ACID MIXTURE LIQUID RECOVERY SYSTEM, ACID MIXTURE LIQUID RECOVERY METHOD, AND SILICON MATERIAL CLEANING METHOD

摘要

PROBLEM TO BE SOLVED: To provide technology which recovers high purity hydrofluoric and nitric acids under stable system operation from exhaust gas generated from a silicon etching tank.SOLUTION: Etching of a polycrystalline silicon lump in a silicon etching tank 1 generates exhaust gas containing hydrofluoric and nitric acids. This exhaust gas is suctioned by a hood 2 and sent to a scrubber 4A through an exhaust duct 3. The scrubber 4A is composed of an absorbent tank 7 at a lower stage and a filler tank 9 at a middle stage, and the absorbent tank 7 is provided with a hydrofluoric and nitric acid recovery line 13, by which hydrofluoric and nitric acids are recovered from a second cleaning tank 14. The exhaust gas is absorbed by an absorbent (water or hydrogen peroxide solution) accommodated in the absorbent tank 7. Use of water or hydrogen peroxide solution as the absorbent has an advantage that even when silicon fluoride becomes a polymer compound after hydrolysis, the resultant compound does not cause strong swelling and precipitates in the absorbent tank 7 without being gelatinized, so that operation of the scrubber will in no case be disabled.