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Regional mapping of non-profilic sediment of the SHP development in Tanzania

Renewable Energy Definition

Renewable energy is a term used for forms of energy which are not exhausted by use over time. It means that the renewable resources can be regenerated or renewed naturally in a relatively short time scale. The forms of energy include chemical (energy of chemical reactions), electromagnetic (energy associated with electrical or magnetic forces), heat (kinetic energy of particles inside the bodies), light (radiant energy), mechanical potential energy (energy of gravitational field), mechanical kinetic energy (energy of moving mass) and nuclear (or mass) energy.

The sources of renewable energy can be derived from the sun’s energy (direct solar radiation, biomass, wind, hydropower), earth’s interior (geothermal) and tidal energy (wave, tidal, Oceanic Thermal energy Conversion). The availability of these sources would vary,  depending on their attractiveness to the end user.

Criteria for Energy Source to be Renewable Energy

The criteria for energy sources to be renewable energy include;

(i)                  To be replenished

(ii)                The rate of being used should not exceed the rate of renewable energy re-generated

(iii)               Unlimited supply of energy source

Solar energy is a result of radiation from the sun. The amount of solar radiation generated can be affected by climate and the cloud cover, latitude of the site and time.

Biomass resources suitable for energy production covers a wide range of materials, from firewood collected in farmlands, Solid Municipal Waste (SMW) and natural woods to agricultural and forestry crops grown. It is the energy derived from photosynthesis process and is essentially a chemical solar energy storage. During application of energy resulted from biomass, some energy can be escaped in any forms of energy especially radiation energy which can be used during photosynthesis process to create plant’s food.

Wind is caused by movement of air from high pressure (North/South poles) to low pressure areas (Equator). Due to the west east earth’s rotation caused wind to curve to the west toward equator creates – trade wind (0⁰- 30⁰ N or S of the equator) and polar easterlies wind types (60⁰-90⁰N or S from the equator) and also causes wind to blow away from equator to curve to the east - prevailing westerlies wind type (30⁰-60⁰ N or S from the equator). Also wind can be caused by unequal amounts of solar energy received at different latitudes.

Geothermal energy refers to heat stored beneath the surface of the earth. It originates from the

earth’s molten interior and the decay of radioactive materials. Waves store energy from the wind and can be caused by friction between wind and water surfaces such as in the ocean. Tides are caused by the gravitational attraction of the moon and the sun acting upon the oceans of the rotating earth, caused the surface of the oceans to be raised and lowered periodically which energy can be extracted. Ocean Thermal Energy Conversion (OTEC) is a means of converting into useful energy with only adequate temperature difference of 20⁰C between surface water of oceans in tropical and sub-tropical areas.

By definition, renewable energy should provide a continuous and unlimited supply of energy. However, technical difficulties, the intermittent nature of some of the renewable energy resources, as well as other constraints still pose limits to their wider deployment. For instance the non renewable energy (Fossil fuel) can be a renewable energy if the rate of fossil fuel to be re-generated in specified time is direct proportional to the rate of  extract and use it.

How Mercury Solution affect the Artisanal miners?

How the mercury solution affect the villages around the Active mines?

The Artisanal miners use mercury solution to capture the gold particles during processing the solution-water+grinding rocks..............
coming soon

Acid Mine Drainage Article

Acid Mine Drainage

By Ombeni J. Mdee, 2010

School of Mines and Petroleum Engineering

University of Dodoma

ombenijohn@gmail.com

Acid mine drainage (AMD) is a byproduct of the mining process and poses a serious threat to groundwater, streams, aquatic life and, ultimately, humans. AMD forms during metal or coal mining when sulfur-bearing minerals are exposed to water and air, forming sulfuric acid. Heavy metals leached from rocks can combine with the acid and dissolve, creating highly toxic runoff. Prediction of the acid mine drainage (AMD) relies on the questions that need to be answered include: What is the acid generation potential and neutralization potential of the different rock types that will be exposed during the mining process? What potential contaminants/metals occur in the rocks that will be exposed? Under what conditions will exposure and transport of the contaminants take place at the mine site?

Introduction

Acid Rock Drainage (ARD), or acid mine drainage, occurs when sulfide minerals are exposed to air and water. This causes the sulfide minerals, which are unstable in a surface environment, to break down into a weak hydrosulfuric acid, while simultaneously making the metals in the sulfides available for mobilization in the water. Iron sulfides like pyrite and pyrrhotite are the most common acid-causing sulfide minerals, while lead, cadmium, copper, zinc and mercury sulfides are the most damaging in terms of releasing metals harmful to the environment. While the pH (hydrogen ion concentration) must generally remain low for these metals to remain in solution and be harmful to aquatic and, in higher concentrations, to humans, another suite of metals also contained in sulfide minerals can remain in solution even if the pH is of the effluent, or the receiving water, is later raised. This suite of metals includes arsenic, selenium, and thallium, which, like the other metals mentioned, can be harmful to aquatic life, animals that drink the contaminated water, and even to humans.

