Environ. Sci. Technol. 1986, 20, 1013-1016 (11) Kleindienst, T. E.; Edney, E. 0.; Namie, G. R.; Claxton, L. D. Atmos. Enuiron. 1986,20, 971-978. (12) Singh, H. B.; Salas, L. J.; Smith, A.; Stiles, R.; Shigeshi, H. U S . Environ. Prot. Agency 1981, EPA-600/S3-81-032.
Received for review October 30, 1985. Revised manuscript received April 28, 1986. Accepted May 7, 1986. Although the
research described in this article has been funded wholly or in part by the U S . Environmental Protection Agency through Contract 68-02-4033 to Northrop Services, Inc.-Environmental Sciences, it has not been subjected to the Agency's required peer and policy review and therefore does not necessarily reflect the views of the Agency, and no official endorsement should be inferred.
Dissolution of Iron Sulfates from Pyritic Coal Waste Patrick J. Sullivan" Western Research Institute, University of Wyoming Research Corporation, Laramie, Wyoming 8207 1
Shas V. Mattigod Department of Soil and Environmental Sciences, University of California, Riverside, California 9252 1
Andrew A. Sobek Research and Development Center, B. F. Goodrich Company, Brecksville, Ohio 44141
N
A pyritic coal waste was leached under saturated con-
ditions for 6 months. Waste samples were removed after 3 and 6 months of leaching. These samples, in addition to a sample with no leaching, were used to make up equilibrium solutions. The leaching data showed a continuous release of iron and sulfate species and low acidity under anaerobic conditions. As leaching progressed, the relatively soluble phases were removed, leaving the control of activities to less soluble primary and secondary minerals. Data from the equilibrium solutions were used to calculate the saturation index for common secondary minerals that could form in the waste/water system. The saturation index data show that (1)the common iron mineral phases under anaerobic and acid conditions will continually dissolve, (2) halotrichite may be controlling the activities of Fe(II), Al, and SO4,and (3) illite may limit the activities of Mg, K, and Si. These data indicate that changes in the solid phase with leaching will change the long-term geochemistry of the wastelwater system.
Introduction When pyritic coal refuse and/or coal spoil is exposed at the earth's surface prior to burial, pyrite can be oxidized by gaseous oxygen, dissolved oxygen, and dissolved ferric iron. The stoichiometry of these reactions are given by Stumm and Morgan ( I ) :
+ 7/202 + HzO = Fe2+ + 2S042-+ 2H+ Fe2+ + 1 / 4 0 z + H+ = Fe3+ + 1/2H20 Fe3+ + 3H20 = Fe(OH),(s) + 3H+ FeSz + 14Fe3++ 8H20 = 15Fe2++ 2S04,- + 16H+ FeS,
(1) (2)
(3) (4)
After pyrite is oxidized (eq l), ferric iron is produced extremely slowly (eq 2). This second reaction, however, can be accelerated by microbial catalysis to increase the overall rate of ferrous iron oxidation. With the generation of ferric iron, insoluble ferric hydroxide can form under proper pH conditions (eq 3). Pyrite can also be oxidized by ferric iron resulting in the generation of more acidity and ferrous iron (eq 4). The continuation of this process requires that pyrite be oxidized (eq 1). With pyrite oxidation, Nordstrom (2) proposes the formation of secondary iron phases that include (1)ferrous 0013-936X/86/0920-1013$01.50/0
Table I. Mineral and Chemical Characteristics of Refuse (from Reference 5) mineral
percentage
quartz pyrite gypsum siderite jarosite total clay illite degraded illite kaolinite
10 25 5
