Process for the preparation of sulfide-free alkali liquor using copperoxide
The invention relates to a process for the preparation of an essentially sulfide-free alkali liquor starting from a pulp mill alkali sulfide source, characterized by reacting in alkaline medium the alkali sulfice source with copper (II) oxide and/or copper (I) oxide, optionally with the addition of water, in a mole ratio oxide to sulfide (calculated as alkali sulfide) (charging) of at least 0.9 and allowing the mixture obtained to react at a temperature of from 30.degree. to 130.degree.0 C. to form hydroxide in an amount equivalent to the amount of sulfide and to precipitate a solid phase consisting essentially of copper (I) sulfide, copper (II) sulfide or a mixture thereof, whereupon the solid phase is separated in a way known per se to obtain an essentially sulfide-free alkali liquor, the reaction time of the precipitation reaction being adjusted with regard to the charging and temperature selected so that the residual concentration of copper ions in the final alkali liquor is below 1 mmole/l.