Hg - Hidrokimia Air Asam Tambang

8/17/2019 Hg - Hidrokimia Air Asam Tambang

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HIDROKIMIA

AIR ASAM TAMBANG


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Peristilahan

• Acid Mine Drainage (AMD) – Air yang terkontaminasi akibat

kontak dengan aktivitas

penambangan

• Acid Rock Drainage (ARD) – Batuan alami yang bersifat

asam

Keduanya menghasilkan air

asam Bagaimana

membedakannya?


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KARAKTERISTIK AMD

• Meningkatnya keasaman = Penurunan pH

• Peningkatan konsentrasi logam

• Peningkatan Sulfat• Peningkatan zat padat terlarut


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Hg, Pb

As, Se

Cd, Sb,

Ag, CN

Cu, Zn

Pb, U

Cr, Fe

Hg

Metals


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Efek thd Aliran Sungai

• Air menjadi berwarna: – “Yellow boy”

• Oksida besi, umumnyamemperlihatkan karat di

dasar aliran

– Putih• Aluminum

– Hitam

• Mangan – Ditentukan oleh besarnya

pH-nya.


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Perubahan dalam teknologi

tambang

• “Produk lama”

– Tambang yg sdh ditutup – Tumpukan tailing

/waste rock

– ARD

• “Cara Baru”

– Pengolahan dengan teknologi sianida “heap

leach”


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Kimia AMD

• Pelapukan Piritpirit

air

+ udara

pH rendah+ Logam

Jenis Logam: Kaya As, Sb, Zn, Cu…

Fe, Al, Mn

Kaya Sulfate


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Mineral yang kaya Pirit

Logam-logam sulfida

Fe - pyrite, marcasite, pyrrhotite

Hg - cinnabar

Pb – galena

Ag – acanthite, galenaAs – arsenopyrite, As-rich pyrite, orpiment, tetrahedrite, enargite

Ni – pentlandite, millerite

Cu – covellite, chalcocite, djurleite, bornite, chalcopyrite, enargite

Cd – greenockiteZn – spahlerite

Co – cobaltite


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Besi-SulfidaPyrite (FeS2) Pyrrhotite (Fe(1-x)Sx)

Marcasite (FeS2 ) Chalcopyrite (CuFeS2)

Galena (PbS) Sphalerite (ZnS)

Arsenopyrite (FeAsS) Bornite (Cu5FeS4)


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Kimia AMD

4FeS2 + 14 H2O + 15 O2 → 4Fe(OH)3 + 8 SO42- + 16 H+

Oksida besi

Keseluruhan

menghasilkan air asam


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Oksidasi Pirit: IIFeS2 + 7/2O2 + H2O Fe

2+ + 2SO42- + 2H+

FeS2 + 14Fe3+ + 8H2O 15Fe

2+ + 2SO42- +16H+

FeS (s) + O2 2

Fe(II) + S22-

+ O2

Fe (II) + SO42-

+ FeS (s)2fast

fastmicrobial

+ O2

slowinorg.

Fe(III) = Fe(OH) (s)3

Sumber:

Stumm and Singer (1980)


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Kinetik Oksidasi Pirit

Assumed Conditions/Predicted Half Times

Oxidants pH log[O2] log[Fe3+

] log[Fe2+

] t1/2________________________________________________________

O2 2.0 -7.0 -- -- 780y-3.6 -- -- 16y

Fe3+

2.0 -- -2.0 -4.0 4.4d -2.0 -2.0 150d

Sumber: Langmuir (1996) menggunakan kecepatan rekasi dari

Williamson & Rimstidt (1994), Py Area=0.05 m2/g


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Oksidasi Pirit: III

• Kimia

– Oksigen, Fe(III), Air, Larutan

buffer

• Fisika

– Tekstur, Ukuran Butir

– Temperatur

• Biologi

– Oksidasi Fe- dan S-oleh bakteri


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Bakteri sebagai Katalisator

Reaksi AMD


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Efek Temperatur thd Oksidasi


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Proses buffering ARD selama Oksidasi

Mineral


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Proses buffering ARD selama

Oksidasi Mineral

pH

Time

Buffering of Mineral A

(e.g. calcite, dolomite)

Buffering of Mineral B

(e.g. ankerite, siderite)

Buffering of Mineral C

(e.g. Al(OH)3)

Buffering of Mineral D

(e.g. feldspars)


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Kimia AMD

• Luas permukaan kontak – Semakin luas permukaan semakin cepat bereaksi

– Lebih kecil butiran lebih luas permukaannya


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Pengolahan AMD

Cara Aktif dan Pasif

• Aktif

– Penambahan alkalinitas untuk meningkatkan pH

– Efektif tetapi mahal

• Pasif

– Menggunakan cara-cara alami – Perawatan mudah dan murah

– Tergantung dari volume


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Contoh Pengolahan AMD cara

Pasif


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Pengolahan AMD cara Pasif

InputFe , SO , H , Me

3+ 2- +

4 ΣOutput=

Cleaner

Plant uptake

ReducingSO to H S

ppt (Fe,Me)S4 2

2-

Oxidizing

ppt of Fe-OH-O-SOadsorption4

[inc. pH]

See Kwong & Stempvoort (1994)(Mt. Washington, B.C.)


