The invention relates to a process for the preparation of an essentially sulphide-free alkali liquor starting from an alkali sulphide source, characterized by reacting in alkaline medium the alkali sulphide source with copper (II) oxide and/or copper (I) oxide, optionally with the addition of water, in a mole ratio oxide to sulphide (calculated as alkali sulphide( (charging) of at least 0.9 and allowing the mixture obtained to react at a temperature of from 30 to 130 DEG C to form hydroxide in an amount equivalent to the amount of sulphide and to precipitate a solid phase consisting essentially of copper (I) sulphide, copper (II) sulphide or a mixture thereof, whereupon the solid phase is separated in a way known per se to obtain an essentially sulphide-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.
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