Study On Chloride Removal From Poly Crystalline Silicon Wastewater Treatment

With the rapid development of photovoltaic industry in recent years,polycrystalline silicon attracted extensive attention as the raw material of solar cells production.Main production technologies of polycrystalline silicon include modified Siemens process,metallurgical process and silane process,in which modified Siemens is the most widely applied mainstream production process of polycrystalline silicon.In modified Siemens method process,different degree of wastewater could be produced,affected by variety of process conditions,equipment operation and management level,the components and water volume of wastewater could change.The chloro-silicane emissions lead to content of chloride ion in drain off water on the high side,which affect its reuse and emissions.Besides,considering the emission amount of chloro-silicane is high in whole production process,how to reasonable use these water,improve the utilization of the water of polycrystalline silicon system,standard emissions,and reduced pollution are important processes that necessarily to be concerned.This study focuses on the application of ultra-high lime with aluminum on water drainage treatment of polycrystalline silicon production,and the reduction of chloride ion content in drain water.The experimental results with influence factors show that the chemicals applied wet feeding method is more advantageous to increase chloride ion removing rate,of which removal efficiency is better than dry feeding and useful for the control and operation of production process.The addition procedure is to add calcium hydroxide followed by sodium aluminate,which is conducive to the improvement of removing rate.When the addition ratio(calcium hydroxide:sodium aluminate:chloride ion)is 10:5:1(mole ratio),the chloride ion removing rate was the highest.But by comparison of the costs of removal and disposal,the most cost-effective ratio is 6:3:1(mole ratio).In terms of guarantee the removal effect,this ratio also reduced the costs of addition chemicals and solid waste disposal.The best reaction time is 3.5 h,but when the reaction time is 1～2 h the disposal is most cost-effective.Increasing chloride concentrations helps improve the removal of chloride ions.When the concentration of chloride ions is too high,twice or multiple chloride removal processes can be taken into account(chloride removing rate can reach more than 80%).On the choice of dosing position,dosing chemicals in the import of wastewater treatment system is superior to that of the water drainage of system,which could take advantage of the existing waste water treatment equipment to reduce input costs.In terms of the overall effect,it is possible to be used for engineering that the method to use ultra-high lime with aluminum process to reduce the chloride ion content in wastewater of polycrystalline silicon production.