=Paper=
{{Paper
|id=Vol-1815/paper27
|storemode=property
|title=Knowledge Modelling and Comparison of Cyanide-free Gold Leaching Processes – Research Summary
|pdfUrl=https://ceur-ws.org/Vol-1815/paper27.pdf
|volume=Vol-1815
|authors=Maria Leikola
|dblpUrl=https://dblp.org/rec/conf/iccbr/Leikola16
}}
==Knowledge Modelling and Comparison of Cyanide-free Gold Leaching Processes – Research Summary==
https://ceur-ws.org/Vol-1815/paper27.pdf
262
Knowledge Modelling and Comparison of Cyanide-free
Gold Leaching Processes – Research Summary
Maria Leikola
School of Chemical Technology, Aalto University, Helsinki, Finland
maria.leikola@aalto.fi
Abstract. There is increasing pressure from authorities in many countries to find
cyanide-free methods for gold processing due to environmental and safety risks.
Therefore, it is now under investigation whether the knowledge extraction and
formalization procedure can be applied for comparing cyanide-free leaching
methods for a certain type of raw material. Research is needed to determine and
code the similarity models related to cyanide-free processes. The task is chal-
lenging, since most of the processes are still in the development phase and there
is not much information available on the new-coming processes.
Keywords: Case-based reasoning, Gold leaching, Cyanide-free
1 Introduction
At the moment, primary gold production is based on cyanide leaching of gold ores [4].
Cyanide has been the sole industrially utilized gold leaching method for decades, but
due to health and environmental risks, great legislative pressure is building up for
searching optional leaching methods. Currently there are several cyanide-free extrac-
tion processes under development for gold ores and concentrates, such as the ones based
on chloride [3], bromine-bromide [4], and glycine [5]. Only one cyanide-free gold
leaching method, thiosulfate, is in industrial use [2].
The author is conducting doctoral studies in Aalto University, Finland with the aim
to develop a tool for comparing cyanide-free gold leaching methods. The tool will
uti-lize case-based reasoning (CBR), which uses fuzzy logic to compare real life cases
with the user’s input material [1]. A CBR tool already exists for comparing
established, in-dustrial process chains [6]. In that project, CBR was selected as the
decision method, because it enables the comparison of cases with several different
variables and exact matches are not needed as it merely compares the similarity of
previous cases with the new case in question [7]. However, the research topic of this
doctorate is very different due to the early stage of development in the field of
cyanide-free gold processing. The case base will be composed of laboratory
experiments instead of whole industrial pro-cesses. Where Rintala et al. [6, 7]
developed a CBR tool for selecting whole process chains for gold processing, from
ore to final product, this project aims for a tool comparing an individual treatment
Copyright © 2016 for this paper by its authors. Copying permitted for private and
aca-demic purposes. In Proceedings of the ICCBR 2016 Workshops. Atlanta,
Georgia, United States of America
263
i.e. gold leaching stage. The preliminary title of the doc-toral thesis is “Knowledge
modelling and comparison of cyanide-free gold leaching processes”.
In addition to the CBR tool, new hydrometallurgical research will be made in the
field of cyanide-free gold leaching. When possible, this new information will be incor-
porated into the CBR tool, either as additional cases or as a basis for constructing sim-
ilarity models.
2 Research tasks
The tasks of the research project are divided into two categories; implementation of the
process selection tool (T1) and evaluation and development of existing cyanide-
free leaching methods (T2).
2.1 Task 1
The first task is divided into four sub-tasks. First, the amount and quality of the relevant
and available information needs to be mapped (T1.1). Then a simple prototype tool
is developed for general use (T1.2) and a user interface will be constructed (T1.3).
After the construction of the prototype tool, a more complex tool will be
implemented for professional use (T1.4).
2.2 Task 2
Task 2 is also divided into four sub-tasks. First, the most promising cyanide-free gold
leaching methods are determined for further inspection (T2.1). Simultaneously, an ex-
tensive literary research is conducted to support both T2.1 and the construction of the
CBR based tool (T2.2). Then the functionality of selected leaching processes is exper-
imentally verified (T2.3). Challenges detected during the experiments are taken under
closer inspection and attempts will be made to discover solutions to these
processing difficulties (T2.4).
2.3 Research period abroad
A half-year research period is being arranged to the research group of Professor
Thomas Roth-Berghofer in the University of West London (UWL). Their group has
extensive knowledge on CBR applications and this collaboration will greatly benefit
both univer-sities.
2.4 Schedule
The schedule for the research work that will be carried out are presented in Table 1.
The doctoral dissertation will be composed simultaneously with the research work
over the three-year-project.
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Table 1. Schedule for the research tasks.
Objective 2016 2017 2018
T1 Implementation and development of cyanide-free process selection tools
T1.1 Information qualification
T1.2 Prototype tool
T1.3 User interface
T1.4 Tool for professional use
Process evaluation and experimental research
T2.1 Process selection
T2.2 Literature research
T2.3 Experimental research
T2.4 Process development
2.5 Progress so far
This project began in February 2016, when the author started as a doctoral candidate in
the research group of Hydrometallurgy and Corrosion in Aalto University. Since then,
a conference paper for ICCBR’16 has been completed and a non-peer-reviewed paper
has also been written for a gold processing conference ALTA2016. Altogether, the pro-
ject has advanced as planned; all tasks scheduled to begin during spring 2016 have been
initiated (T1.1; T1.2; T2.1; T2.2; T2.3).
