21-Mat-B2 Pyrometallurgy, December 2018: worked solutions

Paper format. National Exams, December 2018 — 12-Mtl-B2, Hydrometallurgy and Electrometallurgy. Three hours, closed book, approved Sharp/Casio calculator only. Six numbered Problems, each worth 20 marks: Problems 1 and 2 are compulsory; the rubric asks for any 3 of the remaining 4 (Problems 3-6). All six Problems are answered here, since this set is a study resource rather than an exam script. Given constants: R = 8.314 J/(mol K); F = 96,485 C/g-eq; for all aqueous species, activities are taken equal to concentrations.

Note on the exam title

Nothing on the paper is a pyrometallurgy (roasting, smelting) question — the syllabus actually examined is aqueous flow-sheeting terminology, cyanide-complex electrochemistry (Eh-pH diagram reading), metal-hydroxide speciation/solubility, sulfide precipitation, and electrowinning energetics.

Reference texts. The answers below are keyed to the works normally recommended for this syllabus code:

F. Habashi, A Textbook of Hydrometallurgy, 2nd ed. — leaching, solubility/speciation diagrams, solvent extraction, ion exchange, cementation and precipitation, electrowinning and electrorefining.
M. L. Free, Hydrometallurgy: Fundamentals and Applications, 1st ed. — Eh-pH (Pourbaix) diagram construction and reading, aqueous speciation, electrochemical cell design.
W. G. Davenport, M. King, M. Schlesinger & A. K. Biswas, Extractive Metallurgy of Copper, 4th ed. — electrowinning/electrorefining energy balances and current efficiency.
D. M. Marsden & C. I. House, The Chemistry of Gold Extraction, 2nd ed. — cyanide-complex electrochemistry, gold cementation and auxiliary oxidants (Problem 3).
T. Rosenqvist, Principles of Extractive Metallurgy, 2nd ed. — general extractive-metallurgy context.

21-Mat-B2 Pyrometallurgy: December 2018