Adsorption of H4SiO4 as a hydrolysate of sodium silicate on surfaces of fluorite (111), calcite (104), and scheelite (112): A density functional theory approach

Abstract

H4SiO4, a hydrolysate of sodium silicate, is the important species in the adsorption process during flotation separation. In this work, the interaction mechanism and adsorption behavior in the surface-chemistry of H4SiO4 molecule on the most stable surfaces of three calcium minerals, fluorite (111), calcite (104), and scheelite (112), were investigated systemically by using ab-initial calculation because the lack experimental approaches at the atomistic level. The results indicated that electrostatic interactions occurred between the electronegative oxygen atom of the H4SiO4 molecule and a calcium atom on the mineral surfaces, hydrogen bonds was observed between the hydrogen atoms of the H4SiO4 molecule and an oxygen atom or a fluorine atom of the calcium mineral surface, and the OH groups of H4SiO4 were significantly stretched during adsorption. The adsorption energy of H4SiO4 molecule on the surfaces of fluorite (111), calcite (104), and scheelite (112) were-1.72,-1.21,-1.55 eV, respectively. Hence, fluorite and calcite were the most and the least sensitive mineral to the adsorption of H4SiO4 during flotation separation, respectively. The electronic structure show that the chemisorption of H4SiO4 molecules on the surfaces of calcium minerals could change electron distribution and the overlaps between Ca-3p and O-2s orbitals and Ca-3d and O-2p orbitals, which led to the formation of new O-Ca bonds.