cooler is supplied to vapor generation.