Mining and mineral processing waste management based on nickel

8/12/2019 Mining and mineral processing waste management based on nickel

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Mining and mineral processing waste management based on NICKEL MISE 3

ARDHI UNIVERSITY

SCHOOL OF ENVIRONMENTAL SCIENCE AND TECHNOLOGY

DEPARTINMENT OF MUNICIPAL AND INDUSTRIAL SERVICES ENGINEERING

MI 321, MINING AND MINERAL PROCESSING WASTE MANAGENMENT

TITTLE: NICKEL

NAME OF STUDENT: MANYAMA KAARE

REG #: 2795/T.2010

YEAR OF STUDY: 3, SEMESTER ONE 2012/1013

BSc. Municipal and industrial services engineering

DATE ,4th

January 2013


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CHAPTER ONE

1.0 INTRODUCTION

1.1BACKGROUND

Nickel (Ni) is a silvery-white, hard metal. Although it forms compounds in several oxidation

states, the divalent ion seems to be the most important for both organic and inorganic substances,

but the trivalent form may be generated by redox reactions in the cell. Nickel compounds that are

practically insoluble in water include carbonate, sulfides (the main forms being amorphous or

crystalline monosulfide, nis, and subsulfide Ni3S2) and oxides (nio, Ni2O3). Water-insoluble

nickel compounds may dissolve in biological fluids. Particles of the same chemical entity (oxidesand sulfides) have different biological activity depending on crystalline structure and surface

properties soluble nickel salts include chloride, sulfate and nitrate. Nickel carbonyl (Ni(CO)4) is

a volatile, colorless liquid with a boiling-point of 43 0C it decomposes at temperatures above 500C. In biological systems, nickel forms complexes with adenosine triphosphate, amino acids,

peptides ,proteins and deoxyribonucleic acid.

Nickel is widely distributed in nature, forming about 0.008% of the earths crust. The core of the

earth contains 8.5% nickel, deep-sea nodules 1.5%; meteorites have been found to contain 5

50% nickel ,The natural background levels of nickel in water are relatively low, in open ocean

water 0.2280.693 g/litre, in fresh water systems generally less than 2 ,Agricultural soils

contain nickel at levels of 31000 mg/kg; in 78 forest floor samples from the north-eastern

United States of America, concentrations of 8.515 mg/kg were reported .The nickel content is

enriched in coal and crude oil. Nickel in coals ranges up to 300 mg/kg; most samples contain less

than 100 mg/kg but there is a large variation by region . The nickel content of crude oils is in the

range


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1.2 OBJECTIVES

To enable Municipal and industrial services Engineering students to be in a position in mining andmineral processing waste managements.

1.3 METHODOLOGY

In carrying out this study, the following methods where involved;

Literature review Consultation from the professionals Lecture notes

1.4 SCOPE OF THE REPORT

This report mainly limited in NICKEL: how it mined, processed, waste generated from it and

how to manage those wastes.


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CHAPTER TWO

2.0 HOW NICKEL MINED AND PROCESSED

2.1 TYPES OF MINING OPERATIONSeveral factors (location, geometry, morphology, depth, economics, environment, andeven

mining tradition) underlie the choice of method(s) for mining a specific ore deposit. Depending

on this method, and on the size of the mine site, the projects display different ore-extraction

capacities, and consequently larger or smaller quantities of mining waste. A major difference

from the environmental standpoint can also be demonstrated in the composition of the waste

associated with the mining method employed.

2.1.1 Open pits and quarries

There are many alternatives within open pits and quarries but the great principles are identical.

Most industrial materials and shallow metallic deposits (< 300 m) are mined by this method,

which is the cheapest in practice. The scale of the projects, and particularly their depth, is

conditioned by an economic threshold above which it is better to continue mining through

underground workings.

