Assignment for Part I: HSC

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1 Thermodynamic and process modelling in metallurgy and mineral processing S 17 May 2017 Assignment for Part I: HSC In order to pass the first part of the course, students are required to make a simulation assignment and write a report based on their work according to the instructions given in this document. Goal of the assignment After making this assignment students know how to use computational thermodynamics (CTD) software as a part of research and development in the context of metallurgical and mineral processes. Some general issues concerning the assignment The assignment consists of six tasks all of which must be done. Different modules of the HSC software are needed to complete different tasks. During the course, there are 12 lectures during which the simulations required in different tasks could be made. In 2017, these lectures are on Mondays from 10 to 12 and on Tuesdays from 12 to 14 on weeks with an exception of week 41 during which there are no lectures. During these lectures it is also possible to practice the use of different modules with additional exercises that can also be found from the course www-site: During the lectures it also possible to ask instructions concerning the assignment as well as the additional exercises. University of Oulu Oulun yliopisto P.O.Box 8000 FI University of Oulu oulu.fi T fax If all the tasks are not finished by the end of week 42, you should contact Eetu-Pekka Heikkinen and ask where and when HSC software can be used outside of the lecture times. If you have a lisence for the HSC software, you are of course free to use the software on your own time whenever needed, although also in this case you should be aware of the deadline for the report (cf. last chapter of this document). 1 / 7

2 Target of the simulation The purpose of the simulation assignment is to study the roasting process of the concentrate consisting of zinc and iron sulphides taking place in the temperature range of C. During this process zinc and iron sulphides react into corresponding oxides. This kind of oxidating roasting process is often used as a pretreatment for the hydrometallurgical production of certain metals; e.g. the Boliden Kokkola zinc plant has an oxidizing roasting process for the zinc sulphide concentrate preceding its leaching. The purpose of the oxidazing roasting process is to get the material into a form that can be more easily leached in the following process steps (e.g. zinc oxide is more easily leached into sulphuric acid than zinc sulphide). Task 1 The goal of the first task is to familiarize oneself with the database of the HSC software. Use HSC software database to find out what kind of compounds iron and zinc can form with oxygen and sulphur. Which of these compounds are relevant in this study? Familiarize yourself with the notations used in the HSC database: e.g. how solid, liquid and gas components are denoted in the database? Describe what kind of thermodynamic data can be found from the database using one compound as an example. Task 2 The goal of the second task is to learn how to study individual chemical reactions using the HSC software. Write down all the possible reactions in which zinc sulphide or iron sulphide reacts with oxygen to form a corresponding oxide as well as sulphur dioxide. Check if zinc and/or iron can exist in various oxidation states. Use Reaction Equations -module of the HSC software to estimate the spontaneity of these reactions at 900 C. Furthermore, use the same module to estimate whether these reactions are endothermic or exothermic at the same temperature. Finally, use H, S, Cp and G Diagrams -module to draw a diagram which can be used to compare the stabilities of different oxides and sulphides of zinc and iron in the temperature range of C. Task 3 The goal of the third task is to learn how to draw Ellingham diagrams (i.e. free energy diagrams) using thermodynamic data from the HSC database. First, use H, S, Cp and G Diagrams -module to draw two separate Ellingham diagrams: one for oxides (of iron, zinc and sulphur) and other 2 / 7

