text: A separation process is a method that converts a mixture or a solution of chemical substances into two or more distinct product mixtures, a scientific process of separating two or more substances in order to obtain purity. At least one product mixture from the separation is enriched in one or more of the source mixture's constituents. In some cases, a separation may fully divide the mixture into pure constituents.  Separations exploit differences in chemical properties or physical properties (such as size, shape, mass, density, or chemical affinity) between the constituents of a mixture.
  Processes are often classified according to the particular properties they exploit to achieve separation. If no single difference can be used to accomplish the desired separation, multiple operations can often be combined to achieve the desired end.
  With a few exceptions, elements or compounds exist in nature in an impure state.  Often these raw materials must go through a separation before they can be put to productive use, making separation techniques essential for the modern industrial economy. 
  The purpose of separation may be:
  * analytical: to identify the size of each fraction of a mixture is attributable to each component without attempting to harvest the fractions.
  * preparative: to "prepare" fractions for input into processes that benefit when components are separated.
  Separations may be performed on a small scale, as in a laboratory for analytical purposes, or on a large scale, as in a chemical plant.