Method of recycling phosphating sludges

A process for recycling phosphating sludge which accumulates in the zinc phosphating of metal surfaces and which, in addition to phosphate and small quantities of other metals, contains an excess of iron over zinc, said process comprising steps of:

• (a) converting the phosphating sludge into an aqueous mineral acid solution using a mineral acid selected from the group consisting of hydrochloric acid, nitric acid and sulfuric acid,
• (b) adjusting the pH value of the aqueous solution obtained in accordance with (a) to values of <0.85,
• (c) contacting the aqueous solution obtained in accordance with (b) with an extractant consisting essentially of (i) a water-insoluble organic solvent, (ii) a complexing agent for iron(HI) ions selected from the group consisting of acids of phosphorus soluble in the organic solvent and corresponding to general formula (I):
• ##STR2## in which R and R' are selected from the group consisting of OH, alkyl, aralkyl, alkoxy and alkylphenoxy and R and R' may be the same or different, but cannot both be OH, and, optionally, (iii) a solubilizer,
• (d) selectively removing iron from the aqueous solution obtained after step (b) by liquid/liquid extraction with the extractant recited in step (c), and
• (e) reusing the aqueous solution obtained as raffinate after the liquid/liquid extraction of step (d) in a phosphating process.