3 one for sulphides (of iron and zinc). Take into account all the possible oxides and sulphides of zinc and iron. Creating Ellingham diagrams with the HSC software is relatively easy and fast as long as the considered compounds can be assumed to be pure, invariant phases and as long as there is no need for the scales showing the partial pressures of the gas components. In order to draw an Ellingham diagram with scales for partial pressures and/or for compounds with varying activities it is necessary to transport required thermodynamic data to some other software (e.g. MS-Excel) which can then be used to create the diagrams. Choose one reaction that you have considered (i.e. formation of certain sulphide or oxide) and use either Reaction Equations - or H, S, Cp and G Diagrams -module to calculate the values of Gibbs free energy of formation for this reaction as a function of temperature (e.g. from 800 C to 1000 C). Copy and paste this data to the Excel worksheet and use Excel to create an Ellingham diagram in which the values of the Gibbs free energy of formation are shown for the reactions in which either element (i.e. either zinc or iron) or the compound (i.e. oxide or sulphide) has an activity differing from one (e.g. 0.1 or 0.01). Additionally, complete the diagram with lines representing the conditions in which partial pressure of either oxygen (O 2 ) or sulphur (S 2 ) - depending on the reaction you are considering - has certain constant values of your choice (e.g. 1, 0.1, 10-2, 10-3, 10-4 atm, etc.). To calculate the values of Gibbs free energy corresponding certain constant values of partial pressure, keep in mind that the y-axis of the Ellingham diagram, i.e. the Gibbs free energy for the oxide formation: m Me O g n Me O 2 ( ) m / n 2 / n is as follows: G 0 R R T ln K R T ln 1 po R T ln p 2 O2 in which: 0 G R equals the standard Gibbs free energy for the considered reaction, R equals the gas constant, T equals temperature, K equals the equilibrium constant for the considered reaction and po 2 equals the partial pressure of oxygen. If you have chosen to consider sulphide formation, corresponding equation can be written for the dependency of partial pressure of sulphur and Gibbs free energy of formation. 3 / 7

4 To take into account the activities differing from one, use the following equation: R T ln 0 po GR n R T ln a 2 Mem / no2 / n m R T ln a Me in which: R equals the gas constant, T equals temperature, po 2 equals the partial pressure of oxygen, 0 G R equals the standard Gibbs free energy for the considered reaction, n equals the stoichiometric coefficient of the oxide (compound) in the formation reaction, a Me m n O 2 / n / equals the activity of oxide (compound), m equals the stoichiometric coefficient of the metal in the formation reaction and a Me equals the activity of metal. Once again, the equation is written for the formation of oxide, but similar equation could be written for sulphide formation, too. Task 4 The goal of the fourth task is to learn how to use the HSC software to draw phase stability diagrams (Kellogg-type diagrams) for three-componentsystems showing the stabilities of different compounds as a function of conditions such as partial pressures of gas components and temperature. Use Lpp Stability Diagrams - and Tpp Stability Diagrams -modules of the HSC software to create phase stability diagrams in which Zn-O-S as well as Fe-O-S systems are considered in the temperature range of C. First, use the Lpp Stability Diagrams -module to create diagrams in which the stabilities of different compounds (metals, oxides, sulphides, sulphates) are shown as a function of partial pressures of oxygen (O 2 ) and sulphur dioxide (SO 2 ) in constant temperature. Several diagrams are needed to show the influence of temperature on the stabilities. You can for example create diagrams for 800, 900 and 1000 C. Secondly, use the Tpp Stability Diagrams -module to create diagrams in which the stabilities of the studied compounds are shown as a function of temperature and partial pressure of either oxygen or sulphur dioxide. In this case the other partial pressure must be considered as constant. Create diagrams with different constant values for the partial pressure. 4 / 7

