text: Green rust compounds can be synthesized at ordinary ambient temperature and pressure, from solutions containing iron(II) cations, hydroxide anions, and the appropriate intercalatory anions, such as chloride, sulfate, or carbonate.
  The result is a suspension of ferrous hydroxide () in a solution of the third anion. This suspension is oxidized by stirring in air, or bubbling air through it.  Since the product is very prone to oxidation, it is necessary to monitor the process and exclude oxygen once the desired ratio of  and  is achieved.
  One method first combines an iron(II) salt with sodium hydroxide  to form the ferrous hydroxide suspension.  Then the sodium salt of the third anion is added, and the suspension is oxidized by stirring in air.
  For example, carbonate green rust can be prepared by mixing solutions of iron(II) sulfate  and sodium hydroxide; then adding sufficient amount of sodium carbonate  solution, followed by the air oxidation step.
  Sulfate green rust can be obtained by mixing solutions of ·4 and  to precipitate () then immediately adding sodium sulfate  and proceeding to the air oxidation step.
  A more direct method combines a solution of iron(II) sulfate  with , and proceeding to the oxidizing step.  The suspension must have a slight excess of  (in the ratio of 0.5833  for each ) for the green rust to form; however, too much of it will produce instead an insoluble basic iron sulfate, iron(II) sulfate hydroxide ()·n. The production of green rust is reduced as temperature increases.