Environment & Tailings

Bacterial Sulfate Reduction of Metal Contaminated Water – Treatment Process

Bacterial sulfate reduction has been identified as one process by which constructed wetland systems remove contaminant metals from coal and metal- mine drainage. Under anaerobic conditions, sulfate-reducing bacteria oxidize simple organic compounds (CH2O) with sulfate, and thereby generate hydrogen sulfide and bicarbonate ions:

SO4-² + 2CH2O → H2S + 2HCO3-…………………………………………..(1)

Hydrogen sulfide reacts with many contaminant metals to form insoluble metal sulfides:

H2S + M+² → MS + 2H+…………………………………………………….(2)

where M includes metals such as Fe, Zn, Mn, Ni, Cd, Cu, and Pb. Bicarbonate ions can consume protons to raise the pH of acidic water:

HCO3- + H+ → CO2 + H2O…………………………………………………..(3)

Most wetlands constructed with an organic substrate and receiving sulfate- enriched mine drainage develop an anaerobic zone in which sulfate reduction becomes established. However, the main flow path of water in these wetlands bypasses the anaerobic zone and is therefore minimally affected by sulfate reduction. As an alternative, the entire flow of contaminated water could be directed through enclosed reactors, within which an organic-rich, anaerobic environment favorable for sulfate reduction is maintained. The design of such a reactor system for treating metal- contaminated water requires:

  1. exclusion of oxygen,
  2. a source of sulfate (generally the contaminated water),
  3. a source of simple organic
By |2018-09-30T14:30:22+00:00September 25th, 2018|Categories: Environment & Tailings|Tags: |Comments Off on Bacterial Sulfate Reduction of Metal Contaminated Water – Treatment Process

How Strong are Cement Grout Plugs in Salt

Shafts and boreholes that penetrate aquitards can provide hydraulic connections between aquifers containing fresh water and formations containing saline waters. Contamination of high quality groundwater can result if such connections are not sealed adequately.

Seals or plugs in boreholes, shafts, or drifts connecting aquifers bearing unsaturated brine or water with salt mines, or, more generally, excavations in salt, may have the additional function of preventing the inflow of water or unsaturated brine into the openings. Such inflows could cause salt dissolution, with resultant collapses and deformations of the overburden that may be difficult to predict. Overburden deformations could further affect aquifers as well as the ground surface.

Push-out Test Experimental Procedure

A steel rod transmits the load to the plug. The applied load is measured with the compression machine gage and with a load cell. The top and bottom axial displacements of the borehole plug are measured with linear variable differential transformers (LVDT’s) and with dial gages. Two cylindrical jackets with horizontal arms are clamped onto the loading rod to mount the top LVDT and dial gage for top plug displacement measurements. An L-shaped rod is screwed into the bottom of the cement plug. The horizontal arm of this rod supports

By |2018-09-24T19:11:28+00:00September 23rd, 2018|Categories: Environment & Tailings|Tags: |Comments Off on How Strong are Cement Grout Plugs in Salt

Sulfate Ion Reducing Bacteria for Dilute Acid Mine Drainage

The procedure for treating dilute acid mine drainage and similarly polluted water needs to be changed. The economic pressure is exacerbated by legislation which classifies as hazardous waste the precipitates from conventional lime treatment plants. Since acid mine drainage invariably contains sulfate ion, one solution is to use anaerobic Desulfovibrio desulfurcans bacteria to reduce the sulfate ion to sulfide ion, and precipitate heavy metals. Since Desulfovibrio requires anaerobic, low Eh, neutral pH, and organic energy sources, the real problem is to devise a method of contacting dilute acid mine drainage with the sulfide ion produced by the bacteria.

There are three proposed systems for acid mine drainage reclamation with the aid of Desulfovibrio. The use of an organic dam such as Dugan had observed is supported by favorable results in the column test. However the columns reached a plateau in ability to precipitate due to the toxic effect of high concentrations of zinc to the Desulfovibrio.

The method of harvesting the sulphide directly from the culture not only keeps a viable culture growing at optimum conditions, but alleviates the problem of dissolving the sulphide gas in the mine water. Further work is aimed at confirming bacterial growth rates and determine volumetric flow

By |2018-09-24T14:09:22+00:00September 20th, 2018|Categories: Environment & Tailings|Tags: |Comments Off on Sulfate Ion Reducing Bacteria for Dilute Acid Mine Drainage

Gold Mill Tailings Restoration

Environmental Setting

A basic understanding of the climatic characteristics, geology, surface and groundwater hydrology conditions together with the physical and chemical characteristics of selected mill tailings deposits will aid in understanding the environmental problems associated with tailings disposal and restoration.

