Defluorination settling agent and application of defluorination settling agent in wet-process refined phosphoric acid pretreatment

The invention provides a defluorination settling agent applied to refined wet-process phosphoric acid pretreatment for arsenic acid removal, the defluorination settling agent is an aqueous solution with the mass percent concentration of 5%-15%, and the solute of the defluorination settling agent is a nonionic surfactant and an anionic surfactant which are prepared according to the mass ratio of 1: (10-50); the non-ionic surface active agent is one of maleic acid-acrylic acid copolymer, acrylamide-methyl acrylate-2-acrylamide-2-methylpropanesulfonic acid copolymer and AM-AA-DMA copolymer or any two of maleic acid-acrylic acid copolymer, acrylamide-2-acrylamide-2-methylpropanesulfonic acid copolymer and AM-AA-DMA copolymer which are prepared according to the mass ratio of 1: 1; the anionic surfactant is one of oil-based polyoxyethylene (10) ether phosphate, sodium octyl sulfate, sodium alpha-olefin sulfonate, sodium lignin sulfonate, disodium stearyl sulfosuccinate and ammonium lauryl sulfate. According to the