Characterization of waste - Kinetic testing for assessing acid generation potential of sulfidic waste from extractive industries

This Technical Report describes the performance and evaluation of kinetic tests for sulfidic waste material that, according to previous testing (primarily acid base accounting), is likely to go acidic or when the result of such testing is inconclusive. This Technical Report also covers the issue of drainage from sulfidic material that is likely to be well buffered but that will produce a neutral drainage potentially affected by sulfide mineral oxidation. This Technical Report will not include aspects of sampling and testing that are already covered in the overall guidance document for characterisation of extractive waste (CEN/TR 16376) or in the guidance document on sampling of wastes from extractive industries (CEN/TR 16365).

Charakterisierung von Abfällen - Kinetische Prüfung zur Bewertung des Säurebildungsverhalten sulfidischer Abfälle der mineralgewinnenden Industrie

Caractérisation des déchets - Essais cinétiques pour la détermination du potentiel de génération d'acide des déchets sulfurés des industries extractives

Le présent Rapport technique traite de la performance et de l’évaluation des essais cinétiques pour des déchets sulfurés lorsque des essais antérieurs (notamment le bilan acide-base) montrent leur tendance à l’acidité ou lorsque le résultat desdits essais ne permet pas de tirer des conclusions. Le présent Rapport technique aborde également la question du drainage issu de matériaux sulfurés qui a de bonnes chances d’être neutralisé par un tampon, mais qui va produire un drainage neutre risquant d’être affecté par l’oxydation des minéraux sulfurés.
Le présent Rapport technique n’aborde pas les aspects de l’échantillonnage et des essais qui sont déjà couverts dans le document guide général relatif à la caractérisation des déchets d’extraction (CEN/TR 16376) ou dans le document guide relatif à l’échantillonnage des déchets des industries extractives (CEN/TR 16365).

Karakterizacija odpadkov - Kinetični preskusi za ocenjevanje celotne kislinske kapacitete odpadkov iz industrije bogatenja mineralnih surovin, ki vsebujejo sulfid

To tehnično poročilo opisuje izvajanje in vrednotenje kinetičnih preskusov za odpadne materiale, ki vsebujejo sulfid in pri katerih je glede na predhodne preskuse (predvsem vodenje evidenc kislih osnov) verjetno, da postanejo kisli, ali kadar so rezultati navedenih preskusov nedoločni. To tehnično poročilo prav tako zajema vprašanje drenaže iz sulfidnega materiala, ki ima verjetno visoko vsebnost pufrov, vendar bo proizvedel nevtralno drenažo, na katero bo potencialno vplivala oksidacija sulfidnega minerala. To tehnično poročilo ne zajema vidikov vzorčenja in preskušanja, ki so že zajeti v splošnem dokumentu z napotki za karakterizacijo odpadkov bogatenja mineralnih surovin (CEN/TR 16376) ali v dokumentu z napotki o vzorčenju odpadkov iz industrije bogatenja mineralnih surovin (CEN/TR 16365).

General Information

Status
Published
Public Enquiry End Date
29-Feb-2012
Publication Date
20-Dec-2012
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
20-Nov-2012
Due Date
25-Jan-2013
Completion Date
21-Dec-2012

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SLOVENSKI STANDARD
SIST-TP CEN/TR 16363:2013
01-januar-2013
.DUDNWHUL]DFLMDRGSDGNRY.LQHWLþQLSUHVNXVL]DRFHQMHYDQMHFHORWQHNLVOLQVNH

NDSDFLWHWHRGSDGNRYL]LQGXVWULMHERJDWHQMDPLQHUDOQLKVXURYLQNLYVHEXMHMRVXOILG

Characterization of waste - Kinetic testing for assessing acid generation potential of

sulfidic waste from extractive industries
Charakterisierung von Abfällen - Kinetische Prüfung zur Bewertung des
Säurebildungsverhalten sulfidischer Abfälle der mineralgewinnenden Industrie

Caractérisation des déchets - Essais cinétiques pour la détermination du potentiel de

génération d'acide des déchets sulfurés des industries extractives
Ta slovenski standard je istoveten z: CEN/TR 16363:2012
ICS:
13.030.01 Odpadki na splošno Wastes in general
SIST-TP CEN/TR 16363:2013 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST-TP CEN/TR 16363:2013
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SIST-TP CEN/TR 16363:2013
TECHNICAL REPORT
CEN/TR 16363
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
December 2012
ICS 13.030.01
English Version
Characterization of waste - Kinetic testing for assessing acid
generation potential of sulfidic waste from extractive industries