The Black Hills region is in the mid-latitudes which have a prevailing westernly airflow. The weather in this region is typical of a high elevation continental climate, characterized by extremes of summer heat (+100° F, +37.8 degrees Celsius) and winter cold (-30° F, -35.6 degrees Celsius) which are modified by the prominence of the mountainous uplifts. Winters are quite cold with near subfreezing temperatures normally occurring from December through March.

Physiographically, the Black Hills are located in a division of the Great Plains Province. The Black Hills are an elliptical uplift approximately 125 miles (201.2 km) long and 65 miles (104.6 km) wide. Rocks in the region range from Precambrian to Cretaceous. The metamorphic history and structure of the area are complex.

The Black Hills are within the Cheyenne River Basin, most of which is gently rolling plain. Watersheds in the Black Hills possess steep land slopes averaging 27 percent. These slopes are predominantly forested. Topographic conditions are characterized by high relief

By |2018-09-07T17:44:53+00:00September 7th, 2018|Categories: Environment & Tailings|Tags: |Comments Off on Gold Mill Tailings Restoration

Biological Treatment of Cyanidation Wastewaters

Metal complexed cyanides in wastewaters form as a result of interactions of free cyanide with metals present in the wastewater and exhibit varying degrees of stability, toxicity, and treatability. Thiocyanate, a pollutant commonly found in cyanide bearing wastewaters, is formed through the interaction of free cyanide with sulfur containing species (i.e. pyrrhotite) both present in the wastewater.

In certain industrial processes, such as the beneficiation of gold and silver, cyanide is an essential reagent. Since free cyanide, complexed cyanides, and thiocyanate are potentially toxic to humans and aquatic organisms, these compounds must be removed from wastewaters prior to their discharge into surface or ground waters serving as potential potable water sources, marine or fresh water habitats.

Analytical and Toxicologial Testing

Comparison and evaluation of the various treatment processes required accurate and interference free analytical procedures. Concurrently with the pilot plant testing of the chemical and physical treatment processes, research was conducted to evaluate and develop reliable methods for cyanide analysis. Two analytical methods with modification were found dependable and were used extensively in the laboratory during pilot plant evaluations.

Emphasis on specific parameter removal could have resulted in toxic effluents due to pollutants associated with or produced through breakdown of the target

By |2018-08-14T16:46:55+00:00August 13th, 2018|Categories: Environment & Tailings|Tags: |Comments Off on Biological Treatment of Cyanidation Wastewaters

Chemoremediation of Acid Mine Drainage

The chemical alteration of water by acid mine drainage begins with the exposure to the atmosphere of pyrite associated with coal during the mining process. The exposed sulfide minerals, which are relatively insoluble in their original state, are converted by oxidation to soluble sulfuric acid, which in turn dissolves other minerals containing manganese, aluminium and calcium.

FeS2 + 3O2 + 2H2O → 2H2SO4 + Fe +³

The resulting ferric iron subsequently reacts with water to form a ferric hydroxide precipitate, often referred to as “yellowboy”, that settles out on stream beds.

Fe +³ + 3H2O → Fe(OH)3 + 3H+

Experimental

acid mine drainage coprecipitation experiments

After addition of the solution to the reaction vessel, nitrogen was bubbled into the solution while it was being stirred at 540 r.p.m. to remove the dissolved CO2 and O2. Afterwards, desired amounts of FeSO4 .7H2O was added to the solution. Then, the pH was adjusted by adding 4N NaOH or Ca(OH)2 solution and kept constant throughout the experiment. The suspension was oxidized by passing the air. In the former case, the ORP value increases rapidly up to nearly 0 MV from -700 MV at the end

By |2018-08-17T16:37:00+00:00August 11th, 2018|Categories: Environment & Tailings|Tags: |Comments Off on Chemoremediation of Acid Mine Drainage

In-Situ Soil Washing

Chemical manufacturing operation, leaking storage tanks, waste piles and spills are the main sources which cause organic and heavy metal contaminations. Several techniques of cleanup have been developed during the past years and more research needs to be performed. Available remediation techniques have been categorized as on-site and in-situ. The in-situ cleanup methods are necessary for contaminated sites that are inaccessible or simply too large to excavate and treat. In many cases washing with groundwater alone is sufficient to achieve the desired level of contaminants removal for hydrophilic organics while minimizing the cost.