Acid mine drainage is polluted water that normally contains high levels of iron, aluminum, and acid (Hadley and Snow 1974) due to the tendencies that metals be apt to dissolve and mobilize more easily in the acidic waters. Minerals containing sulphur, particularly sulphides such as pyrite (FeS2), have the potential to generate acidity when exposed to air and water; The contaminated water is often reddish-brown in color, indicating high levels of oxidized iron. Mining disturbs pyrite and, as a result, pyrite weathers and reacts with oxygen and water in the environment.

The Oxidation of Pyrite (FeS2)

Pyrite oxidation creates sulfuric acid and ferrous and ferric sulfates. The method by which pyrite oxidizes to form sulfuric acid and ferric hydroxide proceeds and the mechanism of reaction as a three-stage process proceeding both abiotically and by direct bacterial oxidation was presented by Kleinmann et al. (1981);

insert equations

Stage 1: Reaction 1 – both mechanisms, reaction2 – abiotic; gradually is slowing down. Chemical conditions: pH > 4.5; high SO42-, low Fe2+ and acidity.

Stage II: Reaction 1- both mechanisms, Reaction 2 – bacterial oxidation.

Chemical conditions: pH 2.5-4.5, high SO42- and acidity, increasing Fe, low Fe3+/Fe2+

Stage III: Reaction 3 – totally bacterial oxidation, Reaction 4 – rate determined by reaction 3. Chemical conditions: pH <2.5, high SO42-, acidity, high Fe and Fe3+/Fe2+

Reactions 2 and 3 represent the oxidation of ferrous iron to ferric iron and the consequent precipitation of ferric iron as ferric hydroxide. The two reactions account for the characteristic reddish-brown color of sediments contaminated by acid drainage. The three reactions combine to form the fourth stoichiometric equation, describing the complete reaction of pyrite and the formation of sulfuric acid (Hadley and Snow 1974).

Where do Acid Mine Drainage Problems Exist?

AMD can exist during sub-surface mining for gold, copper, silver and other metals found in sulfide mineral-bearing rock. AMD is released from any place where iron sulfides, such as pyrite, are exposed to air and water, including open pits, underground tunnels and waste rock piles. It can occur naturally as part of the rock-weathering process, or during subdivision, highway, quarry and other large-scale construction projects like in North Mara Gold Mines and other Tanzania gold mines.

What are Some Methods to Treat Acid Mine Drainage?

Treatment generally falls into two categories: active and passive.

Active Treatment

The active treatment is like the traditional solution, which involves adding neutralizing chemicals, such as lime or soda ash, to the AMD source or involves physically adding a neutralizing agent to the source of the AMD or directly to the stream that has been impacted. Active treatment can be very successful, however, it necessitates a long-term and continuous commitment to treatment. Many companies use hydrated lime, sodium hydroxide, sodium carbonate, or ammonia to treat acid mine water, with each chemical offering the advantage of neutralizing acidity. Active treatment also does not significantly reduce metal pollution in streams, only increase the acidic pH and all metals that were drained together remains.

Passive Treatment

Passive treatment encompasses several techniques designed to raise the pH and reduce metal loadings through treatment or containment projects. Passive approaches typically are more uniform and less operation-intensive. The drawback is they tend to use relatively more land and initial costs for passive treatment techniques can be higher than active treatment but the treatment is more uniform than active treatment. [www.ehow.com/about 5117508 acid-mine-drainage.html]

The concentration of metals in AMD can impact the selection of treatment mechanisms because metal precipitation can clog passive systems. At a pH greater than 3.5 with oxygen present, ferrous (Fe+2) will precipitate as ferric (Fe+3). If oxygen is low, this precipitation will not occur until the pH reaches 8.5. Similarly, aluminum precipitates at a pH greater than 5 and manganese precipitates at a pH greater than 7. Aluminum flocks are significantly lighter than iron or manganese and can be more readily flushed from a treatment system. The concentration of metals that is allowed to leave the site is also a concern, in that their precipitation on a streambed can have not only an visual impact but an ecological impact.

Mine Capping can prevent or reduce rainfall from reaching acid-forming units in a backfilled mine. Capping is generally used for surface mines. The cap is typically fly ash covered with topsoil and seeded. For capping to be effective, horizontal components of groundwater must be negligible.

Limestone Dumping fines can be placed in an acidic stream for direct water treatment. Benefits from this treatment are temporary, and the approach shocks the system. A variation of this technique involves lining a channel with a steel slag product or soda briquettes. Streams thus treated should flow through a settling pond to collect the metal sludge. The limestone must be periodically replaced. The dosing and replacement rate depends upon the acidity loading. The limestone reacts with acidic water in the following manner:

The natural bicarbonate in limestone neutralizes the hydrogen ions, but the metals in solution may not be simultaneously removed by the process. The resulting, neutralized water is typically still high in iron and sulfate content (Hadley and Snow 1974) which is still increasing unwanted ingredients.

