In order to find the most effective hydrometallurgical method of removing iron, aluminum and calcium from MG-Si, a variety of acid leaching methods were presented. The research results show that the order of capacity of metallic impurity removal is HF, HCl, HNO3 and H2SO4. The most effective hydrometallurgical method is the leaching by mixed acid with hydrofluoric acid and sulfuric acid. Removal efficiency of hydrochloric acid pressure leaching can improved as the pressure increases. Sulfuric acid and nitric acid even using high pressure leaching cannot obtain high impurity removal rate. The leaching by hydrofluoric acid or mixed acid containing hydrofluoric acid and sulfuric acid is very effective on removal of iron and aluminum, but less effective on calcium.

In this paper, removal of iron from metallurgical grade silicon with pressure leaching is carried out. We investigated the factors such as the concentration of hydrochloric, particle size of raw material ground, temperature, pressure and reaction time, which influenced on the removal of iron. The results show that the optimum operating conditions for pressure leaching in hydrochloride are: acid concentration 4 mol/L, diameter for raw material less than 50 μm, leaching temperature 160 0C，leaching pressure 2.0 MPa, leaching time 2.0 h. The content of iron residual in MG-Si powder was reduced to about 200 ppmw. The removal efficiency of iron is up to 90.90 %.

In this study, the mesoporous silica material was hydrothermally synthesized from the rice husk ash of biomass energy industry with cetyltrimethylammonium bromide (CTAB) as template agents. The structure and morphology of mesoporous silica material was investigated based on the analysis of X-ray diffraction (XRD), N2 sorption/desorption (BET), Fourier transformation infra-red spectrum (FTIR). The results indicated that mesoporous silica material was successfully prepared by substituting rice husk ash for the traditional silica source of tetraethyl orthosilicate, and the mesoporous silica material displayed pore sizes in the 2-4 nm range with specific surface areas as high as 363 m2/g.

In this work, graphene quantum dots were simply and rapidly prepared by thermal decomposition of citric acid. The resulting graphene quantum dots shows good dispersion and high crystallinity, the sizes can be effectively adjusted by controlling the temperature of decomposition. The results indicate that with the increase of temperature, the size of GQDs increased from 2 nm to 12 nm. The effect of the size of graphene quantum dots on the optical properties were carefully studied. Based on the optical properties and electrochemical results, the HOMO and LUMO value of GQDs with different sizes were obtained and the band gap becomes smaller from 3.36 eV to 2.87 eV with the increase of size of GQDs, which provides a potential application in the field of optoelectronic devices.

The temperature and velocity distribution of melting pool fields is very important effect to the silicon purification in vacuum induction furnace. A numerical model for the electromagnetic-thermal hydrodynamic coupling field has been developed by using the finite element method (FEM) and a two-dimension numerical simulation for temperature of metallurgical-grade silicon melting in vacuum induction furnace was carried out by using a software Multi-physics Comsol 4.2 in this paper. The results showed that the temperature field was dependent on induction heating times and melting pool position and the maximum temperature grads was 400K in constant temperature stage. With the silicon was molted gradually two vortexes were come into being for electromagnetic stirring in the smelting poor.