Figure 1: Different steps of a mining activity


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As a rule, after the stripping operations (removal of the soil and superficial horizons), actual

mining is carried out in successive steps, imparting a roughly conical shape to the mine . The

mining of each step or bench produces a tonnage of extracted material corresponding to theoverburden surrounding the deposit, which is sent directly to the waste dump, and a tonnage

corresponding to the ore that is selectively routed either for storage or directly to the processing

plant. The variation in the ratio between the tonnage of waste to be extracted and the quantity of

ore recoverable (also called stripping ratio) strongly conditions the economic viability of the

mine. If this ratio becomes too high, especially when the quarry is deepened, it is no longer

economically profitable to continue strip mining.

2.1.2 Underground (quarries and) mines

When deposits are difficult to reach from the surface (depth, cliffs permitting side access), the

only alternative is underground workings. A broad range of methods are available (chamber and

pillar, long-wall, under-level caving, under-level stopping and filling, shrinkage) all of which are

roughly adapted to the characteristics of the ore or the geometry of the deposit: dip of the layers

or veins, thickness, continuity of the mineralization, grade of ore (disseminated or massive). The

workings are generally opened by levels with a 60 m vertical spacing and then sublevels at 15 mintervals. Two criteria are vital for all these workings: selectivity of the ore and its percentage

recovery. All the operations conducted in the ore are connected to one another and to the surface

by a series of passages, all opened in the overburden surrounding the deposit: shafts, inclines,

drifts, chutes, cross-cuts for personnel and machine access, for removal of ore and drainage

water, as well as for ventilation.

2.2 NICKEL EXTRACTION

Nickel ore is usually mined from underground mineand some in open pit mine. The run-of-mine nickel ore will be sent to processing plant which includes crushing process, washingprocess, grinding process, concentration process.

Nickel can be recovered using extractive metallurgy. Most lateritic ores have traditionally been

processed using hydrometallurgical techniques to produce a matte for further refining. Recent


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advances in hydrometallurgy have resulted in recent nickel processing operations being

developed using these processes. Most sulphide deposits have traditionally been processed by

concentration through a froth flotation process followed by pyrometallurgical extraction. Recent

advances in hydrometallurgical processing of sulphides have led to some recent projects being

built around this technology.

Nickel is extracted from its ores by conventional roasting and reduction processes which yield a

metal of >75% purity. Final purification in the Mond process to >99.99% purity is performed by

reacting nickel and carbon monoxide to form nickel carbonyl. This gas is passed into a large

chamber at a higher temperature in which tens of thousands of nickel spheres are maintained in

constant motion. The nickel carbonyl decomposes depositing pure nickel onto the nickel spheres

(known as pellets). Alternatively, the nickel carbonyl may be decomposed in a smaller chamberwithout pellets present to create fine powders. The resultant carbon monoxide is re-circulated

through the process. The highly pure nickel produced by this process is known as carbonyl

nickel. A second common form of refining involves the leaching of the metal matte followed by

the electro-winning of the nickel from solution by plating it onto a cathode. In many stainless

steel applications, the nickel can be taken directly in the 75% purity form, depending on the

presence of any impurities.

2.3 BENEFICIATION OPERATION

Beneficiation of ores and minerals is defined as including the following activities: crushing;

grinding; washing; filtration; sorting; sizing; gravity concentration. In essence, beneficiation

operations typically serve to separate and concentrate the mineral values from waste material,

remove impurities, or prepare the ore for further refinement. Beneficiation activities generally

do not change the mineral values themselves other than by reducing (e.g., crushing or

grinding),or enlarging (e.g., pelletizing or briquetting) particle size to facilitate processing. A

chemicalchange in the mineral value does not typically occur in beneficiation.

2.4COMMINUTION

The first step in beneficiation is comminution. Typically, this is accomplished by sequential size

reduction operationscommonly referred to as crushing and grinding. Crushing may be


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performed in two or three stages. Primary crushing systems consist of crushers, feeders, dust

control systems, and conveyors used to transport ore to coarse ore storage. Size separators (such

as griddles and screens) control the size of the feed material between the crushing and grinding

stages. Griddles are typically used for very coarse material. Screens mechanically separate ore

sizes using a slotted or mesh surface that acts as a "go/no go" gauge. Vibrating and shaker

screens are the most commonly used types of separators. After the final screening, water is

added to the crushed ore to form a slurry. Grinding is the last stage in comminution. In this

operation, ore particles are reduced and classified (typically in a hydrocyclone) into a uniformly

sorted material between 20 and 200 mesh. Most facilities use a combination of rod and ball mills

to grind sulfide ore.