Caractérisation des déchets - Essais cinétiques pour la Charakterisierung von Abfällen - Kinetische Prüfungen zur

détermination du potentiel de génération d'acide des Bestimmung des Säurebildungspotentials von sulfidhaltigen

déchets sulfurés des industries extractives Abfällen der mineralgewinnenden Industrie

This Technical Report was approved by CEN on 9 April 2012. It has been drawn up by the Technical Committee CEN/TC 292.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,

Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United

Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: Avenue Marnix 17, B-1000 Brussels

© 2012 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 16363:2012: E

worldwide for CEN national Members.
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Contents Page

Foreword ..............................................................................................................................................................4

Introduction .........................................................................................................................................................5

1 Scope ......................................................................................................................................................7

2 Methods ..................................................................................................................................................7

2.1 General ....................................................................................................................................................7

2.2 Planning ..................................................................................................................................................7

2.3 Testing data ............................................................................................................................................9

2.4 Humidity cell test ................................................................................................................................ 10

2.5 Other column tests ............................................................................................................................. 11

2.6 Lysimeter ............................................................................................................................................. 12

2.7 Field test .............................................................................................................................................. 12

2.7.1 General ................................................................................................................................................. 12

2.7.2 Rainfall simulation tests .................................................................................................................... 13

2.7.3 Long-term field tests .......................................................................................................................... 13

2.8 Key testing variables .......................................................................................................................... 13

2.8.1 General ................................................................................................................................................. 13

2.8.2 Sample size and sample preparation................................................................................................ 14

2.8.3 Temperature ........................................................................................................................................ 15

2.8.4 Duration ............................................................................................................................................... 15

2.8.5 Sample selection................................................................................................................................. 15

2.9 Method summary ................................................................................................................................ 15

3 Interpretation and evaluation ............................................................................................................ 17

3.1 General ................................................................................................................................................. 17

3.2 Reaction rates ..................................................................................................................................... 17

3.2.1 General ................................................................................................................................................. 17

3.2.2 Sulfide oxidation rate, assessed by sulfate release ........................................................................ 18

3.2.3 Sulfide oxidation rate, assessed by oxygen consumption ............................................................ 19

3.3 Leaching rates ..................................................................................................................................... 20

3.4 Leaching result evaluation ................................................................................................................ 21

3.5 Application to field conditions .......................................................................................................... 22

3.5.1 General ................................................................................................................................................. 22

3.5.2 Mineralogy/mineral chemistry ........................................................................................................... 23

3.5.3 Particle size ......................................................................................................................................... 23

3.5.4 Texture / hydraulic conditions ........................................................................................................... 24

3.5.5 Air flow / oxygen exposure ................................................................................................................ 24

3.5.6 Temperature ........................................................................................................................................ 24

3.5.7 Microbes (inhibitors/enhancers) ....................................................................................................... 24

3.5.8 Test duration ....................................................................................................................................... 25

3.6 Field test evaluations ......................................................................................................................... 25

3.6.1 General ................................................................................................................................................. 25

3.6.2 Rainfall simulation tests .................................................................................................................... 25

3.6.3 Long-term field tests .......................................................................................................................... 25

4 Recommendations .............................................................................................................................. 27

4.1 General ................................................................................................................................................. 27

4.2 Assess if the material is going acidic or not ................................................................................... 27

4.3 Define sulfide oxidation rate .............................................................................................................. 27

4.4 Define acid consuming reaction rate ................................................................................................ 27

4.5 Assess when the material will go acidic .......................................................................................... 28

4.6 Estimate leaching rates and leachate quality .................................................................................. 28

4.7 Evaluate closure options ................................................................................................................... 28

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Bibliography ...................................................................................................................................................... 29

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Foreword

This document (CEN/TR 16363:2012) has been prepared by Technical Committee CEN/TC 292

“Characterization of waste”, the secretariat of which is held by NEN.

The preparation of this document by CEN is based on a mandate by the European Commission

(Mandate M/395), which assigned the development of standards on the characterization of waste from

extractive industries.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.

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Introduction

A specific feature of sulfide containing waste is the risk for acid/neutral drainage generation (A/NRD). Acid

drainage occurs if the acid generation from sulfide oxidation exceeds the acid buffering from minerals in the

waste while, in this context, neutral drainage occurs when neutralisation generation exceeds the acid

generation.