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Pengolahan AMD cara Pasif

O2H O2

Fe2+

SO42-

Fe(OH)3

Al(OH)3

FeCO3 CaCO3after Ptacek and Blowes (1994)Other authigenic ppts: Goethite, jarosite, schwertmannite

Mine Tailings


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Mekenisme pengendalian ARD

pada Waste Batuan

Precipitation

Tailings

Dam

Oxidation Zone

Seepage

Surface Discharge

Neutralization Zone

Process Water


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pada Tailing

Precipitation

SeepageCollection

Ditch

Surface Runoff

InfiltrationBasal

Drainage

Sulfide Waste Rock


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pada Open Pit

Infiltration

Precipitation

Surface Water Runoff

Groundwater FlowThrough Rockmass

Pre-MiningGroundwater

Table

Post-MiningGroundwater

Table ARD Seepage

ARD Seepage

ARD Seepage

ResidualSulphides

Residual SulphideRock Debris

Ore Body


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pada Underground

Post-MiningGroundwater

Table

ResidualSulphide Exposures

(see inset backfill

alternatives)

Infiltration

ARD

Precipitation

Glory-Hole

Open Pit

MineWorkings

MineWorkings

ARD

Tailings(cemented)

Ore Body

Pre-MiningGroundwater

Table

Backfill Alternatives

Tailings(uncemented)

C D

Rockfill

B

Open Stope

A

SulphideExposure

Water Flow


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Pengolahan cara aktif

Umumnya menggunakan cara :- Oksidasi

- Penambahan Alkali

- Sedimentasi


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Alkali Minerals

• Jenis – Karbonat• Kalsit (CaCO3)

• Dolomit (Ca,Mg(CO3)2)

– Hidroksida

• Fe(OH)3

• Al(OH)3

– Silikat – Lempung


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Contoh Pengolahan Aktif

Iron Mountain, California


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“Pengolahan Cara Baru”

• Cyanide Heap Leach Penumpukandan Peluluhan dgn sianida.

– Umum pada pengolahan emas

– Ekstraksi Au dari bijih berkadar rendah

– Bijih dihancurkan, ditempatkan di ruangterbuka untuk proses CHL

– Sianida disemprotkan di atas tumpukan

– Luluhan Au mengalir melalui bijih

– Larutan disaring dihasilkan Au

– Cara yang mudah?


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Kerangka & tahapan


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Penelitian ARD

• Kimia air tergantung kepada: – Derajat & tingkat oksidasi

– Derahat & tingkat pelepasan logam

– Jumlah material

– Contained metals

– Hidrologi dan iklim lolasi hydrology and

– Akumulasi produk yang

mudah teroksidasi

– pH/kontrol kelarutan,reaksi selama aliran

– Kontrol Teknologi


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Site Characterization

• Design

• Field investigation & Sampling

• Lab testing


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New Mines vs. Existing Mines

• New Mines• ARD probably not evident

• Objective is to determine ARD potential

• Fresh samples used for testing and prediction

• Long term behavior based on kinetic testing, modeling and

prediction

• Existing and Abandoned Mines

• ARD may be evident/mature

• Field reconnaissance used to define ARD

• Historic data (time trends) extremely useful• Limited laboratory testing required

• Field instrumentation and monitoring possible

• Background altered, requires simulation


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Design

• Review existing data, e.g: – Geology & mine plan

– Drill core logs

– Water quality monitoring results

– Assays on ore/waste rock and tailings – Waste type volumes

– Waste placement history

⇒Develop reconnaissance & sampling

plan


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Field Investigations

• Objectives – Detect early signs of ARD

– Determine potential for ARD

– Assess factors that control ARD – Evaluate control measures

– Determine environmental impact

– Assess compliance with regulatorystandards


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• What to bring:

– Eyes that know what to look

for

– pH and conductivity meters

– Acid bottle, hydrogen

peroxide, sulfate kit

– Geological pick, hand lens,sampling bags, camera,

GPS unit

– Site map, history, data

2.2


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Field Investigations• Things to look for:

– Visible pyrite or other sulfides (oxidation) & calcite

– Red, orange, yellow, white, blue staining (precipitates, water)