2.5 FLOTATION

The second step in the beneficiation of sulfide ore is concentration. The purpose of concentration

is to separate the valuable mineral from nonvaluable minerals (referred to as "gangue"). There

are a variety of concentration methods. Selection of a method to use for a ore is based on the ore

mineralogy and mineral liberation size. Froth flotation is the standard method of concentration

used in the copper industry. Differential flotation for complex ores that contain sulfides requires

the use of reagents that

Modify the action of the collector either by intensifying or reducing its water-repellant effect on

the valuable mineral surface. These reagents are known as modifiers or regulators or as

depressants and activators. The most common modifier is the OH (hydroxyl) ion. Lime or

sodium carbonate is used to raise the pH of the slurry and regulate the pulp alkalinity. The

second most common modifier in some metal flotation is the cyanide ion derived from sodium

cyanide. It is normally used to depress pyrite while floating chalcopyrite or chalcocite in rougher

flotation.

2.5 MINERAL PROCESSING OPERATIONS

Mineral processing operations, in contrast, generally follow beneficiation and serve to change the

concentrated mineral value into a more useful chemical form. This is often done by using heat or

chemical reactions to change the chemical composition of the mineral. In contrast to


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beneficiation operations, processing activities often destroy the physical and chemical structure

of the incoming ore or mineral feedstock such that the materials leaving the operation do not

closely resemble those that entered the operation.

2.6 NICKEL PROCESSING

Firstly, the nickel ore mined will be conveyed to a stock bin before crushing and grinding. The

nickel crushing and grinding plant can handle harder nickel ore as well as increasing the plant

throughput.

The outflow from the mill enters a vibrating screen and the oversize is directed to a CS series

cone crusher before being returned to the mill. Screen undersize enters a ball mill/cyclone circuit

before entering the flotation plant rougher cells. After crushing and grinding process, the nickelore will be conveyed to flotation plant. Them the nickel ore will be sent to nickel smelter or

nickel refinery

2.6.1 Nickel ore processing equipment

A fleet of crushing, screening, grinding equipment is used to process nickel ore at high efficiency

and low costs. Beneficiation equipment like feeder, crusher, ball mill, classifier, screen, rocking

bed, magnetic separator, mix tank, flotation machine

2.6.1.1 Features & advantages:

High quality dressing equipment; Installation Services & Automation & Instrumentation service;


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Spare parts and consumables parts support.

2.7 NICKEL CRUSHER:

The nickel crusher is widely used in nickel processing plant. SBM is a major nickel crushermanufacturer in China, Our nickel crusher is from primary crushing, secondary crushing to

fineness crushing. The common nickel crusher are Heavy duty jaw crusher, small jaw crusher,

impact crusher, spring cone crusher, CS series cone crusher, single cylinder cone crusher, HP

hydraulic cone crusher and so on. The crushing capacity of the nickel crusher can be up to 1000

TPH, the final grain size of the crushed nickel ore can be down to 2mm in diameter.

2.8 NICKEL GRINDING MILL:

Nickel mill is the major nickel milling machine to grind the crushed nickel ore. SBM can designand manufacture many types of nickel mills for nickel grinding. The common nickel mills are:

ball mill, Raymond mill, MTM trapezium mill, MTW trapezium mill, ultrafine mill etc. And the

ball mill is the most widely used nickel mill to grind the nickel mill.

The ore is crushed to -5 inches in primary cone crushers, then reduced to -1/2" in short head cone

crushers. The ore is then ground to -100 mesh in ball mills. Using wet magnetic separators the

magnetic ore is separated (pyrrhotite) and further reduced to -200 mesh in a ball mill.

Classification is accomplished with screens and cyclones. The pyrrhotite is then sent to froth

flotation cells, and produces a 3% nickel concentrate.