Test methods for the determination of acid generation behaviour can be divided into static and kinetic tests. A

static test is used for screening purposes. It is usually relatively fast to perform, but gives only indicative

information based on total content of sulfur (or sulfides) and of readily available buffering minerals in the waste

material. Kinetic tests give more detailed information on behaviour based on the determination of mineral

reaction rates under specified conditions. A European Standard, EN 15875, has been established for the

static testing, while this Technical Report gives guidance on how the kinetic testing may be performed and

interpreted.

Kinetic testing has been required as part of permit processes for many new and operating mine sites. Many

different test methods have been used over the last 20 to 30 years. These tests are commonly designed to

avoid that the oxidation rate is limited due to the lack of oxygen or build-up of secondary minerals. Kinetic

tests based on current standards and laboratory-scale standard practise (ASTM D5744 - 96:2001 and

ASTM D5744 - 07:2007; Morin and Hutt, 1997; Lapakko, 2003) are not designed to evaluate short- and long-

term drainage water quality. However, adjustments to the standard protocols can be done to produce

indicative information about short-term drainage water quality. Together with modelling, this information can

be used to predict/estimate long-term drainage water quality.

This Technical Report is a guidance document that discusses the main kinetic test methods that are used

within the mining sector internationally, the applicability of the different tests and how to evaluate the results.

Kinetic test results may provide valuable information, but it is important to understand their limitations. Sulfide

oxidation in the field is controlled by many different factors that may be difficult to simulate within the

laboratory. Some of these factors may in fact be unknown at the time of testing. The complexity of applying

test results to field conditions may to some extent be balanced by long experience in evaluating such data.

The objective of this Technical Report is to support the management of waste from extractive industries by

giving guidance on how to characterize the kinetically controlled process of acid drainage generation.

The target audience of the document includes all stakeholders concerned with the management of extractive

waste including the extractive industry, authorities, regulators, consultants, and testing laboratories.

Document structure

This Technical Report is organized to provide the answers to the three main questions below.

What type of data will After introducing the concepts of kinetic testing for assessing acid generation

kinetic testing provide potential of sulfidic waste, this clause (Clause 2) describes what type of

and what methods are information these tests provide. This clause also reviews the different tests

available? methods and the ability to meet the objectives set out for the different kinetic

tests. Methods to evaluate both acid generating reactions and neutralizing
Clause 2 Methods reactions are described.

How can the data be This clause (Clause 3) gives guidance on how results from kinetic tests can be

interpreted? applied. Included in this clause is guidance on how results from the tests may be

used to calculate the bulk oxidation rate for the material; to evaluate the leaching

rates for elements within the test system; and based on the results, to evaluate
Clause 3 Interpretation

and evaluation mineral reactions in the system. Kinetic test relevance for describing field scale

processes is discussed.
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What method to select? The clause ends with recommendations on the selection of kinetic test design

depending on objective(s).
Clause 4
Recommendations
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1 Scope

This Technical Report describes the performance and evaluation of kinetic tests for sulfidic waste material

that, according to previous testing (primarily acid base accounting), is likely to go acidic or when the result of

such testing is inconclusive. This Technical Report also covers the issue of drainage from sulfidic material that

is likely to be well buffered but that will produce a neutral drainage potentially affected by sulfide mineral

oxidation.

This Technical Report will not include aspects of sampling and testing that are already covered in the overall

guidance document for characterisation of extractive waste (CEN/TR 16376) or in the guidance document on

sampling of wastes from extractive industries (CEN/TR 16365).
2 Methods
2.1 General

It is necessary to have a good understanding of the waste material before kinetic (mineral reaction rate)

testing is performed. This together with well-defined objectives will aid in selecting the methods. This clause

describes the planning of kinetic testing, key elements to analyse for, and the main methods used by the

industry.
2.2 Planning

Figure 1 shows a flow chart of the different steps to consider when planning for kinetic testing. A number of

the steps in the flow chart are not further discussed in this document. More details on topics related to

sampling are found in CEN/TR 16365, e.g. supporting information, data quality, documentation and reporting

are discussed in overall guidance document (CEN/TR 16376). Additional information that puts kinetic testing

in a wider context may also be found in the overall guidance document.
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Figure 1 — General outline of the steps involved when performing kinetic testing for assessing

acid/neutral generation potential of sulfidic waste from extractive industries

The only kinetic test method that has been standardized is the so-called humidity cell test (HCT)

(ASTM D5744 - 96:2001, ASTM D5744 - 07:2007 and ASTM D5744-12; Sobek et al, 1978). This method has

been used extensively in the mining sector. The method is designed to evaluate long-term acid generation

potential and not to predict long term mineral reactions and mineral leaching in the actual tailings

management facility (TMF) or waste rock dump, as pointed out by Sobek et al (1978) and re-emphasized by

Lapakko et al (2003) and EIPPCB (2004).