– Dead vegetation or bare ground

– Melting snow or steaming vents on waste

– Dead fish or other biota

– Low pH in seeps, groundwater, decants & streams


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• Things to log in the field:

– Paste pH

– Paste conductivity

– ‘Colour’ – Lithology

– Sulfide content

– Secondary mineralogy

– Degree of ‘fizz’ – Moisture content

– Grain size


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• General Methodology

– Visual observation of site

– Paste pH and water quality data

– Field extraction testing

– Classify types of wastes

– Solids sampling (for lab testing)


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• Geochemistry: – Low paste pH of mine wastes

– High conductivity of waste paste

– Contaminants in leach extraction tests

– Static (ABA) tests• Products from Reconnaissance:

– Physical disturbance and drainage map

– Waste deposit map and characterization

– Exposed rock map and characterization

– Paste pH and conductivity survey – Observations and sampling map

– ARD site assessment report


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Field Paste pH vs. Field Paste TDS

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

Field Paste pH

F i e l d P a s t e T

D S

Dike samples

Leach Pad Samples

Pit Samples

Waste Rock Samples

TDS vs pH


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Sample Selection (New Mines)

• Step 1: On geological sections: – Define rock types

– Define sulfide and alkali mineral distribution

– Preliminary rock units classification

• Step 2: Sample each rock unit class allowing for:

– Area distribution of class

– Variability of rock

• Step 3: Perform static lab tests and use results to refine rock unitclassification

• Step 4: Sample each new rock class and repeat Step 3 untilsatisfied.

• Step 5: Sample each rock class for appropriate kinetic testing anduse results to refine rock classification

• Step 6: Repeat Step 5 until satisfied with classifications and

characterization.


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Sampling (existing mines)• Steps:

– Define geology, mineralization,waste ‘types’ etc.

– Define objectives (i.e. sampling for

reveg, cover, water quality

evaluations etc. may have different

focus) – Consider mine plan and waste

placement history

– Identify sources of samples

– Initial sampling and testing program

– Further sampling if necessary


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Sampling

(Existing Mines)

• A Becker hammer-type drill rig

can be used in order to

minimize sample crushing and

the geochemical disturbance of

the samples• Samples typically collected at

specified intervals (e.g. every

10 ft) & paste pH and EC

measured,

• A sub-set of samples can thenbe selected using observations

and field measurements as a

guide for more detailed

laboratory testing


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Test Methods

• Static ARD Tests

– balance between potentially acid generating and consuming

– tool for waste management

– includes geological/mineralogical

characterization – individual samples

• Short-term Leaching Tests

– readily soluble component

• Kinetic Tests – oxidation and metal leaching rates

– water chemistry prediction


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Geochemical Static Tests

• Objective:

Potentially Acid Generating Mineralsvs

Acid Neutralizing Minerals

• Cautions for ARD assessment: – pH of alkalinity (NP) determination

– Assumes instant availability of NP

– Assumes all sulphur/sulphide

minerals reactive

– Ignores reaction rates (kinetics)

– Extrapolation to field


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• Procedures• Paste pH and conductivity on the ‘as received’ fines

• Acid-Base Accounting Tests

• Net Acid Generation (NAG) - also an accelerated kinetic test

• B.C. Research Initial Test

• Lapakko Neutralization Potential Test

• H2O2 Oxidation (modified for siderite correction)

• Net Carbonate Value (NCV) for ABA Tests

• Leach extraction analyses

• Forward acid titration tests• Multi-element ICP analyses


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Definitions: AP = acid potential

= % S x 31.25

NP = neutralization potential

NNP = net neutralization potential

= NP - AP

NP:AP ratio

= NP/AP

All expressed as:

kg CaCO3 equivalent/tonne, orCaCO3 eq./1000 tonnes

Example: S = 2 %

AP = 62.5 kgCaCO3/t

NP = 90 kgCaCO3/t

NNP = 27.5 kgCaCO3/t

NP/AP = 1.4:1

Note: units and acronyms used are different in Australiasia, local referencesshould be sought for correct usage, terminology, guidelines etc.

I t t ti


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InterpretationStart with

‘guidelines” or

general criteriafor classification,

then develop

site- specific

criteria

Typically criteria arebased on a ‘set’ of

tests, not just one

type of test e.g. ABA

& NAG results

0

5

10

15

20

0 5 10 15 20

AP (kg CaCO3/t equiv)

N P

( k g C a C O 3 / t e q u i v )

1:1 ratio3:1 ratioNon-acid

generating

Potentially acid

generating

Uncertain acid

generating potential

0

2

4

6

8

10

12

-50 -30 -10 10 30 50

P

a s t e p H

Non-acid

generating

Potentially acid

generating

Uncertain acid

generating potential

Documents

Hg - Hidrokimia Air Asam Tambang