Convergent, divergent and transform plate boundaries.
Nickel can be recovered using extractive metallurgy. Most lateritic ores have traditionally been processed using pyrometallurgical techniques to produce a matte for further refining. Recent advances in hydrometallurgy have resulted in recent nickel processing operations being developed using these processes. Most sulphide deposits have traditionally been processed by concentration through a froth flotation process followed by pyrometallurgical extraction. Recent advances in hydrometallurgical processing of sulphides has led to some recent projects being built around this technology. Nickel is extracted from its ores by conventional roasting and reduction processes which yield a metal of >75% purity. Final purification in the Mond process to >99.99% purity is performed by reacting nickel and carbon monoxide to form nickel carbonyl. This gas is passed into a large chamber at a higher temperature in which tens of thousands of nickel spheres are maintained in constant motion. The nickel carbonyl decomposes depositing pure nickel onto the nickel spheres (known as pellets). Alternatively, the nickel carbonyl may be decomposed in a smaller chamber without pellets present to create fine powders. The resultant carbon monoxide is re-circulated through the process. The highly pure nickel produced by this process is known as carbonyl nickel. A second common form of refining involves the leaching of the metal matte followed by the electro-winning of the nickel from solution by plating it onto a cathode. In many stainless steel applications, the nickel can be taken directly in the 75% purity form, depending on the presence of any impurities. The largest producer of nickel is Russia which extracts 267,000 tonnes of nickel per year. Australia and Canada (particularly the Sudbury Basin) are the second and third largest producers, making 207 and 189.3 thousand tonnes per year.
The Rock cycle is a process whereby all types of rock are formed then eroded and "recycled" through different depositional processes. Sedimentary rocks can provide evidence that the rock cycle exists by looking at it under a microscope. Sedimentary rocks are formed by the lithification of grains of different sizes shapes and compositions. By detemining the compositions of the grains within a sedimentary rock through a petrographic microscope or through a scanning electron microscope (SEM) then it can be seen that some grains are composed of minerals that are solely igneous in origin. Likewise, sedimentary rocks can be metamorphosed to form meta-sediments.