Environment & Tailings

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

How to Recover Metal from Mine Drainage Water

To recover metals as sulfide concentrates from contaminated waste streams using hydrogen sulfide (H2S) generated by the bacterial digestion of waste organic materials.

The goal of this research is to develop a treatment method for metal mine effluents that will rival the cost and convenience of conventional lime treatment, and that will provide better effluent water quality, result in less expensive sludge disposal, and allow for the selective recovery of metals.

How it works

In this method (fig. 1), indigenous sulfate-reducing bacteria are used to generate H2S gas in an anaerobic bioreactor containing sulfate-rich mine water and inexpensive, degradable organic matter such as food processing wastes or primary sewage sludge. As H2S is formed, it is sparged from the bioreactor by an inert carrier gas to create a gas stream containing about 0.3 pct H2S. When the gas comes in contact with a metal-contaminated mine effluent, the heavy metals precipitate as relatively insoluble sulfides. Elemental sulfur (S°) also may be formed. By adjusting the pH, the composition of the precipitated concentrates of metal sulfide can be manipulated. For example, the pH of mine water containing Cu, Zn, Fe, Al, and Mn (pH <3) can be controlled so that a copper sulfide

By |2018-04-21T10:42:59+00:00April 21st, 2018|Categories: Environment & Tailings, Recycling|Tags: |Comments Off on How to Recover Metal from Mine Drainage Water

Magnesium Oxide to Remove Metals in Water

Conventional practice for treating mine drainage and other water sources contaminated with heavy metals is lime precipitation and settling of the hydrous oxides. This produces a voluminous toxic sludge that results in another type of disposal problem. In addition, settling of the precipitated hydrous oxides often does not produce sufficiently pure water to meet statutory limits for discharge, so the decant has to be polished by filtration through sand or other granular media. Metal hydroxides are difficult to filter because of their small size and their low resistance to the hydraulic shear forces encountered in conventional granular filters. Flocculation with organic polyelectrolytes is often necessary to achieve efficient filtration.

Magnesium oxide (MgO) is similar to lime (CaO) and can be used analogously to precipitate heavy metals. Although MgO is less soluble than lime at high pH, in acidic to slightly alkaline water it provides more neutralization capacity per unit weight than lime, owing to its lower molecular weight. When a stoichiometric excess of MgO is used to precipitate heavy metals from wastewater, the resulting sludge is up to 4 times more compact than that produced by liming. This was attributed to the unique positive electrokinetic charge of the MgO surface at

By |2018-04-14T09:11:19+00:00April 14th, 2018|Categories: Environment & Tailings|Tags: |Comments Off on Magnesium Oxide to Remove Metals in Water

Passive Acid Mine Drainage Water Treatment

Summary and Conclusions

The treatment of contaminated coal mine drainage requires the precipitation of metal contaminants and the neutralization of acidity. In conventional treatment systems, distinctions between these two treatment objectives are blurred by additions of highly basic chemicals that simultaneously cause the rapid precipitation of metal contaminants and the neutralization of acidity. Passive treatment differs from conventional treatment by its distinction between these two treatment objectives. It is possible to passively precipitate Fe contaminants from mine water, but have little effect on the mine water acidity. Alternatively, it is possible to passively add neutralizing capacity to acidic mine water without decreasing metal concentrations.

Waters that contain high concentrations of bicarbonate alkalinity are most amenable to treatment with constructed wetlands. Bicarbonate acts as a buffer that neutralizes the acidity produced when Fe and Mn precipitate and maintains a pH between 5.5 and 6.5. At this circumneutral pH, Fe and Mn precipitation processes are more rapid than under acidic pH conditions. Given the ability of bicarbonate alkalinity to positively impact both the metal precipitation and neutralization aspects of mine water treatment, it is not surprising that the most noteworthy applications of passive treatment have been at sites where the mine water

By |2018-03-24T06:00:23+00:00March 24th, 2018|Categories: Environment & Tailings|Tags: |Comments Off on Passive Acid Mine Drainage Water Treatment

