Abstract: A pilot-scale study on the effect of flooding unoxidized and oxidized Cu/Zn tailings demonstrated the technical feasability of this technology to remediate a mining site where over 3 million tons of tailings were impounded. Full-scale flooding of the tailing pond with free running water was undertaken after the construction of an impervious dam; approximately 2 million m3 of surface water at pH 7,4 completely covered the tailings after 16 months. The minimal water column over the tailings was established at 1,20 m and reached 4,5 m, depending on the site topography. Water and tailings samples were collected from 9 different locations from the surface of the man-made lake using a specially designed borer and were analyzed for pH, conductivity, iron- and sulfur-oxidizing bacteria activity and numbers as well as the sulfate reducing bacteria (SRB) population. We showed that over a four year period of flooding, the overall population of iron-oxidizers decreased considerably; their numbers drastically fell from 1x106 to 1x102 active cells per g of oxidized tailings while the SRBs increased from 101 to 105/g. The pH of the influent, the reservoir and the effluent water remained fairly constant between 6,9 up to 7,4 over the entire period. During this time, interstitial water pH increased from 2,9 to 4,3 in flooded tailings where lime could not be incorporated in the first 20 cm of tailings; elsewhere, the pH of the tailings suspensions remained fairly constant around neutral values (pH 7,0). Dissolved oxygen was measured at fixed intervals and remained also constant between 6 and 7.5 mg/L while water temperatures fluctuated below freezing point to +20C respectively in winter and summer season.

Abstract: Rodiek, J., Verma, T.R. and Thames, J.L., 1976. Disturbed land rehabilitation in Lynx Creek Watershed. Landscape Plann., 2: 265-282. The Lynx Creek Watershed is located on the Prescott National Forest about 8 km south of Prescott, Arizona. The watershed, with an area of 7304 ha, has experienced intensive copper and gold mining activities in the past. Approximately 13% of the area still consists of patented mining claims (mainly copper). There are numerous abandoned mine shafts, waste dumps and mine tailings in the area. Past mining activities in the watershed have caused significant deterioration in water quality within and downstream from the mining sites. Mine drainage includes water flowing from mine shafts, surface runoff and seepage from mining dumps. Drainage from the numerous old mining sites contributes to the toxic mineral and sediment pollution of the water resources in the area. The pollutants in the form of dissolved, suspended or other solid mineral wastes and debris, enter in the streams of ground water. Aquatic life and recreation potential of the watershed is greatly reduced by the water pollution problem from the abandoned mines. The pollutants from the abandoned mines enter into Lynx Lake which is located 10 km southeast of Prescott. Lynx Lake, a trout fisheries lake, was created by a dam built in 1963 by the Arizona Game and Fish Department. The lake is 22 surface hectares in size with the storage capacity of 1.85 x 106 m3. The average yearly flow of sediment into the lake is 2900 m3. The sediment is slightly acidic and has a high concentration of copper, manganese, iron, zinc, and sulfates. The Sheldon dump and tailings pond are considered two major sources of pollution. Increasing need to direct additional attention toward mineral related problems made it necessary to coordinate U.S. Forest Service efforts with others involved in mining and reclamation. The Forest Service started SEAM (Surface Environment And Mining) in 1972 to coordinate interagency reclamation efforts. The Sheldon Mine dump and tailings pond were undertaken as a reclamation project through the coordinated efforts of the Forest Service, and the School of Renewable Natural Resources, University of Arizona at Tucson. The project is aimed at reclaiming some of the abandoned spoils in the Lynx Creek watershed and monitoring of water quality in the creek to evaluate the effectiveness of reclamation procedures. The reclamation approach includes recontouring, revegetating, drainage control and visual impact modification activities. The results to date have been encouraging. There was an excellent vegetation cover established within 5 weeks of seeding. Runoff and sediment control on the regraded slopes seemed quite effective. The methodology and technological experience gained from the reclamation project will provide invaluable information for reclaiming any abandoned mining sites within the Ponderosa Pine Ecosystem.

Abstract: In nature, pyrite is initially oxidized by atmospheric O2, releasing acidity and Fe2+. At pH below 3.5, Fe2+ is rapidly oxidized by T. ferrooxidans to Fe3+, which oxidizes pyrite at a much faster rate than O2. Commonly, limestone is used to prevent pyrite oxidation. This approach, however, has a short span of effectiveness because after treatment the surfaces of pyrite particles remain exposed to atmospheric O2 and oxidation continuous abiotically. Currently, a proposed mechanism for explaining non-microbial pyrite oxidation in high pH environments is the involvement of OH- in an inner-sphere electron-OH exchange between pyrite/surface-exposed disulfide and pyrite/surface-Fe(III)(OH)n3-n complex and/or formation of a weak electrostatic pyrite/surface-CO3 complex which enhances the chemical oxidation of Fe2+. The above infer that limestone application to pyritic geologic material treats only the symptoms of pyrite oxidation through acid mine drainage neutralization but accelerates non-microbial pyrite oxidation. Therefore, only a pyrite/surface coating capable of inhibiting O2 diffusion is expected to control long-term oxidation and acid drainage production. The objective of this study was to examine the feasibility in controlling pyrite oxidation by creating, on pyrite surfaces, an impermeable phosphate or silica coating that would prevent either O2 or Fe3+ from further oxidizing pyrite. The mechanism underlying this coating approach involves leaching mine waste with a coating solution composed of H2O2 or hypochlorite, KH2PO4 or H4SiO4, and sodium acetate (NaAC) or limestone. During the leaching process, H2O2 or hypochlorite oxidizes pyrite and produces Fe3+ so that iron phosphate or iron silicate precipitates as a coating on pyrite surfaces. The purpose of NaAC or limestone is to eliminate the inhibitory effect of the protons (produced during pyrite oxidation) on the precipitation of iron phosphate or silicate and to generate iron-oxide pyrite coating, which is also expected to inhibit pyrite oxidation. The results showed that iron phosphate or silicate coating could be established on pyrite by leaching it with a solution composed of: (1) H2O2 0.018-0.16 M; (2) phosphate or silicate 10-3 to 10-2 M; (3) coating-solution pH [approximate]5-6; and (4) NaAC as low as 0.01 M. Leachates from column experiments also showed that silicate coatings produced the least amount of sulfate relative to the control, limestone and phosphate treatments. On the other hand, limestone maintained the leachate near neutral pH but produced more sulfate than the control.