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- W1970616510 abstract "This paper describes the results from an experimental study of the purification of dilute hydrofluoric acid (5 wt.%) by ion exchange. Hydrofluoric acid was prepared by dilution from technical grade concentrated HF; important amounts of metal impurities were found in the diluted acid, mainly Na, Fe, As, B, Ca, K, Mg, Mn, Mo, PO43−, and Ti. The semiconductor industry developed the Semiconductor Equipment and Materials International (SEMI) standards to establish the quality requirements for the chemicals used in this sector; one of these standards, SEMI C29 was proposed for 4.9 wt.% HF. Grade 2 HF accounts for impurity levels in the range of 10 ppb. Taking into account this reference, 17 impurities exceed the limits of the standard: Al, As, B, Ca, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, Ti, Zn, Zr and PO43−. The purification was performed with two columns containing commercial cation and anion resins from Dow, Bayer and Rohm and Haas companies. Different resin samples were immersed in 5 wt.% HF at different contact times up to 30 days in order to determine any weight change due to chemical attack; no weight losses were detected, however the weight of the two weak anion resins increased more than 20% indicating the interaction between these resins and HF. The metal pollutants were found in both cationic and anionic forms, due to the high concentration of fluoride, and its ability to form cationic and anionic complexes; the speciation of impurities was calculated using the Visual Minteq software. The results from the purification experiments show that 14 of 17 impurities fulfill the requirements of the standard C29, Grade 2. The limits of Al, B, Cu, Li, Mn, Mo, Ni, Ti, Zn and Zr are easily attained, while the concentration of K, Mg and Ca are very close to the limits. As, Fe and PO43− were poorly retained in the resins and their concentrations exceed the limits of Grade 2; more selective resins need to be investigated to reduce the concentration of these impurities in HF matrices. In the case of Na, although removal was higher than 95%, the limit was exceeded due to the high initial concentration." @default.
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- W1970616510 date "2007-08-01" @default.
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- W1970616510 title "Purification of dilute hydrofluoric acid by commercial ion exchange resins" @default.
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- W1970616510 doi "https://doi.org/10.1016/j.seppur.2007.01.002" @default.
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