Treating a water system containing or in contact with a metal sulphide scale
to inhibit, prevent, reduce, dissolve or disperse iron sulphide deposits. A solution
of tris(hydroxyorgano)phosphines (THP) and tetrakis(hydroxyorgano)phosphonium salts
(THP+ salts) and sufficient of a chelant (amino-carboxylates or amino-phosphonates)
to provide a solution containing from 0.1 to 50% by weight of said THP or THP+
salt and from 0.1 to 50% by weight of said chelant, is contacted with the metal
sulphide scale thereby to dissolve at least part of said scale in said solution.
