Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Patent
1992-07-31
1993-05-18
Silverman, Stanley S.
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
210720, 210724, 210913, 423 55, 423607, 204DIG13, C02F 162
Patent
active
052118533
ABSTRACT:
A process for precipitating and removing chromium compounds in which chromium is in the hexavalent state from aqueous liquids, particularly, alkaline earth metal or alkali metal chlorate-rich solutions containing chloride, chlorate, and bichromate ions produced by the electrolysis of brine. In the process, hydroxylamine, hydroxylamine sulfate, hydroxylamine formate or hydroxylamine hydrochloride is used as a reducing agent to react and co-precipitate at a neutral or acid pH with hexavalent chromium ions present in the aqueous liquid, the reaction and precipitation taking place, generally, at a pH of about 4.0 to about 6.5 and, a temperature of about 50.degree. C. to about 100.degree. C. Precipitated oxides and hydroxides of divalent and trivalent chromium can be removed, for instance, by filtration. Reaction time to achieve a level of about 10 parts per million or less of chromium ions in the filtrate varies from less than about 5 hours to less than about 1 hour depending upon selection of reaction temperature and reaction pH. For instance, to achieve a level of 2 parts per million or less chromium ion after removal of the precipitate formed during the reaction at a pH of 5.0-5.5, a reaction time of 10 minutes at a temperature of 90.degree.-95.degree. C. is required. A reaction time of 30 minutes at a temperature of 70.degree. C. or 120 minutes at a temperature of 60.degree. C. provides a similar level of chromate ion removal.
REFERENCES:
patent: 4268486 (1981-05-01), Noack et al.
patent: 4367213 (1983-01-01), Frorucci et al.
patent: 4804528 (1989-02-01), Warren
Jackson John R.
Pitzer Charles L.
Huron Tech Corp.
McCarthy Neil
Pierce Andrew E.
Silverman Stanley S.
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