Effects of ammonium phosphate on the formation of crystal copper sulfide on chrysocolla surfaces and its response to flotation

•Chrysocolla floats with high recovery when (NH4)3PO4 is added prior to sulfidization.•More crystal copper sulfide formed on chrysocolla surface after (NH4)3PO4 addition.•Crystal copper sulfide is mainly composed of stable covellite (Cu+3(S2)2−S−).•(NH4)3PO4 was a special catalyst in the sulfidization flotation of chrysocolla. In this study, for the first time, we applied ammonium phosphate to pre-treat chrysocolla prior to sulfidization flotation. In addition, we investigated the structural characteristics of the copper sulfide film formed on the chrysocolla surfaces and its response to flotation. Micro-flotation experiments revealed that the addition of (NH4)3PO4 prior to sulfidization greatly improves the floatability of chrysocolla and its recovery increased from 8.71% to 87.97% with butyl xanthate as the collector. The results of the field emission scanning electron microscopy analysis showed that numerous regular fragments appeared on the chrysocolla surfaces after the addition of (NH4)3PO4. The X-ray diffraction and X-ray photoelectron spectrometry analysis confirmed that these fragments were newly formed copper sulfide covering the chrysocolla surfaces, during this process a chemical reaction occurred in the slurry system, i.e. the Cu2+ were reduced to Cu+, the S2− were mainly oxidized to S−, (S2)−, (S2)2−. The copper sulfide species primarily in the form of crystalline covellite (Cu+3(S2)2−S−), which is the key to obtaining good flotation recovery. As a specific activator, (NH4)3PO4 participates in the liquid-solid phase chemical reaction between the sulfidizing reagent and the chrysocolla, which promotes the sulfidization reaction of chrysocolla.