The Flotation Behavior And Mechanism Of Aluminosilicate Polymorphic Minerals

Kyanite,andalusite and sillimanite are aluminosilicate polymorphic minerals.The entropy and Gibbs free energy of the three Al₂SiO₅ minerals are very similar,so the ore deposit where two or even three of the Al₂SiO₅ minerals are associated is not rare.The selective separation of two or even three of the Al2SiO5 minerals is very difficult attribute to the same formula of Al2SiO5 and the similar surface properties.There are little research on the technology and basic theory for the flotation of the three polymorphic minerals.Taking the differences of crystal structure as a point of penetration,the surface properties and flotation behavior of the three Al₂SiO₅ mineral were studied by means of surface potential,X-ray photoelectron spectroscopy,infrared spectroscopy and molecular dynamics simulation in this paper,which provide a theoretical guidance for the selective separation of the Al2SiO5 polymorphic minerals.In addition,Quartz is a kind of gangue mineral associated with three Al₂SiO₅minerals,and an effective separation of Al2SiO5 minerals from quartz by flotation is a challenge due to their similar surface properties and surface activation by metal ions which lead to small differences of flotability.This study further investigated the effect of pH,Fe³⁺and sodium silicate on the separation of kyanite from quartz using anionic collector,sodium petroleum sulfonate（SPS）.The coordination number of half of Al atoms in kyanite,andalusite and sillimanite is 6,while that of the remaining Al atoms in each polymorph is 6,5 and 4,respectively.The Raman spectroscopy of the three minerals show that the intensity of characteristic peaks in the range of 700⁸00 cm^-11 which attributed to Al-O_non-bridgingon-bridging symmetric stretching vibrations becomes stronger gradually with decreasing coordination number of Al atoms.The calculated bond order shows that the Al-O bond distance is the longest in[AlO6]octahedral and is the shortest in[AlO4]tetrahedral,and the Al-O bond distance in[AlO5]hexahedra is between[AlO6]octahedral and[AlO₄]tetrahedral.The different Al-to-Si ratio on the surfaces leads to the different surface charge of the three Al₂SiO₅ minerals.X-ray photoelectron spectroscopy analyses show that the Al-to-Si ratio is the highest on kyanite surface while the lowest on sillimanite surface.The results are consistent with zeta potentials of the three Al2SiO5 minerals which showed that kyanite,andalusite and sillimanite exhibited a point of zero（PZC）at pH 6.6,pH 6.0 and pH 5.5,respectively.When octadecylamine（OA）is used as the collector,the order of the floatability is kyanite>sillimanite>andalusite and the flotation recovery of all the three minerals increases with pH and reaches a maximum at pH 6.5 and then starts to decrease.It is concluded that the octadecylamine cations are the main component resulting in the flotation of aluminosilicate polymorphic minerals.Molecular dynamics（MD）simulation shows that the density of states near Fermi level of kyanite（100）plane are mainly from the O2p orbit.The lowest adsorption energy of OA on kyanite surface among the three minerals is related to the strongest interaction of amine cations with the reactive sites of the oxygen atoms by physical adsorption.As a result,the flotation recovery of kyanite is the highest.When sodium hexadecanesulfonate（SHS）is used as the collector,the order of the floatability is andalusite>sillimanite>kyanite and the flotation recovery of all the three minerals decreases with pH.It is concluded that the hexadecanesulfonate anions are the main component resulting in the flotation of aluminosilicate polymorphic minerals.The densities of states near Fermi level of andalusite（110）plane are mainly from the Al3s,Al3p and Si3p orbit.The lowest adsorption energy of SHS on andalusite surface among the three minerals is related to the strongest interaction of sulfonate anions with the reactive sites of the aluminum atoms and silicon atoms by chemical and physical adsorption.Therefore,the flotation recovery of andalusite is the highest.When sodium oleate（NaOL）is used as the collector,the order of the floatability is sillimanite>andalusite>kyanite and the flotation recovery of all the three minerals increases with pH and reaches a maximum at pH 8.0 and then starts to decrease.It is concluded that the oleate anions are the main component resulting in the flotation of aluminosilicate polymorphic minerals.FTIR anslyses confirm that sodium oleate adsorbs onto the surfaces of the three minerals by the chemical interaction.The densities of states near Fermi level of sillimanite（010）plane are mainly from the Al3s and Al3p orbit.The lowest adsorption energy of NaOL on sillimanite surface among the three minerals is related to the strongest interaction of oleate ion with the reactive sites of the aluminum atoms by chemical adsorption.As a result,the flotation recovery of sillimanite is the highest.X-ray photoelectron spectroscopy analyses show that kyanite surface has the highest adsorption of collector OA while andalusite surface has the lowest OA adsorption,andalusite surface has the highest adsorption of collector SHS while kyanite surface has the lowest SHS adsorption and sillimanite surface has the highest adsorption of collector NaOL while kyanite surface has the lowest NaOL adsorption.The adsorption capacity and adsorption energy of the three minerals in the presence of three collectors are consistent with flotation behavior of them.The results of single mineral test,artificial mixed ore test and actual ore test show that a good separation of kyanite from quartz is achieved at pH=4.0 due to the selective adsorption of SPS on kyanite.The hydrolysis species of Iron ions(Fe（OH）_3（s）)alter the activation sites on quartz which became attractive to SPS,enhance quartz flotation and hence exacerbate the separation of kyanite from quartz.The hydrolysis species of sodium silicate（Si（OH）₄ and SiO（OH）₃^-）selectively depress the flotation of iron-activated quartz by covering the activation sites and prohibiting collector adsorption.Although the hydrolysis species of sodium silicate（Si（OH）₄ and SiO（OH）₃^-）also interact with kyanite,SPS still adsorbs on kyanite through reacting with Al atoms and therefore the depression of kyanite flotation by sodium silicate in the presence of Fe³⁺is limited.