Diatomaceous earth filter aid containing a low crystalline silica content
A diatomaceous earth product with low crystalline silica content after at least one calcination step of between about 927° C. (1700° F.) and about 1149° C. (2100° F.) is disclosed. The product comprises natural diatomaceous earth and at least one binding agent comprising potassium silicate. Further the product comprises no more than about 4.0 wt % of crystalline silica and has a permeability in the range of about 0.3 darcy to greater than about 20 darcy. A process for making such diatomaceous earth product with a low crystalline silica content is disclosed. Moreover, a diatomaceous earth filter aid comprising such a diatomaceous earth product is disclosed.
1. A diatomaceous earth product comprising:
natural diatomaceous earth;
potassium silicate; and
no more than about 4 wt % of crystalline silica after the natural diatomaceous earth and potassium silicate are combined to form a mixture and the mixture is calcined at a temperature between about 927° C. and about 1149° C., wherein the diatomaceous earth product has a permeability in the range of about 0.3 darcy to greater than about 20 darcy.
2. The diatomaceous earth product of claim 1 , wherein the permeability ranges from about 0.8 darcy to about 20 darcy.
3. The diatomaceous earth product of claim 1 , wherein the potassium silicate is present in an amount ranging from about 1 wt % to about 10 wt %.
4. The diatomaceous earth product of claim 1 , wherein the permeability ranges from about 1 darcy to about 20 darcy.
5. The diatomaceous earth product of claim 1 , wherein the permeability ranges from about 1.2 darcy to about 16 darcy.
6. The diatomaceous earth product of claim 1 , wherein the crystalline silica is no more than about 2 wt %.
7. The diatomaceous earth product of claim 1 , further comprising:
a setting agent comprising calcium lignosulfonate and magnesium hydroxide.
8. The diatomaceous earth product of claim 3 , wherein the amount of potassium silicate ranges from about 2 wt % to about 5 wt %.
9. A process for making a low crystalline silica content diatomaceous earth product, comprising:
providing natural diatomaceous earth;
treating the natural diatomaceous earth with no more than about 5 wt % potassium silicate to make a mixture; and
subjecting the mixture to at least one calcination step, wherein the at least one calcination step is conducted between about 927° C. and about 1149° C.,
wherein the diatomaceous earth product has a permeability in the range of about 0.3 darcy to greater than about 20 darcy, and wherein the diatomaceous earth product has a crystalline silica content of no more than about 4 wt %.
10. The process of claim 9 , wherein the at least one calcination step is conducted between about 982° C. and about 1093° C.
11. The process of claim 9 , wherein the potassium silicate ranges from about 2 wt % to about 5 wt %.
12. The process of claim 9 , wherein the permeability ranges from about 1 darcy to about 20 darcy.
13. The process of claim 9 , further comprising a step of:
treating the mixture with a setting agent before the at least one calcination step,
wherein the setting agent comprises calcium lignosulfonate and magnesium hydroxide.
14. A diatomaceous earth filter aid comprising:
at least about 95 wt % natural diatomaceous earth; and
about 5 wt % or less potassium silicate;
wherein the natural diatomaceous earth and potassium silicate are combined to form a mixture and calcined at a temperature between about 927° C. and about 1149° C. for at least about 45 minutes to provide the diatomaceous earth filter aid having a crystalline silica content no more than about 4 wt % and a permeability in the range of about 0.3 darcy to greater than about 20 darcy.
15. The diatomaceous earth filter aid of claim 14 , wherein the permeability ranges from about 1 darcy to about 20 darcy.