Process Modelling of Gravity Induced Stirred Mills 397120/s42997650_phd_the¢  power, feed...

download Process Modelling of Gravity Induced Stirred Mills 397120/s42997650_phd_the¢  power, feed rate, slurry

of 211

  • date post

  • Category


  • view

  • download


Embed Size (px)

Transcript of Process Modelling of Gravity Induced Stirred Mills 397120/s42997650_phd_the¢  power, feed...

  • Process Modelling of Gravity Induced Stirred Mills

    Md Maruf Hasan

    M.Sc. (Minerals and Environmental Engineering)

    B.Sc. (Mechanical Engineering)

    A thesis submitted for the degree of Doctor of Philosophy at

    The University of Queensland in 2016

    Sustainable Minerals Institute

    Julius Kruttschnitt Mineral Research Centre

  • i


    Fine grinding is becoming an integral part of mineral processing plants to liberate valuable minerals

    from fine-grained low-grade ore bodies. Stirred mills are becoming recognized by the industry as a

    more efficient technology selection compared to the ball mill for fine grinding (< 100 µm). The

    increasing number of stirred mill installations in mineral processing concentrators has necessitated a

    process model development that enables full circuit modelling and simulation. Many researchers

    have developed mathematical models to assist in the design and optimization of the stirred mill

    operation including gravity induced stirred mills such as the Metso Vertimill and the Nippon Eirich

    Tower Mill.

    Most of the developed models lack sufficient responses to changes in process conditions.

    Furthermore, there is an internal classification effect that is previously mentioned in several

    publications but was not quantified through experiments. Therefore, a research program was

    designed and carried out to describe and model different sub-processes related to the operation of

    the gravity induced stirred mill. The sub-process models (i.e. grinding and internal classification)

    were combined into a single model structure to represent the operation in a gravity induced stirred


    During this research, comprehensive test work was carried out in a batch gravity induced stirred

    mill using Cu-Au ore and limestone to evaluate the effect of operating conditions (i.e. specific

    energy consumption, slurry density, grinding media size and stirrer tip speed) on particle size and

    fines generation (-75μm). The test data showed a finer product size when the mill operates at higher

    specific energy, lower slurry density, smaller grinding media size and higher stirrer tip speed. The

    test work also identified that attrition breakage mechanism is predominant in the gravity induced

    mill. Sub-process models that relate the selection function to the process operating conditions were

    developed. The internal classification effect on mill operation was also measured through test work

    by using industrial grade silica to identify its effect on the mill operation. The result showed that

    particle classification takes place inside the gravity induced mill in certain favorable conditions.

    Models were developed to link the classification parameters and the mill operating conditions to be

    included in the combined model structure.

  • ii

    A process model (using a time-based population balance technique) was developed, integrating

    individual sub-processes models such as breakage, selection and classification functions. The model

    was validated with industry survey data in different process conditions. The validation result

    showed that the developed model was capable to predict the mill product size distribution when mill

    power, feed rate, slurry solids concentration and grinding media size are varied.

    The thesis has successfully developed a process model of the gravity induced stirred mill with

    predictive capability. Moreover, it has developed an in-depth understanding of the laboratory scale

    gravity induced mill behaviour and its breakage mechanism. The inclusion of the classification with

    the breakage process into a single model structure is novel in comminution process modelling.

  • iii

    Declaration by author

    This thesis is composed of my original work, and contains no material previously published or

    written by another person except where due reference has been made in the text. I have clearly

    stated the contribution by others to jointly-authored works that I have included in my thesis.

    I have clearly stated the contribution of others to my thesis as a whole, including statistical

    assistance, survey design, data analysis, significant technical procedures, professional editorial

    advice, and any other original research work used or reported in my thesis. The content of my thesis

    is the result of work I have carried out since the commencement of my research higher degree

    candidature and does not include a substantial part of work that has been submitted to qualify for

    the award of any other degree or diploma in any university or other tertiary institution. I have

    clearly stated which parts of my thesis, if any, have been submitted to qualify for another award.

    I acknowledge that an electronic copy of my thesis must be lodged with the University Library and,

    subject to the policy and procedures of The University of Queensland, the thesis be made available

    for research and study in accordance with the Copyright Act 1968 unless a period of embargo has

    been approved by the Dean of the Graduate School.

    I acknowledge that copyright of all material contained in my thesis resides with the copyright

    holder(s) of that material. Where appropriate I have obtained copyright permission from the

    copyright holder to reproduce material in this thesis.

  • iv

    Publications during candidature

    Journal publication relevant to this thesis:

    Hasan, M., Palaniandy, S., Hilden, M., Powell., M. 2016. Investigating internal classification

    within gravity induced stirred mills. Minerals Engineering 95: 5-13.

    Conference publication relevant to this thesis:

    Hasan, M., Palaniandy, S., Hilden, M., Powell, M., 2014. The Investigation of Particle

    Classification in Vertical Type Stirred Mill. International Conference of Mineral Processing

    Technology – MPT 2014, Vishakhapatnam, India, p.160.

    Publications included in this thesis

    No publications included

  • v

    Contributions by others to the thesis

    Professor Malcolm Powell, Dr. Sam Palaniandy, and Dr. Marko Hilden were responsible for setting

    up this thesis project and establishing the initial research goal. They provided the initial ideas for

    developing the process model and experimental devices and reviewed the experimental design.

    They also made great contributions to the interpretation of the data.

    Dr. Sam Palaniandy organized the experimental device and helped in analyzing the experimental


    Dr. Sam Palaniandy and Dr. Marko Hilden assisted in developing the thesis structure and critically

    reviewed the draft thesis. Professor Malcolm Powell reviewed the final draft for necessary


    Metso Minerals constructed and supplied the batch vertical stirred mill and the limestone sample for

    the test work.

    Mr. Jonathan Worth, Mr. Michael Kilmartin and Mr. John Wedmaier modified and made necessary

    adjustments and repairs to the experimental devices.

    Naren Vijayakumar and Daniel Mitchell provided the ground Cu-Au (-4.75 mm) sample from their

    pilot SAG mill test work.

    Statement of parts of the thesis submitted to qualify for the award of another degree


  • vi


    Firstly, I thank Allah the Almighty, for giving me the opportunity to commence and complete this

    thesis successfully. This research work is a part of larger project funded by Metso Minerals under

    the name of “Collaborative Research on Stirred Milling Technology”. I am greatly thankful to the

    following persons and institutions for their contributions in accomplishing this thesis.

    o To Julius Kruttschnitt Mineral Research Centre (JKMRC) and The University of

    Queensland (UQ) for offering me the scholarship and provide required support and

    environment to conduct the Ph.D. work. It is an honour to become alumni of both JKMRC

    and UQ, and I will remain proud for the rest of my life for this achievement.

    o To my principle supervisor, Dr Sam Palaniandy for his exceptional support throughout my

    PhD life. He provided me the freedom to conduct this research and guided me through all

    the way towards the end of completing this research work. He always gave me the

    confidence and provided me timely feedback for the thesis I wrote. I am also thankful to him

    for his time and patience towards me.

    o To my associate supervisors Dr Marko Hilden and Professor Malcolm Powell for their

    academic support, guidance and time while conducting the research work. They were also

    very helpful by providing me valuable advice for conducting the test work. The weekly

    meeting with all my academic supervisors was very helpful and made me work hard to

    accomplish the goal.

    o To Metso Minerals for the financial support and opportunity to conduct this thesis work. I

    am also thankful to them for providing me the opportunity to conduct experiments in their

    laboratory in York, Pennsylvania during the initial period of this research work.

    o Profes