Environment & Tailings

Mine Drainage Control and Treatment

Standards vary from state to state for reasons which I find impossible to explain. For example, Pennsylvania has set an iron limit of 7 mg/liter (7 ppm) on the discharge from a treatment plant. West Virginia, on the other hand, has adopted 10 mg/liter (10 ppm) in the receiving stream as a satisfactory iron level, thus giving proper credit for the dilution effect of the stream. As you all know, public hearings are currently being held in all fifty states, attempting to develop stream standards which will be satisfactory to both the states and the Federal Water Pollution Control Administration. So, we still are aiming at a moving target.

Now, let’s consider the fate of the ferrous iron and the acid in the water as it moves—miles, in many cases—from its point of formation to its point of discharge. As all of you know, substantial amounts of limestone or calcium carbonate are associated with coal deposits.

The first reaction (Equation 1)—which occurs rapidly—is the reaction of the acid with, say, limestone. Bicarbonate ion is formed and acid in the mine water is neutralized.

After, or simultaneously with neutralization of the acid, another important reaction begins. You will remember that I stated that ferrous,

Design Lime Neutralization Mine Drainage Treatment Plant

The acid mine drainage problem in Pennsylvania is of continuing and growing interest to the coal mining industry, the state government and the citizenry at large. Approximately one-third of the total volume of mine drainage presently polluting the streams of the Commonwealth originates from active coal operations and two-thirds come from “abandoned mine discharges.”

The acidic contamination of surface drainage and mine drainage water from coal mines is normally caused by the oxidation of iron pyrites. Acidic drainage waters contain dissolved iron salts and varying proportions of other dissolved metals. These waters are slightly cloudy, although suspended iron oxides, coal dust, etc., may also be present.

Technically, any acidic effluent from any coal mine could be purified by chemical processes to any desired standard of purity. Chemical treatment has been applied successfully to similar effluents in other industries in order to make them suitable for discharge to municipal sewers or to natural water courses and investigations have confirmed that these processes could be applied to the acidic effluents under review.

The demonstration plant was designed so that it could be readily moved over existing highways and roads in the Commonwealth without special permits. The pilot plant was constructed in a van type trailer

How to Avoid Tailings Dam Trouble

Dams are constructed to retard the flow of water or debris; therefore natural forces are constantly at work to remove such obstructions. To circumvent nature and avoid expensive trouble with a dam requires thoughtful far-sighted planning, careful construction control and vigilant periodic inspections to detect and repair deterioration at its inception.

Although the factuality of the foregoing statements is apparent, all too many have failed to consider them in the past as will many in the future. “The economic, but safe construction of dams calls for the highest order of technical knowledge, practical experience and sound judgment.”

Special Geologic Considerations

A dam may be defined as an impervious membrane which is provided with some means of support and appurtenant facilities to permit the discharge of excessive quantities of flood water, as well as a means of utilizing the water from the reservoir, preferably without pumping. How this impervious membrane and its spillway and outlet works are constructed depends, or should depend, primarily on the local natural conditions, such as rainfall, foundations, abutments, available construction materials and the topographic conditions as they influence the location of the spillway and outlet works and stream diversion schemes. Arroyos have the unfortunate habit of flowing

Acid Mine Drainage Research

The problem of pollution of water by mine drainage is at least as old as the mining industry itself. However, research on the formation, composition, treatment, and abatement of mine water is a relatively recent historical event.

At Bituminous Coal Research, Inc., acid mine drainage control has been an important area of work since 1944, at which time BCR began sponsorship of research at West Virginia University. The work at West Virginia University involved a detailed study of the acid mine drainage problem and led to the identification of iron oxidizing bacteria as important factors in the formation of acid mine water.

Chemical and Physical Properties of Mine Water

In order to appreciate the intent of this work area, a brief review of the formation of mine water is necessary.

Acid mine drainage results from the dissolution of oxidation products of pyrite in normally alkaline ground water together with the subsequent dissolution of other minerals in the resulting acidic solution.

The mechanism of the chemical reactions involved in pyrite oxidation is complex. It has generally been represented by the following overall chemical reaction.

(a) FeS2 + 7O + H2O = FeSO4 + H2SO4

(b) 2 FeSO4 + O + H2SO4 ↔ Fe2(SO4)3 +

Uranium Mill Waste Disposal

The presence of radioactivity in uranium mill wastes has resulted in somewhat unique waste disposal methods. In addition to the common problems of disposing of large quantities of solid wastes, neutralizing acids, minimizing dissolved heavy metals, and clarifying all liquid effluents, the uranium mill operator must sample and analyze liquid effluents for micro-micro quantities of radionuclides such as, radium-226, thorium-230 and lead-210. Special disposal methods or decontamination procedures are required to meet the stringent limitations established by the U. S. Atomic Energy Commission on the concentration of radionuclides in liquid effluents. Routine monitoring of the receiving stream is also normally required.

Description of Liquid Wastes

Uranium extraction techniques generally involve either acid or carbonate leaching of the ores after preparation by crushing, grinding and, in some cases, roasting. Soluble uranium is recovered by ion exchange, solvent extraction, or in the case of certain alkaline leach processes by caustic precipitation. The uranium barren solutions from these uranium recovery steps make up the liquid wastes containing small amounts of radioactivity and varying amounts of dissolved solids.

