Process for removing silica and reducing total hardness from water

Patent metadata

Field	Value
Publication number	US-12404195-B2
Application number	US-202117144339-A
Country	US
Kind code	B2
Filing date	Jan 8, 2021
Priority date	Sep 8, 2017
Publication date	Sep 2, 2025
Grant date	Sep 2, 2025

Abstract

A process for removing silica and reducing total hardness of a natural or waste water containing silica and scale-forming ions comprises adding (i) magnesium hydroxide or a precursor of magnesium hydroxide and (ii) a soluble aluminate compound or a precursor of aluminate to said water while maintaining the pH of said stream at pH>8 to produce a layered double hydroxide in situ, wherein the layered double hydroxide contains the scale-forming ions in a lattice of the layered double hydroxide and silica is incorporated in the lattice of the layered double hydroxide as an interlayer anion and/or bound by the layered double hydroxide via one or more binding modes, wherein the process further comprises a recycling and regeneration step and/or a hydroxide addition step.

First claim

The invention claimed is:

1. A process for removing silica and reducing total hardness of a natural or waste water containing silica and scale-forming ions, the process comprising: adding (i) magnesium hydroxide or a precursor of magnesium hydroxide and (ii) a soluble aluminate compound or a precursor of aluminate to said water while maintaining the pH of said stream at pH >8 to produce layered double hydroxide in situ, wherein the layered double hydroxide contains the scale-forming ions in a lattice of the layered double hydroxide and silica is incorporated in the lattice of the layered double hydroxide as an interlayer anion and/or bound by the layered double hydroxide via one or more binding modes, wherein the process further comprises a recycling and regeneration step;
wherein the recycling and regeneration step comprises:
a) removing layered double hydroxide from the process;
b) regenerating and/or recycling at least a portion of the layered double hydroxide removed from the process to form regenerated and/or recycled layered double hydroxide; and
c) reintroducing the regenerated and/or recycled layered double hydroxide back into the process.

2. The process according to claim 1 , wherein the process is a continuous flow process.

3. The process according to claim 1 , wherein the process is a batch or semi-batch process.

4. The process according to claim 1 , wherein the layered double hydroxide in step a) is at least partially spent after capturing the silica from the water stream.

5. The process according to claim 1 , wherein a portion of the layered double hydroxide is regenerated in step b) by calcining the layered double hydroxide.

6. The process according to claim 4 , wherein the regenerated layered double hydroxide is reintroduced back into the process in step c) pre or post primary influent stream.

7. The process according to claim 1 , wherein a portion of the partially spent layered double hydroxide removed from the process is recycled and reintroduced back into the process in step c) pre or post primary influent stream.

8. The process according to claim 1 , wherein the process of step c) further comprises addition of one or more hydroxides to the process, wherein the one or more hydroxides is selected from the group consisting of i) layered double hydroxide, ii) calcined layered double hydroxide, and iii) layered double hydroxide forming agents such as magnesium hydroxide or a precursor of magnesium hydroxide, and/or a soluble aluminate compound or a precursor of aluminate.

9. The process according to claim 1 , wherein the layered double hydroxide comprises hydrotalcite.

10. The process according to claim 1 , wherein the layered double hydroxide comprises [M (II) 1-x M (III) x (OH) 2 ] x+ [A] x/n ·mH 2 O where M (II) is selected from Mg 2+ , Ca 2+ , Mn 2+ , Fe 2+ , Co 2+ , Ni 2+ , and Zn 2+ ; M (III) is selected from Al 3+ , Cr 3+ , Mn 3+ , Fe 3+ , Co 3+ , and Ga 3+ ; A is selected from Cl − , Br − , I − , NO 3 − , CO 3 2− , SO 4 2− , and/or organic anions; x is between 0 and 1, m is between 0 and 8, and n is anion charge.

11. The process according to claim 1 , wherein the recycling and regeneration step comprises at least 10 cycles.

12. The process according to claim 1 , wherein the pH of the water is maintained at pH from 8 to 11 with a pH buffering agent.

13. The process according to claim 12 , wherein the pH buffering agent comprises a carbonate/bicarbonate pH buffer.

14. The process according to claim 1 , wherein PFAS, PFOS are removed from the natural or waste water by incorporating PFAS, PFOS in the lattice of the layered double hydroxide as an interlayer anion and/or by binding to the layered double hydroxide via one or more binding modes.

15. The process according to claim 1 , wherein organic contaminants comprising detergents, oils and petroleum hydrocarbons or mixtures thereof are removed from the natural or waste water by formation of inorganic-organic complexes with the layered double hydroxides formed in situ.

16. The process according to claim 1 , wherein silica and the scale-forming ions are simultaneously removed from said water.

17. The process according to claim 1 , wherein the layered double hydroxide formed in situ is recycled and mixed with a further water stream to remove contaminants therefrom.

18. The process according to claim 17 , wherein the contaminants are removed via adsorption or ion-exchange processes with the layered double hydroxide.

Assignees

• Commw Scient Ind Res Org

Inventors

• Douglas Grant

Classifications

• C02F2303/16

  Regeneration of sorbents, filters · CPC title

• C02F2101/301

  Detergents, surfactants · CPC title

• C02F2101/40

  containing sulfur · CPC title

• C02F2101/36

  containing halogen · CPC title

• C02F2101/10

  Inorganic compounds · CPC title