Liquid purification or separation – Processes – Using magnetic force
Patent
1991-11-08
1993-04-13
Savage, Matthew O.
Liquid purification or separation
Processes
Using magnetic force
210717, 210722, 210724, 210726, 210769, 210928, C02F 152
Patent
active
052020304
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the purification of sewage water which is contaminated with organic materials and which has a pH lower than neutral. The invention is particularly directed to the purification of industrial effluents from pulp bleaching, particularly chlorine/chlorinedioxide bleaching of chemical pulp.
Industrial effluents of this type are presently purified only insufficiently, whereby the recipients used are subjected to large loads with concomitant ecologic problems. To the extent that the requirements of the environment have been increased the need for effective purification processes therefore arise, and such processes must also be acceptable from an economic point of view. Presently satisfactory purification processes for industrial effluents are needed, particularly for effluents orginating from the bleaching of chemical pulp.
The present invention has for its object to provide a simple and effective process for the purification of such industrial water effluents. Another object is to provide a process which is acceptable from an economic point of view but also results in a highly effective purification so as to reduce the load on the recipient to a minimum.
For these and other objects which will be clear from the following description the present invention provides a purification process for acid aqueous effluents, said process comprising the steps of: material in particulate form, wherein the iron at least partially is present in a metallic state; the aqueous effluent while dissolving at least part of the metallic iron; processing to an essentially neutral pH; and
It is preferred in the above-defined step a) to introduce also magnetite in particulate form whereby better mechanical processing and better precipitation will be obtained.
The pH-adjustment carried out in step c) above is suitably performed in two stages with a first addition of limestone, i.e. unburnt lime, particulate form with mechanical treatment, and then in a second stage this pH will be further increased by adding a strong base. The strong base can be sodium hydroxide, potassium hydroxide or another suitable base. In this neutralization in two stages the pH-adjustment in the first stage is suitably to a pH of from about 5.5 to about 6.5, such as about 6.0, and in stage two the pH is further increased to an interval lying within the range about 7 to about 8, for example about 7.5.
Before precipitating three-valent iron under oxidizing conditions according to step d) above it is preferred to perform magnetic precipitation of the excess of metallic iron and, optionally the excess of magnetite, and this excess is suitably returned to step a) of the process.
The oxidizing conditions in step d) can be provided by a suitable oxidant, and it is preferred to use air, optionally enriched in oxygen, or hydrogenperoxide.
The abrasive mechanical processing of solid materials in contact with the aqueous effluent that shall be purified is suitably carried out in some sort of grinding mill. It is particularly preferred to use a ballmill operating with iron or steel balls as grinding bodies. During the abrasive mechanical processing that is carried out in such mill the grinding bodies cause the formation of iron ions in that the acid effluent dissolves iron from the grinding bodies in connection with the processing. Generally, the aqueous effluent in which the abrasive mechanical processing takes place has a pH of less than about 3.
The invention will in the following be further described by non-limiting embodiments in conjunction with the appended drawing which shows a diagrammatic sketch in the form of a flow sheet on a preferred industrial process for the purification of an aqueous effluent from the bleaching of chemical pulp.
The effluent referred to in the following specific examples originates from the bleaching of pine sulphate pulp having a kappa number of about 30, said pulp being bleached according to the sequence oxygen gas(O)-(chlorine+chlorinedioxide)-(C.sub.85 +D.sub.15)-alkali extraction(E.sub.1)-chlor
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Savage Matthew O.
Solvator Process AB
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