2.9 NICKEL ORE CONCENTRATION

After mining, the sulphide nickel ores are transported to a concentrator to upgrade their nickel

content. The ores are first crushed and ground, liberating the sulphide minerals from worthless

rock, or gangue. The sulphide minerals are then separated from the gangue, by flotation, and

dried. Nickel Ores grade about 3% Ni content and the concentrates produced after treatment in

the concentrator grade around 11% . The ore is subjected to high temperature pressure acid

leaching followed by solvent extraction to yield nickel metal


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CHAPTER THREE

3.0 MINING AND MINERAL PROCESSING WASTES

3.1 SOURCE AND TYPE OF MINING WASTES

The wastes generated from mining operations include solid waste, wastewater and waste gas.

This waste can affect the environment through one or more of the following intrinsic criteria:

its chemical and mineralogical composition, its physical properties, its volume and the surface occupied, the waste disposal method.

Figure 3: Mining waste types


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Besides these parameters, one must also take into account extrinsic parameters such

as:

climatic conditions liable to modify the disposal conditions, geographic and geological location, existing targets liable to be affected (man and his environment).

Thus, identification of the environmental risks associated with the exploitation of mines and

quarries and with ore processing not only requires the characterisation and quantification of the

different types of waste, as well as a knowledge of the processes used, but also an assessment of

the vulnerability of the specific environments contingent upon the geological and

hydrogeological conditions and peripheral targets. Since this is a generic description, it is

important to keep in mind that not all plants or deposits will release any pollutants to begin with.

F igure 4shows how meteoric precipitation can transfer pollutant from a tailings dam or a

processing plant to the river if the waste management is not efficient. If there is no impermeable

layer, below the deposit, the infiltration of meteoric precipitation through deposit can transfer the

pollutant(s) to the river via groundwater flow. The extraction process can itself modify the water

flow and accelerate this transfer. Infiltration can also occur below a decantation basin.

Figure 4: Pollutant transfer


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3.2. EXTRACTION/BENEFICIATION WASTES

As for example, waste generated from nickel mining extraction/benefication

3.2.1 Waste rock

Mining operations generate two types of waste rock, overburden and mine development rock.

Overburden results from the development of surface mines, while mine development rock is a

byproduct of mineral extraction in underground mines. The quantity and composition of waste

rock generated at someone material mines varies greatly between sites, but these wastes will

contain minerals associated with both the ore and host rock. Overburden wastes are usually

disposed of in unlined piles, while mine development rock is often used on-site for road or otherconstruction. Mine development rock may also be stored in unlined on-site piles or in

underground openings. Waste rock piles may be referred to as mine rock dumps or waste rock

dumps. Runoff and leachate from waste rock dumps may contain heavy metals, and these

piles may generate acid drainage if sufficient amounts of sulfide minerals and moisture are

present.

3.3 HUMAN HEALTH AND ENVIRONMENTAL DAMAGE FROM MINING

AND MINERAL PROCESSING WASTES

3.3.1 Environmental impact/risk

Nearly any portion of waste management units at active mines may be a potential source of

environmental contamination. Waste rock piles and tailings impoundments are of particular

concern since these are the areas in which toxic contaminants most commonly are found.

Contaminants associated with these areas may include heavy metals, reagents, and acid rock

drainage that may degrade ground water, surface water, soil, and air quality during mine

operation and after mine closure. A discussion of the potential environmental effects associatedwith metal mining is presented in the following sections. Specific examples from industry are

included in this section, as appropriate. This section will give a brief overview of some of the

potential problems that can occur under certain conditions. The extent and magnitude of

contamination depends on highly variable site-specific factors that require a flexible approach

to mitigation. However, many of the potential problems can be, and generally are, substantially


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mitigated or avoided by proper engineering practices, environmental controls, and regulatory

requirements.

ENVIRONMENTAL IMPACTS TO GROUND WATER/SURFACE WATER

Sources of ground and surface water contamination include runoff, leachate, and seepage from

tailings impoundments, mine pits and workings (after mine closure), as well as waste rock piles.

