# US 5,350,517 A · Method of recycling phosphating sludges > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,350,517 A - Document ID: US5350517A - Status: Granted - Kind: A - Application number: 08/039,290 - Filed: 1993-04-19 - Granted: 1994-09-27 - Earliest claimed: 1990-10-18 - Assignees: Henkel Kommanditgesellschaft auf Aktien - Inventors: Willi Buchmeier; Wolf A. Roland - Web page: https://patentgrep.com/patent/US5350517A ## CPC - C23C 22/12: containing zinc cations - C22B 3/384: {Pentavalent phosphorus oxyacids, esters thereof} - C23C 22/86: Regeneration of coating baths - Y02P 10/20: Recycling - C23C: COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL (making metal-coated products by extrusion B21C23/22; covering with metal by connecting pre-existing layers to articles, see the relevant places, e.g. B21D39/00, B23K; metallising of glass C03C; metallising mortars, concrete, artificial stone, ceramics or natural stone C04B41/00; enamelling of, or applying a vitreous layer to, metals C23D; treating metal surfaces or coating of metals by electrolysis or electrophoresis C25D; single-crystal film growth C30B; by metallising textiles D06M11/83; decorating textiles by locally metallising D06Q1/04) - C22B: PRODUCTION AND REFINING OF METALS (electrolytic C25); PRETREATMENT OF RAW MATERIALS - Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS ## Abstract Described is a method of recycling the sludge which arises during the zinc phosphating of steel surfaces. The sludge is preferably digested with nitric acid, the iron selectively extracted from the digested solution with liquid/liquid extraction and the extract thus obtained reused in the preparation of zinc phosphating solution. The preferred extraction solvent is a solution of the monoester of 2-ethylhexyl alcohol with phosphoric acid in kerosene. ## Claims ### Claim 1 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. ### Claim 2 (depends on 1) A process as claimed in claim 1, wherein the aqueous solution in equilibrium with the extractant after extraction in step (d) is clear. ### Claim 3 (depends on 2) A process as claimed in claim 2, wherein the iron in the organic phase obtained after the liquid/liquid extraction in step (d) is re-extracted with aqueous mineral acid and the extractant is reused. ### Claim 4 (depends on 3) A process as claimed in claim 3, wherein the iron is converted into its oxide by spray roasting of the aqueous re-extraction solution and the mineral acid accumulating is reused for re-extraction. ### Claim 5 (depends on 1) A process as claimed in claim 1, wherein the complexing agent used in step (c) is selected from the group consisting of phosphoric acid monoalkyl and dialkyl esters, alkyl phosphonic acid monoalkyl esters, dialkyl phosphinic acids and mixtures thereof, the alkyl groups, which may be the same or different, containing 6 to 16 carbon atoms and being branched. ### Claim 6 (depends on 5) A process as claimed in claim 5, wherein phosphoric acid mono-2-ethylhexyl ester is used as the complexing agent. ### Claim 7 (depends on 6) A process as claimed in claim 6, wherein the iron in the organic phase obtained after the liquid/liquid extraction in step (d) is re-extracted with aqueous mineral acid and the extractant is reused. ### Claim 8 (depends on 7) A process as claimed in claim 7, wherein the iron is converted into its oxide by spray roasting of the aqueous re-extraction solution and the mineral acid accumulating is reused for re-extraction. ### Claim 9 (depends on 5) A process as claimed in claim 5, wherein the iron in the organic phase obtained after the liquid/liquid extraction in step (d) is re-extracted with aqueous mineral acid and the extractant is reused. ### Claim 10 (depends on 9) A process as claimed in claim 9, wherein the iron is converted into its oxide by spray roasting of the aqueous re-extraction solution and the mineral acid accumulating is reused for re-extraction. ### Claim 11 (depends on 1) A process as claimed in claim 1, wherein kerosine is a constituent of the extractant used in step (c). ### Claim 12 (depends on 11) A process as claimed in claim 11, wherein the iron in the organic phase obtained after the liquid/liquid extraction in step (d) is re-extracted with aqueous mineral acid and the extractant is reused. ### Claim 13 (depends on 6) A process as claimed in claim 6, wherein the iron is convened into its oxide by spray roasting of the aqueous re-extraction solution and the mineral acid accumulating is reused for re-extraction. ### Claim 14 (depends on 1) A process as claimed in claim 1, wherein the complexing agent used in step (c) is selected from the group consisting of phosphoric acid monoalkyl and dialkyl esters, alkyl phosphonic acid monoalkyl esters, dialkyl phosphinic acids and mixtures thereof, the alkyl groups, which may be the same or different, containing 4 to 20 carbon atoms. ### Claim 15 (depends on 14) A process as claimed in claim 14, wherein the iron in the organic phase obtained after the liquid/liquid extraction in step (d) is re-extracted with aqueous mineral acid and the extractant is reused. ### Claim 16 (depends on 15) A process as claimed in claim 15, wherein the iron is converted into its oxide by spray roasting of the aqueous re-extraction solution and the mineral acid accumulating is reused for re-extraction. ### Claim 17 (depends on 1) A process as claimed in claim 1, wherein a water-insoluble organic solvent which is capable of dissolving both the complexing agent and the complex formed with iron is a constituent of the extractant used in step (c). ### Claim 18 (depends on 17) A process as claimed in claim 17, Wherein the iron in the organic phase obtained after the liquid/liquid extraction in step (d) is re-extracted with aqueous mineral acid and the extractant is reused. ### Claim 19 (depends on 18) A process as claimed in claim 18, wherein the iron is converted into its oxide by spray roasting of the aqueous re-extraction solution and the mineral acid accumulating is reused for re-extraction. ### Claim 20 (depends on 1) A process as claimed in claim 1, wherein the iron in the organic phase obtained after the liquid/liquid extraction in step (d) is re-extracted with aqueous mineral acid and the extractant is reused.