DISSOLUTION OF TETRAGONAL FERROUS SULFIDE (MACKINAWITE) IN ANOXIC AQUEOUS SYSTEMS .1. DISSOLUTION RATE AS A FUNCTION OF PH, TEMPERATURE, AND IONIC-STRENGTH

Mackinawite (tetragonal FeS) is an important mineral phase in reducing sediments and is believed to form in anaerobic sewage sludge. The rates and mechanisms of dissolution of this compound are of interest because of the role it plays in the geochemical cycling of iron and sulfur as well as certain trace metals. An experimental study of the kinetics of the nonoxidation dissolution is described. The results in dicate a two-term rate law, F = k1[H+] + k2, where F is the flux (mol/(cm2-min)) of dissolving FeS, [H+] is the hydrogen ion concentration (mol/cm3), and ki and are rate constants with the values 0.18 ± 0.06 cm/min and (1.9 ± 0.9) X 10-9 mol/(cm2-min), respectively. The k1 term dominates at pHs lower than ~4.3. © 1979, American Chemical Society. All rights reserved.