Method for scale control

Claim 1

A method of inhibiting the deposition of calcium phosphate scale or sludge from an aqueous system, treated with a corrosion inhibitor formulation, which method comprises treating the aqueous system with 1 to 100 ppm, based on the aqueous system, of a formulation which consists essentially of (a) 40 to 69.5% by weight of the total formulation of a phosphono-carboxylic acid selected from the group consisting of a compound of formula II ##STR13## wherein R is hydrogen, an alkyl, an alkenyl or alkynyl group, each having up to 4 carbon atoms, a phenyl group, cycloalkyl group having from 3 to 6 carbon atoms, a benzyl group, a phenethyl group or a residue having the formula: ##STR14## wherein R 6 is hydrogen, an alkyl group having from 1 to 4 carbon atoms or a carboxyl group and R 7 is hydrogen or methyl group; a compound having formula III ##STR15## wherein X is ##STR16## wherein R 8 is hydrogen or methyl; and a mixture of compounds selected from the group consisting of those of formula II and formula III; (b) 30 to 50% by weight of the total formulation of a polyphosphate selected from the group consisting of tetrasodium pyrophosphate, sodium tripolyphosphate or a polymeric sodium metaphosphate of formula: ##STR17## wherein m is an integer from 4 to 20; and (c) 0.5 to 10% by weight of the total formulation of hydrolyzed polymaleic anhydride having a molecular weight in the range of from 300 to 500, as determined by calculation following osmometric measurement on polymaleic anhydride before hydrolyzing, or a water soluble salt of such a hydrolyzed polymaleic anhydride.

Claim 2

A method of inhibiting the deposition of calcium phosphate scale or sludge from an aqueous system, treated with a corrosion inhibitor formulation, which method comprises treating the aqueous system with 1 to 100 ppm, based on the aqueous system, of a formulation which consists essentially of (a) 40 to 69.5% by weight of the total formulation of a phosphono-carboxylic acid selected from the group consisting of a compound of formula II ##STR13## wherein R is hydrogen, an alkyl, an alkenyl or alkynyl group, each having up to 4 carbon atoms, a phenyl group, cycloalkyl group having from 3 to 6 carbon atoms, a benzyl group, a phenethyl group or a residue having the formula: ##STR14## wherein R 6 is hydrogen, an alkyl group having from 1 to 4 carbon atoms or a carboxyl group and R 7 is hydrogen or methyl group; a compound having formula III ##STR15## wherein X is ##STR16## wherein R 8 is hydrogen or methyl; and a mixture of compounds selected from the group consisting of those of formula II and formula III; (b) 30 to 50% by weight of the total formulation of a polyphosphate selected from the group consisting of tetrasodium pyrophosphate, sodium tripolyphosphate or a polymeric sodium metaphosphate of formula: ##STR17## wherein m is an integer from 4 to 20; and (c) 0.5 to 10% by weight of the total formulation of hydrolyzed polymaleic anhydride having a molecular weight in the range of from 300 to 500, as determined by calculation following osmometric measurement on polymaleic anhydride before hydrolyzing, or a water soluble salt of such a hydrolyzed polymaleic anhydride.