Precipitation method refers to adding a solvent that is miscible with the mixed component solution, and changing the polarity of the solvent can change the solubility of some components in the mixed component solution, so as to precipitate them from the solution. For example, in an aqueous solution containing saccharides or protein, ethanol is added in stages, so that the alcohol content is gradually increased, and protein, polysaccharide and polypeptide with molecular weight from large to small are gradually precipitated. Saponins with different polarities can be precipitated step by step by adding ether or acetone into ethanol solution containing saponins.
Buoyancy floating method is a separation technology of insoluble pollutants, which refers to a water treatment method that uses the buoyancy of water to make insoluble pollutants surface and then scrape them off by machinery. Buoyancy flotation can be divided into natural flotation, bubble flotation and reagent flotation. Natural flotation method is also called oil separation method, because it is mainly used for the separation of floating oil with particle size greater than 50~ 60 microns, and the main equipment is oil separation ground. Bubble flotation method is mainly aimed at oil and weakly hydrophilic suspended solids, injecting gas into wastewater, so that fine bubbles and suspended particles in water float to the surface with bubbles and are removed. The main equipment includes booster pump, dissolved gas tank, releaser and air flotation tank. The reagent flotation method is to add flotation agent to water, which changes the surface properties of hydrophilic particles from hydrophilicity to hydrophobicity, reduces the surface tension of water, improves the elasticity and strength of bubble film, and makes small bubbles difficult to break. Flotation agents can be divided into three categories according to their functions: collectors, regulators and foaming agents, most of which are chain-like organic surfactants.