Editor’s Note: We are dedicating each Tuesday in July and August to Copper, number 29 on the periodic table.
Our previous post, Copper Compendium, Part 2: Copper is Key in the Modern Age, looked at some of the many uses of copper which, like every other metal, must be extracted, processed, and purified before it can be used. In this post we’ll examine how copper is made into usable form.
Just how much copper is being processed to meet current demand levels? According to the International Copper Study Group’s World Copper Factbook 2014, global copper mine production in 2013 reached an estimated 18.1 million tones, and smelter production in 2013 reached an estimated 16.8 million tonnes. Refinery production in 2013 increased to 20.9 million tonnes, including 3.8 million tonnes of secondary refined production. In 2013 the largest producer of mined copper was Chile, while China was the largest producer of blister and anode.
Primary copper production starts with the extraction of copper‐bearing ores. Depending on the type of ore and degree of copper purity required, the extraction process may vary but typically includes the following steps:
Concentration: Tailings (contaminants and non-copper bearing minerals) are separated out by flotation, a process in which crushed ore is mixed with water and then chemicals and injected with air.
Smelting: The concentrated ore is heated with an oxygen-removing agent to separate 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.
Refining: The matte is processed again to form a mostly pure copper blister which is further refined, first by fire refining and then by electrolysis.
Copper smelting is a pyrometallurgical process. Copper is also extracted from low grade ores by a two-stage hydrometallurgical technique known as the SX‐EW Process, solvent extraction (SX) followed by electrowinning (EW). This procedure recovers high purity copper from leachate solutions and accounts for an estimated 18-20% of world copper production.
Copper is used in varying levels of purity, or it is alloyed with other metals to impart, enhance, or modify certain properties. Determining the purity of the copper and percentages of any alloying elements present is a very important quality control step, particularly for electronics manufacturing which requires very high purity copper.
In nonferrous 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 in order to improve the refining efficiency of each element. 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 electron probe microanalysis (EPMA). Furthermore, the introduction of EDS multivariate analytical methods simplify the analysis of phase distributions as opposed to just elemental distributions.
Next week we’ll discuss an application note about Cu-compound raw material which was analyzed by phase analysis. It describes a study which analyzed copper-compound raw material by phase analysis using the multivariate statistical analysis of EDS spectral imaging data.