Spent potlining (SPL) from Hall-Heroult cells is a kind of toxic solid waste with recyclable carbon and electrolyte. The recycle of SPL by floatation, which can meet environment requirements and bring economic profits, is focused on presently because of its great potential to be industrialized and spread. However, it is difficult to get a good floatation index in floatation of SPL with carbon content lower than 50%. Therefore, the dressing of SPL with 36.1% of carbon has been investigated in the paper with the interesting potential to improve the quality of floatation products by optimizing floatation conditions, such as grinding size, pulp density and agitation speed of floatation machine. And the comparative experiment has been performed. The results show that quality of both carbon product and electrolyte product were improved under optimized conditions of grinding size of 90% of the particle sizes less than 0.74mm, pulp density of 25% and agitation speed of 1700r/min. The carbon content in carbon product was raised by 5.40 and carbon content in electrolyte product decreased by 0.26 while electrolyte recovery of electrolyte product increased by 4.58.

The modified Siemens process is the primary technology of polycrystalline production at present. The Siemens reactor, which is the main equipment in the modified Siemens process, consists of a chamber where several high purity silicon slim rods are heated by an electric current flowing through them. The temperature on the rod centre must be under melting temperature of silicon (1687K) in order to avoid its breaking-down because of an uneven temperature profile of the silicon rod. Therefore the temperature profile of the silicon rod heated by direct current (DC) has been investigated by molding. The current density profile of silicon rod has also been studied to investigate the interaction of current density and temperature. The results show that the temperature is not homogeneous in the rod and the temperature in the center of the polysilicon rod is 1750K which is much higher than the melting temperature (1687K) when the temperature is 1423K on the surface of polysilicon and the radius of rod is 5cm. Therefore, the maximum growth radius of the polysilicon rod in Siemens reactor should be less than 5cm when the joule heating generated by DC. The current density increases from the center to the surface of the polysilicon rod.

The complex chemical reactions in the Si-Cl-H system with relation to modified Siemens process have been studied in this paper based on the thermodynamic data of related substance. The influence of the temperature, pressure and initial feed ratio (nSi / nSiHCl3) on the silicon yield have been studied. Furthermore, the diagram of Kinetic constant k as a function of temperature for the rate controlled reaction has also been fitted in the SiHCl3 hydrogen system. Finally 1425K, 1.5atm and the initial feed ratio of 15 is the best conditions. Under these conditions, the silicon yield is 34.815%.

Titanium tetrachloride (TiCl4) oxidation is the most important stage in the titanium dioxide production. High temperature, fast reaction and strong oxidation and strong corrosive atmosphere have increased a lot of difficulty to measuring and testing in oxidation reactor. Computational fluid dynamics (CFD) simulation is one of the most valid methods to investigate TiCl4 gas phase oxidation. In this paper, the achievements and progress about fluid dynamics simulations of titanium tetrachloride gas phase oxidation are described. The further research directions and new perspectives in this field are presented.

The new two-tower process of thrichlorosilane distillation consisting of removal of light components after removing heavy components is analyzed by assistant of a chemical process simulation software. In order to achieve lower energy consumption, the parameters for each tower in the new process are optimized, such as the number of theoretical plates, the position of feed plate, reflux ratio and distillate (bottoms) to feed ratio. The results show that the optimum parameters for the first tower are the number of theoretical plates of 32, the position of feed plate of 24, reflux ratio of 2.5 and the distillate to feed ratio of 0.8516. For the second tower, the number of theoretical plates, the position of feed plate, the reflux ratio and the bottoms to feed ratio are 80, 16, 143 and 0.9652 respectively. Applying the optimized results in practical production, mass fraction of PCl3 in overhead of the first tower is reduced by two orders of magnitude, condenser duty and reboiler duty of the second tower are dropped by more than eight percent while obtaining higher purity trichlorosilane products.