ABSTRACT
A recirculating calcium hydroxide loop is provided to facilitate immediate response to calcium hydroxide demands in the various neutralizing units. Metallurgical silicon is first fed to a pressurized, heated vessel where it is reacted with a mixture of hydrogen and chlorosilanes to yield a higher silicon content chlorosilane liquid. Wastewater is generated in both silane and polysilicon production areas as well as in support facilities such as the cooling towers, water treatment system, and sanitary system. Waste generated is separated into four categories for treatment: high-chloride process wastes, low-chloride process wastes, nonprocess cooling wastes, and sanitary wastes. Small amounts of ferric and aluminum hydroxide are also produced, as well as the oxides and/or hydroxides of any and all metallic chlorides present in the concentrated slurry. A portion of the purified polysilicon product rods is etched with nitric and hydrofluoric acid prior to shipment.
