Method for continuously filtering raw brine for use in chlor-alkali electrolysis

A method of continuously processing raw brine with a solids content to obtain a substantially solids-free pure brine (E) for chlor-alkali electrolysis, said method comprising the steps of:

• a) supplying a raw brine (A) with a solids content of from about 300 to 1,500 ppm to a decanter (1);
• b) separating the raw brine (A) into a clear brine (B) with a lower solids content in a range from 30 to 100 ppm, said lower solids content being less than the solids content of said raw brine (A), and an underflow (C) with a higher solids content than said solids content of the raw brine by means of the decanter (1);
• c) supplying a metered fraction of the underflow (C) with the higher solids content as a filtering aid and all of the clear brine (B) to a pressure filter;
• d) during the supplying of step c), controlling the metered fraction and the clear brine (B) during the supplying so that a solids concentration at an inlet to said pressure filter is 5 to 10 times that of a solids concentration in said clear brine (B);
• and
• e) filtering with the pressure filter to obtain the substantially solids-free pure brine (E) containing less than or equal to 1 ppm of retained solids and a thickened slurry (F);
• whereby clogging of the pressure filter is reduced and increased output of said pure brine (E) is possible while maintaining the retained solids in the pure brine (E) at a level of less than or equal to 1 ppm.