For lead and zinc recovered from sulfur-bearing ores, acid generation due to oxidation of sulfides

in the ore body, host rock, and waste material may be of special concern. Acidified water

increases the potential for leaching heavy metals from these sources and facilitates their

transport. Factors that influence the acid generation potential include the sulfide content, the

buffering capacity of the ore and/or tailings, exposure of mineral surfaces in an oxidizing

environment, moisture, and the hydrogeology of the area. Some bacteria are catalysts foroxidation of sulfur-bearing minerals leading to acid generation. These bacteria pose a particular

problem in waste rock piles and tailings impoundments.

As water acidifies, the potential for leaching and mobilization of metals and other contaminants

increases. The suite of elements and minerals that may be associated with lead-zinc deposits

includes mercury, tellurium, cobalt, thallium, pyrite, and pyrrhotite. Lowering of pH affects the

solubility of these constituents making them available for transport in both surface and ground

water. Whether these contaminants will migrate depends on the geochemistry in the vicinity..

However, not all reactions are dependent on low pH. For example, high concentrations of arsenic

have been found to be mobile at a pH of 10.

3.3.2 Environmental impacts/risk to soil

Environmental impacts to soils as a result of mining activities are most commonly associated

with erosion and contamination. However, mining activities also can cause under someconditions. .Erosion may be caused by land disturbances and removal of vegetation related to

mining activities. Under these conditions, precipitation events such as snowmelt may lead to

erosion of soils. Contamination of soils may occur from discharge, runoff, leachate, and

seepage from tailings impoundments, pits and underground workings, as well as waste rock

piles. In addition, deposition of wind-blown particulates from dry tailings impoundments may


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also be a source of soil contamination. Other sources of soils contamination include spills of fuel,

flotation reagents, cleaning solutions, as well as other chemicals used or stored at the site.

Contaminated soils may further act as a source of contamination to ground water, surface water,

and in some instances as a source of air pollution due to re-entrainment and/or subsequent

deposition of particulates. In some instances, direct human contact has occurred when tailings

have been used in sandboxes, as soil amendments, and as construction fill material, although

these are generally historic practices. The calamity of landslide, collapse and mud and stone flow

caused by the waste muck and spoil. The mud and stone flow comprises a lot of mud and stones.

and is one of the common calamity caused by people during the process of mine exploitation

with high energy, and severe damage. The necessary conditions to form the mud and stone flow

are: the huge rain formed naturally and the huge sands and stones formed artificially. The

stripping soil and mucks were stored on the slope or in the valley with mine exploitation and thestability of wall rock got changed. A large amount of discrete solid substances were formed with

the large scale landslide and collapse. Then, the severe mud and stone flow happened with the

support of storm.

3.3.3 Environmental impacts to air

The primary source of air contamination at mine sites is fugitive dust from the dry surfaces of

Tailings impoundments, as well as waste rock piles, if they are exposed to the environment.

Often, tailings impoundments are not completely covered by water, thus dry tailings are

commonly available for wind-blown transport (as discussed above). Deposition of wind-blown

tailings provides exposure routes for contamination of ground water, surface water, and soil.

Potential contaminants include those discussed in the Ground Water/Surface Water Section.

3.4 WASTE LAND RESOURCES

The mining construction facilities and mucks, spoils, tailings will occupy large area of land.

3.4.1 Collapse of the Land Surface in Mining Area

The collapse of the land surface in mining area will destroy the ground and farmland. The

collapse of ground surface is one of the relatively severe geological calamity existed in coal

mines and other underground exploitation mines. The area of ground surface collapsing is 2

thousand m2 with the raw coal exploitation per 10 thousand tons. And the area of ground surface

collapsing is 1.2 times of the coal exploitation. Statistically, in China, the area of ground surface


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collapsing has reached 0.839922 billion m2. For instance, in Kailluan mines, Tangshan City, the

area of ground surface collapsing has got 15 million m2 reducing farmland with area of 93

million m. and the same thing happened in Feicheng City, Shandong Province, and in Xuzhou

City, Jiangsu Province.

