A Fundamental Study On Clustering Flocculation Of Microfine Minerals To Improve Flotation Separation Efficiency

Microfine mineral particles in froth flotation pose two serious problems,i.e.,the low recovery of the value minerals and the mechanical/hydraulic entrainment of the hydrophilic gangue minerals.As a result,effective separation of the microfine minerals by flotation is a major challenge.Most of the current studies focus on improving the flotation of the microfine hydrophobic particles,but the microfine hydrophilic particles(usually gangue minerals),which are still highly dispersed in the flotation pulp,cannot overcome the fluid drag force and are easily transported into the flotation concentrate by mechanical entrainment due to their small size and mass,resulting in a reduction in concentrate grade and flotation separation efficiency.According to the material property of "birds of a feather flock together",a research idea clustering flocculation of the microfine minerals is proposed in this thesis to improve flotation separation efficiency.In the proposed process,the hydrophobic and hydrophilic minerals are separately flocculated to form the hydrophobic and hydrophilic flocs,respectively,with appropriate floc apparent particle sizes,followed by flotation separation.This method can simultaneously lower the entrainment of the gangue minerals and enhance the flotation recovery of the microfine value minerals.The core research idea of clustering flocculationflotation was studied,lowering the microfine gangue minerals,enhancing the flotation recovery of the microfine value minerals,and improving flotation separation efficiency by clustering flocculation-flotation were taken as the main research line,the microfine galena(D50 of 2.4 μm and D90 of 6.2 μm)and microfine quartz(D50 of 3.7 μm and D90 of 11.1 μm),and their synthetic mixtures were used as the samples.In this work,the directional double flocculation,flotation separation,and the mechanisms underpinning the research results induced by polyaluminum chloride(PAC)and polyethylene oxide(PEO)were deeply studied.The study of lowering entrainment of the microfine quartz particles showed that PAC could effectively reduce the entrainment of the microfine quartz to improve the flotation separation efficiency.The addition of PAC was able to lower the quartz entrainment from 9.2%to 5.4%,and the corresponding separation efficiency was improved from 73.9%to 80%.The study showed that the reduction of quartz entrainment was due to the formation of the homo-flocs of microfine quartz induced by PAC,but the addition of PAC did not show flocculation effect on microfine galena.The adsorption rate of PAC on quartz surfaces was found to be higher than on galena,and it was inferred that PAC preferentially adsorbed on quartz in the artificial galena-quartz mixtures.Therefore,lower concentrations of PAC did not reduce the flotation recovery of galena,but at higher PAC concentrations(>150 mg/L),the addition sequence of PAC and KEX was significant for the galena recovery,and the addition sequence of "KEX+PAC"(adding KEX first)generated better results than that of "PAC+KEX"(adding PAC first).The study of enhancing flotation of the microfine galena showed that the combination of a 1 million molecular weight(MW)PEO and the collector KEX could effectively enhance the galena recovery and improve the separation efficiency.Importantly,it was found that the PEO with a MW of 8 million unselectively flocculated both galena and quartz,but the 1 million MW PEO could not flocculate either galena or quartz.However,after the galena was treated with KEX,the 1 million MW PEO was able to flocculate the galena but it still did not show flocculation effect on microfine quartz.Compared with the addition sequence of"PEO+KEX",the addition sequence of "KEX+PEO" was conducive to flocculating the microfine galena,which led to the significantly enhanced flotation recovery of the microfine galena.Although the formability measurements indicate that PEO could enhance the foam stability,resulting in a slight increase in quartz entrainment,the combination of KEX and PEO significantly increased the galena recovery from 83%to 94%,and the separation efficiency was improved from 73.9%to 82%.Based on the study of lowering entrainment of microfine quartz particles and enhancing flotation recovery of microfine galena particles,the research on clustering flocculation-flotation of microfine galena and quartz was carried out indepth,in which the adsorption sequence and adsorption amount of PAC,PEO,and KEX played a decisive role.With the combined use of the three reagents and their adding sequence of "KEX+PEO+PAC",the quartz entrainment recovery was reduced from 9.2%to 6.6%,the galena recovery was increased from 83.1%to 90.2%,and thus the flotation separation efficiency was improved from 73.9%to 83.6%,which not only regulated the mechanical entrainment of the microfine quartz but also enhanced the flotation recovery of the microfine galena.This was due to the chemisorption of xanthate on the surface of galena particles increased its hydrophobicity,and thus the single molecular chain of PEO could be adsorbed to several galena particles through-CH2CH2-driving by the mechanism of hydrophobic force,while the hydrophilic aluminum hydroxyl groups in PAC hydrolysis products adsorbing on the galena reduced the hydrophobicity of galena,which weakened the flocculation effect of "KEX+PEO" on the microfine galena.The first addition of KEX reduced the adsorption of PAC on the galena surface,it was likely that the xanthate chemisorption could inhibit the adsorption of PAC on the surface of galena to some extent.QCM-D analysis showed that the first addition of PEO had little effect on the adsorption of PAC on the quartz surface.Therefore,compared with other dosing sequences,"KEX+PEO+PAC" was the most favorable to flocculate the microfine galena and quartz successively,achieving the research objective of improving the flotation efficiency of microfine minerals through clustering flocculation.PAC and other high molecular weight polymers whose hydrolysis products are mainly cationic components,or cationic flocculants could be chosen to flocculate the microfine hydrophilic gangue minerals with negative charges,PAC is a certain hydrophilic and its aggregation ability is not too strong.Combining its flocculation ability and the effect on the hydrophobicity of hydrophobic minerals,PAC may not exhibit flocculation on hydrophobic minerals.The collector acting on the mineral surface has a synergistic effect on adsorption and flocculation of PEO which is an effective flocculant for flocculating microfine hydrophobic minerals.The combined use of PEO and collector for the hydrophobic minerals could selectively flocculate the microfine hydrophobic particles,in which the adsorption of the collector increases the mineral surface hydrophobicity and the PEO with an appropriate molecular weight should be selected.The findings of this research are not just limited to the flotation system of PAC,PEO,galena,and quartz.The synergistic effect of the collector acting on the mineral surface on polymer adsorption and the resulting selectively should also exist in many other reagent-mineral systems,where interfacial regulation by adjusting the reagent regime creates the prerequisites for separate flocculation of the microfine hydrophobic and hydrophilic minerals to improve the flotation separation efficiency of microfine minerals through clustering flocculation.