5 Task 5 The goal of the fifth task is to learn how to simulate reaction systems in which several chemical reactions are occuring and for which the reactions are not necessarily known in advance. Use Equilibrium Compositions -module of the HSC software to study the oxidizing roasting of the sulphide concentrate (i.e. what happens to iron and sulphides when oxygen is added to the system in temperatures corresponding the roasting conditions). Before simulations, it is not known: - whether oxygen reacts first with iron sulphide or zinc sulphide. - what kind of iron and/or zinc containing reaction products are formed (different oxides of zinc and iron, different sulphates of zinc and iron, compounds containing both iron and zinc). - whether sulphur is oxidized into sulphur dioxide or sulphur trioxide. Since the chemical reactions are not known, the simulation cannot be made by considering individual reactions as in task 2. In the Equilibrium Compositions module it is not necessary to know the occuring reactions in advance. However, one has to know/define the initial composition of the considered system, conditions (T, p) of the system, phases that could exist in the system and constituents of each phase. Consider a system consisting of an ideal gas phase (with O 2, SO 2 and SO 3 as constituents) and invariant solid phases (zinc, iron as well as oxides, sulphides, sulphates, etc. of these two elements). The sulphide concentrate consists of 70 wt-% ZnS, 20 wt-% FeS 2 and 10 wt-% FeS, whereas the roasting conditions are 900 C and 1 bar. Use the Equilibrium Compositions module to simulate how the equilibrium composition changes as oxygen is added to the system. Check also how temperature changes the equilibrium by making the calculations in different temperatures (e.g. 800 C and 1000 C). Use the results of the simulations to answer the following questions: - how much zinc oxide can be produced from one tonne (1000kg) of sulphide concentrate? - how much oxygen must be used for each tonne (1000kg) of sulphide concentrate in order to produce this amount of zinc oxide? - what according to the equilibrium calculations happens if excess oxygen is added to the system? Consider, whether this could also happen in the real roasting process. 5 / 7

6 Task 6 The goal of the last task is to learn how to consider mass and energy balances for given systems with HSC software. Use Heat & Material Balance module of the HSC software to study the heat balance of the roasting process considered in task 5. Consider a system in which maximum amount of zinc oxide is produced from one tonne (1000kg) of sulphide concentrate. Values needed for this task (i.e. input and output materials and their amounts) can be obtained from the previous task. Note that the input values are obtained from the system definition/initial values, whereas the output values are obtained from the results of the equilibrium calculations. Be careful with the units (kmol, kg, Nm 3 )! Temperature of the output materials can be considered as 900 C, whereas the input materials can be considered to have a temperature of 25 C. After entering all the phases and constituents and their amounts, check that the element balance is accurate enough. Make all the necessary corrections for the amounts, if the difference between input and output values is too big. After fixing the element balance, use software to estimate whether the roasting process is endothermic or exothermic. How much heat is needed/released? What would be the final temperature of the products if heat balance were fixed to zero? How the situation would change if the input materials were preheated before the roasting process? Are these values realistic? What is different in the real process in comparison to the simulations? Report based on the simulations Save all your results (values, tables, figures, etc.) as well as other information needed for the report (initial values, assumptions, etc.) while doing the tasks. Using this information write a report that contains following parts: - Introduction, in which the goals of this assignment are presented briefly together with a short description of what the report contains. Suitable length is approximately 1 page. - Descriptions of six tasks as separate chapters. Each chapter should contain goal of the task, description of what has been done (using which modules), used initial values, the most important results and a short discussion in which results are considered briefly. Please note that the purpose of this report is not to be a manual for the software (i.e. you can safely assume that the reader of the report knows already how to use the software), but to provide all the necessary information for the reader to make the simulations himself. Suitable length of each chapter depends on how many figures and tables are included, but 1-5 pages for each task could be used as a rough guideline. 6 / 7

7 - Conclusions/Summary, in which the the assignment and its results are described (very briefly!). It is also possible to describe briefly what have been learned during the assignment and how the assignment could be improved in the future. Suitable length is 1-2 pages. Report is graded from 0 (= failed ) to 5. In addition to checking whether the results are correct or not, coverage, profundity and clarity of presentation are also taken into account in the grading. The assigment and the report can be done alone or as a pair-work. If done in pairs, both students will get the same grade for the assigment. The report may be written in either English, Finnish or Swedish and it should be delivered to Eetu-Pekka Heikkinen (either as a paper copy to the lectures, to his room TF214 or to his mailbox in PR202-2 or as a pdf-file via to eetu.heikkinen@oulu.fi). Deadline for the report is two weeks after the last lecture of the first part, i.e. the 31 st October / 7

Exercises for Part I: HSC

Thermodynamic and process modelling in metallurgy and mineral processing 477415S 17 August 2018 Exercises for Part I: HSC This document contains exercises for different modules of the HSC software. It