Patent GB-799873-A (GB)
Title: Improvements in accelerating the sedimentation of dispersions
IPC: B01D21/01
Filed: 1956-06-27
Abstract: A process for accelerating the sedimentation of dispersions and colloidal solutions consists in using as a sedimentation assistant an anionic aminoplast containing at least one sulphonic acid group.  The process may be applied to flotation slimes and to waste water from waste heaps, foundries and mines, from roasted pyrites and ore and coal flotation, from workingup operations of metals (e.g. pickling waste water from galvanizing plant), and from tanneries, artificial silk works and textile-improving operations (e.g. the weighting of silk).  By stagewise addition of the aminoplasts to waste water or sludges containing compounds of more than one metal as precipitates the precipitates may be deposited fractionally and the metals recovered separately.  One or more other sedimentation assistants may be employed at the same time, e.g. the wood ethers specified in Specification 775,805.  From 3 to 20 grams of aminoplast per cubic metre of liquid to be clarified (containing from 10 to 200 kg. solids) should be added, though 0.5 gram may be sufficient.  The preferred aminoplast is a condensation product of urea and formaldehyde prepared in the presence of sulphurous acid or its salts or after-treated therewith.  Two examples of use relate to waste water from a fine coal centrifuge and one to waste water rich in clay from a lead-zinc ore flotation.  The aminoplast may be obtained by heating 30 per cent formaldehyde solution with urea and sodium sulphite at the boiling point, allowing the product to boil further after acidification, and neutralizing the condensation product with caustic soda solution; or condensing urea with formaldehyde and further reacting the condensation product with bisulphite; or by preparing a urea-formaldehyde condensation product in the presence of 12 per cent of alkali sulphite.ALSO:A process for accelerating the sedimentation of dispersions and colloidal solutions consists in using as a sedimentation assistant an anionic aminoplast containing at least one sulphonic acid group.  The process may be applied to floatation slimes and to waste water from waste heaps, foundries and mines, from roasted pyrites and ore and coal flotation, from working-up operations of metals (e.g., pickling waste water from galvanizing plant), and from tanneries, artificial silk works and textile-improving operations (e.g., the weighting of silk).  By stagewise addition of the aminoplasts to waste water or sludges containing compounds of more than one metal as precipitates the precipitates may be deposited fractionally and the metals recovered separately.  One or more other sedimentation assistants may be employed at the same time, e.g., the wood ethers specified in Specification 775,805. From 3 to 20 grams of aminoplast per cubic metre of liquid to be clarified (containing from 10 to 200 kg solids) should be added, though 0,5 gram may be sufficient.  The preferred aminoplast is a condensation product of urea and formaldehyde prepared in the presence of sulphurous acid or its salts or after-treated therewith.  Two examples of use relate to waste water from a fine coal centrifuge and one to waste water rich in clay from a lead-zinc ore flotation.  The aminoplast may be obtained by heating 30 per cent formaldehyde solution with urea and sodium sulphite at the boiling point, allowing the product to boil further after acidification, and neutralising the condensation product with caustic soda solution; or condensing urea with formaldehyde and further reacting the condensation product with bisulphite; or by preparing a urea-formaldehyde condensation product in the presence of 12 per cent of alkali sulphite.