CS230994B1 - A method for pretreating silicate degreasing baths prior to their regeneration by ultrafiltration - Google Patents

Abstract

The invention relates to the field of metal surface treatment and provides a method for effective pre-treatment of silicate degreasing baths, enabling their regeneration by ultrafiltration. In this method, cationic agents in combination with organic polyflocculants are used to separate colloidal and undissolved components of the bath after its degreasing capacity has been exhausted.

Description

The invention relates to pretreatment of silicate degreasing baths prior to their regeneration by ultrafiltration, the purpose of which is to remove suspended substances, in particular colloidal silicon dioxide, which clog the filter membranes and thereby considerably slow down the ultrafiltration process or make this regeneration impossible.

Methods for pretreating degreasing baths are known.

For example, filtering with very low porosity filtering equipment, however, presents a number of problems with the regeneration of clogged filters. Another known method of pretreating degreasing baths is by centrifuging them, which, however, requires economically demanding instrumentation. The use of conventional coagulants prevents the basic condition of regeneration to avoid altering the chemical composition of the bath.

The drawbacks of the prior art are largely eliminated by the pretreatment of the silicate degreasing baths prior to their regeneration by ultrafiltration according to the invention, wherein the cationic surfactant, for example cetylpiridinium bromide, is added to the silicate degreasing bath in an amount of 50 to 200 mg. and then the bath is homogenized. It is preferred that an organic polyflocculant, for example based on acrylamide, is added to the degreasing bath in an amount of 0.8 to 2.5 mg · 1 * and after the sludge has matured and sedimented, the treated bath is separated. The addition of the polyflocculant increases the pretreatment efficiency, since the polyflocculant promotes the packaging of the resulting sludge. The homogenization of the bath after the addition of the cationic surfactants is preferably carried out at a rapid rate

230 994 at G = 40 to 800 s ^- ^ for at least 2 minutes. The sludge maturation takes place preferably with slow stirring of G = 10 to 50 s ¹ for 20 to 40 minutes.

The addition of a cationic surfactant, as a substance containing positively charged centers, to an exhausted silicate degreasing bath containing a considerable amount of suspended matter, in particular colloidal silica, causes the coagulation of the negatively charged micelles, and the addition of the polyflocculant promotes the packaging of the sludge. There is no change in the chemical composition or the pH of the treated bath, since the coagulating and flocculating agents used are separated together with the sludge. The resulting sludge can be further processed in associated wastewater treatment plants from galvanizing plants. The treatment according to the invention enables the regeneration by ultrafiltration of exhausted silicate degreasing baths, which, due to the drawbacks of the previously known pretreatments necessary for the ultrafiltration itself, can only be carried out with considerable difficulties and low economic yield.

The invention and its effects are further explained in more detail by way of examples of a specific embodiment thereof.

Example 1

190 mg was added to the spent metasilicate degreasing bath (SYNALOD EPCO 3024). l ^"1 of cetylpyridinium bromide (CPB), and homogenization rapid stirring impeller at 150 revolutions per minute for 2 minutes. After stirring, 40 min. sedimentation of sludge. More than 80% of the colloidal silica was removed.

Example 2

For pretreatment of the metasilicate-containing alkaline degreasing bath (SYNALOD 56), cetyltrimethylammonium bromide (CTAB) was used as a coagulating agent

- 3,230,994 mg. 1 and homogenized by rapid stirring for 3 minutes. Then 2 mg was added. l ^_i as PAC acrylamide based (PRAESTOL 2935/74) and begin slow agitation - 20 agitator revolutions per minute, which was held 30 minutes.

Colloidal silica was separated by 97% sedimentation for 40 minutes.

Example 3

To pre-regenerate the silicate degreasing bath (SYNALOD 58), 70 mg * 1 " of cationic surfactants of carbetoxypentadecyltrimethylammonium bromide (STEPEXEX) were added thereto, and after 4 minutes of rapid stirring were added

1.2 mg. l ^"1 as PAC acrylamide based (PRAESTOL 2900). After 60 minutes of slow agitation, 96% colloidal silica was removed by sedimentation ·

The invention can be used for the regeneration of depleted silicate degreasing baths, for example in the surface treatment of metals.

Claims (4)

OBJECT OF THE INVENTION 230 994 Process for pretreating silicate degreasing baths prior to their regeneration by ultrafiltration, characterized in that a cationic surfactant, for example cetylpyridinium bromide, is added to the silicate degreasing bath in an amount of from 50 to 200 mg. 1, whereupon the degreasing bath is homogenized. 2. A method according to claim 1 _(wherein the degreasing bath is added to the organic poly-flocculants, for example based on acrylamide in an amount of 0.8 to 2.5 mg. L ^'1 and after aging of the sludge and the sedimentation bath adjusted separates. 3. Method according to claim 1 or _2f, characterized in that the treated degreasing bath is homogenized by rapid stirring - G = 40 to 800 s ** for two minutes. 4. A process according to any one of claims 1 to 3, wherein the degreasing bath is subjected to slow agitation - G = 10 to 50 sec @ -1 for 20 to 40 minutes after addition of the organic polyflocculant.