Browsing by Author "Dahl, Olli, Prof., Aalto University, Department of Bioproducts and Biosystems, Finland"

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    Advancing Sustainability in Mining - Studies on managerial perspective on strategic environmental management
    (Aalto University, 2022) Ruokonen, Eeva; Dahl, Olli, Prof., Aalto University, Department of Bioproducts and Biosystems, Finland; Biotuotteiden ja biotekniikan laitos; Department of Bioproducts and Biosystems; Kemian tekniikan korkeakoulu; School of Chemical Technology; Dahl, Olli, Prof., Aalto University, Department of Bioproducts and Biosystems, Finland
        Demand for metals and minerals is boosted by global population growth, rising living standards, urbanization and energy transition. Society is increasingly committed to mitigating climate change with carbon reduction measures, and therefore the energy transition to low-carbon technology is the main driver for the current elevated demand for metals. In order to achieve the climate goal of a low-carbon society, our society is moving towards mineral-intensive production of energy. Together with stakeholders' rising environmental expectations regarding sustainably produced metals and minerals, this provides opportunities for those mining companies that can meet these expectations. Therefore it is justified to argue that mining companies can benefit from a strategic approach to their environmental management practices. Moreover, the Finnish State has set the national target of becoming a leader in the sustainable extractive industry, which places even greater importance on mining companies' strategic approach to this matter.     This study extends the current understanding on the measures that senior managers at mining companies in the Finnish context employ to manage environmental considerations. The objective is to understand the key aspects of the strategic environmental management of sustainable mining by answering the following three research questions: Which approaches do mining companies take towards strategic environmental management? Which drivers and strategies advance environmental considerations? Which implementation practices do companies adopt to improve environmental performance and how is the use of voluntary sustainability initiatives perceived?     Based on the findings, mining companies are clearly committed to improving their environmental and social performance, and work to gain stakeholder approval and acceptance. For mining companies, the most important external drivers are environmental legislation and societal expectations, and management expects to gain "a social license to operate" with an emphasis on minimizing emissions. Voluntary sustainability initiatives provide leading practices for improved environmental performance when the mining companies invest in their implementation and incorporate sustainability into their business strategies and practices.     The results also indicate that the maturity of individual companies varies greatly. Some companies demonstrate a strategic approach to their environmental management, maintaining a balance between top management commitments, their implementation and results. For some, there is room to be more proactive in taking ownership of the environmental agenda and setting challenging goals to search for strategic opportunities.     To conclude, there is a positive tailwind for the shift to adopt – to a greater extent – sustainable mining practices. The speed of adoption depends on not only how the companies meet the challenges they are facing, but also how the governmental sector facilitates the change.
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    A Methodology for Systemic Plant Research: An Industrial Case Study Investigating the Effects of Water Quality on Pentlandite Flotation Recovery
    (Aalto University, 2024) Musuku, Benjamin; Heiskanen, Kari, Prof. Emer., Aalto University, Minerals Engineering, Finland; Saari, Eija, PhD, Ecosystem & Innovation Lead Metso, Finland; Biotuotteiden ja biotekniikan laitos; Department of Bioproducts and Biosystems; Kemian tekniikan korkeakoulu; School of Chemical Technology; Dahl, Olli, Prof., Aalto University, Department of Bioproducts and Biosystems, Finland
    The dynamicity and complexity of the recycled process water quality present mineral recovery challenges to the mining industry. Concentrator plant operations are usually optimized using an engineering-centric optimization approach. However, the impact of climate change on the recycled process water quality and pulp chemistry is overlooked. The Kevitsa concentrator plant has shown a cyclic nickel recovery pattern that coincides with the summer seasons. This thesis aims to show how process optimization and related methodologies need to evolve from an engineering-centric approach towards systemic thinking to enable the step change toward a more resilient conversion of mineral resources. This study is structured around the case of the Kevitsa concentrator plant's poor pentlandite recovery during the summer months and is divided into three main parts (a) reviewing the impact of flowsheet modifications and equipment installation, and showing the limitation of the engineering-centric approach, (b) studying the impact of process water quality on electrochemical reactivity of sulphide ore using artificially generated process water from D-loop protocol, and highlighting the gap between laboratory-based studies and plant-based studies, and (c) defining and applying the methods, techniques, and protocols for systemic plant based research on Kevitsa concentrator plant. This study demonstrates the inadequacy of the widely adopted engineering-centric optimization approach. Flowsheet reconfiguration and equipment installation alone are not sufficient to address process water quality effects on valuable mineral recovery. Systemic optimization approach is needed to encompass the effects of climate change on process water quality. The laboratory study has shown that the electrochemistry of the pulp strongly depends on the quality of the recycled process water and the residence time of the ore in the process. Such laboratory studies are not representative enough to mimic real process plant conditions, and as a result, are not able to predict water properties that arise due to process water connecting with the hydrological and climatic setting of the tailing storage facility (TSF). Protocols containing analytical and measurement methods to study the electrochemistry of pulp in the context of an operating concentrator plant are defined in this study. Such protocols allow for a systemic investigation at a plant scale and help to relate the dynamic water property matrix to changes in the mineral surface reactivity and further to plant recovery values. The study has shown that the cyclic variation in ore reactivity is driven by seasonal changes in the physicochemistry of recycled process water which consequently influences the extent of ore oxidation during milling and mineral surface passivation during flotation, resulting in a 20% loss in nickel recovery. The study shows that the process water recycled through the TSF differs significantly from the process waters within the flotation circuits. The knowledge acquired from this dissertation presents protocols and methods that can be used to carry out plant-based studies in optimising the process.
