Applications of in situ synchrotron XRD in hydrometallurgy: Literature review and investigation of chalcopyrite dissolution

Abstract

In situ synchrotron X-ray diffraction (S-XRD) techniques are potentially versatile research tools for advancing the current understanding on dissolution reactions of commercially important minerals. The paper presents a review on the applications of S-XRD to investigate solid phase transformations in aqueous media, with emphasis on reactions relevant to hydrometallurgy, including the dissolution of nickel laterite ores and metal sulfides, such as pyrite (FeS2), bornite (Cu5FeS4) and chalcocite (Cu2S). The results of an in situ synchrotron time-resolved X-ray diffraction (S-TRXRD) study of the dissolution of chalcopyrite (CuFeS2) are also reported. The S-TRXRD measurements were carried out in capillary-based cells containing fine particles by using two different experimental approaches — flow method (FM) and non-flow method (NFM). At 25°C (FM), no transformation of the crystal structure was observed, in agreement with the well-known slow dissolution rate of the mineral. In the temperature range 100–200°C (NFM), the formation of covellite (CuS), elemental sulfur (S8), and metal sulfates (ferrous or cupric sulfates) was detected on CuFeS2 particles. Our results demonstrate that the mineral conversion to such product phases commenced about 10min after the start of measurements, and suggested that the formation of elemental sulfur is possibly related to an initial oxidation of CuFeS2 by Fe3+ ions, followed by CuS oxidation by the same oxidants. The new results in combination with the previous reports demonstrate that the S-XRD techniques can be used to improve our knowledge on key hydrometallurgical processes. This work highlights the features of different experimental set-ups and the possibilities to be explored by applying in situ methods, alone or in combination with other analytical tools.