Handling rinsing water in surface treatment units - where water from different tanks or groups of tanks is separately circulated and treated and is mixed with water from other tanks as appropriate

摘要

The water is conveyed in a closed circuit in which the contaminated rinsing water is renewed. The circuit is divided into a number of separate streams, and the regeneration of physical or chemical properties of individual streams is achieved by mixing with other corresp. streams, and particularly by neutralisation and filtration. The first stream comes from a gp. of circulating water baths and is passed through an ion exchange unit before being returned to these baths. A number of the rinsing stages before the colouring of the eloxal layer, after the colouring of the eloxal layer, before compression of the eloxal layer and after chromate treatment, are included in this first stream. A second stream comes from a second gp. of circulating water baths and is regenerated by neutralisation and removal of solid particles before being returned to these baths. A number of rinsing stages after colouring, after the pretreatment, in particular after the degreasing and pickling, and after the static rinsing, are included in this second stream. The first and/or second streams may be circulated continuously. A third stream consisting of waste water from the static water baths is neutralised by mixing with waste waters contg. acids and alkalis, is filtered and is then added to the second stream in order to neutralise it and remove solid particles. A fourth stream consisting of waste water from a static water bath after the chromate treatment is treated with a reduction agent to reduce hexavalent Cr to trivalent Cr, is neutralised, de-sludged and then recirculated. The waste water from the second and third streams is contaminated with sulphates, and is neutralised with NaOH to precipitate the sulphates, is treated with Ca(OH)2 to further precipitate sulphates, and is neutralised with carbonic acid before being disposed of to a drainage channel etc. USE/ADVANTAGE - Used in surface-treatment units, and esp. those of the eloxal type. The water usage and the contamination of the waste water are kept to a min