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Experimental concentration-time curves for the iron(II) sulphide precipitation process in aqueous solutions and their interpretation |
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| Authors: | David Rickard |
| Institution: | Department of Geology, University of Wales, Cardiff CF1 3YE, Wales, Great Britain |
| Abstract: | The first precipitate formed through the reaction between aqueous Fe(II) salts and dissolved sulphide at ambient temperatures and pH < 9, appears to be a highly disordered gel approaching the composition Fe(HS)2 on a water-free basis. After  0.4 s this precipitate loses sulphide and amorphous FeS begins to appear. The mackinawite structure begins to develop after several hours.The rate of formation of the initial precipitate can be approximated by a pseudo first-order reaction, directly dependent on total sulphide concentration and with an apparent pseudo first-order rate constant of 48 ± 9 s?1. Dissolved Fe concentration does not appear to be rate limiting. The estimated solubility of the initial phase is variable but consistently one to two orders of magnitude greater than the measured solubilities for amorphous FeS. In natural systems this may lead to variable Fe(II) solubilities in sulphidic environments. This initial material may play a more central role in iron sulphide reaction pathways than either mackinawite or amorphous FeS. |
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