Theory And Practice Of Inorganic-Organic Phosphate Synergistic Strengthening Flotation Separation Of Calcium-Bearing Minerals

The flotation separation of scheelite and calcium-bearing gangue minerals has always been a technical problem in the field of mineral processing.Under the situation of scheelite resources becoming increasingly barren,it is of great significance to improve the separation efficiency of scheelite and calcium-bearing gangue minerals for promoting the recovery and utilization of scheelite resources and ensuring the superiority of tungsten resources in China.Therefore,in this study,in view of the difficulty in separating scheelite from calcium-containing gangue such as fluorite and calcite,the influence of inorganic phosphates such as sodium pyrophosphate（TSPP）,sodium tripolyphosphate（STPP）,sodium hexametaphosphate（SHMP）,and organic phosphates such as ethylenediamine tetramethylene phosphate（EDTMP）,hexamethylenediamine tetramethylene phosphonic acid（HDTMP）,and polyamino polyether sodium methyl phosphate（PAPEMP）on the flotation behavior of calcium-bearing minerals in the system with sodium oleate as collector was explored.Meanwhile,the action mechanism of phosphate was investigated by surface wettability measurement,infrared spectrum analysis,Zeta potential test,reagent adsorption amount test,X-ray photoelectron spectroscopy（XPS）analysis,atomic force microscope（AFM）and other testing methods.Finally,the application effect of phosphate was verified through industrial production.The main conclusions of the paper are as follows:（1）The analysis results of crystal structure and properties indicate that the three calcium-bearing mineral crystals are more likely to fracture along the Ca-O（Ca-F）bond,exposing the polar surface with similar properties,which makes the surfaces of the three minerals show poor natural floatability.The unsaturated Ca²⁺on common cleavage planes such as scheelite{001},fluorite{111}and calcite{104}need to combine with a corresponding number of ligands to form a stable coordination structure.According to the steric configuration of the common cleavage planes of the three minerals,the binding of ligands to Ca²⁺on the{001}plane of scheelite needs to overcome greater steric hindrance.（2）The test results of single mineral flotation show that the addition of phosphate increases the floatability difference among the three calcium-containing minerals,and inhibits fluorite and calcite to varying degrees,but has little effect on the floatability of scheelite.The greater the number of phosphate radicals,the stronger the inhibition of inorganic phosphate.The order of the inhibition of the three inorganic phosphates is:SHMP>STPP>TSPP.The longer the hydrocarbon chain length,the weaker the inhibition of the organophosphate.The order of the inhibition of the three organic phosphonates is:EDTMP>HDTMP>PAPEMP.STPP and EDTMP have great potential for flotation separation of scheelite from fluorite and calcite.When the flotation separation conditions are as follows:pulp p H value of 8.5～9.5,STPP or EDTMP of3×10^-5 mol/L,and Na OL of 1.5×10^-4 mol/L,the floatability of scheelite differs greatly from that of fluorite and calcite.The inhibition of fluorite and calcite can be further enhanced when STPP and EDTMP are combined in a 1:1 ratio.（3）The research results of the action mechanism of phosphate present that the contact angle of the three minerals decreases obviously after the interaction with STPP and EDTMP.With the further interaction of Na OL,the contact angle of scheelite surface recovered to be comparable to that after interaction with Na OL alone,maintaining good hydrophobicity and floatability.However,the contact angle of fluorite and calcite did not change much,showing strong hydrophilicity and poor floatability.The test results of infrared spectroscopy,Zeta potential and adsorption amount indicate that STPP and EDTMP can produce more intense adsorption on the surface of fluorite and calcite,making the surface hydrophilic and hindering the further adsorption of Na OL,thus increasing the floatability gap of scheelite,fluorite and calcite.（4）The action mechanisms of the combined inhibitor show that STPP and EDTMP are adsorbed on the surface of the three minerals mainly through the coordination between O and Ca in the terminal phosphate.Affected by factors such as steric hindrance and electrostatic repulsion,STPP,EDTMP and their combination reagents are more likely to coordinate with Ca²⁺on the surfaces of fluorite{111}and calcite{104},and the adsorption density on calcite and fluorite surface is higher than that on scheelite surface.After combined application,STPP and EDTMP co-adsorb on the mineral surface,the area covered by a single adsorption site on the calcite and fluorite surface increase significantly,and STPP bond more Ca particles on the calcite{104}surface,which produce a greater hindering effect on the adsorption of Na OL and further improve the flotation separation effect of the three calcium-containing minerals.（5）The industrial test results show that the application of the combination inhibitor of STPP+EDTMP in the recovery of low-grade scheelite associated with Sandaozhuang deposit in Luanchuan can increase the WO₃ grade of rough concentrate from 1.224%to 1.540%,and the roughing recovery of scheelite from 82.11%to 85.04%.The improvement of rough concentrate grade greatly reduces the consumption of sodium silicate and natural gas in the cleaning section,which can save 10,801.4 yuan per day for the scheelite plant of 10,000 t/d,and the potential economic benefit can exceed 20million yuan per year.The combination inhibitor can improve the recovery and utilization efficiency of tungsten resources in Luanchuan area and have the potential to be popularized in similar scheelite plants.