Energy-Dispersive Spectroscopy Improves Copper Smelting

Electron image of Cu-compound raw material

Copper, (Cu) number 29 on the periodic chart, is a major industrial metal. Copper is highly conductive of heat and electricity and is commonly used for electrical wiring, electronics, pipes, pots, and many other applications in construction, transportation and machinery.

Like every other metal, copper is rarely found in nature alone but rather combined with minerals and rock in ores and must be extracted, processed, and purified before it can be used. The extraction process varies depending on the type of ore and degree of copper purity required but usually includes the following steps:

Concentration: Copper ore contains unwanted materials and non-copper bearing minerals. Flotation, a process in which crushed ore is mixed with water and then chemicals and injected with air, is used to separate out these materials, called tailings, and concentrate the copper. The copper concentrate contains various sulfides of copper and iron, plus smaller concentrations of gold, silver, and other materials.

Smelting: Smelting is the process of extraction and usually involves heating the concentrated ore with a reducing (oxygen removing) agent. Smelting separates the concentrate into layers. The copper-containing layer, called the matte layer, sinks to the bottom while iron and other by-products form slag that floats to the top. Sulfur dioxide, another by-product, can be recycled to make sulfuric acid. The matte is processed again to form a mostly pure copper blister.

Refining: Copper blister still contains enough impurities to require further refinement, first by fire refining followed by electrolysis.

According to the U.S. Geological Survey, U.S. mine production of copper in 2013 was valued at about $9 billion. Three primary smelters, 3 electrolytic and 4 fire refineries, and 15 electrowinning facilities operated during 2013.

Copper is one of the few metals more often used in pure form than as an alloy. Copper must be completely refined and free from impurities to maintain its electrically conductive properties. In non-ferrous metal smelting operations, each element is refined from very complex compound material in which the major elements are copper (Cu), zinc (Zn) and lead (Pb). When smelting copper, it is very important to understand the complex morphology of the various compounds in the raw material to improve the refining efficiency of each element.

Inductively-coupled plasma (ICP), X-ray diffraction (XRD) and electron probe microanalysis (EPMA) can be used for the evaluation of raw materials in copper smelting. However, ICP and XRD can only provide information about average bulk composition. EPMA may take several hours to do a quantitative analysis of a complex sample containing 10 to 20 elements and many phases. EPMA also requires highly experienced analysts to operate the instrument and evaluate a mixed compound material by using electron image contrast.

Recent developments in Silicon Drift Detectors (SDD) have improved the detection efficiency of energy-dispersive spectroscopy (EDS) and significantly reduced acquisition times. Robust peak deconvolution methods have improved the quality of EDS spectral imaging data to near that of EPMA. Furthermore, the introduction of EDS multivariate analytical methods simplify the analysis of phase distributions as opposed to just elemental distributions.

Read study results in which copper-compound raw material was evaluated by phase analysis using the multivariate statistical analysis of EDS spectral imaging data.