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Minor element behavior in the INCO CRED process Qin, Guoming

Abstract

In LNCO's Copper Refinery Electrowinning Department (CRED) the copper sulfide residue containing precious metals (referred as the first stage cake), is subjected to an oxidative pressure leach. The leach - referred as second stage leaching, produces a copper sulfate solution and basic copper sulfate. The basic copper sulfate is releached with spent electrolyte from copper electrowinning containing sulfuric acid to produce impure copper sulfate solution and a precious metals residue. A sample of first stage cake from INCO CRED was shipped to UBC and treated under second stage leaching conditions. The minor element behavior in the process was the objective of the study. The minor elements include cobalt, iron, arsenic, antimony, bismuth, selenium, tellurium and tin. Four important factors that might affect the behavior of minor elements were investigated: Cu/Acid ratio in the feed, Cu/S ratio in the feed, impurity levels in the feed and degree of oxidation. Four series of experiments were performed with filtrate solutions and solid residues analyzed by ICP scan for chemical compositions. Selenium was the minor element of greatest interest due to the difficulty in removing Se from the CRED impure leach solution. Selenium species if present will contaminate copper cathodes and therefore must be removed. The two principal forms of selenium in the CRED streams are believed to be selenite (SeIV) and selenate (SeVI), respectively. INCO CRED had a great concern about selenium speciation in the second stage leaching, which will help to understand the behavior of selenium better and remove it more efficiently. A method for selenium analysis was developed, which was based on Atomic Fluorescence Spectrometry with Hydride Generation (AFS-HG). A pretreatment process was applied to suit the samples in the project and eliminate interferences in Se analysis caused by sulfate and cations. This method was initially applied to samples generated in the UBC lab work. In addition, some samples were taken from INCO CRED plant and analyzed by this method.

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