Kinetic tests can be designed as small laboratory tests or large-scale field tests. During the exploration phase

only smaller amounts of material are available and humidity cell test are the most common kinetic test used.

The interpretation of the humidity cell test may help in defining feasible waste management options.

Most of the laboratory tests are run with relatively small amounts of crushed material (a few hundred grams to

a few kilograms) with an optimal amount of oxygen available. The amount of rinse solution used is intended to

be high enough to ensure removal of all reaction products, so that secondary precipitates do not limit

reactions. However, at higher pH (> 4 to 5) iron oxides are likely to precipitate.

If the exploration project proceeds into mining, larger amounts of material will become available for testing.

This may give the opportunity to design and run tests that are larger and/or more suited to site-specific

conditions (column tests, lysimeter tests, field tests, etc.). These tests will give more reliable results for

evaluating the long-term oxidation and leaching rates.
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Kinetic testing may be performed several times through the lifetime of an extractive operation. It is common to

establish field tests with extensive instrumentation at an early stage of operation. These field tests can be

considered kinetic verification tests and will give valuable information for the final planning for closure.

In summary, the main kinetic tests designs used by extractive industries internationally are:

 humidity cell tests;
 column tests;
 lysimeter tests; and
 field tests.

The humidity cell has a standard protocol while the other methods are site specific and not standardized. In

practise, also the humidity cell test that are being run are for or by the extractive industry commonly deviate

from the standard design by introducing more site-specific aspects.

If the humidity cell protocols are followed, the reaction products are to be flushed out at cyclic intervals.

Column experiments can, however, be designed to allow for build-up of secondary minerals by reducing the

water amount for flushing. The column is likely to induce a concentration gradient along the length of the axis

in the flow direction.

There are also other test methods that can be useful for testing certain processes and reaction rates under

given conditions. The listed four most commonly used tests are described in the following sections

complemented by a few additional tests that may be useful for evaluating reaction and leaching rates.

2.3 Testing data

The kinetic testing data to be obtained from the different tests will depend on the defined objective(s). The

primary data commonly include pH, alkalinity, sulfate and weight of the sample. However, when analysing

leachate samples, it is often beneficial for the understanding of the processes within the tested material to do

a multi-element analysis. Kinetic testing requires collecting and analysing many samples over a long period of

time (months to years). Only a few basic parameters are normally analysed on a regular basis. When there is

a significant change in the basic parameters (e.g. pH and sulfate, see below), a full chemical analysis of the

leachate may be performed to better understand the processes taking place and to provide input data for

estimations/evaluations of drainage water quality.
The key parameters will commonly include:
 alkalinity;
 pH;
 sulfate;
 total dissolved solids;
 key metals (copper for copper mines, nickel for nickel mines, etc.); and
 element concentrations (anions and cations) in the leachate.

In order to understand the geochemical processes taking place within the tests columns information may also

be needed on test conditions and on the tested material. Relevant information may include:

 flow rate of air and water;
 oxygen / carbon dioxide (during the test run, under sealed conditions);
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 temperature (during the test run);
 mineralogy/speciation (before and after testing);
 speciation/element availability (before and after testing) and;
 grain size or surface area evaluation (before testing).

The data is commonly plotted in time versus concentration or accumulated concentrations (Figure 2). These

types of plots help in understanding the processes taking place within the testing material, under the given

conditions of the tests.
SO4
Time
Figure 2 — Time versus pH and cumulative concentrations of iron and sulfate
2.4 Humidity cell test

In the late 1960s, kinetic tests were defined to evaluate and predict acid drainage from coal wastes

(Caruccio, 1968), then called humidity cell tests. However, the method that has been most commonly used is

the method designed by Sobek et al (1978) called simulated weathering cells, also referred to as humidity cell

tests. This test setup has been modified to be more applicable for waste rock material and larger samples.

The original method used 200 g material crushed to less than 2 mm placed in a “shoe box” container; while

the later setup (ASTM D5744 - 96, 1996 and 2001, and ASTM D5744 - 07:2007) suggests using a 1 kg to 2 kg

sample crushed to less than 6,5 mm grain size in a column rather than a shoe box.

The humidity cell test is designed to:
 determine if the material can go acidic or not; and
 assess the rate of oxidation under laboratory conditions.