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    A new manufacturing process for microcrystalline cellulose (MCC)
    (Aalto University, 2017) Vanhatalo, Kari; Dahl, Olli, Prof., Aalto University, Department of Bioproducts and Biosystems, Finland; Biotuotteiden ja biotekniikan laitos; Department of Bioproducts and Biosystems; Clean Technologies; Kemian tekniikan korkeakoulu; School of Chemical Technology; Dahl, Olli, Prof., Aalto University, Department of Bioproducts and Biosystems, Finland
    Microcrystalline cellulose (MCC) is a cellulose-based, powder-like product invented in the 1950s. Today, it is mostly used in medical and food industry applications. The first processing plant with the annual capacity of 6,800 tonnes was built in 1962 in the United States, in the city of Newark, Delaware. Currently, 120,000 tonnes of MCC is produced globally each year, a relatively small number in comparison with chemical pulps, whose production totals around 135,820,000 tonnes. Most of the studies on MCC are focused on the final product itself rather than the production method. This study provides comprehensive scientific examination of the new production method for MCC, including its technological, economic and environmental aspects. The aim was to find a solution for the industrial scale manufacture of MCC while having low production costs that enable significant increase in product capacity and reducing the price of the final product, at the same time discovering new use targets and applications. Carrying out the integration of the process of manufacturing MCC in a chemical pulp mill was the starting point for this work. The raw material used in the laboratory tests was sulphate-based softwood pulp, including both bleached and unbleached variety. Test conditions were selected to enable upscaling the process to a pulp mill. In addition, a new MCC product (MCC with lignin concentration) was developed and the suitability of MCC as raw material for microfibrillated cellulose (MFC) was tested in this study. The results indicate that MCC can be manufactured in conditions that can be realised in an industrial scale process integrated in a pulp mill. Changing the reaction conditions allows manufacturing different qualities of product and by using unbleached chemical pulp as raw material enables to produce totally new products, MCC with lignin concentration. MCC was found to be a suitable raw material in the manufacture of MFC. The results also indicated that the implementation of a stand-alone type plant unit and a MCC plant integrated in a pulp mill is technically possible and also profitable. However, when integrated into a pulp mill, the MCC process was found to be even more profitable, as the mill provides an energy self-sufficient platform that already includes certain equipment, thus reducing investment costs. When examining the new production method from an environmental perspective, it was pointed out that the burden caused by the new method is less severe to the environment than the currently existing methods when using the GWP (global warming potential) as the impact class. Other impact classes were not examined in detail. As a continuation of this study, further research should focus on testing industrial scale process equipment and developing new final product applications requiring large capacity.
