Mfg. high purity lapis lazuli pigment economically

摘要

High purity lapis lazuli pigment is mfd. from the natural mineral Lasurite by first grinding the raw material and milling to a particle size of 100 mu m using a mill (12) and a classifier (13). The powder is slurried to a suspension (18) and sludge is removed by separating off the fraction 10 mu m (20) in a hydrocyclone (19). Pyrites are then separated from the slurry in a 1st indirect flotation step and carbonate removed in a 2nd indirect flotation step. In at least one third direct flotation step (24) at pH 5.5, the Lasurite concentrate is obtained in the slurry (27) using a collecting/foaming reagent based on alkylamine and fluoride ions. This concentrate is adjusted to pH 7-8, washed and concentrated before being de-agglomerated to a 100% 40 mu m sieve grade, high purity, lapis lazuli pigment.