Materials and Methods

Sand  Sieve analysis performed at the sand sample showed that d10 = 0.11 mm and uniform coefficient d60/d10 = 1.76. The uniformity coefficient being less than 2.0 the sand sample was classified as a uniform fine sand.

Chemicals The purity is above 99%. Anthracene’s (C14H10) molecular weight is 178.24 and boiling point is 342°C.

Contamination Procedure of Sand Sand spiking was done by first dissolving anthracene in 200 proof ethyl alcohol. and sand was mixed in a rotary tumbler with this solution for 10 minutes. Then the wet mixture of sand was placed in a hood and the ethyl alcohol was allowed to evaporate. The

By |2018-08-31T16:18:47+00:00August 4th, 2018|Categories: Environment & Tailings|Tags: |Comments Off on In-Situ Soil Washing

Dual-Alkali Scrubbing

SMC’s smelting process is composed of a submerged-arc electric furnace and a top blown rotary converter (TBRC). The 1.5 MW rated furnace operates continuously while the 0.15 M³ TBRC is operated on a batch basis. Process flue gases are combined with tapping hood exhaust air and ducted to a gas cleaning system prior to release to the atmosphere.

The gas cleaning system is comprised of two sections: a baghouse type dust collector for metals recovery; and a dual-alkali FGD system for SO2 removal. The system was originally constructed without a dust collector. However this resulted in unacceptable loss of PGM values.In a dual-alkali FGD process, sodium alkali is used in the absorber for high scrubbing efficiency and scale-free operation. The spent sodium alkali is regenerated with lime or limestone.

Operation of concentrated mode systems under high oxidation conditions is not feasible because settling and filtering characteristics of the resulting combined sulfate/sulfite sludge are very poor. Additionally, a high potential for scrubber scaling is created, lime utilization is poor, and process control is difficult. In the dilute mode, where virtually all sulfite is converted to sulfate before regeneration, the settling and filtering characteristics of the calcium sulfate are very good.

In response to the

By |2018-09-07T17:45:54+00:00August 2nd, 2018|Categories: Environment & Tailings|Tags: |Comments Off on Dual-Alkali Scrubbing

Old Smelter Lead Contamination

Until the 1860’s, Socorro, New Mexico, was primarily an agricultural community with a somewhat constant population of less than 1000. The 1860’s brought attention to Socorro County as many mineral deposits were discovered in the Magdalena mining district (Fig. 1). By the late 1870’s, impressive deposits of lead carbonate were being developed in the Magdalena district at mines known as the Graphic, Kelly, and Juanita.

The need for a large-scale plant to process this ore profitably attracted Gustav Billing, a man financially and knowledgeably capable, who at once perceived the advantages of building a large modern smelter in Socorro, near an adequate supply of water, coking coal, and limestone. By December 1883, the large-scale smelting complex, built southwest of Socorro in an area called Park City (Fig. 2), had three furnaces in production and was the most efficient smelter in the Southwest. The smelter operated for about ten years, but for a variety of reasons closed its doors in 1894, 98 years ago.

During the operation of the Billing Smelter, modern emission controls (the smelter had both bag house and collection flues) for smelting operations did not exist. Though the Billing Smelter was very efficient for its time, it contaminated the soil

By |2018-09-14T23:53:43+00:00July 31st, 2018|Categories: Environment & Tailings|Tags: |Comments Off on Old Smelter Lead Contamination

Environmental Audits at Mining Operation

One of the consequences of this increased public awareness is public concern over the perceived and real consequences of mining operations. Emphasis has been placed on potential releases of toxic and hazardous substances, and possible carcinogens. The result of this public concern is a mounting effort at both State and Federal levels to promote stricter laws regulating the mining industry.

In order to successfully permit, operate and close a coal mining facility, it has become necessary to address not only these major regulatory expectations, but also to comply with numerous other less formally stated requirements. Consequently, both corporate management and on-site mining facility operators must be knowledgeable about changing environmental regulatory requirements, and in some cases, conflicting or overlapping regulations. Unfortunately, many mangers are either unable to maintain and understand this complex regulatory database, or are not aware of its existence. As a result, they and their employees could be vulnerable to both civil and criminal liabilities.

The”Form and Function” of an Audit

Although environmentally-related liabilities associated with coal mining operations and associated property-related transactions have increased tremendously in recent years due to federal and state laws and regulations, no audit standards have been established and the auditors themselves are not

By |2018-09-14T18:32:18+00:00July 31st, 2018|Categories: Environment & Tailings|Tags: |Comments Off on Environmental Audits at Mining Operation

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