Assign_2_2018_flowsheets_min_proc_SOLUTIONS

DEPARTMENT OF MATERIALS ENGINEERING MTRL 358 - Hydrometallurgy I NOTE: Partial or complete copying of another person's work is academic misconduct. See policy on academic misconduct in the syllabus or on the course Vista website. Assignment 2, 2018 - Flowsheets and Mineral Processing SOLUTIONS 1. A simplified flowsheet for the Galvanox process is shown below. This process is being developed at UBC. Chaclcopyrite is the most abundant mineral of copper in nature. However, it resists leaching by conventional hydrometallurgical methods; the mineral rapidly passivates (after a short while it leaches very slowly) when leached in sulfate solution. In this process a copper concentrate is produced which contains pyrite and copper minerals, particularly chalcopyrite. If pyrite (FeS 2 ) is present in the concentrate then chalcopyrite is readily leached. Pyrite, being an iron mineral, often occurs in sulfide mineral deposits. During leaching chalcopyrite is oxidized to form a solution of Cu +2 , Fe +2 and solid elemental sulfur. Pyrite itself undergoes little reaction. (Mainly it seems to act as a catalyst for oxygen reduction.) After leaching the slurry is subjected to solid-liquid separation. The solids may be recycled to leaching to reutilize the pyrite. Much of the solution proceeds to solvent extraction, which is used to obtain a much purer copper solution. The details are not important here. Some of the solution also proceeds to an oxyhydrolysis step (this is done in an autoclave) in which ferrous ion is oxidized to form hematite (Fe 2 O 3 ) and sulfuric acid. This acts as an outlet for iron and prevents its build-up in solution. Hematite is a very suitable iron product for disposal. The solvent extraction process also generates acid, which together with that formed by hematite formation can be reused in the leaching step. The concentrated copper sulfate solution from solvent extraction proceeds to an electrowinning step. Here very pure copper metal is produced by electrolysis. Answer the following questions related to the flowsheet. 1

(a) Write the balanced chemical reaction in ionic and neutral forms for the leaching of chalocopyrite. CuFeS 2 + O 2 = Cu +2 + Fe +2 + S Oxygen is the oxidant, as seen from the flowsheet. The rest is evident from the text. (a) CuFeS 2 = Cu +2 + Fe +2 + S O 2 = ? (b) CuFeS 2 = Cu +2 + Fe +2 + 2S O 2 = ? (c) CuFeS 2 = Cu +2 + Fe +2 + 2S O 2 = + 2H 2 O (d) CuFeS 2 = Cu +2 + Fe +2 + 2S O 2 + 4H + = + 2H 2 O (e) CuFeS 2 = Cu +2 + Fe +2 + 2S + 4e - O 2 + 4H + + 4e - = + 2H 2 O (f) CuFeS 2 = Cu +2 + Fe +2 + 2S + 4e - O 2 + 4H + + 4e - = + 2H 2 O CuFeS 2 O 2 + 4H + = Cu +2 + Fe +2 + 2S + 2H 2 O ionic form Balance + charges with sulfate: CuFeS 2 s + O 2 g + 2H 2 SO 4 aq = CuSO 4 aq + FeSO 4 aq + 2S s + 2H 2 O l neutral form (g) CHECK: Left side Right side 1Cu 1Cu 1Fe 1Fe 4S 4S 10O 10O 4H 4H 0 charge 0 charge OK (b) Referring to the generalized hydrometallurgical flowsheet on p. 30 of the Introduction to Extractive Metallurgy course notes, identify the parts of the flowsheet that correspond to mineral separation, leaching, solution purification and metal production. Use the flowsheet on the page below, circle and label the appropriate parts of the flowsheet. Hand this in with your completed assignment. See flowsheet below (c) Referring to the generalized metallurgical flowsheet that follows, indicate which route corresponds most closely to this process. You may indicate just the number in your assignment paper. See flowsheet below 2

Copy of flowsheet; use this for question 1 (b). 3 Mineral separation - size reduction through to flotation Leaching - mineral dissolution Solution purification - iron is removed from the solution. Solution purification - selective for copper metal production - by electrolysis

Generalized extractive metallurgy flowsheet 1 (c). Route 3 makes the most sense. A concentrate is made and then leached directly. The solution is purified and then metal is precipitated by electrowinning. 4

1 (d). Leaching requires 4 moles of H + /mole of CuFeS 2 . What fraction of the required acid is produced by the oxyhydrolysis step? (Consider the balanced reaction that forms Fe 2 O 3 .) Here a chemical reaction is needed: Fe +2 + O 2 = Fe 2 O 3 (a) Fe +2 = Fe 2 O 3 O 2 = ? (b) 2Fe +2 = Fe 2 O 3 (c) 2Fe +2 + 3H 2 O = Fe 2 O 3 (d) 2Fe +2 + 3H 2 O = Fe 2 O 3 + 6H + (e) 2Fe +2 + 3H 2 O = Fe 2 O 3 + 6H + + 2e - O 2 + 4H + + 4e - = 2H 2 O (f) 2Fe +2 + 3H 2 O = Fe 2 O 3 + 6H + + 2e - 0.5O 2 + 2H + + 2e - = H 2 O 2Fe +2 + 2H 2 O + 0.5O 2 = Fe 2 O 3 + 4H + (Required to estimate stoichiommetric acid formed.) or: Fe +2 + H 2 O + 0.25O 2 = 0.5Fe 2 O 3 + 2H + FeSO 4 + H 2 O + 0.25O 2 = 0.5Fe 2 O 3 + H 2 SO 4 (g) Check Left Right Left Right 1Fe 1Fe 0 Charge 0 Charge 1S 1S 5.5O 5.5O 2H 2H OK This shows that for every one Fe leached then precipitated, 1 mole of H 2 SO 4 is formed = 2 mole H + /mol CuFeS 2 . Hence 50% of the required acid comes from this step . 2. In the zinc Roast-Leach-Electrowin (RLE) process a zinc concentrate is roasted in air to form ZnO. Iron minerals combine with zinc to form zinc ferrite. See the reactions below. ZnS s + 3/2O 2 g = ZnO s + SO 2 g ZnS s + 2FeS 2 s + 7O 2 g = ZnFe 2 O 4 s + 5SO 2 g Zinc ferrite is difficult to leach, whereas ZnO is easily dissolved in diluted acid. Thus high-iron ZnS concentrates are more challenging to treat. A hypothetical sphalerite concentrate contains 48% Zn as sphalerite and 6% Fe as pyrite plus other minerals. What proportion of the total zinc in the calcine will be present as zinc ferrite? 5