The
increasing amount of silicon waste generated from the rapid
developing photovoltaic industry calls for an economical silicon recycling
process. The present work proposes a facile process with which silicon
waste and ironmaking slag containing TiO2 were used as
raw materials to produce titanium silicides, a promising high added
value material. The process was experimentally investigated in lab
scale. The result shows that a high CaO/SiO2 ratio in slag
promotes the reaction. TiSi2 and Ti5Si3 could be synthesized as principal products within 0.5 and 3 h with
CaO/SiO2 = 1.31 in mass, respectively. CaO-SiO2 slag was produced as byproducts. Kinetic analysis indicates that
silicon diffusion in slag is the rate-determining step of the reaction
process. The reaction rate constant is around 1.0 × 10–4 s, and the effective diffusion film thickness in slag side is around
10–3 cm at the silicon–slag interface. Slag
basicity is suggested to increase to 1.31 for a faster silicon diffusion
and further promotion of the reaction rate.
A sustainable simultaneous
synthesis method of TiB2–Ti5Si3 mixtures is developed as an alternative recovery
route of silicon waste from the photovoltaics industry. TiO2–CaO–B2O3 ternary was reduced
by molten silicon at 1500 °C, producing TiB2 within
3 h and Ti5Si3 within 10 h. The lab-scale experiments
were designed to study the reaction kinetics of the reaction. SiO2 diffusion rate controlling kinetic model was derived to describe
the reaction process. The reaction rate constant was recommended to
be ∼5 × 10–4 s–1.
B2O3 content in slag was suggested to have an
insignificant effect on the reaction rate constant, whereas more titanium
and boron could be reduced by silicon with higher B2O3 content in slag. Stability of the reaction interface was
simulated using phase field model. A decreased interfacial tension
in B2O3-containing system was indicated to be
the reason for emulsification of phases.
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