Hematite conditions that favor

The slow reaction process is likely due to multiple factors including (I) hindered reaction kinetics and diffusivity within the viscous gel, (2) inadequate or sluggish dissolution of precursor powder, and (3) a limited potential of iron to form a potassium-based aluminosilicate inorganic polymer. Hematite is not expected to be very soluble in concentrated alkali hydroxide solution, although it dissolution is dependent on the alkali used such that solubility is highest in NaOH, followed by KOH and LiOH. It is expected that as maghemite, magnetite and hematite dissolve, Fe and Fe ions would be released and would then be free to interact with the silica gel. Iron is versatile and can exist in multiple oxidation and coordination states in the final material. In zeolite systems, the more dilute conditions favors the diffusion of iron and other species, and a more thermodynamically stable state can be reached. The use of water-soluble iron sources such as iron nitrate and potassium ferrate in hydrothermal conditions have been shown to be an effective way to produce iron zeolites in which iron is located in tetrahedral coordination. ... 

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