3.4.2 Calamity of landslide, collapse and mud

It is fairly common that the calamity of landslide, collapse and mud and stone flow caused by the

mining waste. On the other hand, the landslide and collapses are also rather common during the

process of mine exploitation. The main reasons include that ,soil discharging area poor setting

and disadvantageous mine exploitation methods, such as collapsing method" and "exploding

method", which made the wall rock unstable, changed the geological construction and caused

the large-scale landslide and collapse

3.5 CONTAMINATING WATER BODY

The waste water and slag will cause water body and soil pollution. The waste water pollution

caused during the process of mineral resources exploitation is one of the main factors making the

quality of water source getting worse. The wastewater causing the water-body pollution during

the process of mining extraction is not only from the oil and gas resources industry, but also

from other mines. For instance, in Cangnan County, Zhejiang Pronvince, during the process of

Alunite exploitation to produce Alum, the river nearby the mine got heavily polluted, and the

banks along the river had changed into storage sites for waste Alum. The exploitation of Alunite

mine had done great harm to the local people and economy. Another example with the coal

gangue. The coal gangue piled in the open air has changed much during the process of

weathering, rain leaching. And with the condition that reducing environment changing into

oxidize one, a series of physical and chemical reactions happened, which made the soluble

inorganic salt leak into the ground surface with the leachate, forming the highly mineralized

water. Thus, a lot of hazardous wastes entered the surface water body and farmland, causing

severe threat to the life of local people and livestocks. The leachate entered the underground

water during the process of discharging, and caused heavily pollution to the land and

underground water nearby. Furthermore, the radioactive pollution will happen during the process

of black shale exploitation because of the radioactive compositions in the shale mine.


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3.5.1 Damages to Drinking Water and Human Health

Because the toxic smelting slags were piled improperly and buried underground randomly,

they had caused great trouble in the past without strict management for the nonferrous metal

mines and related processing factories. Lead, zinc, arsenic and other contaminants in ground

water proximal to mine sites have contaminated drinking water resources,

.


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CHAPTER FOUR

4.0 DESCRIPTION OF MINING-WASTE MANAGEMENT METHODS

4.1. WATER MANAGEMENT

4.1.1 Different steps have to be checked:

Avoid pollution of groundwater and surface water, Collect and treat the polluted water and leachates, Minimise the water volume that require treatment, Manage the dust.

Measures used to control seepage from tailings dams include:

Controlled placement of tailings, Foundation grouting, Foundation cut-offs, Clay liners, Under drains and toe drains, Artificial liners.

1. Controlled placement of tailings is the most cost-effective method of controlling seepage.

Provided that the tailings are of low permeability they will form a cohesive system.

2. Foundation grouting involves the injection of fluidised material and could not be effective

unless there is high permeability rock beneath the impoundment or where there are high

permeability zones in the rock.

3. Foundation cut-offs are necessary when soil foundations are sand or sand and gravel. A

significant reduction in seepage may be achieved by construction of an earth fill cut-off or a

slurry trench cut-off wall. They may be applied to extremely weathered rock such as laterised,

highly permeable rock.

4. Clay liners can be effective in areas where the storage is located in an area of high

permeability. They are susceptible to cracking on exposure to the heat (by sun), which can

increase permeability.

5. Underdrains below the tailings should be constructed. The drains act to attract theseepage

water and discharge it to a collector system, ideally for recycling to theprocess plant.


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Some methods of collecting and treating this seepage are required, such as:

Toe drains, Pump wells, Seepage collection, Artificial wetlands.

6. Artificial liners are used to line waste disposal facilities, often with provision fordrainage

layers beneath the membranes to collect any leachate, which leaks past thefirst. However, these

liners do not seem to be always appropriate for all tailingsdisposal situations (such as in case the

underground water is confined and spoutingout).

The control of the water balance in the system should include process water, tailingswater, storm

water runoff, precipitation, seepage

Figure 4.1 Water gains and losses at a terrestrial impoundment


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Measures to minimize acid drainage and pollution from water containing

dissolved metals, salts and process chemicals.

Minimise percolation to subsoil and groundwater, by low permeability of the substrateand low permeable cover,

Minimize seepage through the impoundment wall, Collect seepage by a collection and treatment system, Minimize influx of surface runoff by trenching and by-passing the tailings depository, Maximize circulation of process water, Minimize infiltration of water into the tailings dam.

