Guanidine compounds for removal of oxyanions from aqueous solutions and for carbon dioxide capture

A method for removing an inorganic oxyanion from an aqueous source containing an inorganic oxyanion salt, the method comprising:

• (i) dissolving an oxyanion precipitating compound into said aqueous source containing said inorganic oxyanion salt to result in precipitation of an inorganic oxyanion compound salt of said oxyanion precipitating compound;
• and
• (ii) removing said inorganic oxyanion compound salt from said water containing the inorganic oxyanion salt to result in water reduced in concentration of said inorganic oxyanion salt;
• wherein said oxyanion precipitating compound has the following formula:
• wherein:
• A is a ring-containing moiety;
• one or more of the hydrogen atoms in Formula (1a) may be replaced with one or more methyl groups;
• Xm− is an anionic species with a magnitude of charge m, where m is an integer of at least 1, provided that Xm− is an anionic species exchangeable with the inorganic oxyanion in said inorganic oxyanion salt in said aqueous source before said oxyanion precipitating compound contacts said inorganic oxyanion salt in step (i), and Xm− is said inorganic oxyanion in the inorganic oxyanion compound salt of said oxyanion precipitating compound;
• and
• n is an integer of at least 1;
• provided that n×m=2.