The tests are commonly performed using 2 kg to 5 kg crushed material (< 6 mm). The material is placed in a

column with a lid. Air is pumped through the column. The original procedure specifies alternating dry air-humid

air, three days each while Price (2009) and EPA method 1627 (2009) recommends using only humid air.

EPA method 1627 also recommends adding 10 % CO to the humid air. Once a week, the sample is rinsed

with a specific volume of water and drained. The collected water is measured and analysed for parameters as

listed above (2.3). The tests are commonly run for at least 20 weeks, but in many cases up to a year or more.

The size of the columns may vary depending on the type of material used. Figure 3 shows a typical column

test setup based on the concepts of the humidity cell test (ASTM D5744 - 96:2001 and

ASTM D5744 - 07:2007; Price, 2009).
Accumalation
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peristaltic pump
air vent
air vent
water supply
irrigation system
irrigation system
sample
perforated support
and �ltermat
plastic tube
air pump
air bubbles

Figure 3 — Illustration of a common setup for humidity cell test for waste rocks and coarser tailings

material (from Walder and Schuster, 2003) based on a standard method (ASTM, 2001, 2007). Column is

commonly 10 cm to 20 cm in diameter and 20 cm to 40 cm high

The column tests with air flowing through and water rinsing through the material to leach the secondary

products once a week for analysis, are not suited for finer grained material with low hydraulic conductivity (see

Clause 3 for further discussion on this issue).
2.5 Other column tests

Column tests, other than the humidity cell test, are designed for site-specific use and are, therefore, not

standardized. They can simulate a natural system to a much greater extent than any of the other laboratory

scale kinetic test methods. The columns can be set up so that a solution, either recirculation or primary, flows

through a column of crushed rock or milled material. The material can be fully or partially submerged. The flow

rate of the solution can be adjusted.
Site-specific conditions included in the test design may be e.g. (Figure 4):

 Tailings may be deposited under water and, therefore, a column with submerged material may give

valuable information. Water current may be introduced in the column to simulate natural conditions

(prSN/TR 9432). Data from columns where waste material is sub-merged in water may be evaluated in

combination with data from standard humidity cell tests.

 Covers considered as a closure option may be tested in a column with fresh material or material that has

reached a steady state release rate, however, this requires full control of oxygen transport (sealed

columns) in order to avoid misleading data to be generated.
air flow
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peristaltic pump
air vent
Air vent
air vent
water supply
water
cover test
table
water-table
control
sampling
points
sampling
points
plastic tube
air pump
air bubbles

Figure 4 — Illustration of a selection designs for column test for waste rocks/tailings material. The

column dimensions are site specific. The right column is a control and the other three are showing

different management scenarios. The control of the water level can be set up in different ways

depending on the objective of the investigation

Water monitoring, sampling, and analysis within the column should be designed for the specific needs of the

site/objectives of the tests. These may be:
 water samples at different depth;
 humidity measurements under a cover;
 dissolved oxygen measurements in the submerged tailings; or
 O / CO measurements below the cover.
2 2
2.6 Lysimeter

The lysimeter test is an important bridge between laboratory scale tests and large scale field tests. A lysimeter

is a device for collecting water from the pore spaces of soils for determining the soluble constituents removed

in the drainage (EIPPCB, 2004) and to evaluate flow and infiltration rates. It may be a stand-alone test system

or combined with other tests and analysis.

Lysimeters are normally used for soil research, but can be used for other permeable material, such as mine

waste material. There is no standardized practice or design. Usually, mining waste lysimeters have a large

diameter compared to the height, and are more voluminous than columns (may be several meters in diameter

and height). They are normally used outdoors. Lysimeters are able to simulate field conditions scaled up from

the laboratory experiments. The main drawback is long test duration. To capture matrix-macro flow issues

within waste rock dumps Smith and Beckie (2003) recommend having lysimeter sizes of at least 4 m x 4 m.

2.7 Field test
2.7.1 General

The main purpose of field tests is to scale up laboratory tests to better reflect site climatic conditions and

actual particle size distributions. Field tests may also be used to evaluate mitigation options, such as mixing of

different waste materials or the performance of different cover designs, or to perform in-field leach tests.

air �ow
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At existing mines, field tests may be the most applicable test method to use for prediction of acid generation

and metal leaching, while the possibility for field tests is limited during exploration. Field tests include:

 rainfall simulation leach tests performed in the field;
 pilot scale tests set under field conditions in a controlled environment;
 collection of seeps from confined waste material; and
 waste dump design with instrumentation.
Rainfall simulation tests and large-scale column/dump tests ar
...

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