4.2 DISPOSAL OF MINING WASTE AND TAILINGS

Disposal of coarse mining waste consists in conversing large areas with dumps or filling

abandoned open-pits By order of importance, the disposal of tailings is generally by:

Terrestrial impoundment (tailings ponds) Underground backfilling, Deep water disposal (lakes and sea) Recycling.

a. Terrestrial impoundment

Terrestrial deposition is the predominant method for tailings disposal. It concerns fine waste and

slurries such as mill tailings. The principle of tailings dams (or ponds) is dispose of the tailings in

an accessible condition that provides for their future processing (once improved technology or a

significant increase price makes profitable). Actually, the vast majority of tailings facilities are

design as permanent disposal facilities. Tailings are often transported to the impoundment via

pipelines.

b. Underground backfilling

This method is possible only for ore deposit without communication with an aquifer. Such anoperation is usually costly and will be carried out for stability and safety reasons.

c. Deep water disposal

The disposal of tailings and solid waste directly into bodies of water although sometimes used in

past operations, is rapidly becoming non-authorized as a standard practice due to the significant

pollution effects it can have on the receiving waters and the possible subsequent impacts on the


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livelihoods of the local communities. This method requires specific conditions. And specific

impact assessments. There seems to be a consensus among scientists that an appropriately

designed underwater disposal of sulphidic tailings is the ideal solution from an environmental

point of view in the short-term with control of the level of water.

d. Recycling

Coarse mining waste and especially barren rock is sometimes considered as materials for roads,

building foundations or cement factories, depending on its geotechnical and geochemical

characteristics. Recycling is not classified as disposal.

4.3 ENVIRONMENTAL ISSUES

Some waste generated by mining operations, due to the mass it represents or to its chemical (or

physical) nature, can pollute the environment, in particular media as water, soil, vegetation, andtargets like the fauna and human. Among the environmental problems, associated with tailings

deposition, the principal ones are:

Safety and stability of dams, Water pollution,

Safety and stability of damsTailings dams need to designed for the mine life and shaped at the initial stage. This reduces the

need for reshaping dams at a later stage and so avoids costly earthworks and double handling.We are conscious that in practice, the building of tailings dam at the initial stage of a mines life

is difficult, due to the fact that in most cases the ore reserve ,the mine life and hence the total

amount of tailings will increase over time. This is due to a continuous development of mining

and processing methods and to the fact that the knowledge on the ore body will increase with

time. The placement of waste on steep slopes is to be avoided when possible so as to reduce the

risk of land slip and dam failure, particularly in areas of high rainfall and areas prone to

landslides, earthquakes and tremors. Embankment of dam are shaped during the building stage

so that slopes are gentle enough to reduce erosion and to allow vegetation to become established

and so reduce the negative visual impact of unsightly waste rock.


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A major factor in the design of tailings embankments is stability, from a geotechnical

point of view. Factors influencing this geotechnical stability include:

Embankment height, Embankment slopes, Strength of the embankment and degree of compaction, Permeability of the embankment and groundwater position in relation to it, Strength and compressibility of the embankment foundations.

The type of dam embankment to some extent dictates the system of tailings discharge to be

adopted. For example, embankments that are designed as water retention structures are made of

low-permeability materials and tailings are discharged well upstream of the embankment.

Water pollutionAcid rock drainage can be a significant concern in the management of waste rock but is not in

the scope of that study .Water pollution may appear at different stages in the management of

tailings. For example, failure of the discharge may cause spills and damage the surrounding

Environment. Alternatively, rain and process water may create leachates when passing seeping

through tailings (essentially in respect of tailings from ferrous and non ferrous ores),giving rise

to:

Sulphide oxidation and potential acid generation Sulphide oxidation and production of soluble salts Metal leaching and migration to the surrounding environment Leaching of residual process chemicals in the tailings, e.g. cyanide, acids, alkalis Geochemistry and toxicity of the waste materials impacting on humans, vegetation and

fauna.

