KINETICS ASPECT OF HYDROCHEMICAL FLUORINATION OF SILICON-CONTAINING INDUSTRIAL WASTE

Abstract

A method for producing amorphous silica from the enrichment wastes of low-titanium vanadium containing titanomagnetites of JSC «EVRAZ ZSMK» – wet magnetic separation tailings is proposed. The use of a NH4HF2 solution makes it possible to practically selectively extract silicon into the solution in the form of ammonium hexafluorosilicate. The extraction of silicon with 1,0-2,5 wt.% NH4HF2 solution for 6 hours reached 46%. The diffusion process of the silicon extraction is described by the kinetic equation 1-(1-α)^(1/3) = 0,0043·exp(-5230/RT)·τ. Amorphous silica obtained by the sol-gel method from a fluoride silicon-containing solution has a highly developed surface 320 m^2/g, the particle size calculated from the average density of «white carbon black» is of 10 nm. The increase in concentration to 20 wt. % NH4HF2 leads to the rise of the silicon solubility and of other tailings components, which are unwanted impurities in the final product. In general, it is shown that the hydrochemical leaching of silicon-containing industrial waste – tailings with weak solutions of ammonium hydrofluoride is promising for the synthesis of pure amorphous silica.

Keywords

• wet magnetic separation tailings
• amorphous silica
• ammonium hydrofluoride
• fluorination
• kinetics of the process