Acid Mine Drainage Water Treatment

Removal of Contaminants by Passive Treatment Systems

Chapter 2 described chemical and biological processes that decrease concentrations of mine water contaminants in aquatic environments. The successful utilization of these processes in a mine water treatment system depends, however, on their kinetics. Chemical treatment systems function by creating chemical environments where metal removal processes are very rapid. The rates of chemical and biological processes that underlie passive systems are often slower than their chemical system counterparts and thus require that mine water be retained longer before it can be discharged. Retention time is gained by building large systems such as wetlands. Because the land area available for wetlands on minesites is often limited, the sizing of passive treatment systems is a crucial aspect of their design. Unfortunately, in the past, most passive treatment systems have been sized based on guidelines that ignored water chemistry or on available space, rather than on comparisons of contaminant production by the mine water discharge and expected contaminant removal by the treatment system. Given the absence of quantitative sizing standards, wetlands have been constructed that are both vastly undersized and oversized.

In this chapter, rates of contaminated removal are described for 13 passive treatment systems in

By |2018-03-24T05:59:57+00:00March 24th, 2018|Categories: Environment & Tailings|Tags: |Comments Off on Acid Mine Drainage Water Treatment

Passive Mine Drainage Treatment

Treatment of Mine Water: The mining of coal in the Eastern and Midwestern United States can result in drainage that is contaminated with high concentrations of dissolved iron, manganese, aluminum, and sulfate. At sites mined since May 4, 1984, drainage chemistry must meet strict effluent quality criteria (table 1). To meet these criteria, mining companies commonly treat contaminated drainage using chemical methods. In most treatment systems, metal contaminants are removed through the addition of alkaline chemicals (e.g., sodium hydroxide, calcium hydroxide, calcium oxide, sodium carbonate or ammonia). The chemicals used in these treatment systems can be expensive, especially when required in large quantities. In addition, there are operation and maintenance costs associated with aeration and mixing devices, and additional costs associated with the disposal of metal-laden sludges that accumulate in settling ponds. It is not unusual for the water treatment costs to exceed $10,000 per year at sites that are otherwise successfully reclaimed. Total water treatment costs for the coal mining industry are estimated to exceed $1,000,000 per day. The high costs of water treatment place a serious financial burden on active mining companies and have contributed to the bankruptcies of many others.

coal-mine-drainage-federal-effluent-limitations

By |2018-03-24T05:59:27+00:00March 23rd, 2018|Categories: Environment & Tailings|Tags: |Comments Off on Passive Mine Drainage Treatment

Bacterial Cyanide Degradation

The toxicity of cyanide to cells is well understood. Yet cyanide occurs as a common metabolite in various plants, fungi, and microorganisms, although its function in these organisms is less clear. Of great importance, especially for the treatment of industrial wastewaters, are microorganisms that metabolize cyanide or cyanide complexes (such as cyanoacetate, thiocyanate, ferricyanide, ferrocyanide, and others), by using the carbon or nitrogen for growth. Pseudomonas putida can use both, but most bacterial strains described so far utilize only the nitrogen from cyanide. These include Bacillus pumilus, Pseudomonas fluorescens NCIMB 11764, and Pseudomonas paucimobilus, all of which convert cyanide to ammonia and carbon dioxide.

The various mechanisms of cyanide resistance and detoxification in microorganisms have been extensively studied, and are reviewed by Knowles and Knowles and Bunch. In contrast, the enzymes responsible for cyanide degradation have only recently been studied in detail. Results of three such studies are summarized here. Ingvorgsen et al. reported that whole cells and cell extracts of the soil bacterium Alcaligenes xytosoxidans subsp. denitrificans catalyze the hydrolysis of cyanide to formate and ammonia. Resting induced cells at a concentration of 11.3 mg (dry wt) per ml reduced the initial cyanide concentration from 0.97M (25,220 ppm) to less

By |2018-04-28T18:42:03+00:00March 18th, 2018|Categories: Environment & Tailings|Tags: |Comments Off on Bacterial Cyanide Degradation

Bacteria & Acid Mine Drainage Treatment Method

Objective: To develop an in-mine water treatment system in which bacterial sulfate reduction and limestone dissolution continuously remove metals and acidity from contaminated drainage.

