Buffer-free process cycle for co2 sequestration and carbonate production from brine waste streams with high salinity

Abstract

A method includes: (1) using a chelating agent, extracting divalent ions from a brine solution as complexes of the chelating agent and the divalent ions; (2) using a weak acid, regenerating the chelating agent and producing a divalent ion salt solution; and (3) introducing carbon dioxide to the divalent ion salt solution to induce precipitation of the divalent ions as a carbonate salt. Another method includes: (1) combining water with carbon dioxide to produce a carbon dioxide solution; (2) introducing an ion exchanger to the carbon dioxide solution to induce exchange of alkali metal cations included in the ion exchanger with protons included in the carbon dioxide solution and to produce a bicarbonate salt solution of the alkali metal cations; and (3) introducing a brine solution to the bicarbonate salt solution to induce precipitation of divalent ions from the brine solution as a carbonate salt.

What is claimed is: 
     
         1 . A method comprising:
 using a chelating agent, extracting divalent ions from a brine solution as complexes of the chelating agent and the divalent ions;   using a weak acid, regenerating the chelating agent and producing a divalent ion salt solution; and   introducing carbon dioxide to the divalent ion salt solution to induce precipitation of the divalent ions as a carbonate salt.   
     
     
         2 . The method of  claim 1 , wherein extracting the divalent ions includes introducing the chelating agent to the brine solution, followed by subjecting the brine solution to filtration. 
     
     
         3 . The method of  claim 2 , wherein subjecting the brine solution to filtration is performed by ultrafiltration, nanofiltration, or reverse osmosis. 
     
     
         4 . The method of  claim 2 , wherein subjecting the brine solution to filtration includes producing a retentate solution including the complexes of the chelating agent and the divalent ions. 
     
     
         5 . The method of  claim 4 , wherein regenerating the chelating agent includes introducing the weak acid to the retentate solution to induce precipitation of the chelating agent and to produce the divalent ion salt solution. 
     
     
         6 . The method of  claim 5 , wherein the weak acid has a pK a  greater than about 3.6 at 298 K. 
     
     
         7 . The method of  claim 4 , wherein regenerating the chelating agent includes adjusting the pH of the retentate solution to about 4 or below. 
     
     
         8 . The method of  claim 1 , further comprising adjusting the pH of the divalent ion salt solution to above about 3.6, prior to introducing the carbon dioxide. 
     
     
         9 . The method of  claim 1 , wherein introducing the carbon dioxide includes inducing precipitation of at least one of calcium carbonate or magnesium carbonate.