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    Studies on phenomena involved in impregnation of industrial wood chips
    (Aalto University, 2024) Määttänen, Marjo; Tikka, Panu, Prof., Finland; Biotuotteiden ja biotekniikan laitos; Department of Bioproducts and Biosystems; Kemian tekniikan korkeakoulu; School of Chemical Technology; Dahl, Olli, Prof., Aalto University, Department of Bioproducts and Biosystems, Finland
    In chemical pulping, cooking chemicals are used to dissolve lignin in wood to release the fibres from the wood tissue. Chemicals must be present in the parts of the wood tissue where delignification takes place before the cooking temperature is reached, as otherwise the quality of the pulp will suffer. The transport of the cooking chemicals takes place by two mechanisms. Penetration fills the fibre cavities with liquid under a pressure gradient enabling faster diffusion of the chemicals into the wood. Diffusion refers to the movement of ions through a liquid from a higher concentration to a lower concentration. Although both mechanisms occur in parallel, their separate and combined influences on impregnation have been seldom studied in the same research. The objectives of this thesis were to clarify and deepen the understanding of the impregnation of industrial chips and the phenomena occurring in the course of impregnation. Therefore, a new experimental method was developed. The experiments were divided into penetration and impregnation experiments. The data collected from the experiments were combined for calculating corrected penetration degree values and the mass and alkali balance involved in impregnation. Based on the data, quantitative results and deeper understanding for impregnation were achieved. The research work confirmed the three defined hypothesis dealing with the influence of the physical properties of industrial chips and the processing conditions on impregnation and the influence of the chemical diffusion and the dissolution of wood on the degree of penetration. Practical outcomes and guidelines for the impregnation of the industrial wood chips were the following. The moisture content and the basic density of wood chips determine the initial penetration degree (PDi) of wood chips: a low basic wood density and a low moisture content result in higher amounts of air inside the wood, which means a lower initial penetration degree of the wood. The lower PDi hinders the whole impregnation process. Therefore, it is recommended to use pre-steaming as a common practice and more emphasis must put on the use of fresh/moist wood chips.The prerequisites for fast diffusion are a high degree of penetration and a high concentration gradient between impregnation liquor and the alkali inside wood chips. On a laboratory scale, for high-concentration liquor, 15 minutes of impregnation time is sufficient for an adequate alkali charge for kraft cooking, but in the case of low-concentration liquor, even 60 minutes is insufficient. Part of the impregnated alkali is consumed during the impregnation, and more at higher temperature. Therefore, there is risk of running out of alkali if the temperature is raised quickly to the cooking temperature after low alkali impregnation. For successful impregnation, proper pre-steaming, a low impregnation temperature and moderate alkali concentration should be used for all wood species.
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    Understanding the effect of metastable sulphoxy compounds on the flotation of sulphide ores
    (Aalto University, 2021) Mhonde, Ngoni Pepukai; Schreithofer, Nora, Dr., Aalto University, Finland; Corin, Kirsten, Assoc. Prof., University of Cape Town, South Africa; Heiskanen, Kari, Prof., Aalto University, Finland; Biotuotteiden ja biotekniikan laitos; Department of Bioproducts and Biosystems; Clean Technologies; Kemian tekniikan korkeakoulu; School of Chemical Technology; Dahl, Olli, Prof., Aalto University, Department of Bioproducts and Biosystems, Finland
    As restrictions on water usage become more prevalent, the practice of water recycling on mineral processing operations is considered best practice. Recycled water in flotation operations is thermodynamically unstable and carries various sulphoxy species that may have a positive or adverse effect on flotation separation. This study intricately focuses on two sulphoxy species, namely tetrathionate and dithionite ions, investigating the interaction of these species with sulphide mineral surfaces and reagents used in the beneficiation of sulphides ores. The effect of microbes present in solutions laden with these sulphoxy species from an electrochemical interactions viewpoint is also investigated. Fundamental studies (microflotation, electrochemistry, zeta potential, FTIR and XPS) and batch flotation were used to study the response of galena, chalcopyrite and pyrite to sulphoxy species and microbes in plant water. The flotation studies showed that metastable sulphoxy compounds reduced the flotation recovery of sulphide minerals. However, chalcopyrite depression only occurred at high sulphoxy species concentrations (ca. 2000ppm). The poor flotation performance of sulphide minerals was attributed to mineral oxidation and passivation by the sulphoxy species as confirmed by X-ray photoelectron spectroscopy studies. Electrochemical rest potential measurements showed that the interaction of thiol collectors and the sulphide mineral surface decreased in the presence of sulphoxy species. This was corroborated by Fourier Transform Infrared Technology measurements where the intensity of xanthate spectra peaks on minerals conditioned in sulphoxy species and xanthate solutions were low in comparison to xanthate peaks on minerals conditioned in the absence of sulphoxy compounds. The solution interaction of xanthate with tetrathionates and dithionites was also considered as a source of poor flotation performance. The degradation of xanthate by tetrathionate ions was not affected by the type of conditioning gas or pH. Xanthate degradation occurred in solution following first-order degradation kinetics with respect to xanthate concentration. The degradation of xanthate by dithionite ions was affected by the type of conditioning gas and it was faster at neutral pH. A mixed microbial community in plant water passivated sulphide mineral surfaces rendering the minerals hydrophilic. Rest potential measurements showed that the interaction between collectors and the minerals decreases in the event that microbes are attached to the mineral surface first before collector addition. The results from the thesis are pertinent to mineral processing professionals. It is evident that critical water quality considerations must be made when altering/controlling the water circuits in new or existing flotation plants. An understanding of the ore tolerance to water quality may aid in ensuring that flotation water recycle configurations do not negatively impact flotation performance.