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US 5,350,495 AGranted
Method for separating impurities from an aqueous alkali metal chlorate electrolyte
AssigneeEka Nobel AB
InventorsStina Eriksson, Ulla-Kari Holmstrom
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AssigneeEka Nobel AB
InventorsStina Eriksson, Ulla-Kari Holmstrom
Estimating the term…
The invention relates to a method for separating sulphate from an aqueous electrolyte in an alkali metal chlorate process, thereby reducing the operating cost and increasing the possibility of further closing the electrolytical production of alkali metal chlorate. Calcium ions are added to a portion of the electrolyte, for precipitating calcium sulphate. By adjusting the pH within the range of from 4.6 up to about 7, and combining the temperature, content of ions and the molar ratio between sulphate and calcium ions added in a suitable manner, the calcium sulphate will precipitate predominantly as gypsum and essentially without inclusions and/or co-precipitation of chromium-containing compounds or chlorate. The precipitate is subsequently removed from the portion of electrolyte, whereafter the thus purified portion of electrolyte is recycled to the chlorate process. Any fluoride ions in the electrolyte can also be removed by the addition of calcium ions and a subsequent co-separation of the calcium fluoride precipitated with the calcium sulphate.
A method for separating sulfate from a chromium-containing aqueous electrolyte in an alkali metal chlorate process, comprising the steps of withdrawing a portion of the electrolyte from said process, filtering the withdrawn portion of electrolyte to remove at least a portion of chromium compounds therefrom, thereafter adjusting the pH of said withdrawn portion of electrolyte to within the range of from 4.6 up to about 7, adding calcium ions to said withdrawn portion of electrolyte to thereby effect precipitation of calcium sulfate, regulating the temperature and ion content of said withdrawn portion of electrolyte, and the molar ratio between added calcium ions and sulfate ion content, such that the calcium sulfate essentially precipitates as CaSO.sub.4 * 2 H.sub.2 O, CaSO.sub.4 * 1/2 H.sub.2 O or CaSO.sub.4, removing the precipitated calcium sulfate from the withdrawn portion of electrolyte, thereby purifying said withdrawn portion, and thereafter recycling the purified portion of electrolyte to the alkali metal chlorate process.
Dependencies are inferred from the claim text.