Gold costs were about $317 per troy ounce in 2007, but these can vary widely depending on mining type and ore quality; global mine production amounted to 2,471.1 tonnes. After initial production, gold is often subsequently refined industrially by the Wohlwill process which is based on electrolysis or by the Miller process, that is chlorination in the melt. The Wohlwill process results in higher purity, but is more complex and is only applied in small-scale installations. Other methods of assaying and purifying smaller amounts of gold include parting and inquartation as well as cupellation, or refining methods based on the dissolution
Industrial separation processes operations are having several different functions: A heterogeneous mixture (e. g. liquid and solid) can be separated by mechanical separation processes like filtration or centrifugation. Homogeneous mixtures can be separated by molecular separation processes; these are either equilibrium-based or rate-controlled. Equilibrium-based processes are operating by the formation of two immiscible phases with different compositions at equilibrium, an example is distillation (in distillation the vapor has another composition than the liquid). Rate-controlled processes are based on different transport rates of compounds through a medium, examples are adsorption, ion exchange or crystallization. Separation of a mixture into two phases can be done