Rapid reduction of copper sulfide (Cu2S) with elemental Fe and Mg using electrical discharge assisted mechanical milling (EDAMM)
Introduction
Advanced materials manufacturing methods for the future are required to be clean, non-polluting, high speed and precision processes; producing highly reliable final products. Many materials are traditionally synthesized by slow chemical reaction processes that require capital and labour intensive facilities, and are both energy and time consuming. In the present world there is strong demand for the development of modern materials and materials processing methods that could offer rapid reaction rates, high energy efficiencies, and be environmentally safe. Electric discharge assisted mechanical milling (EDAMM) is a new and exciting materials processing technique which combines the attributes of conventional mechanical milling with a range of new effects associated with electric discharges [1], [2]. EDAMM involves mechanical milling and simultaneous application of an electrical discharge during processing of powder particles; one of the most important factors of this process being the formation of a dusty plasma environment between the powder particles which leads to formation of ions and free radicals. In addition, the powder particles are constantly being mixed and fractured by the vibrating electrode. All these factors contribute to reactivity enhancement and have the potential to drive the replacement reactions at conditions which are either not possible or require vigorous conditions in conventional processing routes. In this work, we study the application of EDAMM to generate replacement reactions on a laboratory scale. We have taken as a model reaction the displacement of Cu from Cu2S by metals belonging to higher positions in the electrochemical series; in the case of this investigation, Mg and Fe. The mechanism of chemical reactions between powder particles surfaces induced by an electric discharge is complex and poorly understood. It is therefore an additional aim of this work to present experimental results that shed light on factors related to EDAMM that induce chemical reactions.
Section snippets
Experimental
Cu2S powders were mixed with Fe and Mg in proportions required in order to obtain stoichiometrically the complete reduction of Cu2S to Cu + FeS2 or Cu + MgS, respectively. These starting powder mixtures were first mechanically pre-mixed in a conventional ball mill for 1 h under a high purity argon atmosphere. This pre-mixture was then subjected to 5 min of electric discharge assisted ball milling (EDAMM). Electric discharge milling was performed in a modified vibrational laboratory rod mill. The mill
Cu2S–Fe
X-ray diffraction of the pre-mixed Cu2S (chalcosine) and Fe powders, and the same mixture given a 5 min EDAMM treatment are shown in Fig. 2. After 1 h of pre-mixing in conventional ball mill there was no reaction detected between the Cu2S and the Fe (Fig. 2a). After 5 min of EDAMM reaction of Cu2S with elemental iron occurred and the following products were identified by XRD: pure Cu, the bornite phase (Cu5FeS4) and some unreacted iron (Fig. 2b, sample EDAMM processed in Ar for 5 min). SEM
Conclusions
XRD, SEM and EDS and X-ray mapping results demonstrated that Cu2S can be reduced to pure copper by EDAMM, using either Mg as the reducing agent, and partially reduced to and Cu2S + Cu5FeS4 using Fe as the reducing agent. More generally, it is demonstrated that EDAMM can be employed to generate replacement reactions in a matter of minutes, rather than hours or days. Morphological evidence of the existence of deformed and remelted particles was consistent with arguments based on thermodynamic
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