Approach: A section of mine tunnel was converted into a water treatment bioreactor by constructing cinder block dams and filling the area between them with a porous substrate mixture of limestone gravel and compost. Readily fermentable materials such as dairy whey, spent brewing yeast, or sugar were periodically added to the reactor. Mine drainage was impounded behind one of the dams and continuously percolates through the reactor substrate at a controlled rate.

How an Anaerobic Bioreactors Works

The reactor substrate soon becomes anaerobic after it is saturated with mine water. Under anaerobic conditions, sulfate-reducing bacteria consume the organic materials that arc added to the reactor and generate hydrogen sulfide (H2S) and alkalinity. The H2S reacts with dissolved iron and heavy metals to form metal sulfide precipitates. The alkalinity raises the pH of the water and induces aluminum to hydrolyze and precipitate as aluminum hydroxide [Al(OH)3]. Additional alkalinity is generated by the continuous dissolution of the substrate limestone. Metal sulfide precipitates and Al(OH)3 are retained within the reactor, and the treated water is discharged. The underground location of the

By |2018-03-08T10:43:42+00:00March 8th, 2018|Categories: Environment & Tailings|Tags: |Comments Off on Bacteria & Acid Mine Drainage Treatment Method

Passive Mine Drainage Treatment Systems

Passive Mine Drainage Treatment Systems provide a low-cost, low-maintenance method for improving mine water quality on abandoned mine land (AML) sites.

Approach: A model (figure 1) is presented for selecting, designing, and sizing one or several passive mine drainage treatment systems that can be used in remediation of AML. The three principal types of passive mine drainage technologies for the treatment of coal mine drainage are an aerobic system, a compost wetland, and an anoxic limestone drain.

The multistep approach presented here provides a simplified method to characterize the type and magnitude of the water quality problem and then to select either a single treatment system or a combination of treatment systems to address the specific site situation.

How a Passive Mine Drainage Treatment System Works

Step 1. Discharge Characterization.

Characterization of the discharge consists of measuring the discharge flow rate and collecting water samples at the point of discharge for chemical analysis. Both the flow rate and chemistry of a discharge can vary seasonally and in response to storm events. It is important to account for this variability by determining flow rates and water chemistry under various conditions.

Water should be analyzed for pH, dissolved iron (Fe), alkalinity, and hot acidity (using the

By |2018-03-08T10:27:32+00:00March 8th, 2018|Categories: Environment & Tailings|Tags: |Comments Off on Passive Mine Drainage Treatment Systems

Dewatering Placer Tailings Effluent

In the placer mining industry, gold-bearing gravels are generally treated in various washing and screening plants to separate the gold particles from small rocks, fmes, and sand. In this process, the gravel is first sized from 0.5 to 1 in on a vibratory screen. The undersized material is washed into a sluice box while the small rocks, sand, and lines flow off the end into a sump, where the majority of the rocks and sand settle out. Water for the operation is generally taken from a nearby creek or stream. The rocks and coarser particles are removed from the sump on a regular basis. The water, containing sand and clay, flows into the pond system of the mine. In the pond, the rest of the settleable material drops out, leaving the fine-grain silts and clays. With time, some of this material also settles, leaving water contaminated with ultrafine particles that remain suspended for a long time. Contamination of the creek is possible if this water enters the stream.

In the past few years, the placer mining operations in Alaska have received considerable attention from a variety of agencies with regulatory authority, such as the Environmental Protection Agency (EPA), Alaska Department of

By |2018-03-04T08:47:04+00:00March 4th, 2018|Categories: Environment & Tailings|Tags: |Comments Off on Dewatering Placer Tailings Effluent

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