These can also result from:

Seepage through and below impoundment walls

percolation to the subsoil and groundwater overflow of the dam walls or spillways


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CHAPTER FIVE

5: CONCLUSIONS AND RECOMMENDATIONS

5.1 CONCLUSIONS

The mining sector is a major contributor not only to the material needs, but also to the

development and economic growth of the many countries example Tanzania. On the other hand,

it is obvious that exploitation of mineral resources requires a responsible approach to avoid

adverse effects on the environment.

Risks linked to mining wasteAn important conclusion of the study is that the major risks linked to mining waste (not all mine

or all mine waste) are double: Risks linked to the liberation of acidity and heavy metals causedby the modification of the relationship between the minerals, the surface and ground water and

the atmosphere (especially metallic ore). Such risks could correspond to a continuous and long

term pollution, which will not stop before total oxidation of the waste exposed to the atmosphere.

This risk is the combination of a potential source of pollution with transfer pathway and the

existence of targets (human here).Risks linked to the stability of the tailings dam. Such risks

could create spectacular accidents.

Liberation of acidity and heavy metalsA specific characterization of representative waste samples resulting from mining, quarries and

ore processing operations should be carried out on each site. Such characterization should

include specific studies related to the potential of pollution of the waste. Not only the solid

composition but also the nature of the leachates resulting from mining waste should be defined

(as it is a common practice for industrial waste within the framework of the Landfill Directive)

and be correlated to the quantity of corresponding waste. Indeed, the effluents resulting from

deposits of mining waste may be acid and contain heavy metals in significant quantities, with apotential impact on the environment. The leachate of mining waste will also depend on the waste

management practices implemented.


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The different types of mineIt is obvious that the pillar of sustainable development related to the protection of environment

has not always been sufficiently considered, in particular in the past. As a consequence, a

distinction should be made between the following three types of mines:

Abandoned/ old mines Operating mines substantially based on old designed operations Operating mines based on new design

Serious problems are arising from abandoned mines and mines which activity is based on

old operations which have been conceived without environment management. There is a

need of basic criteria for mine closure plans, which can be based on the methodological

For operating mines substantially based on old designed operations, it is essential to

evaluate the reliability of the control routine related to the stability of the tailings dams. It

seems also necessary to improve the waste management conditions of these sites.

Existing mines based on new design ensure a higher level of environmental protection.

However, these sites should also be evaluated with the views of taking additional

measures if necessary. The closure phase should also be carefully prepared. This is often

taken into account.

5.2 RECOMMENDATIONS

To validate this inventory study of the sites of mining waste deposit in each by detailedstudy carried out by a homogeneous multi-disciplinary team, especially for abandoned

and closed mines,

To get information for each site, on solid composition but also on the nature of theleachates resulting from specific and representative mining waste samples

To evaluate different evolution forms of legislation To define basic criteria for mine closure plans, on the base on contaminated lands

approach,

To organise meetings and exchanges of information between industrials and researchersof the Member States


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REFERENCES

1:RITCEY G.M.: Tailings Management Problems and solutions in the mining industry.

ELSEVIER ISBN 0-444-87374-0, 1989

2:UNEP- A guide to tailings dams and impoundment - Bulletin 106 1996

3: UNEP, Environmental and Safety Incidents concerning Tailings Dams at Mines ,results of a

survey for the years 1980-1996, Mining Journal Research Services, May1996

4: BOLIDEN ENVIRONNEMENT Tailings dam failure, Spain, HEALTH AND SAFETY

REPORT

5: ERIKSSON N., ADAMEK P., The tailings pond failure at the Aznalcllar mine, Spain,Paper prepared for the Sixth International Symposium in Environmental Issues and Waste

Management in Energy and Mineral Production, Calgary, Alberta, Canada, June 2000

6:HANNA T., Romanian cyanide spill preventable Mining Environmental Management, A

Mining Journal Publication, p. 14-15 Mars 2000

7: MORIZOT G. Environmental aspect of the use of cyanide in gold and silver ores processing,

Communication 1999

Mining and mineral processing waste management based on nickel

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