Process for preparing a PCC composite product
The current invention relates to methods of the recovery and re-use of minerals obtained from the combustion of the residues of a process to recycle paper.
1. A process for making composite precipitated calcium carbonate particles, the process comprising:
providing ash, at least 25 wt % of the ash, on a dry basis, comprising CaO;
wherein the wt % of CaO is determined by X-ray diffraction; and
wherein the ash is the product of incineration of a material;
forming an aqueous slurry of the ash,
wherein the water used to form the slurry, prior to addition of any optional additives, comprises not more than 500 mg/liter elemental calcium;
and wherein optional additives that are not sources of calcium comprise not more than 5 wt % of the slurry;
and
carbonating the aqueous slurry to form composite precipitated calcium carbonate particles;
wherein no wet milling is performed; and
wherein
either
the only sources of calcium are from the ash and the water used in forming the slurry of the ash, the water comprising not more than 500 mg/liter elemental calcium; and no source calcium is added to the material to be incinerated, or to the incinerator;
or
a source of calcium is added to the material to be incinerated, to the incinerator, to both the incinerator and material to be incinerated, at another point in the process, or a combination thereof, such that the ratio of the weight of calcium added, expressed as elemental calcium, to the weight of ash, is not more than 0.5.
2. The process of claim 1 , wherein a source of calcium is added.
3. The process of claim 2 , wherein the source of calcium is added to the material to be incinerated, to the incinerator, or both.
4. The process of claim 2 , wherein the source of calcium is added to the ash prior to forming the slurry, to the slurry, to the water, aqueous solution, or aqueous dispersion used to form the slurry, or a combination thereof.
5. The process of claim 2 , wherein the source of calcium is added to the material to be incinerated, to the incinerator, or both, and
to the ash prior to forming the slurry, to the slurry, to the water, aqueous solution, or aqueous dispersion, used to form the slurry, or a combination thereof.
6. The process of claim 1 , wherein the only sources of calcium are from the ash and the water used in forming the slurry of the ash, the water comprising not more than 500 mg/liter elemental calcium; and no source of calcium is added to either of the material to be incinerated, or to the incinerator.
7. The process of claim 1 , wherein the provided ash comprises, on a dry basis, at least 30 wt % CaO as determined by XRD.
8. The process of claim 1 , wherein, for the provided ash, the sum of the components comprising the elements aluminum (Al), silicon (Si), and Titanium (Ti), is not more than 25 wt % on a dry basis.
9. The process of claim 1 , wherein, for the provided ash, the sum of the CaO wt % and the CaCO 3 wt %, each as determined by XRD, is at least 70 wt % on a dry basis.
10. The process of claim 1 , wherein the material incinerated to form the ash comprises a wastepaper deink residue.
11. The process of claim 1 , wherein the provided ash has been subjected to an operation comprising dry milling of the ash prior to the formation of a slurry.
12. The process of claim 11 , wherein the dry milling is not more than 150 kWh per ton of dry ash.
13. The process of claim 11 , wherein the dry milling is not more than 25 kWh per ton of dry ash.
14. The process of claim 1 , wherein the material incinerated to form the ash comprises a wastepaper deink residue, and the material is incinerated at a temperature of at least 900° C.
15. The process of claim 14 , wherein the material comprising the wastepaper deink residue is incinerated at a temperature not exceeding 1500° C.
16. The process of claim 1 , wherein forming an aqueous slurry of the ash comprises executing an operation comprising adding ash to water, an aqueous solution, or an aqueous suspension, under agitation.
17. The process of claim 16 , wherein the formed aqueous slurry comprises at least 5 wt % ash, and not more than 35 wt % ash.
18. The process of claim 1 , wherein the water used in forming the aqueous slurry, prior to the addition of any additives, has a pH in the range of 5.5 to 7.0, is recycled water from another process, or a combination thereof.
19. The process of claim 1 , wherein the water used in forming the aqueous slurry, prior to the addition of any additives, comprises not more than 400 mg/liter elemental calcium.
20. The process of claim 1 , wherein carbonating the aqueous slurry comprises executing an operation comprising bubbling a gas comprising carbon dioxide through the ash slurry under agitation.
21. The process of claim 1 , wherein carbonation occurs until the system pH falls to about 8.
22. The process of claim 1 , wherein carbonation occurs for a sufficient period of time for a substantial fraction of the CaO to react with water, dissolve, and then react with the carbon dioxide (CO 2 ), the carbonate anion (CO 3 −2 ), or both.
23. The process of claim 1 , wherein after carbonation, the formed composite precipitated calcium carbonate particles are passed through a U.S. standard 325 sieve, and the pH is adjusted to pH 9.
24. The process of claim 1 , wherein at least 35 wt % of the ash is incorporated into the formed composite precipitated calcium carbonate particles.
25. The process of claim 1 , wherein, for the provided ash, the sum of the components comprising the elements aluminum (Al), silicon (Si), and Titanium (Ti), is about 25 wt % to 35 wt % on a dry basis.