Effects Of Grinding Environment On Flotation Of Sulfide Minerals

Flotation has experienced for more than ten decades. Almost all the sulflde ores, some non-metal ores and oxide ores are currently processed by flotation which is still one of high efficient methods for separation and concentration. As a necessary preparation before flotation, grinding shows great significance for flotation. Grinding, as a kind of complex physical, chemical and physicochemical process, would affect the subsequent sulfide processing considerably. Therefore, it has great importance on theory and practice to study the relationship between grinding environment and sulfide flotation.This study summarized in this PhD thesis was based on authors’deep comprehending and referring of a large number of published literatures, aiming at typical sulfide minerals such as galena, sphalerite, chalcopyrite and pyrite, detecting the changes of the surface properties and the pulp chemistry of those sulfide minerals ground in various environment by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and other modern physical and chemical analysis techniques, studying the effects of different grinding environment and reagent addition on the floatability of single sulfide mineral and on the separation in the dual mineral systems by a great deal of flotation tests. The thesis also discusses the effecting mechanism of grinding environment on floatability of sulfide minerals, and further explores the effects of grinding environment on the separation of real sulfide ores.It is found that there exists intimate relationship among chemical properties of slurry(pH, Eh, dissolved oxygen content and ion concentration), surface properties of sulfide minerals and grinding environment. Grinding in different media leads to different chemical properties of slurry and different surface properties of individual sulfide mineral and the dual mineral systems. Action of local cell of iron media itself and action of galvanic couple between iron media and sulfide mineral, would lead to the higher pulp pH, but lower pulp Eh and lower dissolved oxygen content when being ground with iron media than being ground with ceramic media. At the same time, mechanical force and mechano-chemistry reaction have intense effects on the surface of sulfide minerals ground with iron media, which would result in more serious surface corrosion than being ground with ceramic media, and would form FeOOH on the surface of sulfide minerals, generating considerable difference in surface properties of sulfide minerals between those ground with iron media or ground with ceramic media.The main reasons of causing evident difference on flotation behaviour of sulflde minerals ground with iron or ceramic media including:1. the deposition and adsorption of hydroxy iron complex on the surface of sulfide minerals would enhance the surface hydrophilicity and reduce the flotability of sulfide minerals;2. strong reducing environment caused by ground with iron media would block the moderate surface oxidization of sulfide minerals, which is necessary for flotation, while oxidizing environment caused by ground with ceramic media would be beneficial to the moderate surface oxidization of sulfide minerals;3. galena and chalcopyrite ground with either media, and pyrite with ceramic medium would form a metal-lacking while sulfur-exceeding surface, which would promote flotation of sulfide minerals. There would be equivalent atoms of iron and sulfur on pyrite surface ground with iron media. No matter being ground with iron or ceramic media, sphalerite would have sulfur-lacking while metal-exceeding surface;4. when ceramic is used as grinding media, the oxidizing environment with higher potential would promote the oxidization of xanthate to dixanthogen, but when iron media is used, the situation would be reversed.There are four innovative points in this thesis:1.It is the first systematic study on the effects of grinding environment on sulfide pulp chemistry, surface properties and flotation behaviors of sulfide minerals. Some preliminary findings have been established to describe the rules and mechanisms concerned;2. The research results indicates that sulfides ground with ceramic media have better floatability than being ground with iron media.3. When iron is used as grinding media, the formation of FeOOH on the surface of pyrite or sphalerite would have "shield effect" on the activation of Cu2+and Pb2+;4. It is found that dry grinding is better than wet grinding for the separation of sulfides by flotation.In addition, some knowledges has been gained through experiments in the study:1. Due to E0of HS-to S0is lower than that of sulfide minerals and iron media when the concentration of Na2S is low, it would effectively avoid the peroxidation of sulfide minerals ground with ceramic media, and the formation of FeOOH when being ground with iron media, which would maintain a better hydrophobic surface of sulfide minerals and promote their flotation;2. Because of the formation of CaSO4film on pyrite surface, which would enhance the surface hydrophilicity in acidic condition, pyrite ground with ceramic media would be strongly depressed by CaO;3. The depression of sphalerite or pyrite by Na2S2O3had close relationship with the presence of iron media or iron ion. It would be the main reason of obvious depression of sphalerite ground with iron media by Na2S2O3that the strong hydrophilic substance, Fe2(S2O3)3is formed on the mineral surface.