3 CBR Tool
3.1 Selection of Methodology
Rintala et al. [7] compared three decision support systems (Decision tree, Multi-criteria
decision making, Case-based reasoning) and three optimization methods (Artificial
neural network, Ant colony optimization, Genetic algorithm) for aiding professionals
in designing hydrometallurgical processes. The main reasons for them selecting CBR
as the best option for hydrometallurgical applications were that the exact relations be-
tween parameters aren’t needed and that the system can be used with incomplete input
data. [7] Though this project is different from the one conducted by Rintala et al., it is
similar with regards to the knowledge being fuzzy and the case sources often lacking
information. Therefore, CBR was selected also for this project as the used methodol-
ogy.
3.2 CBR Application
A preliminary knowledge model has already been constructed using the myCBR 3.0 1
open source software and a detailed description of it will be given in the author’s poster
1 http://mycbr-project.net/
265
presentation in ICCBR’16. Naturally, this is just a simple beginning, on which the au-
thor intends to build upon later during this project. In order to illustrate the tool, the
preliminary model is described here in short.
The system utilizes attributes presented in Table 2. The attributes were selected
based on a review article analysis and interviews of hydrometallurgical professionals.
Table 2. Selected attributes for the preliminary knowledge model
Attribute Type of attribute
Method Symbol
Mineral 1 Symbol
Mineral 2 Symbol
Gold content [g/t] Floating point number
Extraction [%] Floating point number
The case base of 24 specimens was compiled from various scientific articles that
presented experimental data on cyanide-free leaching of gold ores. As an example, an
imaginary case is presented in Table 3.
Table 3. An exemplary case
Attribute Value
Method Thiosulfate
Mineral 1 Pyrite
Mineral 2 Hematite
Gold content [g/t] 7.5
Extraction [%] 89.6
Similarity models were developed for each attribute. Only two methods were present
in the cases and therefore the similarity between those values was either 1 or 0. Attrib-
utes of the type Floating point number were given linear distance functions, whereas
the mineralogical attributes Mineral 1 (most abundant in the ore) and Mineral 2 (second
most abundant in the ore) were assigned similarity values based on the types of metallic
and non-metallic chemical elements present in the minerals. The cases were assigned
global similarities from 0.00 to 1.00 based on the combined local similarities.
One possible way for a researcher to utilize the tool is when they are faced with a
gold ore that has not been experimented on with cyanide-free leaching techniques. They
would analyze the material, query its mineralogy and gold content and as a result they
would get the previously conducted experiments on most similar gold ores. This way
they could aquire relevant information about the cyanide-free techniques applicable for
their particular material. Then they could perform experiments on the material, thus
producing a new case for the case base.
At the moment, the solution does not describe the leaching technique in more detail
than just the leaching agent and the acquired result in the form of the Extraction attrib-
ute. As the tool is developed, more process parameters will be added such as tempera-
ture, pressure and solid-liquid ratio.
266
Towards the end of this PhD, an evaluation will be performed in the form of an actual
material that will be queried and laboratory scale test that will be conducted on the basis
of the results given by the CBR tool. Alternatives to CBR have yet to be considered in
this project.
4 Doctoral Thesis
The doctoral dissertation will be a thesis by publication, consisting of a published con-
ference paper and journal articles. At the moment, the scheme for the publications is as
follows:
• Applicability of case-based reasoning for selection of cyanide-free gold leaching
methods
Conference: ICCBR’16, Atlanta Georgia, USA (accepted)
• A case-based reasoning tool for comparing cyanide-free gold leaching processes
• Evaluation of a case-based reasoning tool for comparing cyanide-free gold leaching
processes
• Challenges related to gold ore leaching in chloride solutions – from laboratory scale
to industrial process
5 References
1. Aamodt, A., Plaza, E.: Case-based reasoning: foundational issues, methodological variations,
and system approaches. AI Communications 7(1), 39-59 (1994)
2. Choi, Y., Baron, J.Y., Wang, Q., Langhans, J., Kondos, P.: Thiosulfate Processing – From
Lab Curiosity to Commercial Application. In: Proceedings of the World Gold 2013, pp. 45-
50. The Australian Institute of Mining and Metallurgy, Melbourne, Australia (2013)
3. Lundström, M., Ahtiainen, R., Haakana, T., O’Callaghan, J.: Techno-economical observa-
tions related to Outotec gold chloride processes. In: Proceedings of ALTA 2014 Gold-pre-
cious metals sessions, pp. 89-104. ALTA Metallurgical Services Publications, Melbourne,
Australia (2014)
4. Marsden, J.O., House, C.I.: The Chemistry of Gold Extraction, 2nd edition. Society for Min-
ing, Metallurgy, and Exploration, Colorado, USA (2009)
5. Oraby, E., Eksteen, J.J.: Gold leaching in cyanide-starved copper solutions in the presence of
glycine. Hydrometallurgy 156, 81-88 (2015)
6. Rintala, L.: Development of a process selection method for gold ores using case-based rea-
soning. Aalto University publication series: Doctoral dissertations, Finland (2015)
7. Rintala, L., Lillkung, K., Aromaa, J.: The use of decision and optimization methods in selec-
tion of hydrometallurgical unit process alternatives. Physicochemical Problems on Mineral
Processing 46(1), 229-242 (2011)