The ores from which uranium is recovered in western United States contain in the order of 0.20% to 0.25% uranium oxide (U3O8) , and the radioactive materials

Multi-Stage Flash Evaporation System for the Purification of Acid Mine Drainage

In January of 1964, the Board commenced a vigorous program using appropriated funds and funds donated by the coal industry to finance a research program devoted to seeking solutions to the mine drainage problem. A review of published literature on the treatment of mine drainage indicated that much work done up to that point in time concerned only the mechanism of mine drainage formation and theoretical chemistry.

Mine Drainage Abatement Program

The basic approach of the Department of Mines and Mineral Industries is to divide its abatement efforts into two logical parts:

  1. Reduction of volume or complete prevention of acid mine drainage.
  2. Treatment of acid mine drainage.

The treatment approach is being aimed at each of 2 different objectives; i.e. treatment solely for the return of a legally acceptable discharge to streams of the Commonwealth, or more refined treatment to prepare a satisfactory water for potable use. The work supported by the Department along both of these major lines has borne fruit and is considered to be most encouraging. Moreover, it will continue to lead to significant action programs on the part of State government and private industry.

AMD Processing for Potable Use

The Department of Mines and Mineral Industries as

Limestone Treatment of Acid Mine Drainage

The occurrence of acid mine drainage (AMD) with coal mining has been well documented. Less documentation is available of its association with other types of mining, e.g., copper, gold, zinc, and sulfur. Yet there are many locations in the western states where acid mine drainage is as great a pollution problem as in Appalachia and in some cases, because of the high copper, zinc, and arsenic concentrations, they present an even more difficult problem.

Until a few years ago, it was generally believed that the neutralization of acid mine drainage was uneconomical thus, AMD was allowed to discharge freely into our streams. However, the demand for good water finally dictated that the mining industry be included under pollution laws. In 1964 the Commonwealth of Pennsylvania passed a law requiring that all active mine discharges meet a discharge standard of pH 6-9, iron less than 7 mg/l, and the water must have a net alkalinity. Several other states now require active mines to treat AMD.

In all but a few cases, lime neutralization, often in conjunction with aeration, has been the treatment method used. The high cost of lime as compared to limestone and the poor quality sludge, (slow settling, large volumes, and

Tailing and Mill Process Water System Design Considerations

When the Henderson Project is completed in 1975, it will become one of the Free World’s largest primary molybdenum producers. The Henderson Mine will be located approximately 50 miles west of Denver, Colorado, on the eastern slope of the Continental Divide. Ore reserves are currently estimated to be 303,000,000 tons with a grade of 0.49% MoS2. The mill and tailing area will be located approximately 14.5 miles from the mine in the Williams Fork Valley, which is on the western slope of the Continental Divide. Ore haulage from the mine to the mill will be by ten miles of underground railroad and 4.5 miles of surface railroad. The concentrator has been designed to mill 30,000 tons per day and will yield approximately 50,000,000 pounds of contained molybdenum per year.

One of the first steps in the design of the Henderson Project was the search for a suitable tailing disposal area. Three hundred million tons of tailing will fill a rather large area. The first area considered was the west fork of Clear Creek in the immediate vicinity of the orebody. All facilities necessary for a tailing pond in this area were layed out and a cost estimate was made. However, after

Solids Separation

Gravity sedimentation is one of the most widely used processes for separating solids from liquids whether it be for ore and mineral processing or for treating municipal sewage or industrial wastes. Investment in sedimentation equipment can represent a significant portion of the total capital costs associated with a processing or treatment facility. In spite of the importance of sedimentation, little attention has been devoted in recent years to improving this equipment by applying the basic principles involved in sedimentation. In the water and waste treatment field, design criteria established one half-century ago is still the accepted standard and in reflection of this lack of progress, sedimentation and thickening equipment has remained virtually unchanged.

Tube Settling

It is apparent from the theoretical aspects discussed above that shallow tubular passageways provide one shape which would satisfy the basic requirements for ideal settling conditions in that they could provide shallow depth, a large wetted perimeter, laminar flow conditions, and reasonable overflow rates. For example, a tube diameter of 4 inches at a flow rate of 10 gpm per square foot of tube end area would provide a Reynolds number of less than 100. A one-inch diameter tube, 4 feet long, at a flow

Treatment Methods for Mining and Ore Processing Wastewaters

Increased emphasis on industrial pollution control has intensified investigation of waste treatment technology for methods of reducing the amount of pollutants discharged by industry. The mining and mineral processing industry can point to a record of considerable accomplishment in the field of wastewater treatment and reclamation because these operations are so frequently an integral part of the entire operation of an ore dressing facility.

Neutralization of excessive acidity or alkalinity in wastewater is a fundamental pollution control measure that is required to preserve receiving stream biota. A wide variety of materials are available for pH adjustment but for large consumptive uses first consideration usually is given to a low-cost material such as lime or limestone for acid neutralization and sulfuric acid or carbon dioxide for alkali neutralization. Since neutralization may involve many factors in addition to pH adjustment, the chemical characteristics of the wastewater must be considered.

The use of limestone for neutralizing acidic wastewater is often attractive because this material is available in many areas at the lowest cost per unit of basicity. However, limestone neutralization has a reputation of limited reliability due to the high incidence of failures recorded in the past. It is important, first of all, to establish

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