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¹Minerals have traditionally required little processing, due to the earlier widespread availability of high-grade ore deposits.

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²However, as metal consumption has increased exponentially, these ore reserves have dramatically decreased, leading to the need for relying increasingly on low-grade ore reserves. ³This has had a direct effect on the volume of mined rock, the ore throughput volume and hence the amount of water needed for processing the ore. (Martikainen 2015; Miranda and Sauer, 2010)

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⁴Most mineral unit processes are highly water intensive, as water is used for transporting ore and tailings, dust suppression, minerals separation, and tailings disposal, as well as to stock the tailings (Kemp et al., 2010; Norgate and Lovel, 2004).

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⁵However, the minerals industry is determined to lower the freshwater intake and discharge of process water to surrounding waterbodies due to numerous global water challenges, including water scarcity and limited access to freshwater bodies. ⁶Furthermore, this would reduce the environmental impact of mineral processing plants and would help in obtaining social license to operate (Liu et al., 2013).

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⁷Over the last decade, better water management has become a key issue in tailings disposal operations, and great technical breakthroughs have been made in the form of paste and thickened tailings technologies (Edraki et al., 2014; Franks et al., 2011).

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⁸However, further studies and technical breakthroughs are required to resolve issues associated with water re-use in unit operations and the effects of water quality on process efficiency.

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⁹One solution to this problem has been presented by Atamaca and Kuymcu (2003), who proposed closed water systems as a new approach for managing the water systems inside mineral operation plants.

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¹⁰Closed water systems could eliminate the fresh water intake and discharge of mineral operation plants. ¹¹In their approach, the only water leaving the mineral operation plant would be in the form of moisture in the products and tailings as well as some evaporation within the plant. ¹²This amount of water needs to be replenished, but the rest could be recycled

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¹³Despite the potential advantages of a closed water system, no research has yet to date focused on implementing this approach.

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¹⁴The aim of this thesis is to assess the feasibility of using a closed water system for mineral unit operations, such as comminution circuits, tailings disposal and flotation.

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¹⁵This closed water system approach will be assessed in terms of the time required for process water circulation, the effects of the system on the performance of mineral unit processes (i.e., flotation processes), stability of the water quality in closed water circuits, and the ability of Outotec’s HSC 9- software to accurately model the parameters of the system.

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¹⁶Another aim is to identify the key performance parameters, such as temperature, water pH, as well as the sulphur, metal and oxygen concentrations, in order to develop a research protocol that would enable further development of this approach in practice.

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¹⁷This thesis has been commissioned by Outotec, a Finnish technology provider that designs and delivers tailored solutions for minerals and metals processing, water treatment, and producing energy from biomass and wastes (Outotec, 2015).

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¹⁸The model will be constructed by using the water and mineral processing modules available in Outotec's HSC 9 software.

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¹⁹The thesis will produce a description of the model requirements supported by series of locked cycle flotation tests performed in the Outotec's Research and Development Center in Pori, Finland.

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²⁰Natural nickel-copper-platinum group elements ore will be used for the experimental work. ²¹The case study ore is provided by the First Quantum Minerals Kevitsa Mine, located in Sodankylä.

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²²The rest of this thesis is organized as follows. ²³Chapter 2 explores the use of water in mineral beneficiation plants and provides an overview of the global water-related trends in the mining and minerals industry. ²⁴Chapter 3 provides a short overview of the theory and plant practices in mineral unit processes. ²⁵Chapter 4 describes current and potential water recirculation methods an. ²⁶Chapter 5 presents the concept of closed water circuits for unit operations in mineral processing. ²⁷Chapter 6 explains the methods and materials used for the experimental locked cycle froth flotation tests, and Chapter 7 introduces Outotec’s HSC 9 software used to model the locked cycle test performed in the experimental work. ²⁸The results of locked cycle froth flotation tests and the model are presented in Chapter 8 and discussed in Chapter 9. ²⁹Finally, Chapter 10 presents the conclusions and recommendations for further study.