Anaerobic wetland generates alkalinity through bacterial activity and the use of Fe3+ as a terminal electron acceptor. Limestone can be added to the organic substrate for additional treatment through limestone dissolution. The wetlands are usually 1 to 6 acres in size for seeps, and are sized according to flow rate. In some cases an aerobic settling pond may be needed for metal precipitation reactions before the wetland. These treatments are limited to cases where the discharge has a pH greater than 4 [http://el.erdc.usace.army.mil/elpubs/pdf/sr14.pdf]. The first wetlands were planted with a plant called Sphagnum in an attempt to simulate natural bog-type wetlands (Frostman 1995). The large surface areas of aquatic plants and algae serve as substrate to support bacteria. The filtering and settling mechanisms effectively remove suspended solids that do not normally settle. The decaying biomass of plants and algae provide anaerobic conditions and nutrients to the sulfate reducing bacteria. The large surface area of leaves enhance evapotranspiration and help dispose of excess water (Forstner and Salomons 1988).

Bactericides including antibiotics, heavy metals, detergents, and food preservatives have also been found to decrease acid mine drainage, however, antibiotics and heavy metals are too costly and also too dangerous to the surrounding aquatic life to be effectively used.

Alconox, an inexpensive commercial detergent, and sodium lauryl sulfate both are found to reduce acid production in mine drainage.

Open limestone channels are an important innovation in acid mine drainage treatment. The channels are created by filling drains or lining stream beds with high quality limestone. Results from field sites show that acid and metals in acid drainage were reduced by 25 to 40% even when the limestone became coated by iron and aluminum (Mehrotra and Singhal 1992). Most sites still require chemical treatment to meet effluent standards, however, the costs of the chemical treatment decrease with the initial biological treatment (Kleinmann and Perry 1991).

Biological Characteristics of SRB

Sulfate-reducing bacteria are characterized by anaerobic respiration using sulfate as a terminal electron acceptor. Sulfate-reducing bacteria generally rely on simple carbon compounds such as organic acids or alcohols to serve as electron donors for sulfate reduction, though some are capable of using hydrogen (Logan et al., 2005). When organic matter is used as a carbon source, other heterotrophic bacteria must break it down into simple carbon compounds. Because the precise composition of organic matter is usually unknown, calculations of reducing equivalents may not be accurate. Bench- and pilot-scale studies using the intended carbon source and AMD to be treated are therefore critical to determine sulfate-reduction rates and design efficient, full-scale systems.

What are Some Methods to Prevent Acid Mine Drainage?

In preventing acid drainage, water and air contact with the acidic material must be eliminated. Prevention effectiveness depends on the nature of the mine and the strata's geological characteristics.

Preventing water from reaching underground mines involves the use of diversion ditches and pipes to divert water from acidic areas. Another method to prevent acid drainage is to prevent the material from oxidizing. By burying mine waste, or covering the waste with an impermeable liner, pyrite cannot oxidize and sulfuric acid cannot form.

Conclusion

Both mining industries and government agencies assume the financial responsibility of treating or preventing acid mine drainage but they should think twice on the effect of acid drained to the surrounding active mines. The best way to prevent or limit ARD is to restrict the amount of oxygen that is available to oxidize the sulfides, because it is almost impossible to keep water from contacting this material once it has been mined. Once acid rock drainage has begun, it is almost impossible to stop completely. The costs of waste dump construction for potential acidic mined rocks are high, but the benefits to society and the environment are far greater in the long run

For economic reasons, treatment is the most practical solution to acid drainage pollution

References

• Frostman, Theodore. "Poster session peat/wetland treatment systems for water quality". The 1995 International Conference. Tappi Press, Atlanta. 1995.

• Forstner, U; Salomons, W., eds. Environmental Management of Solid Waste. Springer-Verlag Berlin Heidelberg. 1988.

• Hadley,R; Snow,D., eds.Water Resources and Problems Related to Mining. American Water Resource Association. 1974.

• http://www.ehow.com/about_5117508_acid-mine-drainage.html#ixzz10Fk7RonP

• http://el.erdc.usace.army.mil/elpubs/pdf/sr14.pdf

• Investigation of trace metal concentrations in soil, sediments and waters in the vicinity of gold mines in North West Tanzania reported by Norwegian University of Life Sciences (UMB) and University of Dar es Salaam.

• Pollution of wetlands in Tanzania, National Environment Management Council by S. Mkuula

Effect of Environmental on Mining Industries in Tanzania

How far Mining industries in Tanzania affect the environment?

How far people around the active mines become affected?


Did the mining Industries perform their operation according to the proposed EIA?